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PAN AMERICAN HEALTH SECOND MEETING
ORGANIZATION 17-21 June 1963Washington, D.C.
ADVISORY COMMITTEEON MEDICAL RESEARCH
PLAGUE IN THE AMERICAS
Ref: RES 2/12
23 April 1963
PAN AMERICAN HEALTH ORGANIZATIONPan American Sanitary Bureau, Regional Office of the
WORLD HEALTH ORGANIZATION
WASHINGTON, D.C.
RES 2/12
PLAGUE IN THE AMERICAS
Table of Contents
Section Page
A Introduction 1
B General Remarks 2
C Present Status of Plague in Argentina 12
D Present Status of Plague in Bolivia 22
E Present Status of Plague in Brazil 42
F Present Status of Plague in Ecuador 67
G Present Status of Plague in Peru 89
H Plague in the United States 109
I Present Status of Plague in Venezuela 121
J List of Research Needs 132
K Research Plan Outline for Plague Studiesin the Peru-Ecuador Focus 136
L Research Plan Outline for Plague Studiesin Venezuela 143
i
RES 2/12
PLAGUE IN THE AMERICAS *
SECTION A
INTRODUCTION
Since the birth of the Pan American Health Organizationplague has been an important albeit diminishing problem of themember countries. The initial meeting of the Organization, thenknown as the International Sanitary Bureau, was the First Inter-national Sanitary Convention held in Washington D.C. from 2 to4 December, 1902. One of the main concerns of the founders was:"The adoption of measures for the disposal of garbage and wastesto prevent the spread of bubonic plague and other diseases".
In the years following, the application of classical meth-ods has driven plague into the endemic foci of today. Whilecurrent control and containment measures have been more or lesssuccessful, it has become obvious that before further progresscan be made against plague it will be necessary to undertake athorough study of the nature of the disease in its present cir-cumstances.
As a first step in a program to include the needed ecol-ogical studies, a thorough study and evaluation was begun of allinformation on plague in the Americas contained in the technicalliterature, official reports and other sources. Based on thesedata and observations to be made in the plague foci, there willbe designed a series of ecological research studies.
This document contains a summation of the basic informa-tion available on plague in Argentina, Bolivia, Brazil, Ecuador,Peru, United States, and Venezuela. The data contained wereobtained from the technical literature and official reports.Included also in this document are a listing of research needas,and preliminary outlines of two field research projects, i.e.Peru and Venezuela. In undertaking the exhaustive studies nec-essary and in the preparation of this document the Organization.has had the capable services of Dr. Robert Pollitzer on assign-ment from Fordham University, and Dr. K. F. Meyer, DirectorEmeritus of the George Williams Hooper Foundation, University ofCalifornia Medical Center, together with the secretariat servicesof Dr. A. N. Bica and Dr. E. C. Chamberlayne.
* Prepared for the second meeting of the PAHO Advisory Committeeon Medical Research, 17-21 June 1963. The present documentrevises and completes RES 1/13 presented at the first meetingof the PAHO/ACMR.
- 2 -RES 2/12
SECTION B
GERERAL REMARKS
As can be gathered from the adjoined tabulations, plagueis at present manifest in the western part of the United Statesas well as in five South American countries, namely Bolivia,Brazil, Ecuador, Peru and Venezuela. Generally speaking, theecology of the disease is of a uniform pattern, characteristicalso of other countries with a vast hinterland like for instance,South Africa, which had become plague infected during the presentpandemic: entering through sea-ports, the infection involvedfirst the rat-populations in these urban areas and soon also inmore or less distant cities and towns, the rat epizootics invar-iably leading to considerable epidemics; however, though oftenslowly, the infection inexorably spread to rural areas of thehinterland where owing to the presence of susceptible wildrodent species, it found conditions for its persistance compa-rable in principle to those in the ancient plague foci of CentralAsia, Though in some of the affected South American countriesor parts thereof the common rats are still involved in the man-ifestations of plague, in other foci these rodents have ceasedto play a role or have been relegated to a secondary role, be-coming but temporarily affected when the disease is rampantamong the wild rodents and thus, like the house mice and, more Ooften, the domesticated guinea-pigs serving merely as linkas inthe chain of events leading to a transition of the infectionfrom the wild rodent reservoir to man (which, however, may alsobe effected through direct contact with wild rodents or throughtheir fleas).
Thus, as these brief general statements suffice to show,considerable variances in the plague situations in the individ-ual countries, or even foci involved, are bound to exist, andthese variances are further accentuated by the presence of dif-ferent wild-rodent and wild-rodent fleas species in the variousaffected localities. Therefore, in order to arrive at an ade-quate appreciation of the plague situations in the presentlyinvolved American countries, it is necessary to deal individuallywith each of them.
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RES 2/12
TABLE II
Plague Incidence in the Americas from 1956-1962
(Figures culled mainly from the WHO weekly Epidemiological Record)
II.1 ArgentinaYear Plague Incidence
1956
1957
1958 One plague caserecorded in the MisionesProvince (see "Reportedcases of notifiable dis-eases in the Americas1949-1958", PAHO/WHOpublication Nº 48 - 1960,p. 70)
1959
1960
1961
1962II. 2 Bolivia
Year. Plague Incidence
1956 Three cases rec-orded in the Santa CruzDepartment, Valle GrandeProvince (see PAHO/WHOpublication Nº 48)
1957 -
1958
1959
1960 Small epidemic (12cases) recorded at Pucar,Santa Cruz Department, ValleGrande Province
1961 20 plague cases with8 deaths were recorded from26 March to 1 April in VillaSerrano, Boeto Province,Chuquisaca Department (WHOWeekly Epidemic Record 36,1961, 16:165)
1962
- 4 -
- 5 -
TABLE II (Cont'ed)
States affected
Pernambuco
III.3 Brazil .
Case incidence
Per State Yearly total
4 4
1957 Alagoas 5
Bahia 20 37
Pernambuco 12
1958 Bahia 25 25
1959 Bahia - 16 16
1960 Alagoas 13 28
Bahia 13
Rio de Janeiro 2
1961 Alagoas 12
Bahia 15
Ceará 7
Minas Gerais 2 106
Paraiba 31
Pernambuco 39
1962 Alagoas 1
Ceará 16
Paraiba 3
Pernambuco 13
Rio Grande do Norte 3 36
RES 2/12
Year
1956
- 6 -
TABLE TI (Cont'ed)
LocalitiesProvinces
Tungurahua
Manabi
'Chimboraz
LoJa
affectedCantons
Ambato
Jipijapa
EI.S 2/12
Case incidencePer Canton Per Province
18 18
12 I2
7
43
1957 Los Rios Vinces 5 5
Chimborazo Guano 12 12
Loja 62 79
1958 Chimborazo Guano 7
Riobamba 1 8
Loja Celica 9
Calvas 3
Puyango 1
Macará 1 14 22
1959 Chimborazo Guano 11
Riobamba 10 21
Loja Celica 4
Macará 1
Loja 7
Catacocha 1
Paltas 6 19 40
Year
1956
YearlyTotal
80
.
RES 2/12
TABLE II (Cont'ed)
II.4 Ecuador (Cont'ed)
LocalitiesProvincesYear
1960
affectedCantons
Case incidence YearlyPer Canton Per Province Total
Chimborazo
El Oro
Loja
Riobamba
Alausi
Guano
Piñas
Celica
Paltas
Calvas
Macará
Tungurahua
Chimborazo
Loja
El Oro
Manabí
Pichincha
Ambato
Riobamba
Guano
Calvas
Celica
Paltas
Pinas
Zarumln
Manta
Portoviejo
Rocafuerte
Quito City
Chimborazo Aluisi
Riobamba
* Infected in Manabi
35
5
10
10
15
5
1
7
17
12
1961
37 77
8
2
7
17
8
1
1
2
3
2
9
8
36
23
10
2*
1962
69
2 105
21
6 27
- 8-
TABLE II (Cont ed)
II.4 Ecuador (Contted)
Localities affectedProvinces Cantons
El Oro Pifas
Loja Calvas
Celica
Macará
Paltas
Puyango
Manabi Chone
Jipijapa
Junin
Manta
Montecristi
Portoviejo
Rocafuerte
Santa Ana
Sucre
24 de Mayo
Case incidencePer Canton Per Province
2 2
19
23
10
.1
3 56
13
1
1
86
9
26
16
12
74
3 241
I1.5 Peru
Localities affected Case incidenceYear Department Province Per Province Per Department Total
1956 Piura Ayabaca 8
Huancabamba 16 24 24
1957 Piura Ayabaca 9
Huancabamba 14 23
Ancash Huaraz 11
Recuay 3 14 37
RES 2/12
Year
1962
YearlyTotal
326
-9-
TABLE II (Cont'ed)
II.5 Peru (Cont'ed)
LocalitiesDepartment
Tumbes
Piura
Lambayeque
Cajamarca
Ancash
affectedProvince
C. Villar
Ayabaca
Paita
Sullana
Lambayeque
Hualgayoc
Huaraz
Case incidencePer Province Per Department
3 3
24
1
6 31
7 7
3 3
5 .. 5
1959 Piura Ayabaca 10
Huancabamba 4
Paita 1 15
Cajamarca Hualgayoc 18 18 33
1960 Piura Ayabaca 15
Huancabamba 117 132
Cajamarca Hualgayoc 7 7 139
1961 Piura Ayabaca 3
Huancabamba 65 68 68
1962 Amazonas Bagua 25 25
Piura Ayabaca 48
Huancabamba 44 92
Cajamarca Jaén 47 47 164
RES 2/12
Year
1958
YearlyTotal
49
- 10 -
TABLE II (Cont'ed)
II.6 United States
'StateCounty orLocality Cases
--
BES 2/12
.
1952-1955
1956 California Condado 1 1County
Colorado Boulder 1 1 SThe patient,who fell illin Texas, hadbecome infectedin Colorado
1958 -.-
1959 California Mono Ct'c: 1
'Tolumnoe t?. 1
New Mexico Bernalillo Cty. 1
Maryland Frederick Cty. 1 4 (Laboratoryinfection)
1960 New Mexico Chaves C-',r: 2 2
1961 New Mexico Santa Fe Cty. 3 3
1962 - -
-q
YearAnnualTotal Remarks
1957
- 11 -
TABLE II (Cont'ed)
II.7 Venezuela
Localities involvedYear State District Municipality
1956 Aragua Ricaurte Tejerías
1957 - - -
1958 - - -
1959 - - -
1960 - - -
1961 Aragua Ricaurte Tejerias
Marido
El Consejo
Turmero
Case incidence
3
-(a)
2
1
31962 Aragua Ridaurte La Victoria
Renarks - (a) The Weekl.y Epidemiological Record for 1960 (vol. 35,7:80) stated that evidence of plague in a wild:ro-dent (Sigmodon hispidus hirsutus) was detected onJanuary 26 in the locality last found affected byhuman plague in 1956.
RES 2/12
YearlyTotal
3
6
1
RES ?/12-12-
SECTION C
REVIEW AND EVALUATION OF THE PRESENT STATUS OF PLAGUE!N ARGENTINA
Incidence of the Disease
Dealing with the early history of plague in Argentina, Pol-litzer made the following statement:
"Apparently by-passing Buenos Aires and the Argentinianports on the Paraná River, plague became manifest first in SouthAmerica at Asunción, situated far inland in Paraguay, which hadbeen reached in April 1899 by an infected steamer. From this orig-inal focus the disease was soon carried back to Rosario and otherriver ports in Argentina, at the end of the year also to BuenosAires.
The initial period of the infection thus established wasfollowed first by a stage during which plague was carried inland byrail, then by further progress of the pest to remote regions in theinterior provinces of Jujuy and Salta on the Bolivian border in thenorth to Patagonia in the south, thus became gradually involved(Sussini, 1939).
As pointed out by De la Barrera (1942), generally speakingthe inland foci of plague in Argentina fell into two greups:
(a) those in the central part of the country, particularlyin the provinces of Rio Negro, La Pampa, Mendoza and San Juan,with a sparse population and no agriculture. Since grain storeswhich might have attracted'the rodents to the settlements were ab-sent, contact with infected animals was'restricted to chance meet-ings in the fields, and the incidence of human plague was conse-quently low.
(b) Those in the north, especially in Santiago del Estero,Tucumán and Salta, where accumulations of agricultural productsattracted the rodents to the settlements and houses, and the inci-dence of human plague was accordingly higher."
As estimated by Moll and O'Leary (1945) the number of plaguecases in Argentina from 1899 to 1930 amounted to about 6,200. Thefurther incidence of the disease up to 1952 is shown in the follow-ing table:
e
RES 2/12- 13 -
Year Cases Deaths Year Cases Deaths Year Cases Deaths
1931 37 24 1938 15 8 1945 ? 3
1932 61 19 1939 5 4 1946 10 3
1933 63 25 1940 228 192 1947 4 0
1934 45 40 1941 56 28 1949 12 4
1935 15 10 1942 38 19 1949/50 0 o
1936 31 21 1943 2 1 1951 1 0
1937 20 18 1944 107 63 1952 2 1
Note: In 1940 the provinces of Santiago del Estero, Córdoba and Tu-cumán were mainly involved, in 1944 Salta and JuJuy provinces.
Though these figures show the trend of the infection rather:than the exact incidence of the disease, which was probably higher,they indicate that during the period under review on the whole theplague situation was favourable. The ports remained free after 1931with the exception of a small outbreak (8 cases with 3 deaths) inNovember 1946 in Buenos Aires (Moll and O'Leary). Considering thelarge extent of the areas involved, the morbidity in the ruraldistrícts was as a rule rather low and as is characteristic of syl-vatic plague, the human attacks of bubonic plague were usually notgrouped together but appeared in numerous foci independent of oneanother (Outes and Villafañfie Lastra et al., quoted by Pollitzer).It must be noted, however, that the incidence of pneumonic plaguewas comparatively high and that repeated though usually limitedepidemics of this type were observed. Miyara and his associates(1947) recorded 27 such outbreaks with a death toll of 222 and oneinstance of recovery for the period 1913-1918.
It is interesting that, whereas early in the period under re-view the plague incidence was higher in summer, later on there wasa notable increase of manifestations recorded in autumm and winter(Villafafie Lastra and collaborators.)
Only two instances of plague have been reported in Argentinafrom 1952 to date, namely (1) one recorded in a 1960 PASB report asoccurring in 1958 in the Misiones Province; and (2) another in JujuyProvince, mentioned without date in a note recently received fromDe la Barrera who, referring to both these attacks stated that
"A scrutiny of the scanty existing documentation renders theexactness of their diagnosis doubtful".
It would appear, therefore, that since 1952 Argentina has beenpractically free from human plague.
RES 2/12
Giving in the above mentioned note an overall picture of thepresent plague situation in Argentina, De la Barrera stated that
1. Infection of the common rats, while frequent in the past,has been rarely met with durlng the period from 1940-1952 and not atall since the latter year.
However, deratization in the ports and cities being doneirregularly and inadequately, R. rattus and R. norvegious continueto be abundant (extraordinarlly so in some localities)-Their mostfrequent flea in the areas with a hot or temperate climate iG Xenop-sylla cheopis. In the colder regions Nosopsyllus fasciatus andN. londinensis are present. Generally the flea indices are low.
2. Though since 1942 no exhaustive studies have been made,sylvatic plague has been met with in some localities. The findingsof infected animals have been isolated and no reference has beenmade to epizootics. No new foci of sylvatic plague have been detected.
3. As shown by De la Barrera, the following wild-rodentfleas are capable of conveying plague by their bite:
Polygenis platensis cisandinus,Panallius byturus,Polygenis byturus,Delostichus talis.
Foci of sylvatic plague have been found in the following lo-calities:
Locality Province Longitude (WG) S. Latitude
Chafaritos Córdoba 658 302 30'
Rio Negro/La Pampa 659 30' 382 40'
Telen La Pampa 669 362
Mendoza 68- 20' 33"
Las Toscas Mendoza 688 40' 34- 10'
Icaño Catamarca 652 10' 282 50'
Rio Seco C6rdoba 638 30' 30P 30t
Tucuman/Sant iagoDel Estero 649 30' 308 30'
Salta 64Q 30' 259 35'
eo
__ __ __
- 14 -
58º 4o' ' 38ºQuenquén Buenos Aires 32'
RES 2/12- 15 -
Ecological Observations
Common rats
To judge from the compilation of Moll and O'Leary (1945),R. norvegicus was generally predominant among the common rats ofArgentina in the towns as well as in the rural areas. R. r. rattuswas less common, R. r. alexandrinus least frequent.
As summarized by Pollitzer, the relative epidemiological im-portance of the common rats and of the wild rodents in Argentina aswell as the question of a transition of plague from the former tothe latter or vice versa have been the subject of much debate. Nodoubt can exist that originally the infection spread from the rats(probably from R. norvegicus) to the wild-rodent species (VllafañeLastra et al., 1942) and it is also certain that foci have becomeestablished where wild rodents alone are responsible for the causa-tion of human plague as well as for the perpetuation of the infec-tion. However, in other localities a spread of the disease from thesylvatic rodent fauna to the rats was observed and the latter thenplayed a subsidiary or even a preponderant role in the causation ofhuman attacks. De la Barrera (1942) maintained in this connectionthat opportunities for contact between the wild and the commensalrodents were present, particularly in the agricultural areas of NorthArgentina where both were attracted by the grain stores, and a study-of the available literature confirmed that an involvement of the com-mon rats in the chain of infection was far more frequently notedthere than in the central provinces.
Wild rodents and lagomorpha
In an undated reprint of an article entitled "Roedores sil-vestres infectados por Pasteurella pestis en la República Argentina`",published in the book Primeras Jornadas Entomoepidemiol6gicas Argen-tinas and recently forwarded to the present reporters, De la Barrerafurnished the following excellent list of wild rodents and lagomor-pha found naturally plague-infected in Argentina:
First found infected:
Species Year Locality Observer
Cavia aperea 1924 Santa Rosa,La Pampa* Uriarte and González
Cavia pamparum 1942 Necochea, Bue-nos AiresProvince Alonson Mujica
Microcavia australis 1934 Pichi-Mahuida,australis Rio Negro
Province Llosa
* Cavia aperes is not indigenoua in this region* Cavia aperea ís not Indíigenous in thís regíon
- 16 -
Species
Microcavia australisjoannia
Microcavia australissalinia
Galea musteloidesmusteloides
Galea musteloideslittoralis
Galea musteloidesleucoblephata
Lepus europeus
Sylvilagus brasiliensis
Graomys griseoflavusgriseoflavus
Graomys griseoflavuscentralis
Graomys chacoensis
Graomys medius
Graomys cachinus
Eligmodont ia morenoi
Hesperomys murillus cor-dobensis
Hesperomys launcha
Hesperomys venustusvenustus
Year Locality
1939 La Paz, Men-doza
1940 7 de Abril,Santiagodel Estero
1940 Metán, Salta
1934 Fortin Uno,Rio Negro
1937 Santa Rosa,Mendoza
1935 Fortin Uno,Rio Negro
1942 Salta
1934 Fortin Uno,Rio Negro
1942 Rio SecoC6rdoba
1940 E1 QuebrachalSalta
1940 PellegriniSantiagodel Estero
1940 El QCebrachal,Salta
1940 7 de Abril,Santiagodel Estero
1934 Fortin Uno,Rio Negro
1940 7 de Abril,Santiagodel Estero
1940 Santiago delEstero
RES 2/12
Observer
De la Barrera
De la Barrera
De la Barrera
De la Barrera and.Riesel
De la Barrera andCorica
De la Barrera
Alvarado
De la Barrera andRiesel
Savino and Goobar
De la Barrera
De la Barrera
De la Barrera
De la Barrera
'De la Barrera andRiesel
De la Barrera
De la Barrera
e
.4
RES 2/12
Species Year Locality Observer
Hesperomys himaculatus 1940 Santiago delEstero De la Barrera
Akodon dolores 1940 Santiago delEstero De la Barrera
Lagostomus maximus 1940 Santiago delEstero Alvarado
Oryzomys flavescens 1940 El Quebrachal,Salta De la Barrera
Phyllotis darwini 1940 El Quebrachal,vaccarum Salta De la Barrera
Holochilus balnearum 1940 7 de Abril,Santiagodel Estero De la Barrera
Details in regard to some of these species furnished by De laBarrera in the above quoted contribution and in n aarticle publishedin 1953 in the Bulletin of the World Health Organization were asfollows:
... Microcavia australis (Caviinae); an animal somewhat smallerthan an adult guinea-pig, distributed all over Argentina west of the63rd meridian from Santa Cruz to Jujuy, but more abundant in thesouth than north of C6rdoba. Digs burrows, which as a rule are in-habited by 3-8 individuals. Cohabits sometimes with Galea.Herbivorous and diurnal, not penetrating into human habitations, butventures into their immediate vicinity. Its skin cannot be utilized,its meat is but rarely consumed.
Flea index: 20 in winter, 3 in summer. Most frequent fleas(a) in the north Craneopsylla wolffhuegeli (43%); Panallius galeanus36%); Polygenis byturus (19% ; (b) in the south Delostichus talis(45%); Hectopsyllagem-na (20%); Dysmicus barrerae (9%J; Panalliusgaleanus (8); Hectpsyl la cypha (7s); Polygen is platensis cisandinus
M. australis is apt to be decimated by plague epizootics. Atransition of the infection from it to man is usually due to directcontact with the carcasses with which the children often play.
... Galea musteloides (Caviinae) occurring in three subspeciesshowing the same geographical distribution as M. australis, butbecoming progressively more frequent towards the north. As notedabove, G. musteloides sometimes lives together with the latter rodent,the habits of which it shares.
- 17 -
- 18 - RES 2/12
Fleas: (a) in the north Tiamastus cavicola (64%); Ph. bytumus(13%); P. trypus (11% ); Cr. wolffhuegeli (5»); (data for the extremenorth).(b) in the south Panallius galeanus (47%); H. gemina (16%);H. cypha (9%); D. barrerlae~ (); P. platensis cisandinus (59)·
G. masteloides suffers from intense epizootics whenever plaguebecomes present.
·... Cavia pamparum (Caviianae) this species which is abundant inthe coastal areas of Argentina (Buenos Aires, Entre Rios, Corrientesand Santa Fé) does not dig burrows but shelters under sufficientlyhigh vegetations. Diurnal in habits, it úhows a lesser tendency thanthe above mentioned- rodents to approach human habitations.- Its meatis rarely consumed.
The flea index for C. pamparum is extremely low (o.04-0.1).-Though like the above mentioned species highly susceptible to ex-perimental infection with P. pestis and abundant in the most plague-affected regions, C. pamparum was found but once naturally infected.
Graonys griseoflavs (Cricetinae); two subspecies of thisrodent (Gr. gr. griseoflavus and Gr. gr. centralis) are widely dis-tributed in Argentina from Santa Cruz to JuJuy and from the 62ndmeridian to the west, while six other species of the same genus areoccurring less abundantly in the center and north of the country.Nocturnal and basically arborer,! Graomis friseoflavus which isslightly smaller than R. rattus, is prone to settle down in manylocations including hollow trees, nests of birds, burrows of otheranimals, bushes and even the thatch of the roofs of rural houses,in which latter it feels as much at home as in the open.
The flea-index of Gr. griseoflavus varles from 3-12. Inthe south its flea fauna consists mainly of P. platensis cisandinus(86%); which also abounds in the nests of the animais; other speciesmet with are Cr. wolffhuegeli (11%); Dysmicus hapalus (1%); andDelostichus talis (0.5%); in the north P. platensis cisandinus Isreplaced by P. byturus (20%); P. galleanus (14iT); and Cr. Wolff-huegeli (63%).
Invariably involved in the epizootics, Gr. griseoflavuspresumably plays a dangerous role in the spread of the infectionamong the wild rodents and is also apt to convey the disease to vocdcutters and other workers in the forests. Moreover, acting on ac-count of its ubiquity as a link between the sylvatic fauna and therats, this animal is likewise able to take an ominaus part in thecausation of intradomestic plague manifestations.
... Hesperomys (Gricetinae); as described by De la Barrera, sincespecies of this genus are distributed in Argentina from Chubut toJujuy, of which faur have been found naturally plague-infected.Though these rodents, which are somewhat larger than M. musculus, are _said to be arboreal, they are also met with in burrows, thus having eample opportunities of coming in contact with other sylvatic species.It is not surprising, therefore, that they become almost invariablyinvolved in the plague epizootics.
RES 2/12- 19 -
The flea-index of Hesperonys (in the north of the country)varies from 2 to 5. Their predominant flea is Cr. wolffhuegeli (51%);followed in frequency by P. byturus (39%) and P. galeanus MIU).
... Oryzomys flavescens (Cricetinae); this arboreal species, ofthe same size as the hesperomys, though widely spread in subdomesticenvironments-as well as in the open, was but-rarely met with natu-rally plague-infected. --Its flea-index was 1-3 with Cr. wolffhuegeliforming 65% of the flea-fauna, P. rimastus 22% and P. pl. cisandinus5%. However, in the north of the country P. rimastus was found to bereplaced by P. byturus (30%).
... Eligmodontia morenoi and E. hirtipes jucunda (Cricetinae);these rodents of the same size and habits as the foregoing species,are met- with only in the north of the country. They have been foundplague-infected in pirguas (rough structures for the storage of maizeand other agricultural products), where they are apt to live togetherwith other wild rodents and R. r. alexandrinus.
... PhyLlotis darwini vaccarum (Cricetinae); somewhat smaller insize than Graamys and of arboreal habits, this species also oceursonly in the north of Argentina, where it has been found plague-infected in maize pirguas. Its flea-fauna is unkown.
Holochilus balnearum (Cricetinae); this rodent, of the samesize as Phyllotis, though of aquatic habits, is met with also on firmground where it is apt to penetrate into the storages of cerealskept near the houses. It has been found naturally plague-infectedin these locations. Its fleas have not been determined.
Akodon dolores (Cricetinae); of the same size as M. musculus,abounds in the center of Argentina, living in small burrows or belowshrubs, but was only on rare occasions found plague-infected. Itsfleas include Cr. wolffhuegeli (64%); P. byturus (28%); and Panalliusgaleanus (7%).
... Lagostomus maximus (Chinchillidae); as stated by De la Barrera:'This large rodent is represented by three subspecies distrib-uted over the whole country from the 40th degree latitude toJujuy. Strictly nocturnal, herbivorous, burrowing, it is anagricultural pest. Does not approach the houses. The younganimals are sometimes hunted for the sake of their skins andmeat."
Found but accidentally plague-infected, this species does notseem involved in the conveyance of the infection to man. It is muchinfested by fleas (index 10-30, conparatively highest in old animals).The fleas found on Lagostomus are: in the south and center: P.irritans (73O); Hectopsylla stonys (25%); in the north PanalliUsgaleanus (66%); P. irritans (21%); Hectopsylla stomys (11l).
... Lepus europaeus (lagomorpha); this cosmopolitan species ofhares abounds everywhere in Argentina, where it is much hunted for tbhesake of its skin and meat. It is slightly flea-infested, almost ex-clusively by P. irritans.
- 20 - RES 2/12
These hares have been invariably found. plague-affected in thecourseof the epizootics, but their infection-rate was always low.For this reason human infections due to the skinning of the carcassesof the animals were also not numerous.
... Sylvilagus brasiliensis (lagomorpha); this animal, which is alittle smaller than a rabbit, is met with only in the north of thecountry (Salta, JuJuy, Formosa, Misiones). Only two instances ofplague infection have been detected in this species up to 1952. Itsflea fauna has not yet been investigated.
As has been stated in earlier parts of these reports, De laBarrera, no doubt influenced in the first line by his long and ampleexperiences in Argentina, postulated that all wild rodents and lago-morpha found plague-affected in South America are equally susceptibleto the infection, their comparative importance in the maintenance andspread of the disease depending solely upon differences in their pop-ulation density and ecology. The present reporters had to point out,hovever, that observations made elsewhere, for instance in the UnitedStates, proved or at least suggested that a distinetion had to bemade between (a) species or races of wild rodents or lagomorpha serv-ing mainly or solely as fuel for the spread of plague and (b) such -which - possibly because more resistent to infection with P. pestis - $4were capable to' act as permanent reservoirs of the disease. Thequestion whether such differences existed also among the plague-affected species in South America was in the opinion of the presentreportera still sub judice. They considered in this connection theprobability that during the interepizootic periods plague might berestricted to territorially quite límited strongholds of the infectionand pointed out that the detection and thoraugh investigation of suchlocalities would go a long way to establish which species of rodentsor lagomorpha were instrumental in bridging over the gaps between themanifestations of epizootics.
It might seem at first glance that Argentina, where plague isnow at low ebb, might be a suitable locale for such studies. However,due account has to be taken of the disproportion between the enormoussize of the potentially still affected areas and the now apparentlyrare and rather unpredictable reappearance of quite limited manifesta-tions of sylvatic plague.
Concluding remarks
Reassuring as the recent absence of plague in man and apparentlyeven in the conmon rats of Argentina is, one should not forget thatin view of the undoubtedly continued existence of sylvatic plague,however little manifest at present, the possibility of a recrudescenceof the disease cannot be altogether excluded.
RES 2/12
REFERENCES
De la Barrera, J. M.
Idem
Idem
Miyara, S. et al.
Moll, A. A., andOlLeary, S. B.
Outes, J. D.
Pan American SanitaryBureau
Pollitzer, R.
La peste-rural en la Argentina. Pri-mer Congreso Nacional sobre Enferme-dades endemoi-epidémicas. Buenos Aires(1942): 431-432
Rongeurs sauvages infectés par Pas-teurella pestis en Argentina. BulletinWorld Health Organization9(1953)5: 701-705. (See also Spanishversion "Roedores silvestres infecta--dos por Pasteurella pestis en la Repúí-blica Argentina". Boletín Oficina Se-nitaria Panamericana 36(1954)4: 434-W371.3
Roedores silvestres infectados porPasteurella pestis en la RepúblicaArgentina. Publicado en el volumen-de Primeras Jornadas entomoepidemio-16gicas Argentinas. (Undated)
La peste rural en la provincia de Men-doza. Estudio clinico-epidemiol6gico-.Revista de la Asociación Médica Argen-tina 61(1947)601-602: 161-182
Plague in the Americas. Publicación225, Oficina Sanitaria Panamericana(1945)
Boletín Sanitario (Buenos Aires)3(1939): 636. (Quoted by Pollitzer,1954).
Reported cases of notifiable diseasesin the Americas. Scientific publica-tions 48(1960)
Plague. WHO monograph series 22(1954)
Peste. In: Décima Conferencia Sani-taria Panamericana, Resumen de sus la-bores. Boletin de la Oficina SanitariaPanamericana 18(1939)1: 33
Villafañe Lastra, T. deet al.
Epidemiología de la peste en la provin-cia de Córdoba, Primer Congreso Nacio-nal sobre enfermedades endemo-epidémi-cas. Buenos Aires (1942): 594-596
- 21 -
?u5sínio, M.
- 22 - RES 2/12
SECTION D
REVIE AND EVALUATION OF THE PRESENT STATUS OF PLAGUE,IN BOLIVIA
Incidence of the Disease, , , ,~~~~~~~~~~~~
The tabulations of the plague outbreaks in Bolivia from 1921 to 1948furnished in a report by-De la "er8rera (I955)and,. in a mcre. elaborateform,.by Macchiavello (1959) may thus be reproduced in a somewhat modified form:
Macchbiavello
Cases/DeathsLocality
Observa-tions onEpizootics De ia Barrera
1921 I-VI Padcaya,'Arce Prov.TariJa Dept.
1921-22 XII-V "I
V-VII Vallegrande Prov.,Santa Cruz Dept.
1,525/642
?375/300
?300/88
El Filo, Cordillera.Prov., Santa CruzDept.
Iataral (same prov.and dep.)
1932-33
? ?
Huayrahuasi Grande,Tomina Prov., Chu-quisaca Dep. 1,500/800
1933 VIII llataral (as above) ? ?
XI . Iosquerillas (?)
XII Montecanto, TominaProv.
Pampas del Tigre,Boeto Prov., Chuqui-
saca Dept.
LO/12
? ?
None Recorded 1,525 casesuith 842 deaths fromJanuary to August
i" Recorded 300 deaths
Mentioned about 2CO0 c.
"1 No record
tl ti n
Recorded an outbreakin this locality inDecember 1932
et
Recorded an outbreaktaking place fromNovember 1933, toJanuary 1934, inPadilla, TominaProvince, extendingfron there as far as
? the Azero River
Year and.Month
1928
.1929
1930
" '1934
.
RES 2/12- 23 -
Cases/Deaths__aLocalityt
Postrevalle(Vallegrande Dept.) 16/?
Observa-tions onEpizootics De la Barrera
None
1934-35 x-II Yanakur}-o, E1 Rosal,Tomina Prov.
Postrevalle (asabove)
VI Villa Serrano,Boeto Prov.
