Trop. Anita. Hlth Prod. (1993) 25, 203-214

E F F E C T O N H E R D H E A L T H A N D P R O D U C T I V I T Y O F C O N T R O L L I N G T S E T S E A N D T R Y P A N O S O M O S I S B Y

A P P L Y I N G D E L T A M E T H R I N T O C A T T L E

R. G. R. Fox, S. O. MMBANDO, M. S. Fox and A. WILSON 1

Mkwaja Ranch c/o Amboni Ltd, PO Box 117, Tanga, Tanzania; 1Cooper Zimbabwe (1992) ( Pvt) Ltd, PO Box 2699, Harare, Zimbabwe

SUMMARY

A large cattle ranch was established in 1954 in a heavily tsetse infested part of north-east Tanzania. Trypanosomosis was controlled for 30 years by prophylactic drugs but in 1988 drug resistance seemed to be developing as cases of trypanosomo- sis were being confirmed 4 or 5 weeks after treatment with isometamidium chloride ( Samorin ). Herd health had deteriorated and productivity was uneconomically low. In order to control the tsetse population the 8,000 cattle, grazing over 250 km', were regularly dipped in the synthetic pyrethroid deltamethrin ( Decatix Cattle Dip and Spray formulation). Within a year the tsetse population, as monitored by traps, had decreased by more than 90%. Disease mortality decreased by 56% and a range of productivity measures such as calving percentages and weaning weights were raised to levels above those prevailing before the decline in herd health.

INTRODUCTION

This paper describes work on Mkwaja Ranch, Tanzania from 1989 onward which was not an experiment or a trial: it was an operation to control tsetse populations in order to restore the ranch to an economically viable state. It was fortunate that the management and resident veterinarians had kept detailed records since the ranch was set up in 1954 and further extensive documentation was published in ILCA report No. 9 (Trail et al., 1985). The laboratory on the ranch was staffed by trained microscopists who were able to carry out packed cell volume (PCV) and other tests and many thousands of blood film examinations per annum. It was thus possible to derive valuable scientific information particularly relating to the effect of chronic trypanosomosis on general herd health and productivity and the effect of delta- methrin applied to cattle for tsetse control. Large scale studies of this nature are rarely possible under the conditions of management and husbandry in Africa.

Background information on Mkwaja ranch Mkwaja ranch is situated on the coast of north-east Tanzania in Pangani District,

100 km south of Tanga (Fig. 1). The ranch has a bimodal annual rainfall of approximately 1,000 ram but droughts

do occur. Soils are mainly low fertility sandy loam with black cotton days in the val- leys. The vegetation is coastal forest mosaic with some gallery forest, scrubby areas and wooded pastures. There are large areas of doum palm and Acacia zanzibarica. Up to 75% of the area is available for grazing (Trail et al., 1985) but there are large thickets which are impenetrable by cattle.

The ranch covers an area of 49,000 ha and it was first established by Amboni Ltd

Reprint requests to: Martin Mitchell, Export Business Group, Pitman-Moore Ltd, Breakspear Road South, Harefield, Uxbridg¢, Middlesex UB9 6LS, UK.

203

204 FOXETAL.

to provide the workers on their sisal estates with meat. Up to I0,000 head have been maintained on the ranch and a further 2,500 head on the sisal estates. The cattle were originally Tanganyika zebu shorthorns but Boran bulls have always been used and the cattle are now considered to be grade Boran.

Tsetse species and attempted control measures

Four species of Glossina have been identified on the ranch. G. morsitans and G. palli- dipes were present in large numbers with fewer G. brevipalpis and comparatively rare G. austeni. They transmit Trypanosoma congolense, T. vivax and T. brucei, the major- ity of cases being T. congolense (Trail et al., 1985).

The ranch area was previously unexploited because of high densities of tsetse fly and the ranch could only be set up in 1954 because of the availability of prophylactic drugs to protect the cattle against trypanosomosis. In the 1970s it was intended to eradicate the tsetse by destroying its habitat together with wild animal carriers of try- panosomes. Half the northern area was cleared of primary bush between 1970 and 1980. Unfortunately the bush re-encroached very rapidly, partly because the cattle grazed down the grass necessary to fuel natural hot fires and partly because the selec- tive feeding by cattle left undisturbed the seedlings of regenerating bush. Another factor favouring bush regeneration was the disturbance to soil caused by mechanical bush cutters. Meanwhile residual ground spraying of tsetse resting sites with DDT and, later, aerial spraying with non residual endosulphan against the tsetse fly were followed by the sterile insect technique (SIT).

