Research Article Detection of Rift Valley Fever Virus

Research ArticleDetection of Rift Valley Fever Virus InterepidemicActivity in Some Hotspot Areas of Kenya by Sentinel AnimalSurveillance 2009ndash2012

Jacqueline Kasiiti Lichoti1 Absolomon Kihara2 Abuu A Oriko3

Leonard Ateya Okutoyi3 James Ogaa Wauna4 David P Tchouassi4 Caroline C Tigoi4

Steve Kemp2 Rosemary Sang45 and Rees Murithi Mbabu1

1 Ministry of Agriculture Livestock and Fisheries PO Box 00625 Nairobi Kenya2 International Livestock Research Institute PO Box 30709ndash00100 Old Naivasha Road Nairobi Kenya3 Kenya Agricultural Research Institute Biotechnology Centre PO Box 57811-00200 Waiyaki Way Nairobi Kenya4 International Centre of Insect Physiology and Ecology Human Health Division PO Box 30772-00100 Nairobi Kenya5 Kenya Medical Research Institute Centre for Virus Research PO Box 54628-00200 Nairobi Kenya

Correspondence should be addressed to Jacqueline Kasiiti Lichoti kasiitiorengogmailcom

Received 29 April 2014 Revised 20 July 2014 Accepted 21 July 2014 Published 13 August 2014

Academic Editor Timm C Harder

Copyright copy 2014 Jacqueline Kasiiti Lichoti et al This is an open access article distributed under the Creative CommonsAttribution License which permits unrestricted use distribution and reproduction in any medium provided the original work isproperly cited

RiftValley fever virus causes an important zoonotic disease of humans and small ruminants in EasternAfrica and is spread primarilyby amosquito vector In this region it occurs as epizootics that typically occur at 5ndash15-year intervals associated with unusual rainfallevents It has hitherto been known that the virus is maintained between outbreaks in dormant eggs of the mosquito vector and thishas formed the basis of understanding of the epidemiology and control strategies of the disease We show here that seroconversionand sporadic acute disease do occur during the interepidemic periods (IEPs) in the absence of reported cases in livestock or humansThe finding indicates that previously undetected low-level virus transmission during the IEPs does occur and that epizootics mayalso be due to periodic expansion of mosquito vectors in the presence of both circulating virus and naıve animals

1 Introduction

Rift Valley fever (RVF) is an acute mosquito-borne viralzoonosis affecting ruminants and humans [1] It occurs inthe form of epizooticsoutbreaks that come in cycles of 5to 15 years following heavy persistent rainfall with floodingthat result in abundance of flood water mosquitoes known totransmit the virus [2] The RVF virus belongs to the genusPhlebovirus of the family Bunyaviridae and causes high feverand abortion in susceptible pregnant animals irrespective ofthe gestation period and high mortality in newborns Thedisease manifests in humans as asymptomatic or mild illnesswith headache fever and muscle and joint pains to severeillness associated with hemorrhagic fever encephalitis orocular disease [3 4] In addition to infected mosquito bite[5ndash8] humans may be infected through handling of blood

and tissues of viremic livestock Rift Valley fever is associatedwith unpredictable human epidemics in Africa [9] and ofteninvolves several countries in the East African region at thesame time [10]

During outbreaks the disease seriously affects ruralpeople in terms of food security and household nutritionthrough direct and indirect losses to livestock productionThe psychosocial distress that communities go through isenormous resulting from loss of family members andorrelatives to disease and general livelihoods due to ban onlivestock movement and livestock product trade andor banon export affecting the economic status of most livestockproducers [11]

RVF maintenance between epidemics is not fully under-stood largely because detection of the virus during theinterepidemic period (IEP) has proven difficult It has been

Hindawi Publishing CorporationVeterinary Medicine InternationalVolume 2014 Article ID 379010 9 pageshttpdxdoiorg1011552014379010

2 Veterinary Medicine International

widely hypothesized that it is maintained through transo-varial transmission in the floodwater mosquitoes of theAedes genus [12ndash14] The unpredictable nature of outbreakshighlights the need for active surveillance to monitor cir-culation of the virus especially during the IEPs [4] toobtain an improved understanding of the mechanisms ofdisease transmission to ruminants and subsequent spilloverto humans which leads to outbreaksThere have been reportsof interepidemic circulation of RVFV in endemic countriesin Africa [15] in a number of Eastern Africa countriesSporadic cases of RVF that occur in such endemic zoneswith manifestation of abortions could easily be confused forother causes of abortion in livestock and be missed out [16]Circulation of RVFV in the absence of clinical disease amonglivestock has also been reported in some of the countries inthe region

Virus circulation occurring among apparently healthyanimals has also been observed in Somalia [17] Uganda [18]Mayotte [13] Tanzania [15] and Madagascar [19] and also inwild animals [20] RVF antibodies have also been detected inKenya in areas where the disease has never been reported [10]further confirming virus circulation without clinical diseaseUsingmodeling it has been shown that RVF virus can persistin an environment as long as the virus remains in a mosquitobreeding site once introduced [21]