1 ,.
I-II Montecanto (as above)
1937-38 E1 TapialXI-IV (?)
XII-III
1938
Entre RíosO Connor Prov.
Monteagudo, AzeroProv., ChuquisacaDept.
12/9
? ?
? ?
? ?
" Huayrahuasi Grande,Tomina Prov. (19 cases)
11" Pencal (VallegrandeProvince)
11
t1
? ?
106/?18 In Rattus Recorded sane outbreak
56/34
IV-VII El Palmar, Gran ChacoProv., Tarija Dept. ?100/?50
None
In Rattus
VIII-X Choreti and Camiri,Cordillera Prov.
1938 IX Various places ofTomina Prov.
151/63Recorded a case inci-
r" dence of 290 in thesetwo localities ("endof July")
? ? None Sachapera, Palmar,Aguayrenda, 90 casesin May
Abopd and Cabezas,Cordillera Prov.
IX-X Carahuaycho, CordilleraProv.
IX La Herradura, CordilleraProv.
1938-9 Entre Rios (as above)XII-I
? ? Apparentlypresent
Cuevo Cordillera Prov.,35 cases in December
? ? In Rattus
1/0.
6/1
si
lNone Recorded 5 cases fromDecember 1938- January1939
Year andMonth
1934
56/34
1935
1937
1t
RES 2/12
Year andMonth
1938-9 XI-II
XII-III
1939 I
VII-X
?IX
XII
1940 I, XII
Cases/Locality Deaths
Muyupampa, Luis CalvoProv., ChuquisacaDept. 16/10
Cuevo, Cordillera Prov. 36/23
Taperillas, L. CalvoProv. 1/1
Camaitindi(?)
Llactonsillos, TominaProvo
Contadero, BellezaTomina Prov.
Charaega (Ovai andOvaicito)
Cuevo (as above)
III Thola, Orcko, TominaProv.
III Entre Rfos (as above)
VII-VIII Ivo, Boyiube (?)
VIII-IX Aguayrenda, Gran ChacoProv.
IX-X Misidn Santa Rosa (?)
XI-XII Camiri (as above)
?XII Postrervalle (as above)
3/3
8/4
12/7
5/3
2/0
71/1
2/?
16/10
3/1
18/15
2/1
?
Observa-tiona onEpizootics De la Barrera
In Rattus
Esperillas, L. CalvoNone Prov., 1 case in
January
.I
Ir
In
"Llantocsillas", LaCrice- Belleza, outbreak
tinae from July - October1939
Vaca Guzmán, L. CalvoNone Prov., 2 cases in
February 1939
"Ovay" near Charagua,L Rattus December 1939
None Recorded 1 case inJanuary, 1 inDecemrber
n
In Rattus
1 case
2 cases in Aarch
Recorded the samedates
None Recorded same outbreek
In Rattus Recorded 6 cases atSanta Rosa de Culevohasta Pirital inOctober
n Recorded same outbreak
None Ipati (?), 1 case inAugust
- 24 -
A
RES 2/12- 25 -
Year andM1onth
1941-42
1942-43 X-I
X-III
X-V
1943 V-IX
Locality
Ipitá (?)
Sapotendi y Kara-Kari (?)
Gutiérrez (?)
Mosqueras (?)
Moreta, O'ConnorProv.
Cases/Deaths
? ?
42/45
?25/?
2/?
8/6
Observa-tions on
Epizootics
None
De la Barrera
Recorded 41 cases at"Sipotendi" and "Kari-Kari
" Recorded 18 cases
? Shortly mentionedthis outbreak
19144 III Arraydn, Boeto Prov.
Alisos, Arce Prov.
¡III-VIII Muyupampa (as above)
VII Campo Grande, GranChaco Prov.
VIII-XI Vallecito, L.Calvo Prov.
!44 VIII-IX El Fraile, Valle-grande Prov.
Temporal, Boeto Prov.
X-XII Santiago Chico, BoetoProv.
945 I-IX Lagunillas y Pueblito
Muyupampa (as above)
IV-VI Vallegrande (as above)
4/?
6/2
4/2
lNone
Ir
.,
n Caviae Recorded 3 casesduring 26 rmay-3 Juime
None Recorded 8 cases inJuly at Yacuiba (?TariJa Dept.)
8/4
2/?
9/Y7
13/?2
25/12
1/0
76/33
Recorded same data
In Rattus Recorded same outbreak
None
Recorded same outbreakas occurring in Valle-grande and its environs
Piraimiri (?)
El Arrayén, BoetoProv.
XI-XII
1946 v
29/7
el
C5
1C
1/?
RES 2/12
Locality
Temporalcillo, BoetoProv.
Cases/Deaths
8/5
Observa-tions onEpizootics De la Barrera
None Recorded same outbreakl(? "Temporalito")
1947
?VII
II
1948 VIII
Choreti (as above)
La Herradura (?)
?Morebeti, CordilleraProv.
Muyupampa (as above)
Tomina
Floripondio, ?Valle-grande Prov.
La Cueva, TariJa Dept.
1/?
2/0
?/17
2/2
9/7
,t
In Rattus
None
4t/4 ?In Crice- Recorded 5 cases. Notina-e rats, Graomys preva-
3/ None Recorded 8 casesnt
3/? None Recorded 8 cases
More detailed data on the plague incidence in Bolivia during the peri-od from 1949 to 1960, recorded by Torres Bracaronte and Gonz6lez Moscoso(19,61) may thus be sunmarized:
Department Province Canton Locality Year Month Cases Deaths
Tarija Gran Chaco Carapar. Comni1n 1950 VIII 3 0
Sanandita 1957 XI 2 0
Chuquisaca Tomina Padilla Thola 19>49 XII 3 2OrckoMuyu 1952 X-XI 14 6OrckoEiTabacal " 3 1
Huayco-pampa 1954 XI 5 5
MonteCantu " 3 1
Asterillo " 1 0
El Salto " 2 1
Year and.-Month
IX-X
- 26 -
RES 2/12
DUe·tent
Santa Cruz
Province Canton Loclity Year
Angostura
GargantaXhasa
Luis Calvo Vaca Guzmin El Pincal
Zudn lcz Mojocoya Bella Vista
Presto Tapirani
H. Siles Fernández Pumamayu
CaSamrnayuCanayu
Ca~amayu
El Rodeo
Florida Cuevas Novillos
Ichilo San Carlos QuebradaSeca
Pozo Verde
Rasca Buchi
Chacos
QuebradaSeca 1951
La Hoyada 1952
Jaboncillo
Fernandez
El Zapallar
Tranca Mayu
El Potrero 1955
Piedra Palta
Duraznillo
N4echo Comido
Valle AltoGrande Seco
Pucard
Month Cases
XI 1
n
1951 '"
1952 IX
1955 VIII
1959 XII
t!
1960 1
Ie
I-II
1950 VI-VII
nc
II
x
II
XI
el
XI-XII
xi
XI
It
Deaths
1
1
0
6
0
3
0
1
1
1
2
1
1
9
1
5
1
4
5
2
8
2
2
5
2
2
2
3
1
2
7
1
2
10
1
7
2
1
8
2
5
1
1
8
1
7
1
1
5
···II Ii__ i
- 27-
- 28 -
Province Canton locality Y
Tranca l2ayitu
Tranca Ma4u
Ca as
La Higuera
QuesilloPampa
E1 Abra
-.=. RES 2/12
ear . Month Cases Deaths_ _ _
XII
e.
Ir
n
9
2
4
1
2
I
5
0
3
0
1
0
Guayabilla
i sko Loma 1956 I
teCañas
La Torre 1960 XI
Cordillera Choreti Yapuy 1952 XII
J_~~~~íc1 x .
Addendum: According to the 11tHO Jeekly Epidemniological Record for 1961(Vol.36, No.16, p.165) 20 plague cases with 8 deaths wxererecorded from 26 liarch to 1 April in Villa Serrano, BoetoProvince, Chuquisaca Department. This, and PASB lealth Sta-tistics, Vol.XI, Nos.l-4 (January-December 1962), are thelatest reports available as of 31 December 1962.
As can be gathered fromi the first of the above inserted tabulations,plague was first recorded in Bolivia in 1921 in the department of Tarijawhich, lyirg in the extreme south of the country, borders on Argentina.Then, after an apparently quiescent period, the presence of the disease w1asagain reported in 1928 in the Vallegrande Province of the Santa Cruz Depart-ment, situated about 400 km north of the first affected area and, as assertedby De la Barrera, not in direct communication with it.
Discussing this quite e:xtraordinary sequence of events, this observerand Macchiavello were in agreement that the initial appearance of plague inBolivia was the result of a spread of the infection from Argentina, but werenot in accord in regard to the manner in which this invasion took place.Referring to this problem in the concluding parts of his report, De la Ba-rrera unequivocally maintained that
"The country was invaded by the disease in 1921, iwhen it ex-isted already twienty years previously in Argentira and Para-guay. Plague began in an area where the domestic rat existsand probably came urith the rat fron the Argentinian borderzone."
L
A
1
1
1
12
3
14
0
1
4
2
2
L .
l'
194 X
-t
- 29 - RES 2/12
Macechiavello, claíimij g that in 1920 and 1921 a serious plague epi-denic vas presentin the border province of Jujuy and in other parts ofArgentina, considered it as posesible that the infection might have beenimported by fleas hidden in a bundle of silk clothes brought in for con-mercial purposes by the first patient affedted by the disease in Bolivia.On the other hand, in his opinion it was
"also probable that the zone of Padcaya mas the seat of anepizootic among vild guinea-pigs, propagated by continuityfrom the enzootic zone of the above mentioned rural plaguearea in Argentina. This seems to be indicated by the sea- ..sonal recrudescence of plague and its quiescence during thecold months from July to November, (followed) by a reappear.-ance in December during the hot and rainy season."
It is true that later on, at the time of the 1944 outbreak at Ali-sos mentioned in the table, the presence of plague in the vwild guinea-pigsof the Tarija focus has been confirmed. Nevertheless, on the whole itseems more likely that, as assimed by De la Barrera, the common rats wvereinstrumental in bringing the infection from Argentina into Bolivia. It issignificant to note in this connexion that Macchiavello (a) ascribed theappearance of plague in the Vallegrande Province in 1928 to the importa-tion of infected rats from Argentina in cargoes destined for the StandardOil Company installations in that area and (b) similarly held the road-building operations and the intensified traffic caused by the Chaco mar(1933 - or, one should rather say, 1932 - to 1935) responsible for a tranc-port of plague-aeffected rats or rat-fleas into Tomina in 1932. He empha-sized, however, that since both these areas vere not inhabited by commonrats, a spread and perpetuation of plague could take place only in the wild-rodent populations. It is certain that purely sylvatic plague focí havebecome established in both provinces. Still, it is not easy to reconcilethe quite exceptionally high incidence of plague in the Tomina Province in1932-33 (1,500 attacks uith 800 deaths) uith the concept of a wild-rodentnature of this outbreak. For this and other reasons one can not claim thatthe problem of the early history of plague in Bolivia has been fully eluci-dated.
ahile venturing no definite statement regarding the origin of wild-rodent plague in that country, De la Barrera felicitously stated that
T'MIrine plague has followed a regular route of invasion, asis the rule by the most easy x.rax, first from west to east,then from south to north. As always it follotred the routesof human traffic from the Argentinian border over Padcaya,Tarija, Entre R!os, Villa Dontes, meeting there irlth anothercurrent, probably also of border origin, from Yacuiba viaAguayrenda and Sachapara. The Chaco war accelerated its prog-ress, carrying it as far as Abapo and Cabezas on the IRoGrande in 1939. The last outbreak vas recorded in 1952."
As De la Barrera added, except at Padcaya all murine outbreaks tookplace at altitudes of less than 1,300 m and in a wlarm and semi-dr-y climate,i.e. an environment suitable for X cheopis.
RES 2/12- 30 -
As a result of the just described progress of the rat-caused iufec-tion and of a .ride spread of the disease among the wild rodent populations,plaeue eventually involved an extensive area bettveen the 18th and 22nd de-grees of southern latitude and the 63rd and 65th meridians west in the.three departments of Tarija, Chuquisaca and Santa Cruz (1Macchiavello, 1959).-As estimated in a report by the Director of the Pan American Sanitary Bu-'reau published in 1958,the regions involved had a size of 10,036 squaremiles, stretching from the Argentine border in the south to the province ofIchilo in the north and from Cordillera Province in the east to that of Zu-danez in the west.
Emphasizing the seriousness of the plague situation in Bolivia intheir 1961 publication, Torres Bracamonte and Gonzdlez ioscoso pointed (a)to the appearance of the disease in the hitherto unaffected cantons of SanCarlos <Ichilo Province of the Santa Cruz Department) in the north and 1Mo-Jocoya (Zudafez Province of the Chuquisaca Department) in the northrwest in1950 and 1952 respectively and (b) to the 1955 invasion of the Presto Can-ton, still farther vest in the province of Zudafiez. More dísquietinglystill, the tuo authors stated that to the area proven to be plague-affected,
"it is even possible to add that of the provinces Tahua-manu and Abuná of the Pando department and that of Vaca Diezin the Beni department, in which according to almost certaindata sporadic human cases and big epizootics among the dones-tic rodents occur--a not strange phenomenon if one considerstheir vicinity with the frontier localities of Brazil, inwhich these rodents abound."
As uill be further discussed belo, it would be most important to es-tablish the authenticity of this claim.
Discussing the ecology of plague in Bolivia, De la Barrera subdividedthe affected area into the following four zones:
(1) Eastern zone, extending fron the cordillera of Incahussi over Cuevoto Cabezas. Though inhabited by common rats infested with X. cheopis,plague w*as also found in vild rodents of this zone. Many of the urbancenters vithin it had lost the importance they had during the Chaco sar,but others, like Camiri and Choreti, had gained in importance oxving to theexploitation of oil-wells.
(2) Southern zone, really consisting of tiio regions -- one in the westround Padcaya, invaded by plague in 1921, and an eastern one, which becameinfected 15 years later. Both these regions are infested with rats andX. cheopis which, however, is less frequent in the highly situated ;.est-ern region.
(3) Central zone, free from rats, extending from the Azero river in thenorth to the Ifao mountain range in the south; ond
(4) Northern zone, situated in the environs of Vallegrande and also freefrom rats.
:
RES 2/12- 31 -
Following a somewhat different systen, &Macchiavello distinguishedbetureen (a) a soutbern zone, comprising the Tarija Department; (b) aneeastern zone, encompassing parts of the Luis Calvo and Azero provinces(Chuquisaca Department) as uell as the Cordillera Province of the SantaCruz Department; (c) sylvatic plague zone of Tomina (Chuquisaca Depart-ment), comprising besides the province of Tomina also those of Azero andBoeto; and finally (d) the sylvatic plague zone of Vallegrande (SantaCruz Department), including, besides the province of that name, parts ofthe Florida and Ichilo provinces and some adjacent localities of Cordi-llera Province.
In constrast to De la Barrera, lacchiavello upbeld that plague inthe oriental zone was exclusively murine in character but that on thecontrary the southern zone
"corresponds in part to murine, in part to sylvatic plague,being really an extension of 'what the Argentinlan authorscalled for many years 'peste ruralt."
Macchiavello admitted that as a rule there existed in the south-ern zone a relation between the urban murine plague and the sylvaticmanifestations in caviae and cricetinae. He maintained, hoyever, thatindependent foci of sylvatic plague existed in some localities. Thus, asalready mentioned above, at the time of the 1944 outbreak at Alisos (Ta-riJa), plague-affected wild guinea-pigs had been found in a region freefrom rats as well as from epizootics among the cricetinae. Generallyspeaking Macchiavello was of the opinion that the subsequent prevalenceof rat-plague detracted attention from the sylvatic origin of the infec-tion in the southern area. However, as has been noted above, the valid-ity of the views held by him regarding the invasion of this zone is opento considerable doubt.
Observations on rodents and lagomorpha
Conmon rats
Investigations made by De la Barrera on a sufficiently large scaleshowed an entire absence of R. norvegicus in the rat-infested part ofthe Bolivian plague areas, all the rats caught belonging to the subspe-cies R. rattus alexandrinus. To judge from the results of trapping andfrom the damage they caused, the population density of these animals rasalarmingly high. In the rural areas they showed little tendency to leavethe houses or their imediate vicinity.
- 32 - RES 2/12
M. musculus
As can be gathered from Macchiavellots report, M. musculus was metwith not only in the rat-infested zones of-the Bolivian plague area, butalso in thbe Tomina and Vallegrande regions.
Visiting a group of houses situated at a short distance from thetown of Padilla where about two weeks ago a plague outbreak involving 12persons had terminated, De la Barrera found one plague-infected house-mouse. Since common rats were absent from this locality but neverthelessthe outbreak was of a familial character, affecting 6 persons in one com-pound and 4 in another, De la Barrera inclined to the belief that M. mus-culus played a causal role in this instance. As no clear-cut evidence ofa wild-rodent epizootic could be found, it could not be established inwhat manner the mice had become infected. Likewise, since the bouses badbeen energetically treated with DDT before De la-Barrerals arrival, itcould not be ascertained which fleas has spread the infection among themice and conveyed it from them to man.
Wild rodents and lagomorpha
As can be gathered from a table inserted in the article of Macchia-vello, he found the following rodent and lagomorpha species in the fourBolivian plague zones distinguished by him:
-t
,-t
-I v--"------·-
ai·- -- ---· llrrn---·----·---------·--------�,,
CUr_4
rfiPSslWr
O*r-
C
sn~
o
H 41
E9 hO
ipa
.n= R
t) X @
,0 z
,-- I1
~4)II
._
*d
,.
N N
a O
C
4w
Mf
0
a)ts
r.f I
c/
CQQ.a )
O X Q w O· u- Q I
:. '$: n g X 9 @ $o aLo ~I t
o0
A
o
sqg.n93
c~IQ
o .
.@ QPcdr
o~
,r"l..,l
a,S :
P4 b Q
t d= X 4 <5 g~~~*~
P; :E M X & A~~*r"
P1 a
z -H
QzD ax w4-P
.H .0 t
m 50 aJ OH 1
90 r4 o q o
Eio A
H o Q)
-H ) ri laI., i.-, 4 o m? w ,1 U 0 U n<0 $
lQ o * o Qm4 > X H P h X X S @ a> 0 @
4 C 0 m m ra .. rd Pc QZ ic vet/2,e9 Qro 0 o h * S
~:~ k ~ Xo o
r a 3 S j:o O0
~ X >a o o o
i ^ oh
ló, 9
1 1 1 1 ,1
a °
~~~0
o p
E3o a o P1 O i c~ c~~~~~~~c
S o 4 ~ ux o u
e :1 O O hiES~ · o
-~~~~
~m co~c
"- ~ ~ ~ ~ . 4. -~ 0 0-"'-- I~-'~
W car
G? COtOm 0
.e a>
PQ mEa1 > 0. Vd m D 1 h4o E3 0 CQ bD si@
h 9 t,° ?, ci 1 g
Ci : H H
r z
:o m o~
RES 2/12
Besides R. rattus and M. musculus, De la Barrera encountered thefollowing species of rodents and lagomorpha in Bolivia:
Species Found in
Graomys griseoflavusGr. mediusEligmodontia hirtipes hirtipesEurysygomatomys spinosusPhyllotis wolffsohniPh. nogalarisProechimys longicaudatus
longicaudatusAkodon mollisOxymycterus doris
0. paramensis
Rhipidomys leucodactylus
Rh. collinusHolochilus chacariusOryzomys legatus
O. sp.
Oryzomys longicaudatuslongicaudatus
O. boliviaeOlygoryzomys stolzmanniO. sp.Hesperomys fecundusH. muriculus
Oecomys mamoraeSylvilagus brasiliensisLeptosciurus leucogaster
Guerlinguetus ingramiLagidium viscacciaLagostomus maximus immolisDasyprocta variegata boliviae
Cnmiculus paca
Galea musteloides(? G.m. deramissa)
Cavia tschudii atahualpae
All the plague areasPadilla, ZudafiezZudafiezFloripondioValle Grande, SamaipataSerrano, LaderaBuen Retiro, Agua Hedionda, Flori-
pondio, NóvltlosValle Grande, Pucara, QuirusillasAgua Hedionda, Lagunillas, RIo
Grande, El FrailePadilla, Cuevo, Valle Grande,
Serrano, El RosalPadilla, Serrano, Camiri, Entre
RPosPadilla, Agua HediondaBuen Retiro, Lagunillas, PadillaPadilla, Serrano, Valle Grande,Villa Montes
Serrano, Lagunillas, Gutiérrez,RIo Grande, Pucara, Valle Grande,Samaipata, Cabezas
TariJa
TrinidadPucaraBuen RetiroEntre Ríos, Villa MontesBuen Retiro, Agua Hedionda, Samai-
pata, Padilla, Serrano, Camiri,Villa Montes
Buen Retiro, TrinidadBuen Retiro, Agua Hedionda, CamiriBuen Retiro, Samaipata, Agua He-
diondaBuen Retiro, Floripondio, NovillosCuesta de Monos, ZudafiezNueva EsperanzaBuen Retiro, Agua Hedionda, Trini-
dad, Samaipata, Lagunillas, Gu-tierrez, Pirirenda, Curiche, No-villos, Floripondio
Buen Retiro, Trinidad, Puerto Cés-pedes
Valle Grande, Pucara, Samaipata,Aiquile, Totora, Zudafez, Cuevo,Quirusillas, Padilla
Trinidad.
4
*,-
D
- 34 -
RES 2/12
Referring to observations made in the case of a few of the previ-ously mentioned species, De la Barrera recorded the following data:
(a) Graomys griseoflavus. Confirming the findings previouslymade in Argentina, De la Barrera proved the occurence of natural plaguein this rodent species during a 1954 epizootic at Pucara (Valle GrandeProvince) in which also Galea musteloides vas implicated. Like in Argen-tina, Graomys griseoflayus, leading partly a sylvatic and partly a domes-tic existence, functioned as a dangerous liaison animal between the wildand the intradomestic rodent fauna..
(b) Hesperomys muriculus. This rodent which partly led an arbo-real existence, was less agile than Graomys but was nevertheless apt topenetrate into the houses - usually during the night. Like Graomys itwas mainly infested by fleas belonging to the genus of Polygenis.
(c) Galea musteloides. As noted above, this rodent which be-longs to the family of Caviidae, was found plague-affected at Pucara.Being much hunted for the sake of its meat, it was potentially ratherdangerous. Still, no definite information was available that the hunt-ing of these animals and the handling of their carcasses formed an im-portant source of human plague infection in Bolivia. 97. % of the fleasfound on G. musteloides belonged to the species Tiamastus cavicola.
(d) Dasyprocta variegate boliviae, an animal of comparativelylarge size was also intensively hunted for the sake of its meat. Thoughliving in burrows situated in the open spaces, this "Jochi colorado"was apt to enter the plantations. It appeared to have been implicatedin the plague manifestations at Buen Retiro (Vallegrande zone) in 1950.It is important to note that the fleas found on this rodent includedbesides P. irritansa Tiamastus cavicola and Rhopalopsyllus species alsosuch belonging to the genus Polygenis.
(e) Cuniculus paca, an animal of nocturnal habits which wasalso much hunted, had thus far not been found involved in the plagueepizootics. Its fleas included, besides Rhopalops llus species, Poly-genis robertí beebei and Adoratopsylla (Tritopsylla) intermedia oxyura.
(f) Domesticated guinea-pigs. As can be gathered from De laBarrera's report (a) breeding of guinea-pigs in -the houses vas less gen-eral in Bolivia than in some of the other South-American countries; and(b) no detailed information was available regarding a participation ofthese animals in the plague manifestations. Since, however, the pres-ence of X. cheopis was proved in the case- of the few specimens examinedby De la Barrera, the domesticated guinea-pigs are at least potentiallyrather dangerous.
Information on the role played by the various species of wildrodents and lagomorpha found naturally plague-infected in Bolivia (seelast column of the table inserted on p.33) in the perpetuation andspread of the infection is still deplorably scanty. Macchiavello merelymentioned in this connexion that investigations made from 1941-1944 in
- 35 ~
- 36 - RES 2/12
the Tomina zone and at Alisos (Arce Province) had proved the existenceof sylvatic plague in caviae and cricetinae and, as has been discussedabove, considered it as possible that the former animals were the fonsand origo mali in the southern Bolivian plague area. Some further in-formation may be culled from the brief reports on a few subsequentplague outbreaks rendered by De la Barrera, whose statements in pointmay thus be summarized:
Locality and timeof the outbreaks
Floripondio(Vallegrande Prov.)1947
Observations on humanplague
5 cases (3 in one house)
Observations on rodent andlagomorpa
Graomys griseoflavus was foundto be predominant among thewild rodents
Buen Retiro(Vallegrande Prov.)Aug. - Oct. 1950
15 victims, most of whomcontracted the infectionin the fields
The human outbreak was pre-ceded by a most intense epizo-otic in the wild rodents Which,however, was apparently not in-vestigated. According to the;subsequent observations of De-la Barrera, Hesperomys muricu-lus was the most numerous wild-rodent species, while Graomysgriseoflavus was less fre-quent. Both of these rodentswere apt to penetrate into thehouses.
Also found were Oecomys mamoraeand Olygoryzomys sp. The pres-ence of Dasyprocta, Cuniculusand Sylvilagus seems to haveattracted attention during the1950 epizootic.
Pucara 9 suspicious cases(Vallegrande Prov.)August 1954
Epizootic involving Grao9nysgriseoflavus and Galea muste-loides, in both of which thepresence of plague was con-firmed by De la Barrera.
Padilla(Tomina Prov.)Feb. - March 1955
12 bubonic cases(6 in one house, 4 inanother)
Information on the presence ofan epizootic not conclusive.The rodent species subsequentlyfound by De la Barrera includedbesides M. musculus (foundplague-infected as stated above)Hesperomys venustus, Graomysgriseoflavus, Oryzomys legatusand Galea sp.
04
O
4
o
--
- -
RES 2/12
De la Barrera emphasized that the fev wild rodents dissected byhim (apparently 3 Graomys and one Galea), tbough showing an abundanceof P. pestis in their organs, exhibited hardly any macroscopic signs ofplague, having thus evidently been the early victims of an overwhbelminginfection. It would not seem justified to conclude from these few obser-vations, made during an acute epizootic, that the two species invariablydevelop this type of the disease and thus, because highly susceptible toplague, are incapable of serving as the reservoir of the infection. How-ever, it would be equally unwise, rashly to exclude this possibility un-til systematic field and laboratory studies on the role not only of thesebut also of the other wild-rodent and the lagomorpha species met with inthe Bolivian plague foci have been made.
Observations on fleas
Rat and mouse-fleas
While the occurence of X. cheopis was naturally restricted to thezones infested by the common rats, it would appear that L. segnis, thespecifie'flea of the housegmouse, was met with the plague-affected re-gions of Bolivia in general. Macchiavello recorded the presence of thisflea not only on its specific host but also (no doubt occasionally) onwild rodents (Hesperomys, Graomys griseoflavus), while De la Barrera enu-merated L. segnis among the fleas met with on the common rats. Otherspecies found by him on the latter included, besides X. cheopis, P. irri-tans, Ctenocephalides canis, Ct. felis felis, Craneopsylls minerva,Neotyphloceras crassispina hemisus, Polygenis byturus and P. tripus.Since no doubt Polygenis fleas play an important role in the conveyanceof plague in Bolivia, the occurence of representatives of this genus onthe common rats deserves great attention.
P. irritans
To judge from the data furnishedj ¥De la'Barrera,' P. irritans wasmet with throughout the plague-affected Bolivian areas. It apparentlyabounded in the houses, but was found to infest not only the common rats,the domesticated guinea-pigs, dogs and cats but also some wild rodents,including Dasyprocta variegata, Graomys griseoflavus, Oligoryzomys sp.and Rhipidomy collinus.
Pleas of wild rodents and lagomorpha
Exact data on the flea infestation of a few species of rodents orlagomorpha, specimens of which could be procured through shooting or dig-ging out the animals from their burrows, were recorded by De la Barrerathus:
-37 -
RES 2/12
Galea musteloides *'
Number
Tiamastus cavicola 865
Neotyphloceras cr. hemisus 8
- - crassispina 5
Polygenis platensiscisandinus 4
- "- byturus 1
- "- n. sp. 2
Tunga penetrans
Craneopsylla minerva
Tiamastus n. sp.
1
1
1
Dasyprocta variegate boliviae*
Number 1
97.4
0.9
0.5
0.40.1
0.2
6.1
0.1
Rhopalopsyllus australistamoyus
Rh. lugubris
Rh. crypturi
Tiamastus cavicola
Pulex irritans
Polygenis klagesi samuelis
P. roberti beebei
25535
1
2
1
1J_~
296 99.7%0.1
888 99.8%
Number
Rhopalopsyllus lugubris 35
- ,_ - austr. tamoyus 3
Adoratopsylla int. oxyura 4
Polygenis roberti beebei 2
Neotyphlocerascrassispina hemisus 1
77.7
6.6
Lagidim viscaccia - ;
Tiamastus sp. n. 55 (98.2%)
Dysmicus simonsi 1 ( 1.7%)
8.856 (99.9%)
4.3Lagostomus maximus immolis
2.2 Pulex sp. n. 13 (100%)
45 99.6
The flea specieEor potential ecologicslows:
Graomysgriseoflavus *
s met with onal importance
other rodents and lagomorpha of actualwere recorded by De la Barrera as fol-
Craneopsylla minerva, Hectopsylla eskeyi, Polygenisbyturus, P. klagesi samuelis, P. roberti beebei, P.tripus and two new polygenis species, Pulex irritans,Tiamastus cavicola.
e4
86.111.8
0.3
0.6
0.3
0.3
0.3
*'
- 38 -
w
4
Hesperomystiuriculus
Oryzomys sp.
Olygoryzomys sp.
Oxymycterusparamensis *
Rhipidomysleucodactylus *
Sylvilagu sbrasiliensis *
Elipmodontiahirtipes hirtipes
Euryzygomatomysspinosus
LagidiumViscaccia
Lagostomusmaximus immolis
Leptosciurusleucogaster
Oecomysmamorae
Oryzomyslegatus
Phyllotisnogalaris
Proechimyslongicaudatus
Rhipidomyscollinus
* Found naturally pla
- 39 - RES 2/12
Craneopsylla minerva, Hectopsylla eskeyi, Neotypb-loceras crassispina hemisus, Polygenis byturus, P.klagesi samuelis
Polygenis byturus, P. tripus
Ctenocephalides felis felis, Polygenis bohlsibohlsi, P. roberti beebei, Pulex irritans, Tungapenetrans
Neotyphloceras crassispina hemisus, Polygenisbyturus
Craneopsylla minerva
Ctenocephalides felis felis, Polygenis klagesisamuelis
Polygenis byturus
Craneopsylla minerva, Polygenis atopus, P. robertibeebei, P. n. sp. (prox. byturus)
Dysmicus simonsi, Tiamastus n. sp.
Pulex n. sp.
Polygenis bohlsi bohlsi, P. n. sp. (prox. byturus)P. n. sp. (prox. litargus)
Polygenis bohlsi bohlsi, Tiamastus cavicola
Polygenis tripus
Neotyphloceras crassispina hemisus
Craneopsylla minerva, Polygenis bohlsi bohlsi, P.klagesi samuelis, P. roberti beebei
Craneopsylla minerva, Pulex irritans.
tgue- infected.
RES 2/12
These observations leave little room for doubt that Polyrgenis Vfleas play the main role in conveying plague among the wild rodents and,since the latter often penetrate into the humen habitations, are alsoapt to initiate plague manifestations in the intradomestic rodent faunaor directly in man. Pending further investigations it is uncertain,however, whether these fleas are also responsible for the frequent intra-domestic spread of the disease. As has been discussed in the report onPeru, this is a problem which can be solved only through a systematicstudy of all potentially involved fleas including the subspecies of P.irritans.
Epidemiological observations
To judge from the incomplete available information, the humanplague outbreaks in Bolivia were usually of the bubonic type. The onlyknown exception was the epidemic in the department of Tarija lastingfrom December 1921 to May 1922 (375 attacks with 300 deaths) during whichthe presence of pneumonic features attracted attention. It is, however,not certain whether all of the 87 patients showing signs of lung involve-ment suffered from primary pneumonic plague.
To judge from De la Barrerays report, the occurence of humanplague manifestations has been notified in Bolivia in all months of theyear. However, outbreaks of murinle origin took their onset most oftenduring the period from July to December (specially in July-August and inDecember), those of wild-rodent origin from July to November with clearperiods in February and again in May - June.
As has been stressed already, a characteristic but still unex-plained feature of the Bolivian plague manifestation was the frequentintradomestic spread of the infection, leading to the successive appear-ance of several attacks of the disease in one and the same household.