The aerial spraying was costly and the DDT was environmentally unacceptable. The SIT trial only involved one of the 4 species of tsetse fly, G. morsitans, and the 1 km of cleared barrier failed to prevent re-invasion (Williamson et al., 1983). There are many wild animals on the ranch and the buffalo, warthog, bushpig, elephant, sable antelope, waterbuck, giraffe, hippopotamus, reed buck and grysbok remain host carriers of trypanosomes.

Ticks and tick-borne diseases Intensive tick control by weekly or twice weekly dipping depending on the season,

has been practised since the ranch was set up. Latterly, dioxathion (Delnav) was used. The tick species recognised on the ranch are Amblyomma spp., Hyalomma spp., Boophilus decoloratus and Rhipicephalus evertsi but they are present in low numbers. East Coast fever, babesiosis, cowdriosis and sweating sickness do not occur. In spite of the intensive tick control, consisting of weekly dipping in dioxathion throughout the year and mid week acaracidal hand dressing with dioxathion in oil, anaplasmosis due to Anaplasma marginale has been responsible for a large part of the disease mor- tality in recent years. On Mkwaja ranch, calves are not dipped until they have been weaned at 8 months of age. During this period they can be infected with anaplas- mosis without showing symptoms and thus become premune carriers, probably for life (Norval et al., 1984).

The disease is easily transmitted by several species of single and multi-host ticks including B. decoloratus, B. microplus, Hyalomma spp. and R. evertsi, and also by several types of biting flies (Norval et al., 1984). This is unlike babesiosis whose premunity is short and which can only be transmitted by the one host Boophilus spp.

Chemotherapy and prophylaxis Quinapyramine chloride and sulphate (Antryeide Prosalt) was used for trypanosomal prophylaxis until 1964 when isometamidium chloride (Samorin) was introduced. This

DELTAMETHRIN CONTROL OF TSETSE FLIES 205

was administered as a block treatment at 0"5 mg/kg body weight. One month after each treatment, a monitor group in each herd was tested for trypanosomes every 2 or 3 weeks and when 20% were positive the entire herd was retreated. In the mean- time any positive cases were treated with diminazene aceturate (Berenil). All pre- weaning calves were treated at monthly intervals with Berenil.

In 1980 the regime was changed to using Samorin, administered at I mg/kg. Routine examinations were carried out in every herd some 2 months post treatment and, as soon as the first positive cases were revealed, the whole herd was treated with Bcrenil and one week later with Samorin. As a result herd health and productivity were acceptable (Trail et aL, 1985).

The deterioration in herd health

In 1988/89 the interval of treatment with Samorin at 1 mg/kg was reduced to 5 weeks when positive cases of trypanosomosis were confirmed in blood films 4 weeks after treatment with Samorin. The dose was later reduced to 0-5 mg/kg because of possible toxicity. Chronic trypanosomosis was probably also occurring subclinically causing a "thin cow syndrome" (Dowler et al., 1989). This condition was identified by visual observation and PCV tests and these cases usually responded to treatment with Berenil at 7 mg/kg.

General herd health had deteriorated, the cattle generally had an unhealthy appearance, and mortality was high. In spite of the excellent tick control the main confirmed cause of mortality was anaplasmosis. Closure of the ranch was imminent because of financial loss. Then, by careful examination of the seasonal occurrence of tsetse, trypanosomosis and anaplasmosis, the hypothesis was developed that the incidence of anaplasmosis and diseases in general was related to stress from chronic trypanosomosis (Fox, 1989). This led to the decision to seek new and more effective means of tsetse control.

Proposed new methods of tsetse control

Considerable progress has been made in the use of traps and baited insecticidal targets for tsetse control (Vale, 1982; Lavissi6re et aL, 1990). The use at Mkwaja ranch of odour baited deltamethrin treated targets (Vale et aI., 1985) was consid- ered, but these would have been costly and have taken too long to deploy. It had been shown that cattle treated with deltamethrin act as effective lethal targets (Thom- son, 1985) and they could be used to control tsetse over large areas (Thomson et aL, 1989; 1991) in Zimbabwe and Zanzibar. After consultation with Dr G. A. Vale it was decided to use this method.