Dealing in the introduction to his study with the various geo-graphical zones of Bolivia, Macchiavello spoke inter alia of a Zona deSelvas y llanos tropicales (zone of tropical forests and plains> whichcomprised besides the departments of Tarija in the south and of SantaCruz in the east those of El Beni and Pando in the northwest, claimingthat common rats and X. cheopis were present in all these areas.
Reference to the Amazonian zone of Peru was again made by De laBarrera in the following important etatement:
"The technical workers of the Bolivian Health Servicehave considered the possibility that the Amazonian zonewill soon be reached by plague infection.
Since we have studied preferentially the zone which istoday the extreme northern limit of the spread (of plague)and have dealt also, though less intensively, with theregion which extends as far as Trinidad, we consider notto have sufficient information to attempt a prediction
-41 -RES 2/12
upon the future of plague. However, we can say that, asfar as is known, the climatic and telluric conditions aswell as those of the fauna and flora in the Amazonianzone offer no obstáacle to a diffusion (of the infection).The periodic inundations of vast stretches exert a doubleinfluence upon the fauna of the small rodents: On theone hand they diminish the populations of the rodents, onthe other hand they concentrate the animals in the areasinhabited by man. Only large field studies, the founda-tion of which will be the repeated determination of thedensity of the species, will shed light upon the respec-tive influence of these two factors, antagonistic as faras the diffusion of plague is concerned.
Murine plague has its natural reservoir, the domestic rat,and its vector, Xenopsylla cheopis, abundantly distributedin the zone. The traffic by river is the most probableroute of access.
As far as sylvatic plague is concerned, it will continueits spread towards the north, capriciously and incontrol-lably as always."
As has been stressed in the first part of the present report, intheir 1961 article Torres Bracamonte and González Moscoso claimed thatparts of the Pando and Beni departments had been reached by plague, theinfection having become manifest in the form of large rat epizootics andsporadic attacks in man.
Pending a confirmation of this still somewhat vague informationit would be premature to consider a plague invasion of the Amazonianbasin as a certainty. That, however, the possibilities for such a spreadof the disease exist, is undeniable and the present reporters would failin tbeir duty if they would not stress the urgent necessity of a surveyto assess the imminence of this great potential danger. Though presum-ably in view of the safeguards created by the international sanitary regu-lations an entrenchment of plague in the Amazonian basin would not be dan-gerous for the world at large, it would undoubtedly lead to most dire con-sequences for the local populations.
REFERENCES
De la Barrera, J.M. (1955) Informe final respecto al problema de lapeste en Bolivia, (Unpublished typescript).
Macchiavello, A. (1959) Estudios sobre peste selvática en Anmérica delSur. V. Peste selvática en Bolivia. Consideraciones generalessobre la geografía e historia de la peste. Bol. Of. Sanit.Panamer. 46 (1959) 6:509-524
Torres Bracamonte, F. and González Moscoso, R. (1961) Estado actualde la peste en Bolivia. Rev. de Salud publ. Boliviana2(1961) 2:11-16
- 42 - RES 2/12
SECTION E
REVIEW AND EVALUATION OF THE PRESENT STATUS OF PLAGUEIN BRAZIL
Incidence of the Disease
As summarized by Pollitzer (1954), it is generally acceptedthat plague, imported by the sea-route; first appeared in 1899,when Santos and a few months afterwards Sato Paulo, lying inlandfrom that port, became infected. From then onwards up to 1906Rio de Janeiro, Fortaleza in the state of Ceará, Pernambuco, RioGrande do Sul and other ports became successively involved. From1907 onwards the infection began to spread to inland cities andtowns but disappeared since 1934 rapidly from these centers whilepersisting in rural areas which remain in part involved to date(see Barreto and Castro, Mem. Inst. Osw. Cruz 44 (1946), 505).The total incidence of the disease from 1B99 to 1949 is shown bythe following approximate figures (Moll and O'Leary, 1945; A.Cas-tro, communication to the WHO Expert Committee on Plague, 1950and, fron 1949, WHO Epid. and vital statistics rep. 13 (1960),N9 8):
Period
- 1929- 1934
Cases
5,638535
Period
1935 - 19391940 - 19441945 - 1949
Cases
1,223812
1,090
3,125
Deaths
490205195
890
Details of the plague incidence in Brazil from 1935 to 1949are given in the following table (A. Castro, loc. cit. and, for1949, the above mentioned WHO statistical report):
Year Sáo PauloCases Deaths.
Rio de JaneiroCases Deaths
Minas GeraisCases Deaths
North-East Brazil TotalCases. Deaths Cases Deaths
1935 21936 311937 11938 -
1939 41940 -
1941 -
1942 -1943 -19441945 -1946 -1947 -19481949
1935-1949 38
1 - - - - 56921 328
0 - - - - 35- 12 8 - - 1342 - - - 107.- - - 255
7 4 - - 295- - .- 3 0 32- - - .- - 66
154....- - 192
- - - 34 23 2987 3 81
. . .. . - 386_- _ _- - 91241 19 12 44 26 3023
(* One recovering case in Sergipe in 1946 not included).
18991930
.,
4
232115.1553435383
7223642488
5417
28r
57135936
1461112553023566
15419233288
38691
3124*
233136
1561455387722364271115417
890
-
--
RES 2/12
The trend of the infection in the north-eoatern statesduring the period under review is illustrated by the followingtabulation:
Bahia
ux0a>
8 w
Cearám Ca0>
CO -
1935-39 74 23 79 31 317 95
Pernam-Paraiba buco
Ia 8a c
14 6 673 297
1940-44 256 36 126 39 108 21 - -
Piauí
(9
16 6
Totalc >O
1173 4-55
312 105 - - 802 201
1945-49* 53 8 319 48 249 44 23 3 354 53 - - 998 156
1935-49 383 67 524118 674 160 37 9 1339 455 16 6 2973 815
*) Until June 30
From statistics recorded in the Informe Epidemiológico Se-manal for 1950-1956 and for 1962 (up to 5 September) and the sum-maries on the incidence of plague published in the 1958-1962 vol-umes of the WHO weekly epidemiological Record thl following fig-ures on the plague incidence in Brazil from 1950 onwards can beculled:
1950 1951 1952 1953 1954 1955 1956 1957 1953 1959 l960 1961 1962
Alagoas 19BahUi 15Ceará 2Paraiba 5Pernambuco 7Minas GeraisRio Grandedo jforte
46
6
411
23 4
52020
4
16 6 2 3
131325
4 12 - -
1215731392
1
163
13
- _ _ _ - - - 3n,
miO de Janelro _4 . - - -_
Totals 48 16 62 U 6 27 4 37 25 16 28 106 36
:) In the case of souñe years thess figure eare slightlylozier tlian those. publishod in ather WRO tecords. The statisticsquoted were preferred however, because they could be supplementedby information on the plague incidence in the municipios (counties)of the various states, thus giving a detailed pictire on the re-cent trend of the infection.
The incidence of the disease in the various counties of thesestates is shown in the following tabulations:
Period Al1agas
m
o IBE
- 43 -
CM
Ni l I S I- I I1' I I, I i
r-
r-
",..0 I I I r-- .I . I i I I. I-- Ci
,-4
L.\ CU l '11 t l i .
Lr I I I a I
OC
I\ " I i3 'I I 3I3 I3 1 1
I'
3 ¡ :¡ ¡ d ¡ 3 .
in I I I I C I I I
oV. 0
C) c d. ud r i cd c ze I d i
Pa4 -1 3 3 Z 1 P C 1 1 C I íHCO
o
· ~~ F9 (d k a,~~~e
RES 2/12
Bahia
Municipalities 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962
AndaraiBaixa GrandeBarrada Estiva -
Campo FormosoCastro Alves 4Cicero Dantas 2Conc. do Coité -Feira de Santana -IbiqueraIbit araInhambupe 4Ipirá 1ItaberabaJaraguariJiquiéMacajubaMacaúbasMaracasPiataPocoesRiachao do Ja-
culpeRibeiro doPorbal 1
Rui BarbosaSta. Terezinha -SeabraSenhor do Bonfim -Serra PretaVitoria da Con-
quistaSerrinha 3
- 2
- 1
-
-
-
l
-
-
-
-
-
2
1
1
4
- - - - - - 2 6
2- 1
21
- - - - 9- 1 - - -
15 4 1 3 4 20
3
11
1
7
5
4
2
1
1
916u
2
12
1
4
11
13
- 45 -
Totals 20 95 i6 13 15
RES 2/12
Ceará
Municipalities 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962
Araripa .- - - - - - - - - 2 ~Baturité - - - - - - - 3Crato .. 1 -Ipu - 2 - - - 1 - - -Itapira - - - - - - - - - - - - 9Ipueiras - - - - - 3 - - - - - - -Jardim - - - - - - - 4Jardim 4Pacoti - 4 - - -Palmacia - -Milagres 2 - - -
Total 2 6 -4 7 16
Paraiba
Municipalities
Aroeiras - - - - 10 1Boqueirao - - - - - - 2 -Campina Grande - - - - - - - - - - 16 1Cuité - - - - - - - - - - - 3 -Princeza Izabel 5 - - - - - - - - - - - -Puxinaña - - - _ _ - 1
Total 5 _ _ 31 3
Rio Grande do Norte
Municipality
Coronel Ezequiel - - - - - - - - - - - - 3
Total _ _ _ _ _ 3
e-
-46-
1,
i,
RES 2/12
Pernambuco
Municipalities 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 1960 1961 1962
Aguas Belas 3AngelimAraripinaArcoverdeBelo JardimBezerrosBodocóBom ConselhoCanhetinhoCaruaruCorrentesCupiraExuGaranhuns 1Inajá 2PanelasPedraPesqueira 1San Bento do Uno -Sao CaetanoTriunfoNot located
1 1
1 23 1
1- 1
1 1
10 -
2
1- 2- 3
- 13
- 3- 1- 1
2
- 1
- 13- 6
Total 7 6 16 6 2 3 4 12 - - - 39 13
Minas Gerais
Municipality
Coronel Murta - - - - - - - - - - 2 -
Total - -_ _ - - 2 -
Rio de Janeiro
Municipality
Teresopolis - - 3 - - - - - - - 2 - -Not located - - 1 - - - - - - - - - -
Total - 4 - - - - - - - 2 - -
-47 -
RES 2/12
Cautious though one ;ust be in evaluating merely statisticalevidence, it is nevertheless safe to state the following:
1) Plague seems to have permanently disappeared only fromtwo Brazilian states, namely Sao Paulo in the South and Piaui inthe northeast, while it continues to occur in all other formerlyinfected states.
2) While occuring in a quite or fairly continuous mannerin two of the latter (Bahia and Pernambuco), in the other af-fected states apparently clear periods seem to alternate recentlywith such during which an incidence of the disease becomes oncemore manifest.
3) It is a priori unlikely that, as was formerly believed,the long continued existence of plague in the states of Bahia andPernambuco has been due solely to a persistence of the infectionin the common rats and not to the presence of wild-rodent reser-voirs. It is, therefore, most gratifying that, as will be dis-cussed later, recent investigations of De la Barrera have adducedprima facie evidence for the existence of sylvatic plague foci inBrazil.
The existence of such foci is also 'suggested by the statis-tical data for Pernambuco, where the disease was found to becomerepeatedly manifest in previously affected counties (see e.g.Garanhuns and specially Bom Conselho). The evidence for the Oexistence of such foci of the infection in Babia is not clear-cut.
4) Pending further investigations it is impossible to saywhether the recrudescence of plague in the apparently not perma-nently affected states is the result of a re-importation of theinfection from adjacent permanent foci or of a continued latentexistence of enzootics.
5) It is disquieting, but at the same time interesting tonote that in the not permanently affected north-eastern statesafter more or less quiescent periods the disease has become rathermore frequent in 1961. It is tempting to assume that this in-creased frequency of human plague is the result of a high inci-dence of the infection in the rodent populations which, havingbeen decimated by a past epizootic, had become numerous once more.
6) Of great interest are also (a) the reappearance ofplague after a long absence in Minas Gerais, (b) the possibleexistence of a plague focus in the Teresopolis county of Riode Janeiro State, manifested by the occurrence of a few humanattacks in 1952 and again in 1960, and (c) the appearance forthe first time (recorded) of plague in Rio Grande do Nortestate.
RES 2/12
There are thus ample opportunities for ecological studiesin Brazil which, by proving the existence of circumscribed strong-holds of the infection, might in their turn lead to a better con-trol of the plague situation.
Summarizing past experiences, Pollitzer stated that, as wasto be expected, the seasonal incidence of plague in Sao Paulo wasdifferent from that farther north. Most of the bubonic attacksin Sao Paulo occurred during the sultry days of summer with thepeak in January. In marked contrast to this a pneumonic plagueoutbreak at Sao Paulo in 1936 took place during the winter inJuly, and the same held true of an earlier pneumonic plague epi-demic at Santa Maria in the state of Rio Grande do Sul in 1912.
The period of maximal plague incidence in Rio de Janeirowas from September to January, commencing thus earlier than inSao Paulo.
Though the seasonal plague incidence in the north-east ofBrazil was not as clear-cut as in the south of the country, itwas during the period from 1935 to 1949 in general comparativelyhighest from July to October. However, according to Barreto(Bol. Ofic. Sanit. Pan-americ. 19 (1940), 886), the onset of theplague season in Ceará fell already into May/June. Both thereand in Pernambuco the period of maximal plague incidence coincidedwith the harvest season.
The seasonal incidence of plague during the period from 1950to 1961 is shown in the following table:
Total case incidence from 1950-1961
by monthsRio de Janeiro
Month Alagoas Bahia Ceará Paraiba Pernambuco Minas Gerais (State)
I 1II 5 4 8III 2 17 4 3IV 1 3 2V 3 2 2 2VI 1 2VII 24 5VIII 4 34 4 10 3
IX 17 20 5 6 11X 27 13 25 1XI 32 20 17 10 2XII 6 4 4 13 18
Thus, though in the state of Pernambuco in particular humanplague was recorded throughout the year, recently also the caseincidence in the northeast of Brazil is highest from July toAugust to November or December.
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While, as noted above, occasional pneumonic epidemics oc-curred*, bubonic plague is largely preponderant in Brazil. The Omortality from the disease is generally low and atypically mildattacks of the disease have been found frequent.
Ecological Observations
Turning attention to the ecology of plague in Brazil, itis distressing to note that recent information is available onlyin regard to the affected areas in the north-east of the country,The latest publication dealing with Minas Gerais is the study ofMacchiavello and Martins de Almeida (1947) and no record refer-ring to the recent plague manifestations in the state of'Rio deJaneiro could be found.
For the discussion of the ecological situation in North-east Brazil it is proposed to concentrate attention upon therecent article by De Freitas (1957) and the ample report renderedin 1960 by De la Barrera. The voluminous studies on these areasby Macchiavello must be considered as out-dated not only becausethey were published over twenty years ago' (1941) but also becausethey led this author to the no longer tenable conclusion that
"The domestic black rat, R. rattus was proved to be themost important factor in rural plague in north-east Brazil, bothhuman plague and plague among other rodents being accidental and Osecondary to plague in this rat" (l.c. - Public Health Reports,1941).
Observations on the common rats and house mice
Briefly summarizing the results of the early observationson the incidence of the various species and sub-species of thecommon. rat in Brazil, Pollitzer stated that
"While R. rattus was preponderant in the rural areas ofthe north-east, Norway rats were most common in some of theports and in Sao Paulo State. In Rio de Janeiro this speciesand M. musculus were more frequent than R. rattus and rattusalexandrinus".
* In addition to the earlier mentioned manifestations of thistype De la Barrera referred, without giving details, to a pneu-monic plague focus observed in 1957 at Macajuba, while De Freitasquoted a report on "Peste pneumonica em Pesqueira", rendered in1950 by him and Valenga Junior at the VIII Congresso Brasileirode Higiene. Unfortunately the transactions of this congress werenot a-ailable to the present reporters.
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RES 2/12
Results of trappings made during the period from 1952 to1955 in urban centers as well as in the rural plague foci ofthe states of Alagoas and Pernambuco culled from the articleby De Freitas are set forth in the following table, in whichfcr the convenience of record also data on the incidence of themarsupialia are entered*.
Monodelphi sdomestica
Didelphisparagua-yeinsis
Vi, osaPalueira dos
Indios
- 50 221
1 27 136
PERNAMBUCO
Bodocó - - - - 281 224Caruaru - 44 7 2 127 35Pesqueira - 354 24 1 345 25Triunfo - 158 10 20 1,128 85Garanhuns - 90 15 61 150 98
As far as these figures go, R. rattus rattus seemed to bepractically absent in both states, R. alexandrinus more frequentin Pernambuco than R.r. frugivorus, while the reverse held truein Alagoas. The absence or rarity of M. musculus trapped in mostof the districts was probably but accidental. The general fre-quency of the marsupialia, which are apt to maintain liaisonbetween the wild and the peri- or intra-domestic rodents, issignificant.
In the material collected by De la Barrera in the ruralhouses and the fields of various stations in the states of Per-nambuco and Ceará, the common rats and house mice figured asfollows:
Species
R.r. rattus (houses)R.r. alex. (houses)R.r. frugiv. (houses)
PernambucoNo. Per Cent
5 1.7231 81.348 16.9
No.
69130
CearáPer Cent
4.771.623.6
Number NumberR.r. alexandrinu4 (fields) 5 1R.r. frugivorus (fields) 7 14Mus miasulus (houses) 173 92Dto. (fields) 27 32
State anddistrict
R.r.rattus
R.r.alex.
R.r.frugiv.
ALAGOAS
Musmusculus
86 28
546
* The corresponding statistics furnished by De Freitas for thestate of Ceará are not ample enough to deserve attention.
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RES 2/12
Thus, while R.r. alexandrinus was found to be the most _prevalent rodent, Norway rats appeared to be absent from therural localities studied by De la Barrera. That, however, thisspecies continues to be present or even prevalent in some ofthe ports of North-east Brazil, is proved by the following 1956statistics quoted by the just-mentioned author:
Recife Fortaleza(Pernambuco) (Ceará)
No. Per Cent No. Per Cent
R. norvegicus 846 62.1 - -R.r. rattus 19 1.3 360 14.8R.r. alexandrinus 77 5.6 1,172 48.3R.r. frugivorus 419 30.7 896 36.8
Totals 1,361 99.7 2,428 99.9
Discussing the ecology of the common rats in the localitiesstudied by him, De la Barrera pointed out that, being not impededby the presence of the Norway rats, the rattus subspecies wereable to occupy the groundfloor of the rural habitations. In hisopinion the rats inhabiting the houses and those of the fieldshad little contact, each group thus leading an independent exist-ence. Concerning the relation between the common rats and thewild rodents he maintained that
"the sylvatic fauna approximates the human habitation suf-ficiently that the Rattus, in its nocturnal excursions and with-out removing far, enters in contact with the wild rodents ortheir nests and, consequently, with their fleas."
According to the observations made in Minas Gerais at thetime of the 1946-1947 outbreak, R.r. alexandrinus and R.r.frugivorus seem to have been the prevalent species both in thetowns and the rural habitations, but Macchiavello and Martinsde Almeida referred also to some trappings of R.r. rattus, ap-parently in the rural areas. The conclusions the two authorsreached in regard to the role of these rodents in the outbreakwere that
(a) An extensive migration of R. alexandrinus had takenplace, standing in connexion with the cultivation ofmaize;
(b) These rats invaded the human habitations immediatelybefore the appearance of' plague and
(c) died in the barns and maize plantations;
(d) The fleas of these rats were X. cheopis and the-humancases occurred in sites with epizootics among R.alexandrinus, being caused by fleas leaving the deadrats;
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(e) The infection was probably derived from the municipioof Salinas (in the north-eastern part of Minas Gerais)and neighbouring locations in the north - an endemicplague focus - being conveyed by some commercial prod-uct - possibly jute bags - in a not established manner.
Ctservations on Wild Rodents
The comparative frequency with which the wild rodents andlagomorpha of Brazil known to suffer from spontaneous plaguehave been caught according to Freitas in Alagoas and by De laBarrera in the states of Ceará and Pernambuco is shown in thefollowing table:
SpeciesAlagoas (
No. Per Cent No.Ceará PernambucoPer Cent No. Per Cent
Cavia apereaCercomys cunicularius 18laurentius
Cercomys inermis 976Galea spixii 518Hesperomys tener 34Hesperomys sp.Holochilus sciureus 609Kerodon rupestris 14Oryzomys laticeps
intermedius 2Oryzomys subflavus 2,064Thomasomyspyrrhorhinus 176
Zygodontomys pixuna 5,489Lepus sp.Sylvilagu sbrasiliensis 14
0.18
9.815.210.34
6.120.14
0.0220.75
1.7655.19
82 23.29 106 5.35
34 9.66 50 2.52
14
25
3.982238
0.101.160.40
7.10 434 21.94
197 55.1119
1,3360. 91
67. 54
0.14
Totals 9,944 99.66 352 99.14 1,978 99.94
As will be gathered from this table, Zygodontomys pixunawas the by far most common wild rodent in all three states,followed in frequency in Alagoas and Pernambuco by Oroyzonryssubflavus. In Ceará Cercomys cunicularius laurentius wascaught more frequently than the latter rodent, but the totalnumber of captures in this state was too small to'render thisobservation significant.
The information furnished by De la Barrera in regard tosome of the above enumerated species may thus be summarized:
Galea spixii (preá) - Various species of both genera ofthe sub-family of caviinae, all known under the commonname of preá, are met with in Brazil, the genus Caviabeing represented by the domesticated type species Caviaporcellus, by C. aperea and C fulgida, the genus Galeaamong others by G. spixii. It is important to note thatthis animal, like the other free-living species of preas,is much hunted by the inhabitants of Ceará and Pernambucofor the sake of its meat.
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Unlike in Argentina, the Galea species of North-east Brazildo not live in subterranean burrows but shelter by preference insites covered by a low and dense vegetation. They are often met within localities frequented by other naturally plague-infected wildrodents and. thus apt to become involved in the epizootics. Themortality among them sometimes becomes so considerable as to leadto a stoppage of their hunting. However, as deplored by De laBarrera such occurrences have never been made the subject of bacte-riological studies. Still, no doubt exists that the préas (G. spixii,and also Cavia aperea) suffer from spontaneous plague and instancesare on record in which the handling of their carcasses led to theappearance of the disease in man.
The flea index, determined by De la Barrera on 31 G. sixi, L
averaged 2.7, practically all the fleas being Polygenis bohlsijordaní. Tiamastus cavicola, though common on the caviinae else-where in South America, appeared to be absent in Pernambuco.
Kerodon rupestris (mocó) - This species which, as describedin detail by De la Barrera, lives in chinks and crevicesof rocks, is also much hunted for the sake of its meat andsometimes even bred in captivity. It freely approacheshuman habitations without, however, entering them.
As noted by several observers the flea-index of this spe-cies is rather low. Thus, De la Barrera, examining eightspecimens, which had been killed by shooting, could collectonly two fleas--both P.bohlsi jordani.
According to this author, considerable uncertainty existsregarding the occurrence of natural plague in the mocó. Ithas been found susceptible to experimental infection andMacchiavello and his associates observed deaths from plegueamong animals of this species kept in captivity at the timeof an outbreak in rats and man.
De la Barrera, while admitting that K. rupestris was poten-tially dangerous because being hunted, pointed out that thisrodent did not enter human habitations, had only limited con-tact with other sylvatic species, had few ectoparasites, andwas neither frequent nor widely spread.
Cercomys cunicularius laurentius (punaré) - This animal,- whichis also used for food in north-east Brasil, though apt to liveunider rocks, is likewise found in other locations. It wasrepeatedly caught in the vicinity of Kerodon rupestris--a factdeserving in the De la Barrera's opinion some attention, be-cause in contrast to the punaré it is regularly flea-infested.
Zygodontomys pixtuna - Though adaptable to various environments,this rodent has some predilection for humid locations. It isby far the most frequent among the sylvatic rodent species innorth-east Brazil.
V
RES 2/12
Oryzomys subflavus - Knowm as rato de cana or under othercommon names, this rodent is next in frequency after Z.pixuna. It builds its nests in various locations, in-cluding heaps of stones, between dry boughs, in hollowsof trees, etc.
Thomasomys pyrrhorinus - This small animal is also knownunder different names, like rato de fava or de palmatório.It lives in small colonies in nests inside the hollow cftrees. On one occasion it was caught inside a house.
Discussing in a general manner the problem of a penetrationof the wild rodents into the habitations of Pernambuco and Ceara,De la Barrera stated that (a) he practically never caught animalsof these species inside the rural houses; and (b) apparently thereexisted no local rodent species, like the Graomys of Argentina,standing according to its habits between the wild and the 'domes-tic' rodents. He admitted, however, that - as had been claimedby Macchiavello - Monodelphis domestiqa, whlch_wasapt tore -quent the houses, might play the role of a liaison animal betweenthe wild and intradomestic rodent fauna. That this species, whichhas been found naturally plague-infected (see Pollitzer, 1954),was potentially dangerous, was proved by its infestation withPolygenis bohlsi jordani, no doubt the principal, if not the solevector of sylvatic plague in the north-east of Brazil.
Observations on fleas
(a) Fleas of the common rats
Summarizing the results of his observations in North-eastBrazil, Macchiavello (1941) stated that
"Xenopsylla cheopis and X. brasilienis were the most commonfleas in R. rattus and R. alexandrinus (which generallylives in the fields); Rhopalopsyllus and possibly Parapsylluswere found on field rats, preás (Galea spixii) and mocós(Kerodon rupestris), though these rodents were rarely flea-infested. X. cheopis and a Chiastopsylla sp. were discov-ered on Monodelphis caught in rat nests. Some Pulex irri-tans and, rarely, Echidnophaga gallinacea were found onrattus and alexandrinus. However, X. cheopis was the onlyectoparasite found plague-infected. Even when X. brasiliensiswere taken from a rat on which infected cheopis-had beenfound, they failed to produce plague."
In Macchiavello's -opinion a survival of' infected fleas in-the rat nests was responsible for the continuance of subterraneanepizootics which gained new impetus through "the arrival of newsusceptible animals, whether as the result of breeding or throughmigration."
Dealing with the rat-fleas, De la Barrera quoted Simon (1954)who trapped on the floors of 30 houses in the municipios of Viçosaand Quebrangulo (Alagoas State) 6,583 fleas of the following species:
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RES 2/12
Pulex irritansCtenocephalides felisXenopsylla cheopis
5,5061,017
32
Xeno-sylla brasilielsis 15Polygenis bohlsi 0jordani 13
Total 6,583
The results of De la Berrera's own flea collections in var-ious localities of Pernambuco and Ceará may thus be tabulated:
X.cheopi X.bmsiil¡iendis C~tfelis P.Boblsijardani P.irritans
(a) PernambucoR. alexandrinus
(fields)Dto. (houses)Dto. (nests)R. frugivorus
(fields)Dto. (houses)In the houses
2
60204
2 2202
412
119 300
CearáR. alexandrinus 31 -1 19
(houses)R. frugivorus 3 - - 8 ,
(fields)Dto. (houses) 30 - - 9In the houses 77 - 2 62 985
The ubiquity of the wild-rodent fleaa striking feature of these observations.
P. bohlsi jordani forms
In the text of his report De la Barrera stated that the cheopisindex on the common rats varied within wide limits. The rarity oreven absence of this flea on the animals living in the fields wasin accordance with previous observations, Macchiavello for instancefinding in the municipio of Bom Conselho (Pernambuco) a cheopisindex of 4 or 4.3 inside the houses and of 0.75 outside of them.
(b) Wild-rodent fleas
The data furnished by De la Barrera regarding the flea- in-festation of wild rodents known to suffer from spontaneous plagueand of the marsupialia may thus be tabulated:
Polygenis Polygenis Adoratopsylla Pulex Ctenocephalidesbohlsi Jord. tripus antiquorum irritans felis
jal rernamwiucoCercomys cunic.laurentius
Galea spixiiHolochilus
sciureusKerodon rupestrisOryzomys subflavusZygodontomys pixunaNests of wild
rodentsDidelphismarsupialis
Monodelphisdomestica
6335
42
189565
1
53
21711
60 1 7
42
e-
(b)
L
-
-I
- 56 -
1 \ -nAb
1
RES 2/12
Polygenis Polygenis Adoratopsylla Pulex Ctenocephalidesbohlsi jord. tripus antiquorum irritans felis
(b) CearáCercomys cunic.laurentius 86 1 - -
Galea spixii 8 - - 1Holochilus sciureus 2 -Oryzomys subflavus 25 - - -Zygodontomys pixuna 13 24 2 -Nests of wild
rodents - 54 - -
Didelphis marsupia-lis 24 - - - 3
Monodelphisdomestica 5 -
As stated by De la Barrera, Polygenis bohlsi Jordani, theoverwhelmingly most frequent flea of the wild rodents in North-east Brazil, was first identified by Costa Lima in 1937 in col-lections made from Cavia aperea and a 'rato de cano'. Its vectorcapacity, preliminarily established by Simon (1954), was confirmedby experiments made in 1958 by De la Barrera. There can be nodoubt that this flea is practically alone responsible for thespread of plague among the wild rodents and presumably it is alsoinstrumental in conveying the infection from these to the cnmtonrats.
Discussing the problem of the occurrence of X cheopis onthe Brazilian wild rodents, De la Barrera stated that accordingto systematic studies by Moojen and Paracampos this flea was some-times met with in collections made in the field by the lower staff(guardas) of the Plague Prevention Service, but never in signif-icant numbers. More noteworthy still, (a) Macchiavello andMartins de Almeida never found X. cheopis on wild rodents duringthe 1946-1947 outbreak in Minas Gerais and (b) Silva (1945) cameafter an exhaustive investigation to the conclusion that "thefauna of the sylvatic rodents was not found infested by knownvector species." In his own material of about 3,500 fleas col-lected outside, but partly quite near human habitations, De laBarrera never encountered X. cheopis. Considering the numericaldisproportion between the common rats and the wild rodents, hecame to the conclusion that a transition of fleas from the latterto the former was easier than the reverse. The above recordedobservations certainly support this contention.
Epizootological and Epidemiological Observations
As already alluded to, De la Barrera was fortunate to detectin 1957 a sylvatic plague focus at Brejinho in the district ofTriunfo, Pernambuco State. This region had been affected by plaguewith a varying intensity since the major epidemic of 1926, but morerecently human manifestations of the disease had remained isolatedand since 1952 no bacteriological confirmation of the continuedexistence of the infection had been obtained.
RES 2/12
Undoubtedly in 1957 plague had assumed epizootic propor-tions in the wild rodents of this locality, for in marked con-trast what had been observed in the working station of Periperi,only about 15 km. distant, the wild-rodentpopulation was scantyin the Brejinho area and 23 wild-rodent nests were found therecontaining carcasses of Oryzomys, Zygodontomys or Thomasomys.One of these nests contaiIed the carcasses of 3 adult Oryzomyssubflavus which, having evidently succumbed at least two monthspreviously, were no more fit for laboratory examination.
As shown by careful investigations, most (17 out of 23)houses in this rural locality were rat-infested - to a largeextent by R.r. alexandrinus, to a lesser degree by R.r. frugivorus.Besides X. cheopis, abundant on the rats and in their nests, andalso present in the dust swept from the floors, X. brasiliensiswas found on R.r. alexandrinus. Pulex irritans was comparativelyabundant in the houses, Polygenis bohlsi jordani was met with insmall numbers on the rats as well as in the sweepings from thefloor. No evidence of plague infection was found in any of theseectoparasites.
The first plague-affected rodent, an Oryzomys subflavusevidently dead for only a few hours, was found in the open nearthe stone wall surrounding a house. Two days later two morecarcasses were detected - one of a Zygodontomys pixuna, theother of a Hesperomys sp. Though these two carcasses were al- _ready decomposed, it was possible to demonstrate the presence ofplague in them through smear examination and cultivations fromthe bone marrow.
The complete examination possible in the case of the O.subflavus showed evidence of a fulminant infection manifestedmacroscopically only by a diffuse congestion of the inside ofthe skin flaps in the region of the thorax and the abdomen,some subcutaneous hemorrhages and hemorrhagic lesions of thelungs. However, P. pestis was abundant in all organs and, asproved by animal experiments, highly virulent. Tne culturesisolated from the other two carcasses also showed a high vir-ulence. The cultures isolated from the other two carcasses alsoshowed a high virulence.
After De la Barrera had left the locality, the finding of ~dead rats and the appearance of suspicious manifestations in manwere reported in Brejinho but no bacteriological proof for thepresence of plague could be obtained. It deserves attention inthis connexion that evidently ever since the detection of theplague-affected wild rodents energetic measures had been insti-tuted by the local staff to prevent an intradomestic spread of ithe infection.
Making in a later part of his report an unfortunately briefreference to the 1957 plague manifestations in the state of Bahia,De la Barrera stated that
¡
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RES 2/12- 59 -
"1. After a quiescent period of 22 months, plague appearedin Bahia and caused, from 15 August to 31 December, 18cases in 13 separate foci.*
"2. The cases occurred in rural environments.