MATERIALS AND METHODS

Dipping procedures The tsetse control project began in August 1989. The 5 dip tanks in the northern

sector of the ranch were emptied and charged with 5% deltamethrin suspension concentrate cattle dip (Decatix, Cooper (Zimbabwe) Ltd) at the rate one litre of dip to 1,333 litres of water to give a target concentration of 0-00375% of deltamethrin and replenished at one litre of dip to 1,100 litres of water to maintain the concentration.

The cattle were normally dipped every 14 days but during wet weather the interval was reduced to 7 days. After 4 months the dips were muddy so they were cleaned and refilled. Replenishment was then made using the head count system by the addition of one litre of dip per 650 head. This was later discontinued and replenishment was carried out at a 1:1,000 dilution.

206 l~OX g-r Az,.

~ 10 k m ,t

' ® ® , ~ / _

0,.,,.,~,..,.11 ® ® I~ /

/ : \ ° / \ / -..,,

Fig. 1. The location of the trapping points in Mkwaja Ranch.

Tick control test

In order to evaluate the efficacy of deltamethrin for tick control, 5 test groups of 5 cattle were treated with deltamethrin at weekly, or fortnightly intervals, alone or in combination with hand dressing with dioxathion in oil or periodic application of 1% deltamethrin pour on (Spot On, Cooper (Zimbabwe) Ltd). Weekly tick counts were carried out and compared to a similar but untreated control group. The trial began in November 1989, shortly after the introduction of deltamethrin and contin- ued for 6 months.

Cattle distribution

Eight thousand cattle were concentrated in the 250 km 2 of the northern part of the ranch which was developed with dip tanks and watering points. Approximately half of the area is open grassland and the remainder woodland with some large areas of thicket inaccessible to cattle.

Following the usual management practice, the cattle were herded by day and kept in boreas at night for protection from predators.

The infrastructure for new cattle grazing sections was constructed to provide coverage of the whole of the northern half of Mkwaja Ranch. The 250 km 2 was divided into 13 sections. Cattle density averaged 32 head/kin 2 on which 26 were dipped and the remainder were undipped calves. A section usually comprises 4 herds with about 150 head in each.

To ensure full coverage of the whole grazing area and to maximize efficient utili- sation of pastures, segments of each section are allocated to each of its herds. These segments are further subdivided into 3 parts, each being grazed twice a week, with the seventh day a 'free' grazing day, usually coinciding with dipping or veterinary treat- ment days. Herds are driven out, early in the mornings, to the limit of their grazing areas and then grazed slowly back home. This prevents outwardly grazing cattle from satisfying their appetites too soon, lying down and then returning home,

DELTAMETHRIN CONTROL OF TSETSE FLIES 207

leaving outer pastures ungrazed. Both the stocking capacity and quality of pasture grasses available have been considerably improved by this method.

Fly monitoring With the help of the Tanga Tsetse Research Institute, 12 monitoring sites were set

up (Fig. 1), 7 in the northern deltamethrin treated area, 3 in the untreated control area and 2 along the coast. Initially each site comprised 2 NGU traps (Brightwell et aL, 1987) and 2 Challier biconical fly traps, but later 3 NGU traps only were used. Each month traps were positioned 150 m apart and baited with acetone, urine and sachets containing propyl phenol, octenol and methyl phenol mixed in a ratio of 1:4:8. After 4 days (later reduced to 3 days) the flies caught were recorded and the number of flies per trap per day (apparent density) was calculated. In addition, ran- dom sites were periodically monitored by similar methods in other areas. Monitoring began 2 months before the deltamethrin treatment.

Experiments were conducted to determine fly diurnal activity, relating to time of day for the different Glossina species, recorded monthly for 12 months.

Clinical monitoring and other records On Mkwaja Ranch clinical monitoring of disease includes the following:

a) Visual observation for signs of sub-clinical trypanosomosis "thin cow syndrome".

b) Regular blood slide examination from randomly selected animals commencing 56 days from Samorin prophylactic treatment. Initially these are taken every 2 weeks, but after 90 days they are taken weekly.

e) Weekly PCV tests on 5 groups of Berenil treated cows and PCV tests every 2 weeks on Samorin treated breeding cows.

d) Random PCV tests on other herds. e) Clinical examination of sick animals.