"3. An intensive epizootic among wild rodents was detected.
"4. There was no apparent relation between the foci. Withina brief time plague covered a large territory (see map)."
As De la Barrera concluded, there was no doubt that this wasa sylvatic plague outbreak.
It is important to add that thegathered from De la Barrera's map:
following details can be
Localities Dat4affected
1 Baixa Grande2 Macajuba3 Serra Preta4 Feira de Santana5 Riach&o do
Jacuipe6) Jacaraci
7) Conceiqao doCoité
8) Campo Formoso
Total
e of appearanceof plague
AugustAugustSeptemberOctober
Number ofcases
3721
OctoberNovember
DecemberDecember
21
Remarks
Pneumonic focus!
Situated farto the south-west of theother foci nearMinas Gerais
42
22
Commenting on a graph illustrating the possible routes bywhich in North-eastern Brazil plague might reach man, De la Barrerastated:
"1. One encounters in the field numerous species of wildrodents, some marsupialia and a few rats, all infestedby Polygenis bohlsi jordani. Xenopsylla cheopis islittle abundant on Rattus and not met with on the otheranimals.
"2. The same fauna is met with in the sub-domestic environ-ment, but Rattus and cheopis are more abundant.
* "The focus of pneumonic plague in Macajuba is not included."
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"3. Inside the houses there cohabit with man in a permanentmanner Rattus, Mus musculus, dogs and cats. Met with *in the habitations are Pulex irritans, Xenopsyllacheopis, Polygenis bohlsi jordani and some Ctenocephalidesfelis.
"4. The displacements of Rattus are limited and it is pos-sible that the specimens caught in the houses and thefield have independent fixed abodes. It is probablethat the species maintains contact with the sub-domesticmilieu.
"5. Cheopis is more abundant on the rats caught in the housesthan on those gathered in the fields. As this flea wasnot met with on other animals, one has to deal apparentlywith a species particular to the rat and one must consideras confirmed the opinion of some authors that its passageto other animals would be difficult.
"6. The houses are visited by Monodelphis and, sometimes,by Didelphis, which on certain occasions nest there.These marsupialia are always infested by Polygenisbohlsi jordani, while X. cheopis was not found on thecaptured specimens.
"7. Only very rarely were wild rodents found in the houses." O'
"An infection of the domestic fauna is possible by the follow-ing routes:
i. The rats of the houses (could) become infected in the peri-domestic milieu by picking up infected fleas;
ii. The marsupialia visiting the houses could be vehicles ofinfected fleas (P. bohlsi jordani) which they had pickedup in extradomestic environments;
iii. The direct transport of plague or of infected fleas intothe houses by wild rodents, usual in other regions, appearsto be exceptional in North-east Brazil;
iv. It is not impossible that dogs and cats, which often carryP. bohlsi jordani, bring plague to the houses by means cfthis flea;
v. There is no evidence that M. musculus plays a significantrole in the transport of the infection or of fleas;
vi. Man could become infected directly in the fields or bringinfected fleas into the houses in his clothes;
vii. An intradomestic infection of man through P. bohlsi jordani,transported from extrinsic environments, is possible butmust occur more frequently through cheopis coming frominfected rats;
viii. The role of P. irritans is under discussion. In any caseit could not be exclusive, since there is never a lack ofcheopis with a much higher vector capacity."
Expressing his general views on plague in Brazil at the endof his report, De la Barrera stated:
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"1. The incidence of plague in man and the common rats inBrazil has much decreased within the last years.
"2. The ports and cities remain free, the recorded outbreakstaking place in rural localities.
"3. The foci are generally isolated and show a tendency todisappear spontaneously. The focal incidence is low.
"4. Human plague attacks occur almost always simultaneouslywith the infection of the common rats aid, sometimes, ofwild rodents.
"5. An analysis of the epidemiological facts leads to theconclusion that the domestic rat (Rattus) does not playa role in the maintenance of plague and that, similarlyas in the other American countries, the disease has nowbecome limited to the sylvatic fauna of Rodentia andLagomorpha.
"6. This concept was confirmed in August 1957 at Triunfothrough the detection of plague in field rodents with-out a simultaneous infection of Rattus in the houses.
"7. The constant presence in the houses of rats denselyinfested with X. cheopis produces an epidemiologicalsituation different from that of purely sylvatic plague,the rat being the intermediary between the wild-rodent('agrestbte)infection and man.
"8. The transmission (of plague) between the wild rodentsand from them to man is effected through P. bohlsijordani, a flea with a major vector capacity accordingto preliminary investigations and the experiences ofthe Brazilian observers.
"9. The conveyance of plague from the wild ('agreste') orsubdomestic environments is effected by Rattus, directlyor by infected fleas, or by the marsupialia, often byfleas.
"10. Man can coratract the infection in the fields, throughdirect contact with infected rodents or through theirfleas. As a rule, this eventuality is less frequentthan an intradomestic infection through Rattus.
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The Known and the Unknown of Plague in Brazil _
When an attempt is made to determine what is already knownand what is still unknown regarding the ecology and epidemiologyof plague in Brazil,* one must first of all fully agree with Dela Barrera's contention that an entrenchment of the infection inthe wild rodents and lagomorpha has become the fons et origo mali.As has been alluded to already, there can be hardly any doubt thatin Brazil as well as elsewhere plague acts in the herds of theseanimals as a population regulator, becoming active and widespreadwhenever the periodically occurring increases of their numbershave furnished ample fuel for the spread of the infection and beingreduced to a mere flicker after the resulting epizootics have dec-imated the herds. For such a sequence of events alone can explainthe recrudescences of the disease after intervals not rarely solong as to suggest the disappearance of the infection.
VWhether during these quiescent periods a territorial as wellas a numerical reduction of the plague incidence takes place, isstill not definitely known. However, as noted before, there issome statistical evidence for the existence of pockets of the in-7fection where, owing to suitable ecological conditions, an equi-librium permitting the survival of both has been reached betweenthe causative microorganisms and the reservoirs of the disease.As will be discussed later, the recognition of such strongholds ofthe infection would be of great practical importance as well as oftheoretical interest.
Dealing with the ecology of plague in Brazil, De la Barreramaintained that
"Generally speaking all the small rodents of the North-eastcan be caught in the same localities, without however, beingsymbiotic in the strict sense. Some species have somewhatindividual habitats (mocó) but never attain isolation."
"Therefore," De la Barrera continued,""it does not appearthat in Brazil one or a few species play an exclusive rolein the maintenance of plague. The mass of the Rodentia andLagomorpha is homogeneous in respect to their sensitivity,habits and flea infestation, it being thus natural that theinfection makes no distinction."
Noteworthy though this postulation is,based on observEitionsin loco, the present reporters cannot help to point out that (a) ·the question whether the various species concerned are in realityequally sensitive to infection with P. pestis seems not to have
* It must be noted that the statements following above refer solelyto North-east Brazil. The ecology of plague in the states of MinasGerais and Rio de Janeiro is practically still a terra incognita.
RES 2/12- 63 -
been studied sufficiently and (b) marked ecological differencesexist between these species which are bound to influence theircoCparative importance in the causation, spread and maintenanceof the disease. Thus, as shown by the table inserted on page 53,in the three states for which date are available, Zygodontomyspixuna was by far the most numerous species, followed in fre-quency in Alagoas and Pernambuco by Oryzomys subflavus, in Cearápossibly by Cercomys cunicularius laurentius, while most otherspecies were markedly less frequent and some, particularly Kerodonrupestris, apparently rare. Statistical evidence has been alsoadduced to show that the degree to which the various rodents andlagomorpha are infested with the common plague vector P. bohlsijordani varies within wide limits, Kerodon rupestris for instancebeing poorly flea-infested. On the other hand, as De la Barrerastated, this species was one of the few with gregarious habits,whereas many of the other rodents lived isolated or in pairs.
These brief notes suffice to show that the ecology of syl-vatic plague in Brazil is influenced by many variable factors, atleast some of which seem not to have been sufficiently evaluated.Under these circumstances it would seem rash to accept the above-quoted dictum of De la Barrera. Quite possibly further investi-gations will show that in Brazil as well as in other plague areasa distinction will have to be made between (a) wild rodent and/orlagomorpha species of prime importance as reservoirs of the infec-tion; (b) species mainly or solely serving as fuel for the spreadof the epizootics and (c) a third group of species, the naturalplague infection of which is merely of an accidental nature.
There is no reason not to agree with De la Barrera's asser-tion that the transitions of the infection from the now primarilyand permanently plague-affected sylvatic species to the commonrats lead only to short-lasting intradomestic manifestations ofthe disease which become rapidly extinguished even though X. cheopiscontinues to be present and apparently often abundant not only onthe surviving rats but in the houses. Pending further investiga-tions it is not possible, hovever, to accept the tentative expla-nation he offers for this rather puzzling phenomenon, namely thata state of resistance to plague has evolved in the domestic ratpopulations which is of a degree sufficient to impede the continuedspread of the infection from rat to rat but not high enough to barthe initial transition of the highly virulent P. pestis strainsharboured by the wild rodents to the domestic fauna. For, even ifone could admit at all the possibility of the development of sucha relative resistance in rural rat-populations with little plagueexperience, as far as the present observers are aware so far noproof for the existence of said resistance in the rats of North-east Brazil has been brought forward. Thorough studies of thisfactor as well as of the pecularities of the intradomestic plaguemanifestations there in general would be necessary to explain theirunusual course and termination.
Suggestions for Further Plague Investigations in Brazil
One must fully agree with De la Barrera that until recentlyBrazil had an excellent national plague prevention service coveringnot only the plague-affected states of the north-east but also those.of Minas Gerais, Rio de Janeiro and Sao Paulo. The service was or-ganized in three 'circumscriptions' with bases in Recife, Salvadorand Rio. According to his description, the circumeriptions were
"divided into districts and these into sectors (totalling 28).Each sector had a medical officer and had a laboratory, anoffice and annexed service installations for the personnel.A variable number of 'guards' had the following functions:(a) deratization; (b) disinsectization; (c) capture of ro-dents and fleas; (d) house-improvement. The laboratorymade bacteriological diagnoses and prepared skins and skullsof the captured animals for classification in the NationalMuseum of Rio. The fleas were sent to Dr. Lindolfo Guimaraesin Sao Paulo."
Unfortunately, however, De la Barrera had to add
"The decline of the plague incidence recorded during the lastyears rendered unnecessary, in the opinion of the health au-thorities, such a complete organization and for this reasonit was incorporated into the Directorate of Rural Endemics,losing its former importance and 'hierarchical' position.Nevertheless, the installations of the old service were pre-served while its much competent personnel fulfills otherfunctions. ,
If nothing else, the marked deterioration of the plague sit-uation in Brazil in 1961 renders the re-establishment of an inde- -pendent national antiplague service in that country most desirable,if not indispensable. This service should not only energeticallyresume the above outlined functions but ought to devote also full eattention to the problems of sylvatic plague, specially by (a)keeping in the enzootic areas a constant watch on the populationtrends of the wild rodents and lagomorpha so as to become awareof tendencies for an increase of these populations which in theirturn presage the appearance of epizootics; and (b) making system-atic examinations of the pooled organs and/or the pooled fleas ofthese animals so as to detect at the earliest possible moment thepresence or recrudescence of plague in them. As has been notedabove, large-scale investigations of this kind, combined with stud-ies on the comparative susceptibility of the various animals con-cerned to infection with P. pestis may reveal the existence ofspecies of prime importance for the maintenance of plague and pos-sibly even that of limited foci where the infection persists andfrom which it is apt to break out whenever an increase of the ro-dent and lagomorpha populations provides adequate fuel for a spreadof the disease. Though admittedly requiring great initial efforts,such investigations will in the long run greatly facilitate a watchover the trend of sylvatic plague.
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It is hardly necessary to add that (a) the above discussedinvestigations as well as those on the common rats outlined belowought to be undertaken not only in the north-east of Brazil butalso in Minas Gerais and in the small focus persisting in Rio deJaneiro State which latter, though little suffering from manifestoutbreaks, is of great importance on account of its geographicalsituation, and (b) hand in hand with these investigations all pos-sible attention ought to be paid to the early detection, thoroughstudy and effective management of human plague attacks.
In order to get an insight into the problem of the now pe-culiarly limited manifestations of rat plague it would be of par-ticular importance (a) to study the distribution and frequency ofthe common rats throughout the areas invaded or threatened by theinfection; (b) to watch for signs of an appearance of the diseaseamong these animals through large-scale and systematic examinationsof their pooled organs and/or their pooled fleas; (c) to make large-scale tests to assess their susceptibility for or resistance toplague; and (d) to study the frequency and seasonal incidence ofthe rat-fleas, particularly of X. cheopis.
Inasmuch as the enlarged activities suggested above wouldseem to be beyond the capacity of the existing services in Brazil,consideration ought to be given to the re-institution of the na-tional plague service as it once existed or to a similar establish-ment, and to the training of an adequate number of specialists forthis work. International services, such as PASB/WHO, should assistby stimulating a greater interest in the plague problem and in theinvestigations and services needed to contend with it, and in thetraining of personnel.
References
Barreto, J. de Barros: O estado atual do problema da peste noBrasil. Bol. Ofic. Sanit. Pan Americ.19 (1940)-9. Br66-877
Barreto, J. de Barros and Castro, A. de: Aspectos epidemiológi-cos da peste no Brazil. Mem. Inst.Oswaldo Cruz 44 (1946) 3: 505-527
Castro, A. de: Communication to the WHO Expert Committeeon Plague, 1950. --Unpublished document)
De la Barrera, J. M.: Relatorio sobre a peste no Brasil, 1960(Unpublished document)
De Freitas, Celso Arcoverde: Noticia sSbre a peste no nordeste.Rev. brasileira de malariologia e doençastropicais 9 (1957- 1: 123-133
De Freitas, Celso Arcoverde and Valenga Junior: Peste pneum^onica emPesqueira. VIII Congreso Brasileiro diHigiene, 1950
- 66 - RES 2/12
Macchiavello, A. (1941): (a) Contribuciones al estudio de la peste $bubónica en el nordeste del Brasil. Publi-cación 165, Ofic. Sanit. Pan Americ.(b) -Investigaciones sobre peste en el Nor-deste Brasileño. Bol. Ofic. Sanit. Pan Americ.20 (1941) 5: 441-W4I(c) Same special epidemiological and clini-cal features of plague in northeastern Brazil.Publ. Hlth. Rep. (Wash.) 56 (1941) 33: 1657-
Macchiavello, A. and Martins de Almeida, C.: SSbre la peste bubonicaen el Estado de Minas Gerais, Brasil, 1946-1947. Arquivos de Higiene (Rio de Janeiro)17 (1947T1 -134'
Moll, A. A. and OtLeary, S. B.: Plague in the Americas. Publica-ción 225, Ofic. Sanit. Pan Americ. (1945)
Pollitzer, R.: Plague. WHO Monogr. Series Nç 22 (1954)
Silva, M.: Bol. Higiene e Saude Publica, Dec. 1945Tpioted by De la Barrera)
Simon, R.: Monogr. do Servicio Nacional de Peste N94, 195; Fuoted by De la Barrera
t1
e
.19
RES 2/12
SECTION F
REVIEW AND EVALUATION OF THE PRESENT STATUS OF PLAGUEIN ECUADOR
History and recent incidence of plague
In marked contrast to what could be recorded in the case ofVenezuela, the history of plague in Ecuador is rather involved.Dealing with this problem, Jervis Alarc6n distinguished three phases,namely (1) invasion of the seaports and other settlements in thecoastal provinces; (2) spread of the infection by the railway systemto the mountainous provinces of the interior which, taking placeduring the period from 1909 to 1939, successively led to the appear-ance of the disease in the provinces of Chimborazo, Tungurahua andCañar, and finally in the nuall settlement of Guaytacama in the prov-ince of Cotopaxi (north of Tungurahua province), the northernmostlocality reached by plague in Ecuador; (3) penetration of the infec-tion into the rural areas, taking place also in the southern prov-ince of Loja, in which plague, spreading by continuity from adJa- --cent Peruvian areas, became entrenched during the period from 1918-1926.
The first of these three phases commenced in 1908 when theimportation of plague by the sea-route led to an entrenchment of theinfection among the rats of Guayaquil, followed soon by the appear-ance of manifestations of the disease in man. As a consequence ofthis fateful event, during the period from 1908 to 1913 almost allcoastal towns of Guayas and Manabi provinces became plague-infectedand the disease also appeared in the settlements of the coastal prov-ince of El Oro and the inland areas of Los Ríos Pro.vince.
Generally speaking, plague in the coastal areas of Ecuadorbegan to abate in 1924 and disappeared in 1930. However, owing to animportation from Chimborazo Province, the infection again flared upin Guayaquilin 1935 and persisted there until 1939 when the last humancase in that port was recorded. Guayaquil has since then remainedfree from plague even though its rat population continues to be con-spicuous. However, up to the present it came to a repeated reappear-ance of plague in other coastal localities, most frequently in El OroProvince where, according to Jervis Alarcón, 16 cases were recorded -in 1939, 3 in 1940, 4 in 1950 and one in 1954 (community of La Liber-tad). These manifestations seemed to be due to an importation ofinfected fleas in bags of merchandise from Loja Province (JervisAlarc6n).
In 1954 the island of Puná, situated in the gulf of Guayaquil,became the scene of a most noteworthy outbreak which, according tothe just mentioned observer, appeared to be due to an importation ofthe infection in goods from the seriously affected Loja Province rather
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than from El Oro. Notwithstanding this mode of the infection, thecormon rats (R. norvegicus) of Puná town did not become involved,whereas a violent epizootic broke out among the wild rodents of the-island, the plague nature of which was proved through positive find-ings in three species--Sigmodon puna, Oryzomys santhaeolus and anunidentified species of Graomys (De la Barrera). The purely syl-vatie nature of the outbreak is also proved by the fact that all 8persons involved in it had contracted the disease when staying inthe fields to collect wool from the silkcotton tree (the seeds ofwhich form and attractive pabulum for the rodents). Drastic effortsto control the situation through a campaign against the wild rodentswere crowned by success, these animals proving to be practicallyabsent when De la Barrera visited the island in 1957. However, anexportation of the wool led to two plague cases recorded in 1955 atSan Lorenzo, Cant6n of Guayaquil, in Guayas Province.
The information on recent plague manifestations in the coastalareas of Ecuador may thus be summarized:
Locality
JipijapaManabt Province
Vinces, Los RiosProvince
Pinas, and ZaramaEl Oro Province
Nature of Outbreak
The occurrence of 7 plaguecases in this importantinland trading center stood-apparently in causal connec-tion with the importationof material for the manufac-ture of gunny-bags fromChimborazo Province.
In the Daule-Guaya Riversarea not far fr9m the portof Guayaquil, the infectionof this important center ofthe trade in cacao, leadingto 11 human attacks, undoubt-edly also originated in Chim-borazo Province.
Por these two localities 9and 8 cases respectively werereported in this coastalprovince. However, they arecloser to the Loja focus(and may be part of it) thanthey are to the coast.
From summaries published in the WHO Weekly Epidemiological --Record, (Vol. 36, 1961 8:84 and Vol. 37, 1962 29:355) and data fur-nished in the Informe Epidemiológico Semanal of the Pan AmericanSanitary Bureau, Vol. 34 Nº1 to Nº52 and Vol. 35 NMl-14 (1963) it can
Year
1956
1957
o
1]961
e
RES 2/12- 69 -
be gathered that the plague incidence recorded in the coastal prov-inces of El Oro and Manabi in 1960 through 1962 was as follows:
Province Cant6n
El Oro
Manabi
PinasZaruma
1960 1961 1962
/5 8/17-15 8/17
ChoneJipljepaJuninMantaMontecristiPortoviejoRocafuerteSanta AnaSucre24 de Mayo
36
23le
2-/2
- 13_ 1
_ 1;- 86- 9
26}- 16
12-- 774-/69 3/241
Remarks
Localitiées: closerto Loja focus thanto the coast''
All places on/orconnected with thecoast
N. B. Two imported plague cases were recordedQuito (Pichincha Province); believed toManabi.
in 1961 in the city ofhave been infected in
Unfortunately these statistics show that (a) human plague con-tinued to be manifest in 1962 at Manta, where rat-caused outbreakbegan in 1961, thus indicating that the infection continued to existin the rodent population of that seaport and (b) the infection hasspread to the immediate hinterland of Manta, being manifest in theimportant centers of PortovieJo, SantaAna and Montecristí whlch areconnected by rail with Manta, and as far north as Chone and as farsouth as Jipijapa. There can be hardly any doubt that plague hasonce more become entrenched among the rats of at least some of theseplaces, particularly in Manta, Portoviejo and Rocafuerte.
Turning attention to the provinces in the interior of Ecuador,it appears to be indicated for the convenience of record to deal withthe plague manifestations in the provinces of Tungurahua and Caiarbefore devoting attention to the earlier affected Chimborazo Province.
As reported by Jervis Alarc6n, plague appeared first in Tun-gurahua in 1926 in the city of Ambato, which once more recorded anepidemic, involving about 100 persons, in 1929. The disease then-seems to have been absent from the province until 1956 when, prob-ably imported through goods or infected domesticated guinea-pigs froman adjacent area of Chimborazo Province, it appeared in a rural areasituated some kilometers southeast of Ambato. All the 16 attacks inthbe first affected area as well as two afterwards recorded in Ambatocity seem to have stood in casual relation to the infection of
__ __
4
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domesticated guinea-pige. There was only one death in the 18 cases .-in 1956. There were a further 8 cases in the Ambato area in 1961. -It should be noted in this connection that according to a brief state-ment by Jervis Alarc6n t e size of the endemic plague area in Tungu-rahua Province was 40 km'.
The province of Cafiar, south of Chimborazo Province; becamefirst plague-affected in 1933, when about 200 attacks with a highmortality vere recorded in three localities. The disease reappearedthere in 1945 (9 cases with 4 deaths). Afterwards, 10 cases with 6deaths were notified in 1951 at Las Postes, and 8 with 3 fatalitiesat Tambo. While the earlier outbreaks were evidently due to an --importation of the infection from Chimborazo, that of 1953 was sup-posed to stand in relation to the importation of goods from theseverely affected Cariamanga area in LoJa Province. The size of tleaffected areas in Cafiar totalled according to Jervis Alarcón 60 Km .
Dealing with the plague situation in Chimborazo Province,Jervis Alarcón furnished the following valuable general information:
The province has a size of 5784 km2 and had, according tothe 1950 censu.s, 218.130 inhabitants, 72.61% of whom lived in therural areas. The altitude of the various regions varied-from 1,C00tO 3,000 meters above sea level, the temperature from 7º2 18°C.The weather was apt to be changeable even within one and the sameday. The dry season lasted from June to December, the rainy periodfrom December to May.
Plague, undoubtedly imported from the coastal areas, withwhich the Chimborazo Province Is connected by rail, appeared therein 1909, first affecting the towns but becoming rural in characterin 1940. The case incidence of the disease during the first phase(1909-1939) was, according to De la Barrera, 1420 as against an ---occurrence of 269 cases from 1940-1960. Some details--on the mani-festations of the disease during the period from 1946-1956 were setforth by Jervis Alarcón as follows:
Districts DistrictsYear. affected Foci Cases Year affected Foci Cases
1946 2 2 7 1952 2 7 181947 4 5 9 1953 1 1 41948 1 1 1 1954 7 14 271949 0 0 0 1955 3 4 101950 2 2 4 1956 3 6 101951 4 14 25 TOTALS 52 115
According to Jervis Alarc6n the affected areas in the Chim-borazo Province, now all situated in rural regions, have a totalsize of 400 kmF.
e
RES 2/12
The recent plague incidence in Chimborazo Province wasreported as follows in the WHO Weekly Epidemiological Record andthe PASB Weekly Epidemiological Reports:
Year Cantons affected Case incidence per canton Annual Total
1957 Guano 12 121958 Guano 7 .
Riobaeba .1 81959 Guano ' 11
Riobamba 10 211960 Guano 15
Riobamba 10Alausi 10 35
1961 Guano 1Riobamba 1 2
1962 Riobamba 6Alausi 21 27
Characteristic for plague in the Chimborazo Province were(1) A high mortality, amounting,according to Jervis Alarcón,
to 85.7% in 1946 aad 2001 in 1956;'
(2) A high incidence of pneumonic plague, due no doubt tothe prevailing climatic conditions which induced thepeople to crowa together in their houses.
The province of Loja, which, lying in the South of Ecuador,is adjacent to Perú, comprises according to Jervis Alarcón a terri-tory of 9926 km2 and had in 1950 a population of 216,802, almost70% of the inhabitants living in the rural areas of the province.It consists of (a) a low zone, 200-800m above sea-level with atemperature of 18º-30º in the shade, and (b) a mountainous part,1,500-2,500m high with a temperature from 8Q to l9mC. It iB impor-tant to note that the dry season, lasting from May to December, isthe period of the year favourable for the occurrence of plague inthe province, in which -an area of about 3,000 km , situated to alarger part in the low-lying zone, is affected by the disease.
As has been noted above, the ±nfection infiltrated into LojaProvince during the period from 1918.1926, the stages of this processhaving been thus described by Macchiavello (1957)7
1918-21 - Plague became manifest in the Cazaderos--Alamor area;1923 - The presence of the disease in the Canton of Celica
was suspected;1925 - The occurrence of plague was noted in the cantons of
Catacocha (Paltas), Gonzamaná and Cariamanga (Calvas);*1926 - Loja city was reached by the infection.
Considering this evolution, Macchiavello entertained no doubtthat the appearanceof plague in the Loja Province was due to an ex-tension of the previously existing sylvatic focus in the Lancones
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district of Perd into Ecuador, resulting in the entrenchment of theinfection among the wild rodents in a large area situated on bothsides of the frontier between the two countries.
As stated by Macchiavello, during the period from 1925 to-1948 1,617 plague cases with 864 deaths were noted in Loja Prov-ince, distributed as follows:
Cases .Deaths Canton Cases Deaths
AlamorCelicaCatacochaLoja
30523037246
13512518813
MacaráCariamangaGonzamanáAmaluza
TOTALS:
67266210121
3313915774
864
The incidence of the disease in Loja during the period from1946 to 1956 was thus characterized by Jervis Alarc6n:
DistrictsYear affected
19461947194819491950195119521953195419551956
74676596927
Foci ofhuman plague
187201711
9202834
230
Foci ofrodent plague
?
111
5
Cases Deaths
4617382021104164
1ll342
13123313
15813
TOTALS: 68 196 ?17 413 53
Dealing in the text of his article with the distribution ofplague in Loja during the quinquennium from 1952 to 1956, JervisAlarc6n stated:
"The spots (lugares) in these last 5 years are: in theeastern sector 4 out of 9 of the Loja District; 4 out of 8in La Toma; 4 out of 6 in Gonzamaná; 19 out of 23 in Sozo-ranga; 18 out of 22 in Cariamanga; all 7 of Amaluza, allnew; in the western sector 5 of the 7 lugares of Chaguar-pamba; 13 out of 26 in Celica; 9 out of 19in Alamor; 7out of 11 in Pindal; 7 out of 13, all new, in Zapitillo."
Canton
.
_ __ __
RES 2/12- 73 -
According to this observer most severely affected were thedistricts of Cariamanga, Sorozanga, Catacocha, Celica, Alamor andAmaluza, the persistence of the infection among the wild rodentsin them being "the true cause of the rural endemicity" in Loja.This is certainly a clue deserving great attention.
As added by Jervis Alarcón, the plague mortality in theprovince of Loja showed a marked decrease towards the end of theperiod considered by him as shown by the following figures:
Perlod Total cases Recovered Died Mortality J
1926-1936 1479 928 551 37.21936-1946 906 611 295 32.61946-1956 410 369 41 11.1
The comparative benignity of plague in LoJa was also evi-denced by the rarity of the pneumonic type, only one small outbreakof lung pest having been recorded in the Catacocha District in 1939(7 victims).
Data on the recent incidence of plague in the pr~ince ofLoJa, culled from the WHO Weekly Epidemiological Recorda and (for1962) from the PASB Weekly Epidemiological Reports, may thus beset forth:
Year Plague cases Districts involved
1957 62 No details1958 13 Calvas (2), Cariamanga (1), Celica
(9), Macará (1)1959 19 Catacocha (l), Celica (4), Loja (7),
Macará (1), Paltas (6)1960 36 Calvas 117), Celica (1), Macará (11),
Paltas (71961 7 Calvas (2) Celica (3), Paltas (2)1962 56 Calvas (19), Celica (23), Macará
(10), Puyango (3), Paltas (1)
Observations on rodents and other ecologicallyImportant mammals
'Domestict species
As far as can be judged from the rather scanty informationavailable in regard to the occurrence of the common rats in theplague-affected areas of Ecuador, these rodents, while abundant inthe settlements of the coastal areas (where R. norvegicus appears tobe the most frequent species), are irregularly distributed in theinterior, especially in the mountainous districts. Macchiavello
RES 2/12
maintained in this connection in his study on the province of LoJa,that the reason for this unequal distribution of the rats and theirabsence from still many settlements seemed to be that these rodentsbegan to penetrate only since 1920 in the remote interior areas ofEcuador, especially those lying away from roads and railways. Heillustrated the irregular distribution of the three rat species inthe towns of Loja Province by the following table, based upon theresults of captures made from 1938 to 1942:
Towns R. rattus R. norvegicus R. alexandrinus
Loja 14 22 2Guachanamá 0 0 2Federico Páez 2 0 10Zapotillo 0 0 0Cazaderos 1 1 2Zabiango 0 3 0Sozoranga 0 5 4Chaguarpamba 35 47 89Cariamanga (Calvas) 24 53 109Gonzamaná 17 56 260Celica 66 72 173Amaluza -22 329 696Catacocha (Paltas) 6 335 439Macará 5 281 293Alamor 4 50 178
TOTALS: 196 1,254 2,257
To judge from these data, R. alexandrinus was most frequentamong the urban rats in Loja, while R. rattus was rare. As statedrecently by Jervis Alarc6n, R. alexandrinus was also the prevalentrat in Chimborazo Province.
The irregular distribution of the common rats in Ecuador wasconfirmed by De la Barrera (1957) who, however, made almost all ofhis observations in Loja Province and admitted moreover that he haddevoted his main attention to the wild rodent species. As can begathered from De la Barrera's report, he had met in Loja with allthree subspecies of R. rattus, (rattus, alexandrinus and frugivorus)as well as with R. norvegicus. While the latter was of ratherdomestic habits, never leaving the immediate vicinity of the houses,R. rattus was trapped not only in but also round the settlementswithin a radius of 1,200 meters.
Dealing with the role played by the rats in the plague mani-festations of the presently active Ecuadorian foci, De la Barrera(1957) (a) referred to a small 1956 outbreak taking place at Chin-chil, in a region where the Rattus species were absent (domesticatedguinea pigs serving as the means to convey the infection to man);and (b) stated in a general manner that he had not met with rats in
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the plague-infected houses. Maintaining in his final report (1961)that the common rats of Ecuador had become resistant to plague, Dela Barrera came to the conclusion that "there was evidence that inthe actual moment the importance of Rattus as reservoir and spreaderof plague in Ecuador is secondary or nil." He was careful to add,however, that "the great murine communities parasitized by X.cheopissurrounded by sylvatic (plague) infection constitute a tangiblerisk."
Mus musculus
The frequency of the house-mice in LoJa Province is weliillustrated by observations quoted by Macchiavello, according towhich during the period from 1938 to 1942 not less than 49,393 out--of a total of 68,566 captured rodents were M. musculus. In accord-ance wlth these data, De la Barrera stated that this species "wasmet with as usual, in the houses and in the open fields". However,Jervis Alarcón maintained that, though M. musculus was widely spreadin Ecuador, existing also in the mountainous areas, still therewere many communities which had not been invaded by these rodentsor by Rattus, particularly in zones distant from roads and railways.
That the house-mice in Ecuador occasionally may be involvedin the transmission of plague from the wild rodents to the houseshas been confirmed by an observation made in 1956 by De la Barrera:In a house at San Fernándo, a locality round which wild rodentsplague was rampant, 12 plague infected M. musculus were found.Since, however, before this discovery five peop$e had contracted ---the disease, no doubt through the bites of wild-rodent fleas (Poly-genis litargus) abounding in the house, it is possible that theinfected mice were merely victims to the infection instead ofplaying a causative role in the human outbreak.
Domesticated rodents
That the domesticated guinea pigs, amply bred in the housesof the Ecuadorian plague foci and living in closest contact with-the inhabitants, are apt to play an ominous role in the transmis-sion of the infection from the wild rodents to man, has been provedon many occasions. An observation in point, made by De la Barrera,has been quoted above. Owing to the habit of the Indians to send''such animals as presents to their friends, the guinea pigs may alsobecome responsible for a spread of the infection at distance.Another most dangerous practice is the absconding of guinea pigsfrom plague-affected houses of settlements, resorted to by theIndians whenever they fear that as a control measure these animalsmight be taken away from them and be destroyed.
Besides guinea pigs, also rabbits (Oryctolagus cuniculus)are kept in the hauses of the Ecuadorian plague foci, but this isdone on a much more limited scale. Moreover, contact of man withthem is less intimate than that with the guinea pigs (De la Barrera,1957).
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Wild rodents and lagomorpha $
Fairly ample information on the wild rodents of Loja Provincecan be culled from the reports of De la Barrera and Jervis Alarc6n,while the latter also furnished some supplementary data in point forthe province of Chimborazo.
Mostfrequent among the wild rodents in both provinces are twospecies of cricetinae, Akodon mollis and Oryzomrs xanthaeolus (95% ofthe captures of De la Barrera). Both are able to adapt themselves toa wide variety of habitations without predilection for any of them.They are both apt to invade the rural houses at night time. Theydiffer in so far as O. xanthaeolus is more heavily infested with thefleas common to all the small rodents of Loja Province. Both speciesare highly susceptible to infection with P. pestis and thus apt to beinvolved in widely spread acute plague epizootics. As observed byDe la Barrera in 1956 at Santa Ana, plague-affected rodents of bothspecies may be found even inside rural houses.
No ecological data could be found regarding some other Ory-zomys species, including 0. longicaudatus and 0. flavescens, as wellas in regard to Phyllotis fructicicolus which, like the tifo abovementioned species of cricetinae, have been found naturally plague-infected in Ecuador.
Sigmodon peruanus, also belonging to the subfamily of crice-tinae, though less frequent than A. mollis and 0. xanthaeolus, isalso widely spread in Loja Province. According to De la Barrera, itis moving about rather slowly, and therefore, is but rarely met within the houses. Bike its congener, Sigmodon puna, it has been foundnaturally plague-infected.
The squirrel Sciurus stramineus nebouxi, a tree-inhabitatingspecies, though generally of sylvatic habits, not rarely enters thehouses in daytime in search of morsels of food. This species de-serves great attention insofar as, being considered as comparativelyresistant to infection with plague reservoir in LoJa Province, thusbeing responsible for the periodical appearance of acute epizooticsin the highly susceptible cricetinae A. mollis and O. xanthaeolus.It is important to note in this connection that S. stramineus, whichhas been found to be infested at a low rate with the flea Polygenislitargus, is met with in more restricted locations than the saallEcuadorian rodent species. Hence, should the role of S. stramineusas the principal plague reservoir in Loja Province be proved, thelocalities inhabited by it might form strongholds of the infection.
As suggested by Jervis Alarc6n, in Chimborazo Province,Sylvilagus brasiliensis and allied species of lagomorpha, which arealso comparatively resistant to plague, might play a role comparableto that of S. stramineus in Loja. It is noteworthy that Sylvilagus,a large animal hunted for the sake of its meat, also belongs to thespecies restricted in their habitat. Its specific flea is Hoplop-syllus manconia.
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It deserves attention that, in strict contrast to the abovediscussed postulations, De la Barrera insisted that the Ecuadorianwild rodents "constituted by species which live together or enterin contact, are equally sensitive (to plague), are parasitized bythe same fleas and constitute a homogeneous whole in regard toplague. The importance of each species in the transmission dependssolely upon its abundance and its habits."
De la Barrera maintained also that the large rodent species(Cuniculus, Dasyprocta, Sylvilagus and Sciurus) apparently did notplay an important role in the ecology of a plague. It'will be theobject of further investigations to decide whether his contentionsor, perhaps in a modified form, the more plausible suggestions ofMacchiavello and Jervis Alarcón are valid.
Observations on fleas
Rat fleas
Dealing in a general manner with the occurrence of X. cheopisin Ecuador, Jervis Alarcón stated that in the coastal areas up toan altitude of 1,200m., this flea was practically alone met with onthe common rats and was also solely responsible for the conveyance -of the infection in the past epizootics and epidemics. In the moun-tainous areas of the interior, X. cheopis was considerable lessabundant than on the coast, not occurring in numbers sufficient tocause widespread epizootics folloved by epidemics. It was not foundin localities above about 300m., being replaced in the highly situatedareas of Chimborazo Province by Nosopsyllus londinensis. As statedby Jervis Alarc6n, this flea, frequent in altitudes of above 1,40m.,though a less efficient vector than X. cheopis, seemed at low tem-peratures more suited than the latter to serve as a reservoir ofP. pestis and consequently was in Chimborazo Province the flea re-----sponsible (causaút9) for "the maintenance or endemicity of plague"--playing thus a role analogous to that of Polygenis litargus in LojaProvince.
It is striking to note that De la Barrera, reporting on hisinvestigationsin Loja Province, listed among almost 12,000 fleasexamined by him only four X. cheopis, apparently 3 in the nests ofnot determined rodents and one on a lot of 16 domesticated guineapigs.* It has to be noted, however, that (a) as already mentioned,this observer made his studies on wild rodents rather than on rats -and (b) to judge from Macchiavello's article, during the plague out---breaks observed by him in 1943 in the Cariamanga cantón of Loja Prov-ince, X. cheopis was the prevalentflea on the rats (mainly R. Alex-andrinus) and thus evidently served as the vector of the inIfection.Further studies, showing the comparative frequency of X. cheopis inthe various canton. of Loja Province seem thus most necessary.
* Later in his report he also mentioned 2 cheopis fleas found onR. norvegicus.
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Mouse fleas
As stated by Jervis Alarcón, the fleas met with on the house-mice of Ecuador belonged to the species Leptopsylla segnis, Tiamastuscavicola, Pulex irritans and (rarely) X. cheopis. Among 11 fleascollected by De la Barrera in Loja Province from M. musculus, 6 wereL. segnis, 4 T. cavicola and 1 N. londinensis.
Fleas of the domesticated guinea pigs
Referring to the fleas of the domesticated guinea pigs, JervisAlarcón recorded the following figures:
Loja Province Chimborazo Province (Riobamba)
P. irritans 67.7% T. caviocola 69.5%P. litargus 32.1% **Hectopsylla eskeyi 29.4%
The flea incidence on Cavia cobaya observed in Loja Provinceby De la Barrera was as follows:
P. irritans 1,804 Polygenis sp. 2T. cavicola 595 X. cheopis 1H. eskeyi 45 L. segnis 1P. litargus 44 Cten. felis 1
Total: 2,493
The occurrence of Polygenis litargus, the wild-rodent fleamainly responsible for the transmission of plague in LoJa Provinceon the domesticated guinea pigs is of great significance. Tiamastuscavicola, the specific flea of the guinea pig, has been found natu-rally plague-infected in both Ecuador and Perú but is not consideredas an efficient vector of P. pestis.
Fleas of the marsupialia
That marsupialia (Monodelphis and Didelphis), because havingample contact with the wild rodents but also frequenting the houses,are.apt to play a role in bringing infected fleas to the immediateviclnity of man, is confirmed by the following flea list furniahedby De la Barrera for Didelphis marsupialia:
Polygenis litargus*** 4 Rhopalopsyllus cacicus 32P. bohlsi bohlsi*T-* 2 CtenocephtalidesAdiratopsylla felis felis*** 3
intermedia copha*** 3 .'
Neotyphloceras rosenbergi, found by De la Barrera on Didelphisazarae, has also been found naturally plague-infected in Ecuador.
** Ths species and also H. suarezi have been found naturally plague- Oinfected in Ecuador. Both thes.e fleas were also faund on conmmonrats.
~x Found naturally plague-infected.
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Commenting upon his findings, De la Barrera stated that Poly- $genis litargus was not only the flea most frequently met with on thewild rodents of Loja Province but was also found on the common ratsof the rural areas and on the domesticated guinea-pigs. Thoughconsidering this flea as a probable vector, conveying P. pestis notonly from rodent to rodent but also to man, De la Barrera maintainedthat its role had not been definitely proved. It is, however, im-portant to add that these doubts were soon set at rest, Macchiavellorecording one year after the publication of De la Barrera's reportexperimental findings confirming the capability of Polygenis litargusto convey the infection. Though with some restrictions, he con-sidered that it is a "splendid" plague vector. One must however,agree with De la Barrera that most probably this flea is not the onlyvector of the infection in Loja Province, and that thus there is anurgent need to test the capability of the other wild-rodent fleas metwith there, paying prime attention to the several species which, likeP. litargus, have been found to harbor P. pestis under natural condi-tions.
It is disappointing to find that, in contrast to the quiteample prima facie evidence available in regard to the Loja fleas,information on the species probably concerned in the conveyance ofplague in the province of Chimborazo is not only quite scanty, butalso contradictory. Jervis Alarc6n is evidently of the opinion thatin that plague areas N. londinensis found on Oryzomys xanthaeolusand Akodon mollis besides on the rats, plays a role analogous to thatof P. litargus in Loja. However, in his 1961 report De la Barreramade the following statement:
"Though our information on the Siphonaptera of the northernzone (Chimborazo) seems incomplete, there can be no doubtthat the flea species are not the same as in the southernzone. The principal difference is that Polygenis litargusthe predominant and probably the vector species in the prov-ince of Loja, is not met with above 2,200 meters of altitude,being replaced in Chimborazo by Pleochaetis dolens quitanus."
It is clear, therefore, that further studies on the occurrenceand comparative importance of these two fleas are urgently called for.Great attention must also be paid to Hoplopsyllus manconis, thespecific flea of Sylvilagus brasiliensis which, as has been notedabove, is in the opinion of Jervis Alarc6n possible the fons et origomali in Chimborazo.
It has to be added that the present reporters have not beenable to find any information on the rodents and fleas implicated inthe plague manifestations in the provinces of Tungurahua and Cañar.
Ecology and epidemiology of plague
Though, as has been noted already on several occasions and willbe further discussed below, still many gaps in its knowledge exist,it may be claimed nevertheless that the general features of the ecology
RES 2/12- 81 -
of plague in Ecuador have become clear. There can be no doubt thatin the presently affected areas of that country plague is basicallyof a sylvatic nature, the persistence of the infection in wildrodents being responsible for the occasional appearance of the dis-ease in the tdomestic' rodent fauna and in man. Though, to judgefrom the information available only for the two worst affectedareas, the provinces of Loja and Chimborazo, several species of wildrodents and lagomorpha have been found involved in the plague mani-festations, at first glance most seriously affected. There can beno doubt that in these two most numerous and widely spread speciesinfection by P. pestis plays the role of a population regulator, thedisease becoming periodically rampnnt among them when, for reasonait would lead too far to discuss here, the tides of widespread acuteepizootics are followed by periods during which owing to the deci-mation of the herds the infection finds little if any fuel for itsspread or even persistence. It is under these circumstances aplausible idea that the above mentioned cricetinae species do butperiodically suffer from plague, the infection being permanently-harbored by other rodents. As has been stated, this has been ac-tually postulated, Sciurus stramineus being incriminated as the per-manent plague reservoir in LoJa, while an analogous role has beenascribed in Chimborazo Province to Sylvilagus brasiliensis. As willbe discussed in the following part of this report, observations madein Perd lend some support to the view that Sc. stramineus might becapable of serving as a permenent plague reservoir. However, asfar as the present reporters are aware, no proof whatsoever has beenobtained that an identical role might be played by S. brasiliensis.Nevertheless, one may accept it as a working hypothesis that not theCricetinae, but other species of rodents or lagomorpha constitutethe permanent plague reservoirs in the Ecuadorian plague foci. Toconfirm or to establish which species are actually involved, is oneof the urgent tasks of further investigations, because only aftertheir discovery will it be possible to determine whether and wherewithin the affected areas strongholds of plague exist. The recog-nition of such 'elementary focit the existence of which seems tohave been hinted at by Macchiavello and Jervis Alarcón, would be ofgreat importance for an adequate prevention and control of plague.
In contrast to the above-discussed problem, for the attemptedsolution of which in part hypotheses rather than established factshad to be adduced, the manner in which plague finds its way from thewild rodents to man has in the main been elucidated.
As can be gathered from De la Barrera's reports, humaninfection has been sometimes contracted by persons working or stay-ing in the foci of wild-rodent plague. No doubt, however, an in-tradomestic infection of man is the rule in the presently affectedareas of Ecuador. This may be effected in various ways. Thus, asconfirmed by an observation of De la Barrera, plague-infectedrodents may occasionally carry their fleas into the houses thus be-coming capable of conveying the disease to man. Infected wild-rodent fleas may also be brought into the houses in other ways,
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particularly by the marsupialia frequenting the human habitations aswell as their vicinity, and may then directly attack man. It may benoted in this connection that De la Barrera was able to cultivateP. pestis from 2 out of 10 Polygenis litargus fleas collected in aplague-infected haouse.
Ample experiences have shown, however, that often the mani-festation of plague in man is preceded by the infection of the commonrats, the domesticated guinea-pigs or occasionally the mice livingmost or all the time in the human habitations. While there can be nodoubt that wild-rodent fleas are instrumental in conveying the infec-tion to these animals, pending further investigations it is difficultto decide wbich fleas function as the vectors of P. pestis from thelatter to man. It should be noted in this connection that (a)X. cheopis, a notoriously efficient vector, appears to be scanty inthe presently plague-affected areas of Ecuador and altogether absentin their higher parts; (b) N. londinensis, found on the rats inChimborazo Province, is not a highly efficient vector; and (c) itseems to be unknown, to what extent the common rats are infested withwild-rodent fleas. It can be pointed out, however, that according tothe above quoted observations of Jervis Alarcón, the domestic guinea-pigs of Loja Province were to a remarkable degree infested withPolygenis litargus and it seems likely, therefore, that this flea wasinstrumental in conveying the infection from guinea-pig to guinea-pig and from them to man. That p. irritans-, according to JervisAlarc6n, the predominant flea of the guinea-pigs in Loja, played animportant role in this respect, seems at the present state of knowl-edge on this species less likely.* Whether Hectopsylla eskeyi, found -besides the rather inefficient vector Tiamastus cavicola on the guinea-pigs of Chimborazo Province, is of importance in the conveyance ofplague, remains to be seen.
Though instances of the appearance of two or more cases in oneand the same house to be frequent (occurring, according to De laBarrera in 1956 in 42% of the affected habitations), a spread of thedisease from man to man through the agency of infected fleas seemsnot at all likely.
That fundamental differences in the ecology of plague existbetween the Loja and Chimborazo provinces, is confirmed by the factthat the seasons of the appearance of human plague in the two areasare not identical. Jervis Alarc6ón stated in this respect that:
"in Chimborazo between 1946 and 1956, the majority of thecases appeared in the hottest months with a high relativehumidity, from February to May, and the rare cases appearedin the summer months of no excessive heat between Augustand December, whereas in LoJa (plague) became intensifiedafter the rainy season, during the harvest period, i.e.from May to December."
* This point will be further discussed in the report on Perú.
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Recommendations for further investigations
As already repeatedly stated in the foregoing pages, in manyrespects the information available in regard to the ecology andepidemiology of plague in Ecuador is still incomplete. There existsthus an urgent need for further investigations, most essential amongwhich seem the following:
Coastal provinces
Though since the final dissapearance of plague from Cuaya-quil in 1939 the disease does not seem to have any more a permanentfoothold in the coastal provinces of Ecuador, it had to be noted thatwithin recent years repeatedly long-distance sprints of the infectionfrom the endemic foci in the interior have led to the appearance ofthe disease at or near the seacoast. To juáge from the perhaps notcomplete available information, these outbursts could become quiteserious, as in Manta for instance, where a considerable rat-epizooticpreceded and accompanied the marifestation of the disease in man.The fact that such an epizootic could evolve, shows clearly that theresistance of the Ecuadorian rats to plague is not as universal ornot as permanent that it has been postulated. An appraisal or re-appraisal of the plague-receptivity of the rat-population in thevarious communities of the coastal provinces (in the first line inthe ports and other traffic centers) and as far as possible also inrepresentative-rural areas would, therefore, be most desirable. Asshown by large-scale investigations in point made in India, it wouldbe possible to make the susceptibility tests in a central laboratoryto which batches of rats from the various locations are forwarded.An exact knowledge of the plague history in each of these would beof great importance for the evaluation of the results.
Advantage ought to be taken of the trapping of these rats toassess:
(a) the comparative density of the rat populations in com-munities of different size and in the rural areas;
(b) the relative frequency of the two rat species and(though this is of lesser importance) of the subspeciesof R. rattus;
(c) the occurrence and frequency of the various species ofrat-fleas, specially of X. cheopis, in the variouslocations studied.
(Since, however, the frequency the rat-fleas may be subject tomarked seásonal changes, it wol.ld be highly desirable to con-tinue such studies, at least in selected communities, for aperiod not less than a whole year).
Detailed instructions for the trapping of rats, the co3lectionof fleas and the transport of both to the central laboratory, suitableunder the local conditions, ;,ll have to be framed and issued.
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Endemic areas of the interior
1) Ecological and epidemiological investigation $
To judge from the available information, the endemic foci inthe provinces of Loja, Chimborazo, Tungurahua and Cañar have beenfound well delimited. Since, however, the observations in pointwere made some years ago, it will be important to determine in closecooperation with the workers of the National Plague Prevention Serv-ice whether the boundaries of the endemic areas are still the sameat present or whether the foci have shown a tendency to increase ordecrease in size. If possible, large-scale maps, showing the presentboundaries of the endemic foci should be prepared.
As has been mentioned above, it appears that within the endemicarea of Loja Province there exist districts with a particularly seriousplague situation, in which evidently the infection shows a marked oreven permanent tendency to become recrudescent. Every possible effortshould be made to confirm the continued existence of such centers ofthe infection, correlating observatlons on the incidence of humanplague (upon which the information presently available in this respectseems to be mainly based) with particularly intensive studies on therodents and fleas. Efforts should also be made to determine whethersuch centers of the infection exist also in the other three affectedprovinces, specially in that of Chimborazo.
All human manifestations met with by the study group ought tobe made the subject of through investigations. In the first lineefforts should be made to establish which rodents and which fleas wereresponsible for the infection of the patients. The presence of plaguein them ought to be confirmed invariably through adequate laboratorytests and the strains of P. pestis isolated from the sufferers oughtto be kept in a lyophilized state for further study.* Moreover, effortsought to be made to detect the occurrence of subelinical forms of thedisease through clinical and serological surveys of groups of thepopulation actually or potentially under the risk of infection.
2) Investigations on rats, house-mice and their fleas
As has been discussed, the information on the occurrence--of thetwo species of rats and also that on the frequency of the house-micein the endemic areas is rather incomplete. It is, therefore, mostimportant to study the present distribution of these rodent speciesin the endemic areas or, if possible, in the four affected provincesas a whole. The zones inhabited by these animals might with advantagebe indicated in the maps of the endemic areas.
All rats and house-mice found dead or trapped within theendemic areas ought to be dissected and examined for the presence ofplague or of past infection with p. pestis. Advantage olght to betaken for this purpose not only of macroscopic and microscopic ob-servations, cultivation and pooling test but also of serological tests.
* This naturPll:y also holtds true o? the strains isolated from rodentsand fleas.
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The latter well as the pooling tests and perhaps even the cultiva-tions might be made in base laboratories, to which the adequatelyorgans and the blood or serum of the dissected animals are forwarded.
It would be further essential to ascertain whether or to whatextent the rats within the endemic areas are resistant to infectionwith P. pestis. If, as will be probably inevitable, the animalshave to be sent for this purpose to a base laboratory, they wouldhave to be carefully de-flead before they eae dispatched.
The rather scanty information on the flea fauna of the ratsin the endemic areas must be supplemented by further large-scalesurveys. Particularly important is (a) to establish to what extentthe rats of Loja Province are infested with X. cheopis and whichfleas parasitize the rats in its absence; (b) to confirm that inChimborazo Province N. londinensis is the specific rat-flea; and(c) to determine which species infest the rats in the endemic areasof the Tungurahua and Cafar provinces.
While the vector efficiency of X. cheopis may be taken forgranted, it would be important to study the vector capacity of thefleas replacing it, particularly of N. londinensis. Analogousstudies ought to be made also with P. irritans, frequent on thedomesticated guinea-pigs of Loja Province and with Tiamastus cavicolaand specially with Hectopsylla suarezi, infesting these animals inChimborazo Province.
3) Investigations on wild rodents and lagomorpha
As will be gathered from the statements-made earlier in thisreport in regard to the observations on wild-rodent plague in theEcuadorian endemic areas, the most important problem yet to be solvedis which of the several species found to suffer from natural plagueform the permanent reservoir of the infection. Thus far it has beenassumed that in Loja Province the squirrel Sciurus stramineus nebouxiis the fountainhead of the infection, while in Chimborazo an analogousrole of Sylvilagls brasiliensis has been suspected.* Apparently themain argument in favor of these species vas that they were supposedto be less susceptible to plague than the cricetinae. It would seem,however, that this claim is not supported by convincing evidence.Moreover, the present reporters have to point out that the supposedresistance of a rodent species to plague should not be considered asthe sole criterion of its capability permanently to harbor the infec-tion. Experiences In other plague-affected countries have shown thata more or less refractory state to infection with P. pestis may be ofa racial or seasonal nature rather instead of being inherent in the
* No statements in point have been made in the case of the Tungurahuaand Cafar provinces which form in this as well as in many otherrespects still a terra incognita.
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species in question as a whole all the time. Hence, while it iscertainly important to make exact comparative studies of the degreeto which the various species of the Ecuadorian wild rodents areamenable to P. pestis infection, a decision whether or not the abovementioned or other species are the permanent reservoir of the diseaseshould also be based upon careful considerations of their ecology andthe constancy of the occurrence of natural plague in them. As sug-gested with emuch reason by Macchiavello, the best times for observa-tions of the latter kind are the periods or seasons during whichwild rodent plague in general is at an ebb. Findings of the continuedexistence of plague in a rodent species at such times would go a longway to incriminate it as a permanent reservoir of the infection.While paying due attention to these investigations, a careful watchmust be kept also on the trend of the disease in the cricetinae inVhich epizootics become Deriodically rampant. Sincc, ea has beandiscussed eaoye, there is evyery reason to assume that these hightides of the infection and subsequent ebbs are correlated withfluctuations of the pópulation density of the animals, constant orat least periodical surveys ought to be made to assess their fre-quency. Well orgarised observations of this kind would form aneasy mean.to forecast the appearance of epizootics, during cvhichthe risk' of human infection is highest.
In order to ascertain the presence of plague in the wildrodents it is necessary (a) carefully to examine all animals founddead with the aid of macroscopic and microscopic observations,cultivation and, if indicated, animal experiments; (b) to watch forthe occurrence of incipient or latent infection with p. pestis bytrapping* adequate numbers of the rodents and, perhaps after a periodof observation in the live state, sacrificing them and subjectingthem to the above mentioned laboratory tests (substituting poolingtests with their organs to individual animal experiments). Anotherpromising method would be to make tests with the sera of apparentlyhealthy animals. As far as possible, the above outlined tests shouldbe made in a base laboratory, to which the adequately preservedorgans and the blood serum of the animals are forwarded. It isobvious that, whenever necessary, their skulls and skins should be'
preserved for identification tests.
A part of the trapped animals ought to be used for testingtheir susceptibility or resistance to infection with P. pestis.Since tests of this nature presuppose the availability of adequatelaboratory facilities, consideration must be given to the possibilityof forwarding batches of the animals to a base laboratory after theyhave been de-flead and kept for some time in quarantine; one mustfear, however, that the high mortality frequent in wild rodents keptin captivity will militate against the implementation of these pro-cedures. As soon as the importance of a species of rodents or lago-morpha for the permanent harborage of P. pestis has been established,
*In the case of species which are difficult to trap, killing theanimals by an adequate method may become necessary.
RES 2/12
a close study of its ecology, particularly of the limits of itshabitat, must be made and the trend of the infection in the animalsin question mast be taken under constant observation. If theecological conditions warrant this, a pilot study might be made toassess the possibility of eradication campaigns.
4) Investigations on wild-rodent fleas
To obtain an ample material of the Ecuadorian wild-rodentfleas for study is of utmost importance in order (a) to arrive ata better understanding of the comparative frequency of the variousspecies on the dSfferent wild rodents or legomorpha and in theirnests as well as on liaison animals like the marsupialia and on therodent species living in or near the houses; (b) to study at thesame time the seasonal incidence of the various fleas; and (c) toassess the comparative importance of the different wild rodent fleasin the transmission and the inter-seasonal carry-over of--lague.Constant efforts should be made, therefore, not only to collectfleas from all rodents coming under observation but also to makesystematic searches for these parasites in the rodent nests andharborages as well as in tbe houses where the guinea-pigs, veritableflea-traps, are apt to furnish an adequate material.
It is clear that the above outlined investigations wouldyield valid results only when the various flea species met withcan be properly identified--a task which unfortunately could by nomeans always be prope'rly performed by the field workers. Theyshould take care, therefore, to submit representative specimens oftheir collections to an expert for identification. It would becertainly best if for this advantage could be taken of the uniqueknowledge on the South-America flea species possessed by the cus-todian of the Rothschild flea collection in Tring, (England); since,however, the results of his identifications would become availableonly with delay, it would be essential to attach a flea expert tothe study group operating in South America.
To arrange for adequate tests on the vector capacity of thefleas is also difficult. No doubt this task could be performedmost satisfactorily in one of the United States laboratories pos-sessing special experience in this field. Nevertheless it wouldseem well to make prellminary tests of this nature in a base labo-ratory in Ecuador and to attempt at the same time to raise coloniesof the various fleas, lots of which could then be sent to theUnited States for final vector studies.
When investigating the role of the wild-rodent fleas in theindividual endemic areas of Ecuador, prime attention ought to bepaid to the following problems:
(a) Loja Province. Further studies on the distributionand seasonal incidence of Polygenis litargus ought tobe made and its vector efficiency ought to be confirmedthrough further tests. At the same time it should be
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determined through ecological investigations, lab-oratory tests and vector studies to what extent otherspecies of wild-rodent fleas participate in thetransmission of plague. Prime attention should bepaid in this respect to the species already foundnaturally infected.
(b) Chimborazo Province. The distribution and seasonalincidence of Nosopsyllus londinensis, Pleochaetisdolens quit anus and Hoplopsyllus manconis should bethoroughly investigated and large-scale tests oughtto be made to determine to what extent they arenaturally plague-infected. It would be also essentialto compare the vector capacity of these species.
(ci) ITungurahua and Cañar Provinces. Since no informationon the flea fauna in the endemi c areas of these twoprovinces could be elicited, it would te important toestablish by what species the rodents met with areinfested, to study the seasonal incidence of the fleasand determine through ample laboratory tests which ofthem are naturally plague-infected. The vector capacityof the species incriminated in this or other waysshould. then be studied.
It is hoped that for the drafting of a definitive plan forplague studies in other parts of Ecuador it will be possible to take-advantage of the experiences gathered in the course of the investiga-tions in point now envisaged for the Perú/Ecuador border area.
REFERENCES
1) R. Pollitzer (1954) Plague. WIO Monograph Series Nº 22(Summary of the older literature).
2) A. Macchiavello, Estudios sobre la peste selvática en Américadel Sur: II (1957) Peste selvática en las zonas fronterizasde Perú y Ecuador. 1. Peste en la provincia de LoJa, Ecuador.Bol. Of. Sanit. Panam. 43 (1): 1941
IV (1958) Transmisión experimental de la peste por Polygenislitargus. Bol. Of. Sanit. Panam. 45 (2): 112-131
3) J. M. De la Barrera (1957) Informe presentado por la OficinaSanitaria Panamericana, Oficina Regional de la OrganizaciónMundial de la Salud, al Gobierno del Ecuador (Unpublishedtypescript).
14) Idem (1961) Informe al Gobierno del Ecuador sobre peste (Un-published typescript).
5) O. Jervis Alarcón (1958) La Peste bub6nica: Problema de ur-gente resolución. Rev. Ecuat. de Hig. y Med. Trop. 15 (1958)3: 105-137.
6) WHO Weekly Epidemiological Records (1961-30 March 1962) passim.
7) PASB, Health Statistics, Vol. XI, Nos. 1-4 (Jan-Dec. 1962)
- 89 - RES 2/12
SECTION G
REVIEW AND EVALUATION OF THE PRESENT STATUS OF PLAGUEIN.PERU
History and Recent Incidence of Plague
As summerized by Pollitzer, following its importation by the sea-route into the port of Callao in 1903, the disease spread along thecoast of Peru, most of the principal ports becoming infected within twoyears, and eventually invaded 10 of the 20 departments of the country,a.s well as the three special provinces of Tumbes, Callao and Moquegua.The situation became worst in the coastal department of Lambayeque, Li-bertad and Lima, as well as inland in Cajamarca. The total incidenceof the disease may be summarized thus:
Cases
8865692246421087738353
Annual average
8866924641097450
1903-1960 226Q7 227 5
More detailed figures for the period from 1956 to 1962 may be set forththus:
Areas affected
Year Department Province
Incidence
Per Province Per Department Annual Total
1956 Piura AyabacaHuancabamba
1957 Piura Ayabaca 9Huancabamba 14 23
Ancash Huaraz 11Recuay 3 14 37
1958 Tumbes C. Villar 3 3Piura Sullana 6
Paita 1Ayabaca 24 31
Lambayeque Lambayeque 7 7Cajamarca Hualgayoc 3 3Ancash Huaraz 5 5 49
Period
1903-19121913-19221923-19321933-19421943-19521954-1960
816 24
-90- -ES 2/12
Areas affected
Year Department Province
Incidence
Per Province Per Department Annual Total
1959 Piura
Cajamarca
AyabacaHuancabambaPaita-Hualgayoc
As can be gathered from the Informe Semanal issues published in 1960,1961 and 1962, the case incidence of- plague in Peru during these threeyears was as follows:
1960 Piura
Cajamarca
AyabacaHuancabambaHualgayoc
1961 Piura Ayabaca 3Huancabamba 65 68 68
1962 Amazonas Bagua 25 25Piura Ayabaca 48
Huancabamba 44 92CaJamarca Jaén 4I7 47 164
(N.B. Involved were in 1962 the Ayabaca, Sapillica and Suyo districtsAyabaca Province and the Tabacones district of Jaén Province.)
How far this at first glance rather disquieting increase of the
case incidence since 1960 is merely the result of an improved report-ing system, it is impossible to decide.
Dealing with the plague situation in Perd up to 1932, in his
classical study, Eskey stated that the central part of the country,situated between the 7th and l3th degree of latitude and specially
the areas between the 79 and 99 degree with an average annual meantemperature between 699F (20.59C) and 71QF (21.79C) suffered mostfrom the disease. There the infection spread rapidly to rural aswell as urban communities, produced more cases than elsewhere in thecountry, and showed little tendency to disappear spontaneously. How-ever, the degree of rat infestation of the houses was also of impor-tance. Thus the ports of Palta in the north and of Mollendo in thesouth of Peri, though situated well away from the zone where the cli-mate favored the spread of plague, suffered heavily because theirwooden buildings were attractive to the ratso Lima on the contrary,though open to inroads of the infection as far as the climatic con-ditions were concerned, had a lesser morbidity than these two portsbecause of having better class houses.
10
11818
.,
1518 33
151177
1327 139
of
- 91 - -RES 2/12
Generally speaking, the annual plague epidemics in Perd tendedto reach their peak during the summer months. However, there as else-where the plague seasons fell into an earlier period in areas wherethe winter months were warm than in localities with a colder climate.
Human plague in Perú was mostly bubonic, but one pneumonic out-break, claiming 21 victims in the department of Junin is on record.
As described by Eskey, R. norvegicus, R. rattus and R. r. alex-andrinus were common in the towns of northern Perú, while in the cen-tral and southern coastal areas as rule Norway rats greatly exceededthe other two species. X. cheopis was the most common rat flea and,according to Eskey, the only important plague vector.
Recent manifestations of rat-caused plague
Information on further rat-caused plague outbreaks in Perú israther scanty. Ramos Diaz referred to a manifestation of this kind,observed in 1938 in a small village of the Lambayeque Department, sit-uated in a mountainous area 1300m above sea-level. There an epizooticamong R. rattus led to the appearance of the disease in guinea-pigskept in the house of the first victim. Two children in a neighboringhouse to which some garments of this woman had been brought, also con-tracted the infection but recovered under serum treatment. In theopinion of Ramos Diaz, X. cheopis, the principal flea of the rats inthe locality, had been responsible for the infection of the dcmesti-cated guinea-pigs, but P. irritans had been instrumental in conveyingP. pestis from the latter to the first victim. He claimed to haveproved the presence of this organism in a lot of P. irritans collectedfrom a garment used by the second affected family, but the techniquehe used for this purpose can not be considered as fully reliable. Bethis as it may, it is not easy to believe that in a locality whererats infested with X. cheopis had become plague-affected, this vectorhad not been responsible for the human infections.