Diagnosis also takes into account such factors as breed, sex, age, nutritional status, reproductive performance, time post partum and lactation. In addition, records are maintained of mortality from various diseases and accidents, abortions and stillbirths, calving rates and many other productivity parameters. These records are made by the resident veterinarians and management. At Mkwaja, trypanosomosis is controlled by administering Samorin when routine examination of random thick blood slides reveal 10% of animals positive for trypanosomes.

Three groups of steers (total 28) were attached to deltamethrin treated breeding herds in different sections of the northern block of the ranch. Their weights were recorded each month and their growth rate compared to that of 31 steers of similar age and genetic background kept on the sisal estates over 10 km away with compar- able grazing and climate. In this area the tsetse challenge, although not measured, appeared to be much lower because of extensive clearing and cultivation. However, chemoprophylactic protection with Samorin was provided and ticks were controlled with dioxathion acaracide which had no effect on alighting tsetse.

RESULTS

Within 2 months of the start of deltamethrin dipping there was a visible improvement in the general health and appearance of the cattle. Comparing the year before and the year after commencement ofdeltamethrin dipping, there has been a marked decline in infection rates with trypanosomosis and anaplasmosis (Table I).

208 FOX ET AL.

Table I

Trypanosomosis and anaplasmosis infection rates

12 months before 12 months after deltamethrin introduction of

dipping dipping % reduction in positivity

No. slides taken 10,926 18,403 No. (%) positive for trypanosomosis 1,146 (10-5%) 550 (3.0%) 71 No. (%) positive for anaplasmosis 2,280 (20.9%) 512 (2.8%) 87

Mortality/abortions/stillbirths

The average mortality from the listed causes in the years 1986/89 and in the year 1990/ 91 (one year after the deltamethrin treatment began) are set out in Table II and for 1988/91 in Fig. 2. The percentage reduction in mortality in the herd from all diseases was more than 66% and even the mortality caused by hyaenas fell by 74% apparently because healthy cattle are more able to escape these predators. Deaths o f calves between birth and weaning fell by 68 per cent. Abortions and stillbirths in breeding females were reduced by 40% in 1990/91 and the 3 year PCV average before delta- methrin was 26 whereas in 1990/91 it had risen to thirty.

Tsetse populations

These showed a rapid decline soon after deltamethrin dipping began. By April 1990 G. morsitans., G. pallidipes and G. brevipalpis had been reduced by almost I00%, 90% and 70% respectively, (Gao et al., 1990) (Table III). Since then the tsetse populations in the deltamethrin treated area have been less than 10% of those in the control area (Fig. 3) except for a period from November 1990 to January 1991 when a rise in numbers followed an inadvertent fall in the deltamethrin content of the dip wash to 10% of the target concentration.

Nuisance and biting flies

The nuisance and biting flies which usually accompanied the herds were noticeably reduced to a very low level after the first dipping in deltamethrin. Comparative fly counts were not made.

Table II

Mortality and abortion~stillbirth rates and PCI,'s of cattle before and during deltamethrin dipping

3 year av. before 1990/91 % reduction/increase deRamethrin

Mortality from:- All diseases 769 (9.6%) 258 (3.2%) -66 Anaplasmosis 285 (3.6%) 47 (0-6%) -83 Trypanosomosis 32 (0"4%) 11 (0-1%) -66

Hyenas 47 (0-6%) 12 (0-1%) -74

Abortion/stiUbirths 60 (0-75%) 36 (0"33%) -40 Pre-weaning mortality 14.4% 4-6% -68 PCV 26% 30% + 15

No,~

11111

411

# Deaths 9, it

DELTAMETHRIN CONTROL OF TSETSE FLIES

deltarnethdn dipping

Q, (~ commenced \ / i t

, , " 9 • , , , ,', •

t ' ' , , 0 " Q

,, ~ p o ,oa b " : o ~

L ' , , , ~- o o o o o

4 " ~ 8 10 ~ T ; T 8--10 1'272 ; - T 8 10- -~72- 4 6 8 ( 1988 1 9 8 9 1 9 9 0 I 1 9 9 1

Mortality per month - - - .o - - - - A l l d i s e a s e s

• Anaplasmosis

• Tn/penosomiasis

209

Fig. 2. Monthly mortality from April 1989 to March 1991.

Product ivi ty

The calving ra te in the year end ing M a r c h 1991 rose to an all t ime record for the ranch o f 77% (Table IV). Average wean ing weights for the same per iod rose to 145 kg reach- ing 164kg in M a y 1991. The increase is due to the reduct ion in o rpha ns and improved milk p roduc t ion by the mothers . The a b o r t i o n figures (Table I I ) show a reduct ion o f 40% c o m p a r e d to the 3 years p rev ious to de l t amethr in use. W h e n weighed at 38 mon ths o f age, steers in the dc l t ame th r in d ipped herds showed 24% m o r e weight gain than comparab le steers in an ad jacen t a rea p ro tec ted on ly by c h e m o p r o p h y l - axis, their respective mean weights being 312 kg and 237 kg.

Table III

Apparent densities of Glossina species at Mkwaja ranch before and after the application of deltamethrin dip from July 1989 onward (Gao ¢t al., 1990)

Months

Glossina spp. June July Aug Sept Oct Nov Dec Jan Feb Mar Apt 1989 1990

Trial block (northern) GlossinapaUidipes 136"2 85 28 27 9"3 20 30 6.4 8"2 10-5 13 G. m. morsitans 5 3 0-3 0-2 0.4 0 1"01 0 0"01 0.01 0 G. brevipalpis 1-2 1"4 1"0 0"3 0"3 0.2 0-4 0.1 0'1 0.1 0"4

Control block (southern) Glossinapallidipes 183.2 132-7 132 82 97 115 60 28"7 64 148 103"4 G. m. morsitans 10 5 1 1"3 2 1 0"1 0"03 0.I 0-1 0"6 G. brevipalpis 2.4 2"3 2"3 1.3 9-0 1-1 1.2 0-7 1-0 2-4 1-4

The number of tsetse flies in the control area for June 1989 arc incomplete, as some were unidentified due to predation.

210 FOX ET AL.

300

e )

I

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o ) J

~ d area

S o u ~ uml~ed area ~', ,'~ . . . • . - . ; ', /

l

deltamethrin dipping commenced ~ ) M

: # |

# i

, . 0 ) • ) ) r \ : ", , , ,, ', : "e , e ' ' e e, ,,

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I J A N D A M A S O N D S O J F M J J I J F M A I

1989 1990 [ [ 1 9 9 1

Fig. 3. The apparent density of tsetse before and during deltamethrin dipping.

Drug treatments In 1988/89 Samorin was being administered at 0.5 mg/kg 9 times per year but in 1990/ 91 it was possible to reduce this to approximately 3 treatments per year. The cost of drugs and acaracides per head per year is set out in Table V. Because of reduced use of Samorin, Berenil and oxytetracycline, costs have fallen by 48.7% in spite of the considerably greater cost of the deltamethrin dip when compared with the dioxathion acaracide previously used.

Tick control Deltamethdn was registered and widely used as an acaracide in countries such as Australia, South Africa, Zimbabwe and elsewhere (Nolan et al., 1979) some years before its value for tsetse control was realised. As expected when used on Mkwaja at weekly intervals during the rains and fortnightly in dry weather it provided good tick control. Tick counts were not made before using deltamethrin but, on obser- vation, there seemed to be little change in the number of ticks on the cattle.

The proportion of tick species collected on Mkwaja Ranch in the test groups of 5 cattle over the 6 month period was Amblyomma spp. 60%, Hyalomma spp. 34%, Boophilus decolaratus 4% and Rhipicephalus evertsi 2 per cent. The lowest mean tick count was 2"4 ticks/cow/week on the cows dipped fortnightly in Decatix with Spot On

Table IV

Cattle productivity before and during deltamethrin dipping

10 year av. before deltamethrin Apt '90-Mar '91 % increase

% Calving rate 58 77 + 33 Weaning weights kg 124 145 + 17

DELTAMETHRIN CONTROL OF TSETSE FLIES 21 l

Table V

Annual costs of drugs, aearicide and insecticide before and after commencement of deltamethrin dipping in U~lheod

Before After

Samorin 6-4 1.6 Aearieide/inseeticide 1-8 3-5

(dioxathion) (deltamethrin) Bererdl and oxytetracyeline 3-5 0"9 Total 11 "7 6.0

applied on alternate weeks, and the highest, 3.4 ticks/cow/week, on the undipped control cows. These figures are very low with little difference between the treated and untreated cattle (Table VI). This would seem to indicate that the intensive tick control over 30 years had reduced tick numbers to a very low level and conventional tick control with dioxathion and hand dressing was providing very good tick control which was not improved by the introduction of deltamethrin.