As has been noted above, the presence of plague in the Lambaye-que Department was again recorded in 1958, but it would seem that onthis occasion a coastal and not a mountainous area was affected.
Describing a successful anti-plague campaign with DDT and "1080"(sodium fluoro-acetate) in Tumbes, the capital of the department ofthe same name in 1945, Macechiavello stated that before the outbreakfought by him this town had suffered from the disease in 1909, 1915,1922 and 1940. In his opinion the cause of the 1945 outbreak hadbeen the importation of fleas in bags of merchandise from the Lamba-yeque Department. 95% of the rats then present in Tumbes were R. r.alexandrinus, 5% R. rattus, all of which were almost exclusively in-fested with X. cheopis.
As noted above, the presence of plague in the Tumbes Departmentwas again recorded in 1958.
- 92 -
Manifestations of wild rodent plague ç
1) Trujillo area
In reference to the situation in the area of Trujillo, capitalof the department of La Libertad, Macchiavello (1958) made the follow-ing statement:
"During the plague control campaign in Trujillo wecould repeatedly confirm a re-infection derived fromthe surrounding rural area where an epizootic is main-tained in the sigmodons (S. peruanus). Suddenly, du- -ring a season unfavorable for the activity of X.cheopis, plague attains epizootic proportions in therural area, where every day hundreds of Sigmodons suc-cumbed to the infection are found. R. r. frugivoruswhich lives together with Sigmodon in the fields andbreeds particulerly round the small hamlets, was prac-tically not touched by the epizootic during the coldseason, in which X. cheopis remains inactive and in
- which the transmissions from one species to the otherdepend upon P. litargus ..............The epizooticbecomes first manifest in R. frugivorus and afterwardspasses to R. rattus and R. alexandrinus of the settle-ments only when the season becomes favorable for X.cheopis and the infection originally acquired by a fewrats in the fields can spread among these rodents. Du-ring the summer the epizootics in these two rat speciesfollow an independent course and the number of X.cheopis on- the Sigmodons was not more important thanthat of P. litargus recuperated from the rats."
It would thus seem that, while S. peruanus had become the reser-voir of plague, common-rats and X. cheopis were responsible for itsspread in the settlements.
2) Lancones district
In his article on plague in the Lancones district (Sullana Prov-ince, Department of Piura), to which further reference will be madebelow, Macchiavello (1957) fumnished the following data on the earlyrat-caused and cheopis-borne bubonic outbreaks in the provinces ofPaita and Piura.
RES 2/12
PaitaYear City Province
PiuraCity Province
SullanaCity Province Lancones district
90o4 1741905 801906 591907 1771908 2919o9 46190 o 01911 11912 291913 151914 01oQ15 o1916- 501917 01918 171919 1011920 631921 681922 391923 321924 121925-27 o1928 , 31929 131930 -
1748059.
1773946o12915
oo
54o17
1026384423112o313
oO.o
271961213
8740
o1
5592482032o
o
2690140
234992
1769
94~22114932252
1042547o
oOoo1ooo1Ooo3o614
*3317912oooo
ooo.o1ooo1ooo3o
6143317
912o
oo
oo
o
ooo0
ooo
o0oo0
0
oO?
ooo0ooO
As indicated by this table, plague showed little tendency in theprovince of Paita to spread to the hinterland, remaining practicallyrestricted to the port of Paita, while in Piura Province the incidenceof the disease in the capital was often considerably below that inother localitites of the province. As far as can be Judged from theavailable data, plague ceased to be manifest in the latter provincein 1925, in Paita in the year of 1930.
Macchiavello felt certain that the appearance of plague in thecity of Sullana, where the disease was quite.active from 1918 to 1924,was due to an invasion from the two above-mentioned provinces. Therecan be hardly any doubt that this entry of the disease eventually ledto an entrenchment of plague-in the wild rodent population of the Lan-cones district and also of an adjacent Ecuadorian area which, thoughbecoming manifest only in 1946, presumably commenced considerably ear-lier, perhaps already during the period from 1919 to 1921. Macchiavellonoted in this connection that one plague case had been recorded in 1939at Huasimal in the Lancones district and that possibly three human at-tacks occurred there in 1943. The reappearance of the disease in June,1946, in the Lancones district and the simultaneous involvement of the
- -�·-�·cri-----·i-
- 93 -
RES 2/12
adjacent Cazaderos-Alamor area in Ecuador led to en investigation underMacchiavello, the main results were as follows:
a) Domestic rodents and their fleas - The common rats were en-tirely absent in the affected Peruvian area. Their existencein Bolasbamba, one of the affected localities on the Ecuado-rian side, was reported but could not be confirmed. Musmusculus were present in most of the houses but with theexception of one animal trapped in the house inhabited bythe study group, on which one X. cheopis was found, the notnumerous specimens seen were free from fleas. Macchiavello-felt certain that the cheopis had been imported in .the bag-gage of the detachment.
b) Wild rodents - The species of wild rodents met witia and theoccurrence of plague in them is showm in the following table:
Species met with examined plague-infected
Sciuridae:Sciurus stramineus nebouxi 51 14
Criceti-nae:Oryzomys santhaeolus xanthaeolus 18 3Oryzomys nitidus 5 0O. stolzmanni stolzmanni 1 0(0. longicaudatus auctt.)Rhipidonys equatoris 11 3Akodon mollis mollis 3 1*Akodon mollis orophilus 1 0Sigmodon simonsi 1 0
* Found positive in Ecuador.
Dealing with the findings in the squirrels, Macehiavello statedthat (a) only two or three of his positive specimens showed macroscopicsigns of rather subacute plague, associated with the presence of numer-ous P. pestis in their organs; (b) on the other hand guinea-pig exper-iments made with the organs of apparently healthy squirrels gave posi-tive results; and (c) the plague strains isolated from some of thesquirrels showed an attenuated virulence which, however, could be re-stored through guinea-pig passages. He concluded from these findingsthat besides an active form of plague a "residual" type of the infec-tion was apt to occur in the squirrels.
It is important to add that in many of the examined squirrelsorganisms of the aspect of P. pestis were seen in smears but guinea-pig tests made with material from such animals gave a negative result.
- 94 -
RES 2/12- 95 -
In marked contrast to the findings recorded above, most of thepositive cricetinae showed signs of acute plague with numerous P.pestis in the smears. Conmenting on the rarity of positive resultsin these animals, Macchiavello stated:
"The relatively low incidence of plague in the crice-tinae stands in contrast with the relatively high occur-rence of inapparent or resolving plague met with in scirus.This may be due to the fact that the cricetinae are moresusceptible to the infection and succumb to it, being al-most immediately devoured by birds of prey."
c) Wild-rodent fleas - The fleas met with on the wild rodentsall belonged to the genus Polygenis, most of them being iden-tified as P. litargus, while some, found on AAkodon mollismollis in the Ecuadorian part of the focus, were of anotherstill unidentified species. The flea index of the crice-tinae was fairly high (2.4 in the case of 0. xanthaeolus,1.1 in that of Rh. equatoris and 3 in A. mollis), even thoughmost of the animals had been caught with the aid of cyanogas.The flea índex of the squirrels, on the contrary, was only0.22, solely 16% of these rodents being flea-infested. Com-menting on this observation, Macchiavello stated: "in gen-eral the wild-rodent fleas are more sedentary than the rat-fleas and prefer the environment of the homogeneous tempera-ture of the nests or of dark and cool places. The observa-tion that in May (a month with moderate temperature in Lan-cones) the rodents harbor many fleas and of the occurrenceof comparatively many free fleas on the harvested maizefields....makes it probable that at a certain season of theyear the flea índex of the rodents is high and that, un-doubtedly, these free fleas come from rodents succumbed atthat time to plague. This holds true of the squirrels aswell as of the cricetinae in general".
The presence of plague was confirmed with the aid of poolingtests in (a) a batch of 3 P. litargus collected from squirrels, and(b) a lot of 14 fleas of this species, which had been kept under ob-servation in a hollow tree for 6 months. Thus P. litargus, besidesconveying the infection, was evidently also capable of maintaining it.
Referring to his successful vector studies with P. litargus,Macchiavello stressed the willingness and capability of this flea tofeed on man.
d) Epidemiological observations - As can be gathered fromMacchiavello's article, during the 1946 outbreak observedby him, a total of 28 attacks of bubonic plague with 6deaths was recorded, 20 in persons living in 10 differentlocalities of the Lancones district and 8 in people inhab-iting 4 localities of the Cazaderos-Alamor area in Ecuador.As he emphasized, "if not all, so the majority of the casesstood in relation with previous activities in the maize-
- 96 - RES 2/12
fielda. Some fell ill also staying on maize farms. Withrare exceptions, all the individuals slept in places wheresome of them noted an abundance of fleas. At least 6 ofthe patients observed dead rodents in the maize-fields oradjacent fields or found evidence of epizootics among them".
Evaluating these observations and the findings he had made inthe rodents and their fleas, Macchiavello came to the conclusion thatplague in the Lancones district and the adjacent areas of Ecuador wasof a purely sylvatic type, a persistence of the infection in the squir-rels leading periodically to epizootics among the cricetinae which intheir turn were mainly responsible for the appearance of human out-breaks. Polygenis fleas, in the first line P. litargus served in allthese manifestations as the-vector of the infection.
3) Huancabamba and Ayabaca provinces
Whereas no recent information on the Lancones district is avail-able the early studies on the plague situation in the provinces ofHuancabamba and Ayabaca by Macchiavello in 1946-47 have been followedby investigations made in 1955-56 and again in 1960' by De la Barrera who,however, mostly reported on observations in the first mentioned prov-ince (Huamcabamba).
In his report, Macchiavello furnished the following general in-formation on the two provinces:
Huancabamba Province Ayabaca Province
Area (km i2) : ! ' , " 6557 7082Population(1940 census) '. ' : - 51613 75068
Inhabitants'(capital) 2580 2620
Inhabitants(distriets)
Ruancabamba 21605 Ayabaca 24255Canchaque 8540 Cumbicus 13350Huemarca 13242 Frias 18122Sondor 3027 Montero 5777Sondorillo 2462 Sicches 2856
Suyo 6767
The population of these areas consisted almost exclusively ofIndians or mestizos, whose standard of life was deplorably low. Theclimate, and accordingly the vegetation, varied in relation to the al-titude of the different regions, with forests in the low-lying valleys(in some of which tobacco and cocoa were cultivated), scanty growth inthe high regions, cultivations of cereals and alfalfa in the prairieregions and on the slopes of the hills. The plague area of Huancabamba
-1
4
* :
.t
RES 2/12
was mainly wheat-growing, groups of workers migrating from one culti-vated locality to the others to perform the necessary labors and thuswhile soJourning in the fields, being under the risk of infection, ifplague epizootics were present. Of great epidemiological importancewas also the practice of the people to store the harvested wheat intheir houses, especially in the attics with which many of the houseswere provided. Thus, the grain stores in the houses attracting thewild rodents, at the time of epizootics facilities were created fora transition of infected fleas to the intra-domestic rodent fauna ordirectly to man, especially if wild rodents succumbed to plague inthe storerooms.
The intradomestic rodent fauna consisted of M. musculus (which,however, sometimes lived in contact with the cricetinae in the fieldsround the houses) and of the amply bred guinea-pigs. However, Macchia-vello insisted, except in the regions at the foot of the mountains,Rattus was absent.
The prevalent domestic flea, P. irritans, occurred not only--often in almost incredible numbers--in the clothes, on eerthen floors,etc., but also infested the domesticated guinea-pigs, sometimes to ahigher degree than their apecific flea, Tiamastus cavicola. P. irri-tans was likewise found on the house-mice on which, however, it wasoutnumbered by their specific flea, Leptopsylla segnis.
Macchiavello found in the course of his work only one specimenof X. cheopis in the Changra region, a zone situated at low eltitudein the border district between the Ayabaca and Morrop6n provinces inwhich the plague incidence during the 1946-47 epidemic was unusuallyhigh. Generally speaking he upheld that this flea might be presentin the regions at the foot of the mountains. This seemed to holdtrue for instance of the low-lying Chelaco district in the provinceof Morrop6n, the involvement of which in the 1946-47 outbreak presum-ably stood in causal relation to the presence of R. rattus and X.cheopis.
Referring only to the wild rodents and lagomorpha involved inthe 1946-47 outbreak, Macchiavello enumerated the following species:
a) Akodon mollis orophilus, the most prevalent species, oftenand sometimes to a high degree infesting the houses, par-ticularly at the time the grain supplies were stored inthem and apt temporarily to occupy the nests of M. musculus(which thus could become infested with wild rodent fleas)*;
b) An undetermined species of Oryzomys;
c) Oryzonvs stolzmanni stolzmanni (0 longicaudatus stolzmanniauctt. ) also a widely distributed species;
d) Cavia tschudii ssp., a species distinct from the usually do-mesticated Cavia porcellus and, in contrast to the latter,apt to lead a peridomestic or even "sylvatic" existence;
In localitites where no cereals were cultivated, Akodon mollisoroph. was apt to live round the houses, particularly in thestone-walls separating the various properties.
- 97 -
RES 2 /12
e) Sylvilagus species, presumably S. andinus and S. ecaudatus.
The rather scanty data supplied in the study'presently under re-view in regard to the wild-rodent fleas may thus be summarized:
Nurber and speciesof rodents searched
Number offleas found Species of fleas
33 A. mollis orophilus
8 0. stolzmanni
20
8
16 Cavia tschudii
4 Sylvilagus sp.
997
118
Besides 3 L. segnis pleochaes-tis dolens quitanus, P. equa-toris, P. litargus endPlocopsylla mars.
1 P. litargus and 7Pleochaetis, mostly P. dolensquitanus
P. irritans, L. segnis,T. cavicola, Ct. felis,E. suarezi, P1. dolens quitanusand the specific Rhopalopsylluscacicus
P1. dolens quitanus (4),P. litargus (3),Pol. brechinus (33),R. cacicus (Z7),Hoplopsyllus manconis (11),Cediopsylla spyllmanni (40)
-1
N.B. It is also important to note that Sylvilagus and probably also0. stolzmanni were infested only with wild-rodent fleas
Dealing with the history of plague in the two provinces underreview, Macchiavello maintained that the disease first appeared in1920 in Huancabamba Province at Canchaque, situated halfway betweenPiura and Huancabamba City, a locality up to the present infested withR. rattus and X. cheopis. The involvement of the city of Huancabambain 1923 in its turn led to a spread of the infection to the rural areas.From 1928 plague in the capital became sporadic but continued to becomemanifest in more and more distant villages. In Ayabaca Province thedisease was first recorded in 1922, as far as it is known initially ina hamlet near the capital, and also spread in the rural localities.
-1
The affection of both provinces was presumably due to the impor-tation of infected cheopis fleas from the coastal areas in goods or inthe baggage of travellers, the presence of a.numerous and susceptiblewild rodent population offering ample fuel for the spread of disease.To judge from data furnished by Macchiavello human plague in the fociof Huancabamba and Ayabaca which became eventually confluent, showeda seasonal incidence, being manifest in spring and summer, but absentin winter.
.)
A
e-4
- 98 - -
1
RES 2/12- 99 -
Dealing with the types of plague observed in Huancabemba Province,Macchiavello furnished the following global statistics:
Number of patients Total1939-1945 1946-1947 1939-1947
Type of plagwe Men Women Total Men Women Total Men Women Total
Without data 23 7 30Septicemic 2 1 3 5 11 16 7 12 19Bubonic 57 44 103 123 157 280 180 201 381
Totals 127 303 430
As far as these data go, the overwhelming number of the patientswhose histories were known, suffered from bubonic attacks and pneumo-nic plague was altogether absent. However, Macchiavello referred tovague reports speaking of wlhole families succumbing to the diseasewhich were suggestive of the latter type of the plague. It appearedthat under such circumstances the neighbors were prone to burn downthe affected huts without even making sure that all inmates had died.
Comparing the earliez epidemics with the 1946-47 outbreak,Macchiavello stated:
"Before 1946, plague appeared in isolated houses andthe number of human cases did not stand in direct relationwith the plague in the wild rodents, the intensity of whichwas not known. In 1946-47, the intensity of the wild rodentepizootic could be guessed, not only through the rapid andsuccessive infection of 50 odd villages but also throughthe extension of the area in which it was observed. In eachhamlet plague acquired a familial form and it is this appear-ance of the epidemic which favors the false supposition ofan interhuman transmission*, which, moreover, is favored bythe frequent observation that secondary foci appeared in newhamlets precisely in the houses inhabited by members ofplague-affected families who had flown from the infection intheir own villages".
It would also seem that the mortality in the 1946-47 epidemic(52.8%) was markedly higher than that during the period from 1939-46,when 23 out of the 80 patients, about whom details are known, seem tohave succumbed to plague.
* Macchiavello referred in this connection to an unpublished arti-cle on the interhuman transmission of plague and also said inthe above reviewed report that "if P. irritans were a plaguevector, the human population would have disappeared from theAndean territory".
Referring to his observations on plague manifestation in the _rodents, Macchiavello stated to have proved the presence of the in-fection in 15 or 16 out of a total of 124 specimens, namely in oneof 63 house-mice, in 6 out of 33 Akodon mollis, in one (or possiblyin 2) out of 8 0. stolzmanni, in 4 out of 16 Cavia tschudii and in3 out of 4 Sylvilagus. In the opinion of this observer the appear-ance of the infection not only in Oryzomys and C. tschudii, but alsoin Sylvlagus was of a secondary nature. In regard to the last men-tioned genus he noted:
"References to epizootics among the rabbits in therural (agrestes) areas and at the foot of the mountainswere frequent. The tardy appearance of these epizootics.and the fact of finding on the rabbits Akodon fleas in-dicate that the epizootics were secondary, possibly ori-ginating in the deserted wheat fields, where an enormousinfestation of Akodon fleas persited in the empty nestsand where, besides this, occasionally rabbit fleas werefound. These, however, were not found on the Akodonscaptured in houses".
In regard to the role of the wild-rodent fleas Macchiavellostated that, following up his earlier studies on P. litargus in theTrujillo area and the Lancones district he (a) established the vec-tor capacity of Pleochaetis dolens quitanus and, moreover, found thefollowing fleas naturally plague-infected: Cediopsylla spillmanni,Hoplopsyllus andensis, H. manconis, Polygenis brachinus and Spinctop-sylla (Plocopsylla) mars. Positive results were also obtained witha pooled sample containing among other fleas Rhopalopsyllus cacicuscacicus. The majority of the positive fleas had been collected fromplague-affected rodents, but infected Pleochaetis were found also indeserted wild-rodent nests, P. brachinus once in a "domestic" nest.
Commenting on these findings, Macchiavello stated:
"The comparative importance of the 2 Pleochaetis spe-cies and the 3 Polygenis species met with in the transmis-sion of plague among the cricetinae and from these to man, re-mains to be determined. Judging simply by their numericalfrequency, one may infer the preponderant role of Pleochaetisdolens quitanus".
Exact studies were also required to delimit the habitat of thevarious fleas species.
In Macchiavello's opinion P. dolens quitanus was responsiblefor the conveyance of plague to man in the houses as well as in theopen, even though this flea by preference seemed a nest-dweller.Its mean extrinsic incubation period was about 25 days in the lab-oratory, but was probably much longer in the open at high altitudes, 4where from August to November the nights were rather cold.
-
Dro -1--i nAn
RES 2/12
Summarizing and evaluating his observations on the 1946-47 out-break, Macchiavello distinguished between (a) en initial phase inwhich the evolvement of a violent epizootic among the cricetinae,especially Akodon mollis orophilus led to occasional infections offield workers, conveyed by P. dolens quitanus and P. litargus, es-pecially the first; (b) a main phase, in which the wild rodents, at-tracted by the stores of the harvested cereals in the houses broughtthe infection to the villages, an epidemic of a "familial domestic"character ensuing; (c) a final phase in which Sylvilagus, leading bypreference a sylvatic existence and free-living guinea-pigs (C. tschu-dii) became the victims of not properly studied epizootics, in whichprobably Hoplopsyllus and Polygenis fleas were the vectors of the in-fection.
Factors favoring the spread of infection at the acme of the out-break were (1) panicky flight of the people; (2) removal of domesti-cated guinea-pigs to other settlements so as to avoid their destruc-tion by the pleague prevention staff; and (3) involvement of the peri-domestic wild rodent species, particularly Oryzomys sp. and Oryzomysstolzmanni, in the epizootics.
It is important to add that in Huancabamba Province the spreadof plague in man was cut short by the ample use of DDT. However, wildrodent plague continued in enzootic form, leading especially in theformerly infected localities to sporadic manifestations in man. InAyabaca, where less systematic use of DDT had been made, plague showedsome tendency for further progress, reaching in 1953 the districts ofMontero, Suyo and Sicches, adjacent to Ecuador.
The statements of Macchiavello will be evaluated together withthe more recent findings of De la Barrera summarized below:
In marked contrast to the above recorded observations, De laBarrera stated in his 1957 report that R. rattus was found side byside with the ubiquitous house-mice and, usually, domesticated guinea-pigs not only in the houses of Huancabamba city, but also in the ruraldweLlings on that area, in which, however, it was rare. He found noevidence that the common rats were involved in the plague outbreak andexplained the absence of the disease among them by the assumption thatthey were resistant to infection with P. pestis. According to De laBarrera's observations the wild rodent fauna of Huancabamba Provincewas identical with that generally met with in the plague regions ofPerú. Akodon mollis formed 85% of the rodents trapped in the fields,Oryzomys xanthaeolus being accordingly less frequent. Four rodentsof the former species and one of the latter were caught inside ruralhabitations. Plague was confirmed in 1956 in two apecimens only--once in A. mollis and one time in Oryzomys longicaudatus.
Dealing with the wild rodents and lagomorpha. of the plague-affected areas of Perú in general, De la Barrera specially referredto the following species:
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a) A. mollis and 0. xanthaeolus were the species most oftenmet with and most often found plague-infected. Their re-lative frequency varied in different sites, but generallythe first mentioned was prevalent at higher altitudes.
b) Sigmodon peruanus vwas frequently found plague-infected but,as De la Barrera somewhat ambiguously stated "on account ofits much lesser abundance than that of Oryzomys and of Akodon,does not appear to figure on the first level in the list ofplague reservoirs". S. peruanus was a slow-moving animal,which left its dens during daytime. It constructed its nestson the level of the ground under varíous protecting coverages,but if disturbed by man, was apt to hide in cracks of theground. As far as scanty observations went, it was almostexclusively infested with P. litargus.
c) ProechiMys decumanus, a large rodent met with only in thenortiwest of Perú near the Ecuadorian border. It, was al-ways heavily infested with Paol?;.gj:nis .aE, but was alsofound to harbor some P. litargus.
d) Stlv.l.aus braslienss incaJ the rabbit (conejo) of Perú,was aiLo fo~ud llague-infectedt. However, in De la Barrera'sopinion, its affection was "an accident in the progress ofthe wild-rodent enizootics". lbe enecific flea of this spe-cies of lagomorpha was apparently H;_J~oplrs3!.us manconis.
Dealing with the flea fauna of the rodents in !Duancabamba cityand its environs, De la Barrera furnished the follo-ling important data:
City Rural houses Fields Wild rodents Rodent nestsSpecies of fleas N N % N_ __ NN % %N N ..q
Xenopsilla cheopis 52 43.6 31 20.9 18 ~3.9 -
Pulex irritans 38 39.1 27 18.2 3 7.3 1 0.4 1. 1.0Leptopsylla segnis 4 4.1 60 40.5 - 1 0.4 -Ct. felis felis 2 2.2 5 3.3 - 2 0.8E. gallinacea 1 1.0 11 7.0 - - -Pleochaetisdolens quitanus - 7 4.7 10 24.3 44 20.5 10 11.7
Craneopsyllaminerva - 7 4.7 6 14.6 42 19.2 -
Polygenis brachinus - - 4 9.7 95 44.3 55 64.7
N.B. Found only on wild rodents or in the rodent nests were:Neotyphloceras rosenbergi, Ctenidiosomus spillmanni, Plocopsyllahecto, Hoplopsyllus manconis, Plocopsylla n.sp. and Cleopsyllatownsendi. e
.4
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The most significant among these findings are (a) the infestationof the common rats in all locations with X. cheopis; (b) the compara-tively frequent occurrence of P. irritans on this rodent species; and(c) the presence of not inconsiderable numbers of wild rodent fleas onthe rural rats.
In the part of his report devoted to a discussion of thé Peruvianrodent-fleas in general, De la Barrera made the following statements:
a) X. cheopis - Generally speaking this flea was more numerouson the settlement-rats than on those trapped in the fields.Its frequency decreased with the altitude, so that whilestill met with in the Huancabamba region (1900-2000m), itwas absent in the higher parts of the province, e.g. atSilur (2740) and Jacocha (2840m). Which flea replaced itthere, is obviously an unsettled problem. The only factknown in this respect seems to be that De la Barrera foundonly one specimen of Nosopsyllys londinensis in his fleamaterial.
In the opinion of this observer, X. cheopis took no part in thespread of the infection in the Peruvian sylvatic plague foci. Hemaintained in this connection that possibly in the Huancabamba areaand other localities situated near the upper limits of its habitat thevector capacity of this flea was reduced but admitted that this assump-tion did not hold true for other localities like for instance Llampa*and Puná in Ecuador, where conditions for a role of this flea seemedto be excellent. De la Barrera evidently inclined to the belief thatthe failure of X. cheopis to convey the infection stood in relation tothe resistance of its rat-hosts to plague.
b) Pulex irritans was found in great quantities in the garmentsand bedclothes of the inhabitants and, as noted above, was.-byno means rare on the common rats. Of course it was also fre-quent and sometimes prevalent on the domesticated guinea-pigs.
Discussing the possible importance of this flea in the spread ofplague, De la Barrera drew attention to the contention of Karl Jordanand F.G.A.M. Smit that P. irritans was not a homogeneous species butconsisted of several forms, referring with the two varieties met within the Peruvian material, Smit stated:
"The new Pulex is different from the cosmopolitan human flea,Pulex irritans .......... it may well be that the rodent irritanscould also act as a carrier of the wild rodent plague".
Reverting to this problem in a later part of his report, De laBarrera cautiously noted:
* As recorded by De la. Barrera, an epizootic involving mainly Ory-zomys xanthaeolus in the region of Llampa in 1955 led to 6 plagueattacks in man. R. norvegicus, though frequent in that localityin and round the houses, remained free from the infection.
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"The possibility that this flea could be a (plague) vector,specially in interhuman infection, has attracted attention sincelong ago and in this part of America has been given as an ex-planation for the frequent infections among the participants inwakes which, of course, is purely theoretical. Of differentvalue are the experimental data of Burroughs, that P. irritansbecomes blocked and can, as a consequence, transmit (plague).Mention has been made also of the observations made in theBritish Museum regarding the heterogenicity of Pulex irritans....".
There can be no doubt that the recent observations of Jordan andSmit necessitate a reconsideration of the possible role of P. irritansin the spread of plague--a problem which to great advantage could bestudied in the course of the proposed plague investigations in SouthAmerica.
c) Tiamastus cavicola was frequent and often prevalent in Perúon the domesticated guinea-pigs and occasionally was alsofound on the domestic mice. De la Barrera thought that thisflea, though not a good vector, might play a role in the in-tradomestic spread of plague.
d) Wild rodent fleas - According to De la Barrera's observations,Polygenis litargus was not only the most frequent flea on thewild rodents, but was also met with on R. rattus living underrural conditiona as well as on the domesticated guinea-pigsand in small numbers in garments. Though not yet aware ofthe studies on the vector capacity of this flea, De la Barreraadmitted that it might play a role in the conveyance of plagueeven to man. He reiterated, however, that certainly it wasnot the only plague vector, as it was absent in the sylvaticplague areas situated above about 2200m. where its place wastaken apparently by Pleochaetis dolens quitanus.
Referring briefly to the 1956 plague outbreak occurring in nu-merous foci lying at high altitude in Huancabamba Province, De laBarrera summarized that the epidemic, being preceded by a wild-rodentepizootic, remained restricted to rural areas, neither the rats northe human population of Huancabamba city becoming involved. Instancesof an appearance of successive attacks in one and the same householdwere evidently frequent. De la Barrera considered it as significantthat (1) in all houses with multiple attacks one or more of the firstaffected patients died no doubt after they had developed a general-ized infection; and (2) P. irritans abounded in all the dwellings.
According to De la Barrera's final report, the plague outbreaklin the province of Huancabamba in 1960* was also characterized by the
* As stated in this report during the first 5-1/2 months of 1960a total of 101 plague cases was recorded in Perd, distributedin the following provinces: Huancabamba (77), Ayabaca (15),Hualgayoc (7), and Canchaque (2). The total mortality was 36%.
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frequent occurrence of several attacks in the affected houses, in whichoften infection of the domesticated guinea-pigs preceded the appearanceof human infection. Which species of fleas were responsible for theconveyance of the disease from these animals to man, was not clear.
As surmarized in the 1960 report, the sallent features of thisas well as of the previous recent outbreaks were:
1) A sylvatic origin;2) Absence of the infection from the centers of the population;3) Seasonal incidence during the rainy period (i.e. usually
from November to April or May);I4 Frequency of multiple attacks in one and the same house;5) High mortality due to frequent lack of treatment.
Evaluation and recommendations for further investigations
The task of evaluating the present plague situation in Perd isfraught with great difficulties in so far as fairly up-to-date informa-tion, comparable to that available for Venezuela and Ecuador, could beobtained only for the sylvatic plague focus in the provinces of Huan-cabamba and Ayabaca. To what extent plague is still active in theLancones district formerly studied by Macchiavello, could not be as-certained, while for the other recently affected parts of Perú reallynothing is known than the bare figures recording the appearance orrecurrence of the disease. Hence, should it be considered advisableto make plans for plague investigations in Perd on a country-wide scale,it would be indispensable to establish through consultations with thePlague Prevention Service and, if necessary, through a preliminary sur-vey to what extent it would indicate to envisage work in the last men-tioned areas. If work in the Lancones district would be called for,it ought to be done according to the plan set forth in sufficient de-tail in the preceding section of this report for the adjacent areas inEcuador. Indeed, since these and the Lancones district are but com-ponent parts of one common plague focus, work in these parts could beprofitably done only by an international team having free access tothe plague areas situated south and north of the border between thetwo countries.
Ln view of this and since there can be hardly any doubt that,even if a country-wide plan for plague investigations in Perú wouldbe decided upon, priority would have to be given to the most seriouslyaffected Huancabamba-Ayabaca focus, it seems legitimate to concentratefor the present attention upon this area.
While the earlier investigationa made in this focus leave noroom for doubt that it is one of sylvatic plague, the question whichspecies of wild rodents is or are the reservoir of the infection,does not yet seem to have been satisfactorily answered. As has beennoted, in contrast to the conclusions reached on other South Americansylvatic plague foci Macchiavello maintained that in the Huancabamba-Ayabaca area the infection is permanently harbored by species of cri-cetinae which, because apparently highly and uniformly susceptible toplague, are periodically decimated by wide-spread epizootics. Thus,
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in the opinion of this observer, the other species of wild rodentsfound plague-infected, including Sylvilagus, which has been incrim-inated as reservoir of the infection in Ecuador, play only a second-ary role or, as maintained by De la Barrera, become in part only ac-cidentally involved. The present reporters do not wish categoricallyto refute these postulations. They must insist, however, that thescope of the observations upon which they were based, is really insuf-ficient for a final decision of the problem. Thus, in order to solveit, further large-scale and systematic observations, made not only atthe rather impropitious time of the plague seasons but continuedthroughout at least one year, preferably for a longer time, are in-dispensable to ascertain where and in what species plague persistsduring the interepizootic periods. It deserves great attention inthis respect that, as mentioned by Macchiavello, apperently thesestronghoids of the infection are limited in their number and theirextent. To prove the existence of such "elementary" foci and thor-oughly to study their ecology would be not only scientifically val-uable but of great practical importance.
The question which fleas are responsible for the spread of syl-vatic plague in the Huancabamba-Ayabaca focus is also by no means set-tled. While several species have been found naturally infected, ex-perimental studies to assess their vector capacity have been made onlyin the case of Polygenis litargus and Pleochaetis dolens quitanus. Toconfirm the results of these tests, to determine the vector capacityof at least the flea species which have been or will be found naturallyinfected and thoroughly to study the distribution of the various spe-.cies, would be a second task indispensable for a thorough knowledge ofthe ecology of the disease in the focus.
While Macchiavello found in the past the common rats to be pres-ent only in the low-lying valleys of the Huancabamba-Ayabaca area, Dela Barrera's more recent experiences indicate the presence of theserodents in all parts of the focus, though rarely in the rural habita-tions. At the same time the latter observer insisted that the rats,because resistant to infection with P. pestis, were not involved inthe plague manifestations. To judge from the published information,however, it would seem that the postulated resistance of these rodentshas not been confirmed through laboratory tests. To fill this gaphandin hand with systematic investigations on the distribution of thecommon rats in the focus, would be a third important object of theproposed studies.
A further unsettled problem is which flea replaces X. cheopison the rats in the highly situated parts of the focus. Besides ade-quate studies to settle this point, systematic investigations wouldbe called for to study the frequency of X. cheopis in the rural areasas well as in the towns within the zone of its habitat. Due attentionought to be paid in the course of these investigations to the occur-rence of this flea on hosts other than the common rats, particularlythe domesticated guinea-pigs. If found to be rare or absent on the *rodent species other than the rats, tests ought to be made to assessthe capability of X. cheopis to subsist and feed upon the domesticatedguinea-pigs and on other rodents it might have an opportunity to attack.
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The assumption of De la Barrera that in localities near the upper li-mits of its habitat X. cheopis is a less efficient plague vector thanusually ie an interesting one. However, it would be rather difficultto test the validity of this postulation.
To judge from the hitherto available information, the mechanismby which the infection originating in the wild rodents of the Huanca-bamba-Ayabaca plague focus ultimately finds its way to man, has notbeen fully elucidated. This transition of the infection could be sat-isfactorily explained in the past when, following the pattern of"purely" sylvatic plague, the sporadic human affections were mainlyif not solely contracted in the fields. However, attention had to bedrawn to the fact that from 1946-47 onwards an intradomestic type ofinfection was the rule, often resulting in the appearance of not onebut some successive attacks in one and the same house. There can belittle doubt that an affection of domesticated guinea-pigs, due tothe bites of infected wild-rodent fleas, was often a link in the chainof factors leading to the appearance of plague in man. However, it isatill quite uncertain, which flea species are responsible for the hu-man infections. Attention has been drawn in this connection to thepossibility that the appearance of successive plague attacks in oneand the same household might be the result of an intrahuman spread ofthe infection conveyed by P. irritans. As mentioned earlier in thisreport, the recent discovery that this species is not homogeneous hasled to the suspicion that some of the subspecies composing it mightbe efficient plague vectors. It would be essential, therefore, tomake a thorough comparative study of the vector efficiency of thesubspecies of this flea met with the Huancabamba-Ayabaca focus. Atthe same time, however, systematic studies of the intradomestic andperidomestic flea-fauna in general are called for, paying special at-tention to the houses and settlements recently or presently attackedby plague.
A close study of the manifestations of plague in man would haveto form an integral part of the proposed investigations. The recordson the incidence of the disease ddring. recent years would hae. to becarefully gone through so as to detect localities in which plague hasappeared repeatedly or even perennially and every possible effortwould have to be made to elucidate the reasons for such a persistenceof the infection. As proposed already in the report on Ecuador, allhuman plague manifestations met with by the study group ought to bemade the subject of thorough investigations. In the first line effortshould be made to establish which rodents and which fleas were res-ponsible for the infection of the patients. The presence of plaguein the latter ought to be confirmed invariably through adequate lab-oratory tests and the strains of P. pestis isolated from the sufferersought to be kept in a lyophilized condition for further study. More-over efforts ought to be made to detect the occurrence of subclinicalforms of the disease through clinical and serological surveys of groupsof the population actually or potentially under the risk of infection.
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In his reports De la Barrera Justly and laudably stresses thenecessity of improving the case-finding system so as to reduce thedeplorably high mortality from plague in patients who, because de-tected not timely enough or even not at all, could not be given thebenefita of treatment. ,While thoroughly concurring with this pleathe present reporters wish to emphasize the necessity of going onestep further by trying to detect not the early incidence but the im-minence of human plague through a constant watch over the fluctua-tions of the density of the rodent populations and the frequency ofplague manifestatione in them. Every possible effort ought to bemade therefore in the course of the proposed studies to work outsuch a System of gauging the plague situation in the Huancabamba- ~Ayabaca focus. For in this way the contemplated work would not onlycontribute materially to a knowledge.of the ecology and epidemiologyof plague in South America and possibly pave the way for future at-tempts to control the situation but would be of immediate benefit tothe people exposed to the risk of infection.
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SECTION H
BRIEF OBSERVATIONS ON THE INCIDENCE AND ETIOLOGY OF PLAGUE IN THEUNITED STATES
The incidence of human plague in the United States from thefirst recorded appearance of the disease in the port of San Franciscoin 1900 up to 1962 is summarized in the following tabulation:
Rat Caused Epidemics of Plague in U.S.A.:
Year Cases Deaths
San Francisco, California
Seattle, WashingtonNew Orleans, Louisiana
Pensacola, FloridaGalveston, TexasBeaumont, TexasLos Angeles, California
Total
190o-41907-819071914-151919-21920192019201924
120 114186 92
3 331 1025 1110 418 1214 641 4
-v448 28 ~
Infections Contracted From Wild Rodents or Through Their Fleasduring the period 1908-1951 (after Link)
Years of Detection
Wild-rodent Plague Human Plague Cases Deaths
CaliforniaOregonUtahNevadaIdahoNew MexicoArizona
Totals
1908193519361936193619381938
1908193419361937194019491950
1908-51
Remarks: While most of these cases occurredpneumonic outbreak of wild rodent origin took placeCalifornia, in 1919 and claimed 13 victims.
80111161
521oo13o
91 57
singly, oneat Oakland,
The incidence of plague in the United States for 1952-1962,as reported by the U.S. Public Health Service, may thus be summarized:
State
-----
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REPORTEDYEAR FROM
HUMAN RODENTCASES PLAGUE REPORT AND FINDINGS
1950 Pecos,New Mexico
Lea County,New Mexico
Arizona
1951 Hobbs, Lea CoantyNew Mexico
United States
Santa Fe, N.M.
1952 Tacoma,Washington
1952-1955
1953 Douglas County,Nevada
1954 Tacoma,Washington
1 fatal
1
1
Bubonic Plague reported by NewMexico Health Department, died4 July 1950, Pecos, N.M.
Bubonic Plague for 27 Jan. 1950
Date and place of occurrenceunknown
1 fatal
1 fatal
Date unknown- week ended 21 Feb.1951 stated the patient saw thephysician on 9 Jan. 1951 anddied the same day
For the week ended 18 Aug. 1951
Sylvatic Fleas from 2-white mice foundinfected. Trapped 14 milessoutheast of Santa Fe City on18 April 1951
Sylvatic Positive specimens found inGrant, Yakima, and in Lincolnand Douglas Counties, Mayand June 1962
No cases of human plaguereported
2 suspectcases
The Nevada Department of Healthreported on 20 Oct. 1953 "thetwo men made rapid recoveryfrom their infection followingthe use of two antibiotics. Themen were entirely recovered be-fore we received the report t1tall tests were negative forpla~ge.The nature of their infectionwas never determined". Dr. Linksreport of 12 May 1953, stated'both patients had inguinalbuboes presumably resulting frormexposure to wild rodent fleas...both patients had received peni-cillin at first and streptomycinsubsequently...". On evidence im-possible to distinguish betweenwhat might be plagueor tlaremia.
Sylvatic Fleas from 3 rats trapped irTacoma were positive forPasteurilla pestis on 24 Oct.1954. Area declared free of in-fection 20 January 1955.
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REPORTEDYEAR FROM
HUMAN RODENTCASES, PLAGUE REPORT AND FINDINGS
1956 Oxnard,California
1 Confirmed 25 May 1956 in Oxnard,Calif. Man had been fishing inSespe Creek, Ventura, on 16 June1956. From NOVS, CommunicableDisease Suimmary, week ended 23June 1956, "this is the firstcase of human plague reported inthe United States since Jan. 1951when a case occurred in New Mexico.The last previous case in Califor-nia was reported in 1947. In 1948there were no cases in the UnitedStates, but 3 cases were reportedin 1949 and the same number in1950. Of these 5 were in NewMexico. The óth occurred inArizona in 1950.
1957 HamakuaHawaii
District,
Wichita Falls,Texas
1 fatal
Sylvatic District was reported as infectedwith plague in June 1957. It wasdeclared free of infection l9July 1960.
Case of Bubonic Plague reportedin Wichita Falls on 11 Sept. 1957.Infection said to have been con-tracted on camping trip nearBoulder, Colorado. Investigationthat followed in Colorado werenegative for plague. This was notcarried as confirmed case of plaguein the annual report because theattending physician did not reportit as such. Following an inquiryfrom NOVS, in Feb. 1960, the HealthOfficer of Texas advised NOVS thatthis was a confirmed case of plagueand should be charged to Colorado.As Colorado refused to accept theresponsibility the case was to bereported as a case of plague forTexas.
1958 Klamath County,Oregon
-Syivatic Specimens collected from groundsquirrels, marmots, etc., for theperiod December 1957 throughMay 1958 were positive for plague.Area not put on infected localarea list of WHO.
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REPORTEDYEAR FROM
HUMAN RODENTCASES PLAGUE REPORT AND FINDINGS
1959 Contra CostaCoQuty, Caifornia
1959 Sonora, ToulomneCcunty,California
Sandia Park,New Mexico
Maryland
Northeast FresnoCounty, California
1 Confirmed case-in Boy Scout re-ported on 30 June 1959. He hadbeen camping in area of TiogiaPass,Yosemite National Park, MonoCounty. Mono County was declaredthe infected local area. WHO WERN228, 10 Juit.1959 carried théinfected local area as Contra Cos-ta County and as Mono County thefollowing week. The area wasremoved from the infected localarea list the week of 24 July 1959.
1 Case of Bubonic Plague reportedin veterinarian residing in Sonora,July 1959. Onset of symptoms8 July 1958. Sonora was declaredthe infected local area and wasremoved from the infected localarea list 7 August 1959.
1 Confirmed case reported on 24 July1959 in a 12-year old white female,in Sandia Park, N.M. Date of on-set 7 July 1959, date of death13 July 1959, probable source ofinfection jack rabitt. Daughterof an air force pilot stationedat Kirkland Air Force Base,Albuquerque. Bernalillo Countyexcluding the city of Albuquerquewas declared free of infection15 October 1959.
Pneumonic Plague reported in alaboratory worker
Plague in Chipmunk fleas reportedSylvaic in mountainous area Northeast
Fresno County, Calif. Area of in-fection declared as Fresno County,exclusive of all towns. Area notlisted in the infected local arealist of WHO.
1
1960 Roswell, CkavesCounty, New Mexico
2 cases reported in Air Force per-sonnel 5 March 1960. 1st case mále,age 24, date of onset 23 Feb. 1910 con-firmed by blood culture and avariety of other tests.
2nd case, not confirmed by labora-tory. Symptoms were milder than lstcase and clinical picture the same.Both had hunted rabbits on 19 Feb.1960 on the base and again the nextday some 30 miles north of Roswell,N.M. Chaves Cty. excluding Rosvelldeclared area of infection. Areadeclared free of infection 25 Nov-ember 1960.
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0
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REPORTEDYEAR FROM
HUMAN RODENTCASES PLAGUE REPORTS AND FINDINGS
1961 Santa Fe,New Mexico
2 lst case, septicemic form, enteredhospital in Santa Fe on 29 June1961 and died 30 June 1961. Lumber-man who lived in a remote area ofPecos.
2nd case in telephone lineman whobecame ill 4 August 1961. Clini-cal diagnosis. Treated beforecultures were taken. Serology(convalescent serum about 1 weeklater) was positive dilution of1:80. Reported 8 Aug. 1963 toForeign Quarantine. The infectedlocal area for these 2 cases wasthe Northwest Corner of San MiguelCounty. Declared free of infection15 Septenber 1961.
1961 Cambridge,Massachusetts
1 1 confirmed case of plague reportedin Cambridge Mass., on 1 Aug. 1961,died 29 July 1961. Diagnosis ofplague made at time of autopsy.The case originally diagnosed asstreptococcal septicemia. Notcarried as a case of plague offi-cially. Man, 37-year old, Asso-ciate Professor, Harvard Univ.,had been in New Mexico until20 July with a group from GeologicalSurvey. WHO notified area notsignificant to international traf-fic on 9 Aug. 1961. The WHO WER4 Aug. 1961, listed Santa Fe witha note that the case occurred inan isolated area; it was notcarried on the infected localarea list.
1962 No cases
__
__
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A tabulation showing the annual incidence of plague in Cali-fornia is contained in Tables I, II, and III appended to this Section.
At first glance these data seem to indicate that the evolutionof the plague in the United States was in accordance with the patterntypical for several other countries invaded by the sea-route during thepresent pandemic, an initial 'inurine" phase of the infection eventuallyleading to a spread of the disease to the wild-rodent populations. How-ever, in the opinion of some observers the appearance of plague in NorthAmerica was due not to its recent introduction by sea, but to an earlyimportation through wild rodents which, coming overland across the landbridge later replaced by the Bering Strait from Central Asia, broughtP. pestis with them as a population regulator. This fascinating hypo-thesis was rejected by other authors, mainly on the ground that, incontrast to the plague strains isolated from the Central Asiatic wildrodents, those from both the rats and the wild rodents in America failedto produce an acid reaction in glycerol-containing media. At the sametime some of the opponents to the above-mentioned hypothesis consideredit as likely that plague existed in California before its appearance wasofficially recorded in 1900, the infection having been imported fromthe China coast (affected since 1867) at an earlier date. The sameapparently holds true of the sylvatic manifestations, wild-rodent plague,though definitely detected in California in 1908, having evidentlyexisted in the Contra Costa county of that state since 1903 at least.
While, as shown by the above-inserted table, rat-caused epidemicsceased to occur after 1924, the infection among the wild rodents per-sisted and spread so that according to statistics of Link, quoted byPollitzer, by 1946 besides California 14 other states had become in-volved thus:
Year of Year ofState Detection State Detection
California * 1908 Arizona * 1938Montana 1935 New Mexico * 1938Oregon * 1935 Colorado * 1941Idaho * 1936 North Dakota 1941Nevada * 1936 Oklahoma 1944Utah * 1936 Kansas 1945Wyoming 1936Washington 1937
* Human plague
Fortunately, as indicated in this table and in that insertedabove, the presence of wild-rodent plague led to mostly rare human in-fections in only eight of these states.
As shown in two tables attached to this Section (see Tables IIand III) large numbers of wild rodent and flea species have been foundinfected in the various foci of the United States. Attempting a classi-fication of the former, Eskey and Hass, in their classical study on
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"Plague in the Western Part of the United States" (1940), came to theconclusion that at least three groups of rodents constituted the greatprimary reservoirs of the infection--the ground squirrels (Citellus),which were widely involved in the coastal regions and in the northernpart of the Intermountain Plateau: the wood-rats (Neotoma) whichformed the plague reservoir in the southern deserts, and finally theprairie dogs (Cynomys) which harbored the infection in the plateauregion of Arizona and New Mexico. It deserves, however, great attentionthat Kartman and his associates, confirming findings recorded by Meyerin 1943, came to the conclusion that
"Historically, emphasis has shifted frcm the large colonialrodents such as ground squirrels to the small, inconspi-cuous native field voles and mice such as Microtus andPeromyscus."
It is of great importance to note that wild-rodent fleas havebeen found upon serveral occasions on the common rats and that isolatedinstances of rat plague conveyed by such fleas have been detected.Thus Meyer and Holdenried (1949), working on a Californian ranch wherewild-rodent plague was present, found the infection also in R. rattusand R. norvegicus which were in part infested with ground-squirrel fleas.Observations in point were also recently made by Kartmen and associateswho were able experimentally to confirm the transition of wild-rodentfleas to rats with radioactively tagges Malaraeus telchinus. It is, how-ever, reassuring to find that thus far the recent strictly sporadichuman infections with P. pestis were invariably of the pattern of purelysylvatic plague, having been contracted away from the settlements inthe wild-rodent foci. Thus, the only distressing feature of the situ-ation is that owing to the paucity of the human attacks quite oftenthe occurrence of human plague is not recognized early enough to savethe patients or a diagnosis is even arrived at only after the death ofthe victims. To alert the medical profession and the public in thisrespect is therefore an important task.
-
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TABLE I
HUMAN CASES OF PLAGUE BY RODENT.SOURCE
CALIFORNIA 1900-1962
Source
Years
Total 1900-1959
19oa19011902190319041907190819091910191119131914191519191920192119221923192419251927192819331934193619371941194219431944*194719561959
Total
409
2232422010
180942521114
221
382131131211
Rats
342
32391710
1784
Wild Rodents . Unknown
56
3
13323'21114
122
382
131121211
112
10
3
111
2
.
1
1
112
Years in which no cases were reported are omitted
* 1 Lab. infection - San Francisco
o
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aw
1i
iy
1
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TABLE II
LIST OF WILD RODENTS AND LAGOMORPHA FOUND NATURALLY PLAGUE-INFECTEDIN THE WESTERN UNITED STATES
FAMILY ANDSUBFAMILY
Thomomys bottaeTh. fossorKangaroo rats:Dipodomys sp.Dipodomys ordiPerognathus parvusWood rats:Neotoma algibulaN. cinerea occidentalisN. desertorumN. fuscipesN.F. mohavensisN. intermediaN. lepidaN. micropusGrasshoper mice:Onychomys sp.O. leucogaster
0. torridusPeromyscus boyliiP. leucopusP. maniculatus
P. truei gilbertiP. truei trueiP. truei nevadensisReithrodontomys
megalotisSigmodon hispidusVoles:Lagurus crutatusMicrotus californicusM. montanusM. manusM. townsendiSquirrels:Citellus armatusC. beecheyi beecheyiC.B. douglasiC.B. fisheriC.B. nudipesC. beldingi beldingiC.B. oregonus
California, ? ColoradoColorado*
TexasWashingtonWashington*
Arizona, New MexicoCaliforniaNevada, UtahCalifornia, Oregon*NevadaCalifornia? UtahTexas
Texas*New Mexico* and otherWestern areas*New Mexico*Arizona*New Mexico, California*New Mexico, California*Washington*CaliforniaCalifornia, New MexicoUtahCalifornia*;, Kansas*New Mexico*New Mexico*
Washington*CaliforniaOregon, Washington*Washington*Washington
Western part of U.S.A.CaliforniaCalifornia, OregonCaliforniaCalifornia*CaliforniaCalifornia, Nevada,Oregon
Rodents:Geomydae(Gophers)
HeteromyidaeDipodomyinae
MuridaeCricetinae
MuridaeMicrotinae
Sciuridae
___
- 117 -
SPECIES STATE
FAMILY ANDSUBFAMILY
Sauirrels:C. Columbianus columbianusC.c. ruficaudusC. idahoensisC. lateralis chrysodeirusC. lateralisC. leucurusC. mexicanusC. richardsoni elegansC. r. nevadensisC. r. richardsoniC. spilosoma majorC. townsendiC. tridecemlineatusC. variegatus grammurus
C.V. utahC. washingtoni loringiC.w. washingtoniPrairie dogs:Cynomys sp.Cynomys gunnisoni gunnisoniC.G. zuniensisC. leucurusC. ludovicianus
C. parvidensFlYing squirrel:Glaucomys sabrinus lasivusMarmots:Marmota flaviventris subsp.
M. fl. avaraM. fl. engelhardtiM. fl. nosophoraChipmunks:Tamias minimusT. quadrivittatus fraterTamiasciurus douglasi
Rabbits:Lepus californicusSylvilagus audoboniiS. bachmaniS. nuttalli
WashingtonOregonIdaho*CaliforniaWyomíing*Arizona*, California*New Mexico*WyomingNevadaMontana* (a)New Mexico*Idaho*New Mexico*, Texas*Utah, Arizona*, Colorado*New Mexico*
UtahWashingtonWashington
Colorado*, Texas*New MexicoArizona, New MexicoWyoming*Colorado, Kansas,Montana, New Mexico,Texas Wyoming
Utah (b)
California
Colorado, OregonNew Mexico* (c)Oregon*Montana, Utah, WyomingMontana
Washington*California, NevadaCalifornia
CaliforniaNew MexicoCalifornia*Washington
Remarks: * The presence of natural plague infection was detected onlyin the fleas infesting these rodents.
a) Also found naturally plague-infected in Alberta andSaskatchewan, Canada.
b) A prairie dog, Cynomys mexicanus, was also found naturallyplague-infected in North Mexico.
c) Naturally plague-infected fleas were found on this sub-species in British Columbia, Canada.
- 118 -
SPECIES
RES 2/12 3-
STATE .Sciuridae(cont)
LAGOMORPHA:Leporidae
.
y
RES 2/12
TABLE III
LIST OF WILD-RODENT AND LAGOMORPHA FLEAS FOUND NATURALLYPLAGUE-INFECTED IN THE UNITED STATES
SPECIES LOCALITY USUAL HOSTS
Anomiopsyllus sp.A. hiemalisAtyphloceras sp.A. multidentatusCatallagia decipiensC. wymaniDiamanus montanusFoxella ignotaHoplopsyllus anomalusH. glacialis affinisHystrichopsylla linsdaleiMalaraeus telchinusMegabothris clantoniMeringis shannoni
Monopsyllus eumolpiM. exilisM. wagneri
Opisocrostis hirsutusOpisodasis keeni nesiotus
Orchopeas leucopusO. neotomaeO. sexdentatusPeromyscopsylla hesperomys
adelphaStenistomera macrodactylaRhrassis bacchi bacchi
(-Thr. gladiolis)Thr. bacchi johnsoniThr. focusThr. stanfordi
New MexicoTexasWestern part of USAWestern part of USAWashingtonCaliforniaWestern part of USAColoradoWestern part of USANew MexicoCaliforniaWestern part of USAWashingtonWashington
Western partTexasWestern part
of USA
of USA
Western part of USACalifornia
New MexicoNew MexicoWestern part of USA
New MexicoNew Mexico
Western part of USAWestern part of USAWestern part of USAWestern part of USA
NeotomaNeotomaLagurus, PeromyscusPeromyscusLagurus, PeromyscusMicrotus, PeromyscusCitellusThomomysCitellusSylvilagusMicrotusMicrotus, PeromyscusLagurus, PeromyscusLagurus and other
wild rodentsTamiasOnychomysLagurus, Peromyscus
and other wildrodents
CynomysMicrotus, Peromyscus
ReithrodontomysPeromyscusNeotomaNeotoma, Peromyscus
PeromyscusPeromyscus
CitellusLagurus, PeromyscusOnychomysMarmota
- 119 -
RES 2/12
REFERENCE LIST
Meyer, K.F.
Meyer, K.F.
Link,
Link,
Link,
Link,
V.B.
V.B.
V.B.
V.B.
Kartman, L.
Kartman, L.
et al. Sylvatic plague studies. J. Inf. Dis. 73 (1943)l44-157
and Holdenried, R. Rodents and fleas in a plague epizooticin a rural area of California. Puerto Rico J. of Publ.Hlth and Trop. Med. 24(1949) 3:201-209
Plague CDC Bull. 9(1950)8:1-14
Plague in North America Bol. Ofic. San. Panam. 30(1951)26
Plague. Amer. J. Trop. Med. 31(1951)4:452-457
A history of plague in the United States of America-Publ. Hlth. Monogh. NP 26(1955)
et al. Ecological studies of wild rodent plague in theSan Francisco Bay area of California. Amer. J. Trop.Med.and Hyg. 7(1958)1:112-114
New knowledge on the ecology of sylvatic pla8ueAnnals N.Y. Acad. of'Sci. 70, Art. 3(1958):668-671
l
6..
(O
-Y,
- 120 -
Ow
RES 2/12
SECTION I
REVIEW AND EVALUATION OF THE PRESENT STATUS OF PLAGUEIN VENEZUELA
History and recent incidence of plague
As can be gathered from the article of Diaz, the statements whichwere summarized and supplemented by Pollitzer and recently confirmedby De la Barrera, plague appeared in 1908 in the port of La Guaira andsoon spread from there to Caracas, where it continued to occur until1919, leading to a total of 204 cases with 99 deaths.
Even before this "urban" phase of the disease had come to an end,the infection had spread in 1910 to rural areas of Miranda State, inparts of which it continued to become manifest from time to time until1951. An adjacent part of Aragua State, reached by the infection in1939, has remained involved to date. As can be seen from a table in-serted in Pollitzer's book, the total case incidence in Miranda Statefrom 1910 to 1933 was 206. The recently available information of theplague manifestations in that state as well as in Aragua may be sum-marized as follows:
Miranda State
Year Locality
1950 La Palma
1951 Mostaza(Munic. ofSan Pedro)
Caseincidence Remarks
5 No details known
8 According to De la Barrera, five personswere attacked in Puerto Escondido duringthe last week of July in one house, whereone month before dead rats had been found.In the nearby community of Puesto Topo dela Mina three plague cases were recordedin one and the same house on 31 July, 15August and 30 August.
Aragua State
Year Locality Cases Deaths
1939 Ricaurtedistrict,
La Florida
11 8 As stated by Díaz, this outbreak tookplace in the Hacienda La Florida,where 4 plague-affected rats had beenfound and X. cheopis and X. brasilien-sis were met with in most of the houses.
Remarks
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RES 2/12
Year Locality Cases Deaths Remarks
1943 Ricaurtedistrict,
aj) GuayitaTejerías;
Munic.
b) Trapichede Medio,
E1 ConsejoMunic.
1948 La Horqueta
1949 Las Palomas,La Pepefña
1953 Ricaurtedistrict,
CapachalTeJerias
Munic.
1960 Ricaurtedistrict,
TejeriasMunic.
1961 Ricaurtedistrict
Marino dist.
10 3 According to Diaz the first 3 attacksoccurred in a house where 20 domesti-cated guinea-pigs had died, the nexttwo in a neighboring house. The otherfive sufferers were obviously infectedduring a wake held in. the latter house,which appeared to have. been much in-fested by rats and fleas.
7 2 These attacks took place one monthafter the just mentioned outbreakand appeared to be epidemiologicallyrelated to it.
7 3 As related by De la Barrera, 4 personsfell ill with plague in one house bet-ween 23-24 May and 3 more from 27 to30 May.
2 1 No detail known
1 ? No details known
According to the WHO Weekly Epidemio-logical Record 35 (1960) 7:80, evi-dence of plague was found on 26 Jan-uary within the confines of TejeriasMunicipality in a Sigmodon hispidushirsutus. This is undoubtedly the an-imal succumbed to "super-acute" plaguereferred to by De la Barrera.
3 ? As summarized in Vol. 36, Nº 28, p. 305of the WHO Weekly Epidemiological Re-cord, two bubonic cases were reportedin April in the Tejerfas Municipalityand one in June in the E1 ConseJo Mu-nicipality, a dead rat having beenfound in the house of one of the suf-ferers.
3 ? According to the same source, threebubonic cases were detected in Junein the Tumero Municipality of theMerino district.
0
A·
.
-v
- 122-
RES 2/12
Year Locality Cases Deaths Remarks
1962 Ricaurte 1 ? As reported in the Weekly Epidemio-district logical Record 3_7 (1962) 8:93, one
patient suffering from "bubonic syl-vatic plague" was found in La Victo-ria Municipality in February of thepresent year.
As far as reliance can be placed upon these pertly not yet con-firmed data, it would appear that within recent years the plague mani-festations in Venezuela were restricted mostly to the Ricaurte districtof Aragua State, where the area of the TeJerías Municipality seems toform a particularly persistent focus of the infection, Certainly oneshould be most cautious to use the absence of manifestations of thedisease in man as a means to assert the absence of plague in an area,since--as was actually the case in Venezuela--the infection may re-main latent in the wild rodents for prolonged periods. Nevertheless,one might reasonably ask if (a) the now involved area in that coun-try is less extended than was stated by Diaz, who estimated that theterritories affected in the Miranda and Aragua States measured about1000 km2 (386 sq. miles) or whether (b) within this area strongholdsof the infection (called "elementary" plague foci by some recent So-viet authors) do exist, where the infection is particularly apt topersist during the interepizootic periods and which, therefore, mayform the starting point of epizootic waves. As will be discussedlater in this report, the detection of such territorially limited,particularly active plague foci within an affected area is a matterof utmost importance.
Observation on rodents end other ecologically important animals
(1) "Domestic" species
As stated by De la Barrera, whose carefully checked observationsdeserve most credence, Rattus norvegicus occurs within the presentlyaffected Venezuelan plague areas only in scenty numbers inside thehouses of Las TeJerias town, while R. rattus is amply met with through-out the involved territories. According to this observer, the habitatof R. rattus rattus seems to be confined to the houses and their im-mediate vicinity, but he admits that owing to the small number of theserodents among the trapped animals it was impossible to come to validconclusions regarding their ecology.
To Judge from the large number of their captures, R. r. alexan-drinus and R. r. frugivorus are frequent in both the urban and ruralhouses, the former appearing to be more common in the Venezuelan plaguearea than the latter. Both were also caught within a radius of atleast 500 meters round the houses, having thus opportunities to comein contact with wild rodents approaching the houses.
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RES 2/12
Mus musculus appears to be frequent in both the urban and rural qhabitations of the plague area as well as in their vicinity. As as-serted by Diaz, this species has never been found plague-infected inVenezuela. It is noteworthy, however, that though according to De laBarrera these rodents are scantily flea-infested, besides Ctenocepha-lides felis wild rodent fleas (Polygenis bohlsi bohlsi) have beenfound on them.
Guinea pigs are kept in the rural houses of the Venezuelan plagueareas, but to a lesser extent than is the case in Ecuador and Perd.Nevertherless, the above recorded observations on the 1943 outbreak inGuayita suggest that in Venezuela, as well as in these two countries,the domesticated guinea pigs may be instrumental in conveying plaguefrom the rodents to man.
(2) Wild rodents
Referring in his reports to the wild rodents met with in theVenezuelan plague areas, De la Barrera furnishes the following data:
Species Number of captures Percentage
Sigmodon hispidus 1950 62.9Proechimys guairae 337 10.8Akodon venezuelensis 324 10.4Heteromys anomalus 233 7.5Neacomys spinosus 96 3.1Oecomys bicolor 62 2.0Rhipidomys venezuelae 46 1.4Zygodontomys thomasi 26 0.8Sygmomys alstoni 22 0o.
Remark - For reasons which are not clear, De la Barrera does not in-clude in this list Sciurus granatensis (31 captures) andDasyprocta rubratta rubratta (10 captures).
To judge from the short notes added by De la Barrera, Sigmodonhispidus, Akodon venezuelensis, Neacomys spinosus, Sciurus granatensisend particularly often HeteromyG anomalus were found to enter thehouses. It is important to note that this list includes the only twowild rodent species thus far found plague-infected in Venezuela--Sig-modon hispidus and Heteromys enomalus.
It is possible also significant that, in contrast to the otherspecies enumerated in the list, Sigmomys alstoni, suspected to be aplague reservoir, was not found throughout the affected area restrictedto the vicinity of Las Tejerías. However, this species was also metwith outside the plague area in lower locations with a higher temper-ature, i.e., an environment different from that in most parts of theaffected region.
- 124-
RES 2/12
Dasiprocta rubratta seems to be the only one of the above men-tioned rodents which is hunted. Though it has been found slightlyinfested with the common wild rodent fleas Polygenis bohlsi bohlsiand P.Klagesi samuelis, so far it has been neither plague-infectednor implicated in the causation of human affections.
(3) Lagomorpha
The lagomorpha enumerated by De la Barrera are Sylvilagus bra-siliensis (12 captures) and Cuniculus paca venezuelensis (4 captures)which are both hunted. The former, because known to have been plague-infected elsewhere in South America, and found in Venezuela to harborPolygenis bohlsi bohlsi, certainly deserves attention as a possibleplague reservoir.
(4) Marsupialia
Didelphis marsupialis marsupialis (26 captures), an animal ofnocturnal habits, because much in contact with rodents and, on theother hand, apt to stay round the houses or even to enter them, seemsrather suspect as a liaison animal, capable of bringing infected fleasto the environments of the domestic or domesticated rodents and of man.Actually, De la Barrera noted the presence of Polygenis species, in-cluding P. bohlsi bohlsi and P. klagesi samuelis, on these animals.Itfurther deserves attention that allied species have been found plague-infected in other parts of South America.
Observations on fleas
(1) Rat fleas
The findings on rat fleas recently made by De la Barrera in theVenezuelan plague area stand in a most remarkable contrast to thoserecorded by earlier observers. Diaz (1948) stated in this connectionthat "the rats which frequent the houses, especially in the urban cen-ters, were mainly infested with X.cheopis and X. brasiliensis. Therats of the sylvatic type (i.e. apparently the wild rodents) are mainlyinfested with Polygenis bohlsi, on rare occasions with X. brasiliensis.The fleas index is generally low in the rural zone, in contrest to thehigh indices in the towns and settlements. Among the sylvatic rodents,the Arditta comun (Gerlinguetus auestuans) has been found infestedwith X. cheopis".