DISCUSSION

Tsetse numbers and herd health It was demonstrated in 1989 on Mkwaja (G. A. Vale pers. comm.) that using a slowly moving open windowed vehicle as a trap, large numbers of G. morsitans could be caught in the cab in the control area whereas the adjacent traps in the control area were catching relatively few of this species. Thus the almost immediate improvement in herd health, after introduction of deltamethrin dipping, may have been because

Table VI

Tick counts in cattle dipped in Decatix over a 6 month period

Groups A B C D E F Total (5 cattle)

Dipping frequency (weeks) - 2 2 2 2 I Hand-dressing fequency 1% deltamethrin - - - 2* 4 - Hand-dressing frequency dioxathion in oil - - 2* - - -

Total weekly tick counts

Amblyomma spp. 265 265 209 185 236 203 1363 (60%)

Hyalomma spp. 154 153 136 92 1 i 0 I 17 762 (34%)

Boophilus spp. 19 10 18 24 13 13 97 (4%)

R. evertsi 7 5 4 10 3 5 34 (2%)

Total 445 433 367 311 362 338 2256 Average No. of ticks/head/week 3-4 3"3 2.8 2.4 2-8 2-6

*On alternate weeks to dipping weeks.

212 FOX ETAL.

previously there were large numbers of G. morsitans present which were not detected effectively in the monitor traps.

The vehicle trapping technique failed to reveal any G. morsitans in the treated area. This species favours open grassland so these flies would readily have alighted on the treated cattle and the population of G. morsitans was apparently quickly elimi- nated. The consequent immediate improvement in herd health was followed by a more gradual sustained improvement as the other species of tsetse were reduced, of which the most numerous were G. pallidipes, with some G. brevipalpis. The favoured habitat of these species is the denser woodland not penetrated by cattle from which tsetse can invade the grazing areas. It is planned to eliminate this persistent source of tsetse using strategically placed odour baited deltamethrin treated targets.

Anaplasmosis and other diseases

Prior to the use of deltamethrin large numbers of cattle were infected with and died from anaplasmosis and other disease (Tables I and II). Following the introduc- tion of deltamethrin, the percentage of parasitaemic cattle and the deaths from ana- plasmosis quickly declined. It could be argued that this may have been due to improved tick control but observation and the comparative tick control trial do not support this. Unfortunately, comparative tick counts were not made. Anaplasmo- sis is also readily transmitted by biting flies and the reduction of these could have played a part. However, the theory that the stress ofchronic subclinical trypanosomo- sis caused patent parasitaemia and clinical disease to emerge in premune carrier ani- mals, must be seriously considered. As seen in Figs 2 and 3 mortality from all diseases appears to have declined at more or less the same rate as tsetse numbers.

Productivity

The significant increase in productivity recorded as soon as the tsetse challenge was reduced by the application of deltamethrin is of great importance in Africa. In most situations another benefit would be improved draught power for tillage.

The increasing resistance of trypanosomes to drugs

Forty million head of cattle are living in the tsetse areas of Africa with the aid of drugs. These drugs have saved the lives of millions of cattle over the past 30 years and they will continue to do so. However, trypanosome resistance to drugs is developing elsewhere, just as it did on Mkwaja Ranch, and many of the cattle may be suffering from unrecognised chronic trypanosomosis with the consequent effects on productiv- ity. Unfortunately there are no new drugs on the horizon and new methods of tsetse control must be pursued.

CONCLUSIONS

The results achieved on Mkwaja indicate that in suitable circumstances deltamethrin applied to cattle can control tsetse populations and trypanosomosis infection. Where chronic trypanosomosis is occurring, a marked improvement in herd health and productivity will follow.

ACKNOWLEDGEMENTS

We thank G. A. Vale for his invaluable technical advice, staff of the Tsetse and Try- panosomosis Research Institute, Tanga, for tsetse monitoring work, Amboni Limited for back up support, C. F. Curtis for comments on the manuscript and the European Community for financial support.

Accepted for publication March 1993

DELTAMETHRIN CONTROL OF TSETSE FLIES 213

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VALE, G. A. (1982). The trap orientated behaviour of tsetse flies (Glossinidae) and other Diptera. Bulletin of Entomological Research, 72, 71-93.

VALE, G. A., BURSELL, E. & HARGROVE, J. R. (1985). Catching out the tsetse fly. Parasitology Today, 1, 106- 110.

WILLIAMSON, D. L., DAME, D. A., GATES, D. B., Coas, P. E., BAKULI, B. &: WARNER, P. V. (1983). Integra- tion of insect sterility and insecticides for control ofGlossina marsitans marsitans in Tanzania V. The impact of sequential releases of sterilised tsetse flies. Bulletin of Entomological Research, 73, 391- 404.

CONTROLE DE LA GLOSSINES DES TRYPANOSOMOSES PAR LE TRAITEMENT DES BOVINS A LA DELTAMETHRINE; EFFET SUR LA SANTE ET LA PRODUCTIVITE DU

TROUPEAU R~sumt--Une grande exploitation pour bovins a fitfi fond~ en 1954 dans une region du nord-est de la Tan- zanie, hautement infest~ par les glossines. Pendant 30 ans la trypanosomose a 6tfi controllt, a l'alde de drogues prophylactiques mais en 1988 la resistance ~. ces drogues semble s'~tr¢ developpcr car des cas de typanosomose ont fit6 confirmfis quatre au cinq s~nalnea apr~s traltement au chloride d'isometamidium (Samorin). L'fitat sanitairc du troupeau s'est deterior6 et la productivitfi n'etait plus economiquoment rent- able.

Afin de controler la population de glossines, les huit miUes de bovins p~turant sur plus de 250 km 2, ont 6tfi r~guli~r~ment immerg~s dans des bains de deltamethrine, pyrethroide de synth~se ( ~ t l x cattle dip et spray formulation). En un an, la population de glossines, evalu~ par pi~geag¢ a diminufie de plus de 90%. La mortalit6 due fi la maladie a dimunu~¢ de plus de 66% et plusieurs param~tres de productivitY, tel que le pourccntage de raise bas et le gain de poids ont atteint des niveaux superieurs a ccux enr~gistr~ avant la degradation de l'ttat sanitair¢ du troupeau.

EFECTO EN LA SALUD Y PRODUCTIVIDAD DEL HATO AL CONTROLAR TSE TSE Y TRIPANOSOMIASIS APLICANDO DELTAMETHRIN AL GANADO VACUNO

Resumen--Un hate grande de ganado rue establecido en 1954 en un area densamente infestada del noreste de Tanzania. Tripanosomiasis rue controlada per 30 an6s usando drogas profilacticas, pete en 1988 resis- tencia al fftrmaco parcel6 desarrollarse ya que ca.sos de tripanosomiasis fueron confirmados 4 o 5 semanas desputs del tratamiento con isometamidium chloride (Sarnorin). La salud del hate se bahia deteriorado y la productividad era economicamente baja.

214 FOX~W'AL.

Para controlar la poblacibn de tsetse, las echo rail cabezas de ganado pastoreando sobre 250 km 2 fueron regularmente bafiados con el pyrethroid deltamethrin sinthtico (Decatix para inmersion de bovines y for- mulacion para aspersion). Dentro de un an8 la poblaci6n de tsetse, monitoreada a tray,s de tramps.s, habia disminuido mas de190%. La mortalidad decrecio cerca de 66% y un range de medidas de productividad tales como porcentajes de paricion y pesos al destete fueron incrementatdos a niveles arriba de aqueUos clue prevalecieron antes de la disminucion en la salud del hate.

T H E CTVM LIVESTOCK INFORMATION SERVICE

The Centre for Tropical Veterinary Medicine of the University of Edinburgh possesses a unique collection of books, journals, periodicals, annual reports and theses relating to all aspects of veterinary medicine and animal production in the tropics. The collection includes both historical material from many tropical countries and the most recent studies, including those by the Centre's own staff and students. The Centre also has access to the entire library facilities of The University of Edin- burgh and to other libraries in the United Kingdom and beyond. The staff o f the CTVM library also have immediate access to CD-ROM databases and, by electronic means, to a wide range of external databases.

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