Dealing with the most common fleas in Venezuela, Cova Garcfa andTallaferro (1959) recorde, unfortunately without indicating where theyhad made their investigations, that they had found X. cheopis. notonly on the common ratsbut also on Sigmodon hispidus hirsutus and Di-delphis marsupialis marsupialis. On the other hand, they found Poly-genis bohl.si bohlsi, or both R. norvegicus and R. rattus, and recordedthe presence of several species of wild rodent fleas, including Poly-genis klagesi samuelis and P. roberti beebei on the latter rat.
- 125 -
De la Barrera (1960) recorded the following data on the fleashe had found to infest R. r. alexandrinus and R. r. frugivorus:
Percentages found on:
R. r. alexandrinus R. r. frugivorusFlea species In the houses On the fields In the houses On the fields
P. klagesi samuelis 5.5 7.6 9.4 -P. bohlsi bohlsi 38.8 38.'4 32.0 46.6P. roberti beebei 18.5 38.4 26.6 26.6P. dunni 16.6 7.6 19.0 -P. peronis 3.7 - 1.9 -
P. occidentalis ste-ganus 3.7 - 3.8
Ct. felis felis 12.9 7.6 7.6
Totals 99.7 99.6 110.3 99.8
Total fleas examined: 54 13 53 15
Though the numbers of fleas examined, especially those on therats trapped in the open was too small to give an exact idea of thefrequency of the different species, De la Barrera's findings leave no troom for doubt that X. cheopi-s was absent, the common rats in the Ve-nezuelan pleague area thus being presently infested almost exclusivelyby wild rodent fleas, among which P. bohlsi bohlsi, P. roberti beebeiand, to a somewhat lesser extent, P. dunni, appeared to be most fre-quent
Commenting upon these findings, De la Barrera stated that silceX. cheopis "existed previously and the local climatic conditions havenot become modified, it is logical to attribute the fact (of the dis-appearance of this flea) to the treatment with insecticides effectedby the Pla6ge Prevention Service. During the whole time of our work
- there were but very few fleas (Pulex irritans, Ct. felis, wild rodentfleas, etc.) in the houses. However,the action of the insecticidesdoes not seem to have been so efficacious against these fleas thanagainst X. cheopis. Besides the possibility of a higher senaitivityof the latter, it is necessary to record that this species is essen-tially domestic and probably breeds only in this environment...If so,it is natural that the desinsectization can better reach it".
(2) Wild rodent fleas
Referring to the fleas of wild rodents and evidently also oflagomorpha collected under his direction, De la Barrera furnishedthe following global figures:
RES 2S/12- 126 -
RES 2/12
Species Number collected Percentage
Polygenis bohlsi bohlsi 3,099 50.4P. klagesi samuelis 1,672 27.2P. roberti beebei 491 8.0P. dunni 207 3.3P. occidentalis steganus 65 1.0P. peronis 48 0.7Rhopalopsyllus australis australis 475 7.7Rh. cacicus 80 1.3Rh. lugubris cryctogenes 2 0.03
Totals 6,139 99.63
As will be gathered from the adjoined table (see page 128), thenumber of fleas collected from the specimens of the individual wild-rodent species varied considerable, data of statistical significancehaving been obtained only in the case of some of the species. It ap-pears to be certain, however, that species belonging to the genus Poly-genis which, as has been shown above, also preponderate mostmarkedlyon the common rats, form the overwhelming majority of the wild-rodentfleas in the Venezuelan plague area. There can be also hardly anydoubt that the vectors of the inlfection there will be found among thePolygenis fleas, allied species of which have been found definitelycapable of conveying plague in Argentina, Ecuador and in Brazil. Itremains to be seen, however, which species are implicated in Venezuela.
Observations on human plague
Dealing with the epidemiology of plague in the presently affectedVenezuelan areas, De la Barrera emphasized that (1) though instances ofinfections in the fields had been observed, as a rule man contractedthe disease within the houses, and (2) contrary to what was usuallyobserved in bubonic plague outbreaks, multiple infections in one andthe same house were frequent. Though he postulated that in Venezuela,as well as in South America in general, the common rats had become re-sistant to plague, he was inclined nevertheless to the belief that asa rule their temporary involvement, due to a transition of the infec-tion from the wild rodents, was responsible for the intradomesticallyacquired human attacks. He flurther maintained that the appearance ofmultiple plague attacks in one and the same house could take place onlyif a highly efficient vector-flea was available there. Since in hisopinion the wild-rodent fleas did not fall into this category, he cameto the conclusion that in the plague outbreaks in Venezuela recordedby him, X. cheopis was still responsible for the intradomiciliary con-veyance of the infection.
Evaluating these postulations, one must state that at firstglance the apparently lessened incidence of plague observed in Vene-zuela within recent years, when X. cheopis seemed to be absent fromthe affected areas, seems to speak in favor of De la Barrera's views.
- 127 -
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Since, however, no doubt in the past this flea was considerable morenumerous in the house than the present vectors of the infection (wild-rodent fleas) are now, the lessened incidence of plague and the ab-sence of multiple attacks may be due merely to a scarcity of the vec-tors and not to their lessened capacity to convey the infection. Itwould not seem wise, therefore, to consider the Venezuelan wild-rodentfleas as inadequate plague vectors, before proof for this contentionhas been obtained through appropriate tests.
Summary and recommendations
The recent observations on plague in Venezuela, briefly dealtwith in the foregoing pages, permit to conclude that:
(1) the infection has remained restricted for over two decadesto adjacent districts of the Miranda and Aragua States, thefocus evidently showing no tendency to expand;
(2) possibly at present plague is active only in a limited partof Aragua State which, as has been discussed above, maythus form a permanent stronghold of the infection;
(3) there can be no doubt that wild rodents, two species ofwhich have been found definitely implicated, form the per-manent plague reservoir;
(4) the "domestic" rodent fauna, including,besides the conmmonrats and house mice,in part also domesticated guinea pigs,becomes only temporarily involved in the wild rodent epi-zootics, an event apt to lead to the appearance of plagjein man;
(5) the houses of the plague area having apparently been freedfrom X. cheopis, wild-rodent fleas now form the usual, ifnot the sole, vehicle of the infection not only from rodentto rodent but also from the rodents to man.
Valuable as this information is, it must be realized that itfurnishes only a general picture of the present plague situation inVenezuela, leaving many essential questionE concerning the ecology ofthe disease unanswered. The most importarntamong the problems of thelatter category are that:
(a) the contention that plague is now restricted to a limitedpart of its original focus in the Miranda and Aragua Statesrests only on deductions made from the known incidence ofhuman plague and must, therefore, be confirmed or disprovedthrough wholesale and thorough examinations of the rodentsand their fleas within the maximal limits of the affectedarea,
- 129-
RES 2/12
(b) the hitherto obtained knowledge on the presence of wildrodent plague is rather scanty, es it rests only on theapparently rather occasional detection of the infection intwo of the several wld rodent species (and lagomorpha)met with in the affected areas. It is to be expected thatthe wholesale examinations proposed above will yield fur-ther information in this respect, but in addition to amplefield investigations of as many rodent species as possible,it is also essential to test their susceptibility to plaguein the laboratory. Standard methods must be used for thelatter work so as to detect differences in the plague sus-ceptibility of the various rodent species;
(c) to render the above mentioned field investigations effec-tive and to pave the way for measures of controlling thewild rodents, they must be accompanied, or even preceded,by a thorough study of the ecology of the animals on which,however, presumably much local information is available;
(d) hand in hand with these field and laboratory studies of thewild rodents, thorough parallel studies must be made on thecommon rats, partlcularly in order to determine thelr sus-ceptibility to plague. It has to be stressed in this con-nection that, though it has been often postulated that therural rat populations, not only in Venezuela but in otherwild-rodent plague foci of South America, have become re-sistant to the infection, thus far, the present reportershave failed to find any exact data proving this point;
(e) as has been noted already, it is still unknown which ofthe numerous wild-rodent flea (or, one might safe]ly say,polygenis) species are involved in the spread of plaguein Venezuela. Again, it may be expected that the fieldinvestigations will furnish information on this point,provided that care is.taken to use exclusively lots con-sisting of only one well identified flea species for thecultivation of P. pestis and for pooling tests in guineapigs. However, in addition to this, exact studies have tobe made to determine the vector efficiency of the variousspecies of wild rodents fleas. It would be advisable notonly to use X. cheopis as a standard of comparison in thesetests but also to study the vector efficiency of the localP. irritans and Ct. felis strains;
(f) in the course of the above field investigationa it is alsoimportant to make thorough epidemiological and laboratorystudies of all human plague cases observed at the time. Ifpossible, the plague strains isolated from man as well asfrom naturally infected rodents and fleas ought to be keptin a Jyophilized state for further studies; -
- 130-
RES 2/12
(g) the question whether a campaign against the wild rodentswould be a practical possibility can be decided only afterthe above outlined investigations have been well advanced,particularly after the presently plague-affected area hasbeen adquately delimited;
(h) it ought to be clear that a detailed program for the aboveproposed lnvestigations and studies can be drawn up onlyafter consultation with the medical officers of the Vene-zuelan Plague Prevention Service and a preliminary surveyin order to establish the manner in which the contemplatedwork could be conducted.
REFERENCES
1) R. I. Diaz (1948) Aspectos epidemiol6gicos de la peste en Vene-zuela. Arch. venezolanos de patologia tropical, etc. 1 (1):93-100
2) R. Pollitzer (1954) Plague. WHO Monograph Series Ns 22
3) P. Cova Garcia and Elizabeth Tallaferro (1959) Pulgas más comu-nes de Venezuela. Arch. venezolanos de patologia tropical, etc.3 (1):
4) J. M, De la Barrera (1960) Resumen de los resultados de las in-vestigaciones sobre peste efectuados en Venezuela desde el 19 deSeptiembre de 1959 hasta el 18 de Febrero de 1960. (Unpublishedtypescript)
5) Idem (1960) Informe al Gobierno de Venezuela sobre peste. (Un-published typescript)
6) IWO Weekly Epidemiological Recorda (1960-March, 1962), passim.
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SECTION J
A LISTING OF NEEDS IN RESEARCH
1. PERU/ECUADOR: Plague Ecological and Epidemiological Studiesin the Huancambamba-Ayabaca-Loja focus.
1.1 WILD RODENTS AND LAGOMORPHA
1.1.1 Ecology studies
It is planned to study the ecology of the various speciesof rodents and lagomorpha involved in the plague manifes-tations, particularly in order to (a) delimit their habitat;(b) establish the possible existence of strongholds of theinfection; and (c) to determine the aptitude of the animalsto approach or to enter human habitations or settlements.
1.1.2 Occurrence of natural plague infection
It is proposed to make systematic wholesale studies on theoccurrence of natural plague in the various species of ro-dents and lagomorpha, particularly in order to arrive ata distinction between reservoir species constantly harbor-ing the infection and those getting periodically or occa-sionally involved.
1.1.3 Susceptibility to plague infection
As planned, batches of the species involved in the plaguemanifestations will be experimentally infected with P.pestis strains of standard virulence so as to determinetheir susceptibility for, or resistance against plague.
1.2 FLEAS OF THE WILD RODENTS AND LAGOMORPHA
1.2.1 Distribution of the various flea species
It is planned to make systematic studies so as to determinethe occurrence and frequency of the various flea speciesconcerned on (a) the wild rodents and lagomorpha; (b) thecommon rats, the house-mice and the domesticated guinea-pigs; and (c) in the various parts of the focus and atdifferent seasons of the year.
1.2.2 Occurrence of natural plague in the various species
As projected, the occurrence of natural plague in the var-ious fleas would be determined with the aid of poolingtests.
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1.2.3 Vector capacity
It is proposed to study the vector capacity of the variousflea species found naturally plague-infected, using when-ever possible laboratory-bred strains.
1.3 COMMON RATS AND HOUSE-MICE
1.3.1 Systematic studies are planned to determine the presenceor absence of the two species of the common rats and ofthe house-mice in both the settlements and in the ruralareas of the focus.
1.3.2 Occurrence of natural plague
It is proposed to study the occurrence of natural plaguein the common rats and the house-mice by (a) examining allanimals found dead; (b) making guinea-pig tests with thepooled organs of trapped rats and mice.
1.3.3 Susceptibility to plague infection
Since it has been claimed that the rats in the area havebecome resistant to plague, it is planned to challengebatches of these animals, collected both in the settle-ments and in the rural areas of the focus, with P. pestisstrains of standard virulence.
1.4 DOMESTICATED GUINEA-PIGS
1.4.1 Frequency studies
Observations would be made on the comparative frequencywith which guinea-pigs are kept in (a) the settlementsand (b) the rural houses of the various parts of the focus.
1.4.2 Occurrence of natural plague
It is proposed to keep a watch for the occurrence of natu-ral plague in the domesticated guinea-pigs by a) dissect-ing and examining all animals found dead; and b) sacrific-ing and likewise examining those showing signs of illness.
The bloQd sera of all guinea-pigs under test will be keptin a lyophilized condition so as to make them availablefor further exhaustive studies.
1.4.3 Susceptibility to plague infection
As planned, it will be determined whether differences insusceptibility to experimental infection with variousP. pestis strains exist (a) between the guinea-pigs keptrespectively in recently plague-affected and in plague-free localities and (b) at different seasons of the year.
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1.5 INTRADOMESTIC FLEA FAUNA 7
1.5.1 Occurrence of the various flea species
It is projected to make studies on the occurrence and fre-quency of the various flea species infesting (a) the commonrats; (b) the house-mice arnd (c) the domesticated guinea-pigs as well as (d) on the fleas found free-living in thehouses, paying special attention to the occurrence of (1)X. cheopis; (2) wild rodent fleas and (3) the various formsof P. irritans, the existence of which has been recentlyclaimed.
1.5.2 Occurrence of natural plague
According to the plan, pooling tests would be made withbatches of the various domestic fleas to determine thepresence of plague in these parasites, particularly inlocalities invaded or threatened by plague.
1.5.3 Vector efficiency studies
It is proposed to make vector efficiency studies with theintradomestic flea species, particularly with the variousforms of P. irritans met with.
1.5.4 Action of insecticides
Comparative studies are also contemplated of the actionexerted by DDT and other insecticides on the domestic fleafauna.
1.6 EPIDEMIOLOGICAL OBSERVATIONS
1.6.1 Observations on manifest 'plague attacks
As planned, systematic studies would be made on all humanmanifestations of plague met with by the study group.
1.6.2 Subelinical forms of plague
It is proposed to study the occurrence of subclinical formsof plague with the aid of surveys in groups of the popula-tion exposed to the risk of infection.
1.6.3 Forecasting of plague manifestations
It is planned to explore the possibility of forecasting theoccurrence of human plague manifestations.
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2. ECOLOGICAL AND EPIDEMIOLOGICAL STUDIES IN THE VENEZUELAN PLAGUEFOCUS
2.1 Studies analogous to those outlined above are also contem-plated for the Venezuelan plague focus.
2.2 Pilot study on the control of wild rodent plague
Provided that strongholds of the infection are found in theVenezuelan plague focus, a pilot study is planned to explorethe possibility of sufficiently thinning out the populationsof the reservoir species in these localities so as to cutshort the spread of plague. Consultations with wild-lifeexperts would be indispensable to devise methods suitablefor such atemporary reduction of the populations concernedwhich, as proved by experiences in the Soviet Union, is aneffective method of plague control.
3. ECOLOGICAL AND EPIDEMIOLOGICAL STUDIES IN THE ECUADORIAN PLAGJUEFOCI
In view of the involved plague situation in Ecuador, it isproposed to postpone the framing of a program for studiesin other parts of that country until experiences on thesuitability of the plans contemplated for Peru/Ecuador bor-der area have been gathered.
4. STUDIES OF PLAGUE IN BRAZIL
In the light of knowledge gained in plague studies as out-lined for the other countries, a study of plague in Brazilmay be indicated. Also determinable at that time will bethe nature of such studies.
5. PLAGUE CONTROL
Since the aim of the proposed investigations is not to e-licit facts of merely academic interest but to serve prac-tical ends research would always be directed towards theultimate goal of providing the knowledge and tools to per-mit the national plague prevention services to deal withimminent or actual manifestations of the disease in man.Attention would be paid in particular to studies on thepossibilities of preventing human plague not only by theuse of insecticides (see 1.5.4 above) but also with theaid of potent synergist vaccines in basic and boosterdoses and, whenever indicated by local emergencies, throughadministration of antibiotics or sulfonamides. The ther-apeutic use of these substances would likewise be studiedas much as possible so as to arrive at a fully effectiveyet simple and economical scheme of treatment.
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SECTION K
OUTLINE OF A RESEARCH PLAN FOR STUDIES ON THE ECOLOGY ANDEPIDEMIOLOGY OF PLAGUE IN THE HUANCABAMBA-AYACABA-LOtLA FOCUS,
PERU/ECUADOR
1. General organization of the work
In order to cope with the involved problems to be investigated,the proposed study will be made on four levels:
(a) in the field;(b) in a base laboratory at Lima, Perú;(c) in one of the plague laboratories of the U.S.A. where the
plague strains isolated in the field or at the base labo-ratory will be studied and tests with the sera of plaguepatients, contacts and rodents requiring special tech-niques will be made;
(d) in three reference laboratories, namely the CDC FieldStation at San Francisco, where the vector efficiency ofthe various species of fleas of the focus playing a rolein the ecology of plague will be determined; the U.S.Natural History Museum in Washington, D. C., where finalidentifications of the different rodents and lagomorphamet with in the course of the study will be made; and thebranch of the British Miseum in Tring (England), where theidentifications of the fleas collected in the course ofthe work by the field and base laboratory staffs will beconfirmed.
The division of duties betveen the field staff and the workersat the base laboratory will be made evident when discussing the variousparts of the research program.
2. Personnel required
The personnel necessary for the proposed work is enumerated inthe follovwing raster:
International Staff* National Staff Collaborating Laboratories
1 Ecologist/Epidemiologist 1 Epidemiologist It is expected that the1 Bacteriologist 1 Bacteriologist collaboring laboratories1 Maamologist 2 Clinicians will delegate members of
(part time) their own staff' for the1 Entomologist (flea required work, but funds
expert) 1 Secretary must be available to2 Field Supervisors 4 Qialified Field enable them to come for
Workers necessary consultations1 Part-time Consultant 6 Trappers* to Washington
2 Drivers*Laborers
*_ To be padot f b rEsobga'A To be paíd out of ~theresearch grant.
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In order to assure adequate assistance for this study, keypersonnel of the Peruvian and Ecuadorian staff will be given somepreliminary training abroad.
3. Length of the study period
In view of the large scope of the research program and bear-ing in mind the seasonal changes of the ecological situation, thework of the team must be planned for a period of not less than twoyears, the first year to be used for obtaining an overall pictureof the situation, the second for focussing attention upcn the solu-tions of problems found to be of particular importance.
4. Investigations on wild rodents and lagomorpha
In order (1) to investigate which species of wild rodentsand lagomorpha suffer from natural plague; (2) to establish whichof these species is or are the permanent reservoir of the infectionand (3) to ascertain the trend of the infection in the species in-volved the following investigations are necessary:
4.1 To examine all animals found dead. These after theyhave been preliminarily identified and after their fleasand other ectoparasites have been collected and put intoindividual vials, will be dissected by the field staffwho (a) will note and record all gross signs suggestiveof plague (b) will meke impression films from the buboes(if present) and the spleen, liver and lungs as well assmears from the heart blood and (c) put the bubo, heartand spleen (or a piece thereof) as well as pieces of theliver and lungs into a jar containing 2% saline solutionor Broquet's fluid. In the case of deccmposed or muti-lated carcasses, one or a few marrow bones will be putinto the preserving liquid. After the impression filmsand smears have become air-dry, the properly labelledslides will be put into a jar containing methylatedalcohol. If the dissected animals are small, their car-casses will be put into a jar filled with methylatedalcohol or 10% formol. In the case of larger animalstheir skulls and skins will be forwarded to the base lab-oratory, together with the above-mentioned material. Inthe base laboratory the identity of the dissected animalswill be confirmed or determined and all necessary bacte-riological and serological tests will be made to detectthe presence of plague in the dissected animals. AllP. pestis strains isolated will be kept in a lyophillzedstate for further study in the U.S.
4.2 In order (1) to watch for the occurrence of incipient orlatent infections in the wild rodents and lagomorpha and(2) to obtain specimens for a determination of the sus-ceptibility of the various species to infection with P.pestis, adequate numbers of all species present in thestudy areas will be trapped or obtained by other means.
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4.3 The major part of the trapped animals--if possible aftera period of observation in the live state--will be sac-rificed and material for tests for the presence of plagueinfection in the base laboratory will be obtained in themanner described in paragraph 4.1. Examining this ma-terial in the base laboratory, ample use will be made ofanimal experiments with the pooled organs of lots ofanimals belonging to one and the same species. The ma-terial from animals obtained by killing methods will behandled in an identical manner.
4.4 Lots of not less than 6 animals of the various trappedspecies will be 'dissected, serologically tested and--if possible after a period of observation--will bechallenged with adequate doses of a plague strain ofstandard virulence. It would be desirable to performthese tests in the base laboratory by forwarding to itanimals trapped in localities free from epizootics atthe time in flea-proof cages.
4.5 While it is impossible to predict the number of animalsfound dead, it will be attempted to examine a total ofnot less than 100 rodents and lagomorpha per week or5,000-6,000 animals per year.
4.6 In addition to the above-described work ecologicalstudies will be made to ascertain the distribution ofthe different species and the limits of their habitat.
4.7 A constant watch will be kept for fluctuations in thepopulation density of the various species with aid ofenquiries among the population and the plague preven-tion staff, periodic inspections and systematic trappingoperations in representative plots of standard size,repeated in the various localities at regular intervals.
4.8 The observations on the sporadic, periodic or constantoccurrence of positive findings in the various speciesin combination with the ecological observations and theresults of the resistance studies will be used as ameans to assess the importance of the different rodentsand lagomorpha for the permanent harborage of theinfection.
4.9 By correlating the results of laboratory observationswith those on the population density of the essentialspecies the trend of plague in the focus will be gauged.
5. Investigations on the fleas of the wild rodents and lagomorpha
In order to ascertain the comparative importance of the variousflea species of the wild rodents and lagomorpha in the Huancabamba--Ayabaca-Loja focus for the transmission of plague, the following in-vestigations will be made:
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5.1 Flea collections will be made from (1) all rodents andlagomorpha found dead as well as from those trapped orcollected by other means; (2) rodent nests or burrows,and (3) other sites suitable for the harborage of fleas.
5.2 The collected fleas will be forwarded to the base lab-oratory using separate, adequately-labelled and well-closed vials for the flea lots collected from the in-dividual rodents and lagomorpha, nests, etc. Shouldit be impossible to forward the fleas alive, they willbe put in a preserving fluid like saline solution soas to permit their examination for the presence ofP. pestis.
5.3 In the base laboratory the fleas will be subjected topreliminary identification tests and divided into lotsconsisting of only one species. Representative spec-imens, preserved in alcohol or glycerol alcohol, willbe sent to Tring for final identification.
5.4 Pools of fleas belonging to one and the same specieswill be used for the experimental infection of guinea-pigs so as to detect the presence or absence of P.pestis in the lots under test.
5.5 It will be attempted to handle about 200 fleas fromwild rodents and lagomorpha per week or 10,000-12,000per year.
5.6 As far as possible the species of fleas in which theoccurrence of natural plague has been detected will bebred in the base laboratory and lots of the bred fleaswill be forwarded to the CDC Field Station in San Fran-cisco for vector studies. In the case of specieswhich cannot be bred in the laboratory, lots of thefleas in question collected in localities free from epi-zootics at the time will be sent to San Francisco.
5.7 Detailed accounts of the occurrence of the various fleaspecies found on the different rodents and lagomorphaand in other sites will be kept so as to assess (1) theoccurrence of the various flea species on the differentspecies of rodents and lagomorpha, (2) the location andthe limite of the habitat of the various fleas, and(3) the occurrence of seasonal fluctuations of theirfrequency.
5.8 The results of the examinations of the fleas for thepresence of P. pestis and of the vector capacity studiescorrelated with the ecological observations (5.7) willbe used to determine the comparative importance of thespecies in question for the transmission of plague.
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5.9 In order to ascertain the epidemiological importance ofthe fleas thus incrininated their ability to attack thecommon rats, the domesticated guinea-pigs and man willbe ascertained.
6. Investigations on the common rats and domestic mice
Since it has been maintained so far that the comnmon rats(R. rattus) (a) are not uniformly distributed in the Huancabamba-Ayabaca-Loja focus, being rare in the rural areas and (b) becausebeing resistant to infection with P. pestis, play no role in thetransition of the infection from the wild rodents and lagomorpha toman, the following investigations will be made:
6.1 The comparative frequency of these animals throughoutthe focus will be studied through uniformly conductedtrapping operations in and round the houses.
6.2 Batches of at least 20 live specimens trapped in thevarious towns and rural areas of the focus will beused for uniformly conducted susceptib'ility tests withP. pestis strains of standard virulence.
6.3 In localities where the occurrence of plague among thewild rodents and lagomorpha or in the human populationhas been recorded (a) a careful search will be insti-tuted for rats and domestic mice found dead in or roundthe houses and any carcass found will be examined wviththe aid of the methods described in Section 4.l of thisplan; (b) ample trappings will be made and the trappedrats and mice will be examined for the presence ofincipient or latent infection, laying particular stressupon the performance of tests with their pooled organs.As will be stated below, the fleas collected from therats and house-mice will also be used for pooling tests.
6.4 It will be attempted to examine an average of 60-80common rats and house-mice per week or about 3,000-4,000per year.
7. Investigations on the domesticated guinea-pigs
7.1 Whenever the presence of plague in wild rodents and lago-morpha is detected, a careful watch will be institutedto detect a transition of the infection to the domesti-cated guinea-pigs by (a) dissecting and examining any ofthese animals found dead and (b) sacrificing and likewiseexamining those showing signs of illness.
7.2 Comparative studies will be made to establish whether Odifferences in the susceptibility to experimental infec-tion with P. pestis exist between the guinea-pigs keptin recently plague-affected settlements or houses
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(particularly in places where these animals themselveshave been involved in the manifestations of the disease)and in localities recently free from plague. Incidentalto these investigations it will be studied whetherseasonal changes of the susceptibility to plague existin the domesticated guinea-pigs.
8. Investigations on the intradomestic flea-fauna
8.1 A focus-wide study will be made of the fleas infesting thecommon rats, particularly in order (1) to delimit the areasin which X. cheopis infests these rodents; (2) to establishwhat species replace this vector in localities unsuitablefor its existence and (3) to note the infestation of thecommon rats with fleas not specific to them, particularlywith wild-rodent fleas and P. irritans.
8.2 In the course of the just described work analogous obser-vations will be made on the flea-fauna of the domesticatedguinea-pigs and on the fleas infesting the house-mice.Particular attention will be paid to (1) the occurrence ofwild-rodent fleas and P. irritans on these rodents; and(2) the degree to which an interchange of fleas specificfor the common rats, respectively for the guinea-pigs takesplace.
8.3 Making the above enumerated investigations, attention willbe paid also to the occurrence and comparative frequencyof the different forms of P. irritans on the rodents aswell as in the houses in general.
8.4 Using separate adequately-labelled vials for the lots offleas from the individual rodents or locations, the fleamaterial will be forwarded to the base laboratory for (1)identification and recording of the species met with; (2)pooling tests to detect the presence of plague-infectedfleas and (3) breeding of the flea species, the vectorcapacity of which it is indicated to study. In the caseof species which cannot be bred in the laboratory (pre-sumably in that of the various forms of P. irritans) lotsof fleas collected in locations free from plague will beforwarded to the San Francisco CDC station for vectorefficiency tests.
8.5 Comparative studies will also be made of the action exertedby DDT and other insecticides on the domestic flea fauna.
9. Epidemiological observations
9.1 A close study will be made of all human plague manifesta-tion met with by the research team, particularly in orderto establish which rodents and which fleas were involved
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in the causation of the human infections. Houses in wwhich several plague attacks have occurred will be givenspecial attention in this respect.
9.2 The study group will stand ready to assist the PlaguePrevention Service of each country in obtaining in eachinstance of human plague a confirmation of the diagnosisthrough laboratory tests. The plague strains isolatedin the course of this work will be kept in lyophilizedform for further study in a reference laboratory.
9.3 In order to obtain complete and uniform records an ade-quately prepared record sheet will be used for eachpatient. The help of the Plague Prevention Service willbe enlisted to fill out such questionnaires also forpatients-seen by them in the recent past, and the futureuse of these record sheets will be recommended.
9.4 Efforts will be made to detect the occurrence of sub-clinical forms of plague through physical and serologicalsurveys in groups of the population which have been orare under risk cf infection.
9.5 As discussed at the conclusion of the report on Perú,attention will be given to forecasting the incidence ofhuman plague through a correlation of all available dataon the fluctuations of the population density of therodent hosts of the infection and on the occurrence andfrequency of manifestations of the disease in the herdsof these animals.
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SECTION L
OUTLINE FOR A RESEARCH PLAN FOR PLAGUE INVESTIGATION IN VENEZUELA
In accordance with the recommendations contained in theSection I on Venezuela, a plan for the iivestigation of the ecol-ogy and epidemiology of plague in the presently affected areas ofVenezuela may be itemized as follows:
1. Investigation on wild rodents and lagomorpha, comprising:
1.1 Examination of all animals found dead for the presence ofplague
1.2 Collection of large numbers of apparently healthy animalsby trapping or (as far as necessary) by other means so asto obtain material for
1.2.1 Pooling tests with the organs of sacri-ficed trapped animals or animals ob-tained by killing methods so as to de-tect the presence of plague infection.
1.2.2 Determination of the susceptibility ofthe various species to experimental in-fection with P. pestis strains of stand-ard virulence.
1.3 Ecological studies to ascertain the distribution of the dif-ferent species and the limits of their habitat.
1.4 Observations on fluctuations of the population density ofthe various species.
2. Investigations on the fleas of the wild rodents and lagomorphaby
2.1 Making flea collections from (1) all rodents and lagomorphafound dead, trapped or collected by other means; (2) rodentnests or burrows; and (3) other flea harborages.
2.2 Using pooled lots of fleas belonging to one and the samespecies of the various fleas met with for the experimentalinfection of guinea-pigs so as to detect the presence of in-fected fleas. Cultures will also be made from the fleas todetect the presence of avirulent strains.
2.3 Breeding fleas of the species found to be plague-infected inthe laboratory and using the bred fleas for vector efficiencystudies.
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3. Investigations on the common rats and mice, including
3.1 Studies on the occurrence and comparative frequency of R.norvegicus and R. rattus together with observations ondifferences in the ecology of these two species.
3.2 Tests to detect the presence of plague in these speciesand the house-mice in localities where plague has becomemanifest (examination of all rats and mice found dead andof trapped or killed animals).
3.3 Uniformly conducted susceptibility tests with P. pestisof standard virulence to determine to what extent therats trapped in the various localities of the focus havebecome resistant to plague.
4. Investigations of the domesticated guinea-pigs, comprising
4.1 Observations on the frequency with which these animals arekept in the various localities of the focus.
4.2 Tests to detect the presence of plague in these animals inlocalities where plague has become manifest.
4.3 Comparative studies to establish whether differences inthe susceptibility to experimental infection with P. pestisexist between guinea-pigs kept in recently plague-affectedsettlements or hauses and in localities free from plague.
5. Investigations on the intradomestic flea fauna, consisting of
5.1 Studies to determine the species of fleas habitually oraccidentally infesting the common rats, the house-mice, thedomesticated guinea-pigs and also the marsupialia.
5.2 Pooling tests with the various species of the intradomesticfleas in localities where the occurrence of plague has beendetected.
5.3 Vector efficiency studies with the species of the intra-domestic fleas which seem to be of importance in the con-veyance of plague.
5.4 Comparative studies of the action of DDT and other insec-ticides on the intradomestic flea fauna. L
6. Epidemiological investigations, comprising t
6.1 Thorough clinical studies and laboratory examination of anyhuman plague case met with. The efficacy of antibioticsand sulfonamides for the prevention and treatment of plaguewill also be studied.
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6.2 Efforts to detect the occurrence of subclinical forms ofplague through physical and serological surveys in groupsof the population which have been or are under the risk ofinfection.
6.3 Attention to the possibility of forecasting the incidenceof human plague through a correlation of the data on thefluctuations of the population density of the rodent hostsof the infection and the occurrence and frequency of mani-festations of the disease in the herds of these animals.
7. Evaluation and utilization of the results of the investiga-tions.
The results of the above-outlined investigations will beused
7.1 To determine the present limits of the plague-affectedarea.
7.2 To establish whether within the affected area strongholdsof the infection exist.
8. A decision 4will be made, based upon these data, as to dwhetheror not a pilot study to assess the possibilities of a cam-paign against the wild rodents would be justified.
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