Ruminants such as goats and sheep have been usedas sentinels for surveillance of RVF virus activity [12 2223] involving the detection of antibodies against the virusin sera In Kenya this approach has been mainly limitedto suspected sick or aborting animals [24] and the extentto which asymptomatic but viremic animals may act asreservoirs of infection is unknown Monitoring of infectionin susceptible hosts is therefore an important tool for riskassessment Furthermore data on species susceptibility andon animal demographics can provide useful information inidentifying RVF risk areas and variation [25]

This study reports on themonitoring of RVF virus activityin sentinel herds is comprised of sheep and goats Thiswork was conducted as part of a project geared towardsunderstanding the interepidemic circulation of the virus indiverse host systems and focusing on sites that were recentlyaffected by the RVF outbreaks in 20062007 We sought todetermine the degree and variation of RVF virus exposurein these herds including variation across the selected periodsand sites

2 Materials and Methods

21 Study Area This study was conducted between 2009and 2012 in Naivasha Ijara and Baringo Districts of KenyaThese sites were selected due to historic occurrence ofepizooticsepidemics of RVF in 19971998 and 20062007except for Naivasha where the disease is endemic Ijara andBaringo districts are both semiarid with low erratic rainfallbut prone to flooding in times of heavy persistent rainfallThey are home to predominantly pastoralist communitieswhich maintain large livestock herds However the regionsare geographically far apart in the North Eastern part of

0 50 100 200(km)

Figure 1

Kenya lying close to the Kenya-Somalia border to the NorthEast and Boni Forest and the Tana Delta to the Southwhile Baringo is in the Central Rift Valley of Kenya lyingat the shores of Lake Baringo Whereas RVF epizootics haverepeatedly occurred in Ijara an outbreak of RVFwas reportedfor the first time in Baring in 200607 Through the reviewof records at the district and guidance from the districtveterinary officer (DVO) and the medical officers of healthlocations which reported cases of RVF during the outbreaksin humans and animals were identified for the study Sentinelherds that had no history of RVF vaccination were set up inthe selected locations in the districts as indicated in Figure 1Three sites were identified to represent Ijara two towards theNorth of Boni forest area (Ijara (SangailuGedelun centeredon 13148∘S 407327∘E13837∘S 407133∘E)) and one towardsthe shores of the Tana Delta (Kotile 19658∘S 402063∘E)two in Baringo (Ngrsquoambo 04940∘N 360588∘E and Sala-bani 05507∘N 360501∘E) around Lake Baringo and one inNaivasha (07203∘S 364284∘E) at the base of the escarpment(Figure 1)

In villages at livestockwildlife interface and in closeproximity to forested areas around the lake Baringo wherepasture is available during dry season with livestock grazingin proximity to wild animals and returning to villages duringthe rains The herds identified had over 300 animals andthere was frequent contact between livestock and wildlifeaccording to information given by the local community

Veterinary Medicine International 3

Table 1 Ijara to be at same level with Sangailu because it representsSangailu Gedelun and Kotile as shown below

District Site Sheep Goats TotalNaivasha Mai Mahiu 59 47 106

IjaraSangailu 25 31 56Gedelun 50 mdash 50Kotile 17 139 156

Marigat Ngrsquoambo 50 48 98Salabani 53 25 78

Total 254 290 544

Using the government and community leaders the herdowners were given the background and objectives of thestudy Their role in the project was to provide a subset oftheir herdanimals to be tagged for sentinel surveillance Theselected animals in the herd were to continue to move andgraze together with the rest of the animals

Farmers who agreed to take part in the study by allowingtheir animals to be tagged and sampled signed a consent formand a letter of agreement with the project in the presence of awitness the local administration local veterinary officer andthe livestock ownerrsquos representative This stipulated in detailhow the sentinel herdwould bemanaged by both the livestockowners and the project Funds were set aside for purchasingof antihelminthics for all the animals in the herds cateringfor all the veterinary services and payment of herding fee forthe recruited animals during the project period

22 Selection of Sentinel Animals Young sheep andor goatsaged 12 to 15monthswere identified and permanentlymarkedusing ear tags Ageing of the animals was based on thepresence of the incisor permanent teeth Young femaleswere preferred because they are kept longer for increasingherd size through lambing and kidding thus are rarely soldAfter tagging the baseline blood samples were collected Allsamples were tested for antibodies (IgG amp IgM) to RVFVfor baseline data All selected tagged animals were includedin the study irrespective of whether positive or negative forRVF antibodies During each visit the missing animals werereplaced guided by the selection criteria

The number of animals selected at each site for eachsentinel herd was maintained at above the recommended 40RVF seronegative animals (Table 1) per location This wasattained by recruiting new additional animals during eachvisit to replace those that died or got sold or seroconverted

23 Frequency of Sample Collection After the baseline sam-pling animals were sampled every 4ndash6 weeks up to the endof the rainy season during short and long rains The numberof visits depended on how long the rainy season persistedSamples were forwarded to Central Veterinary LaboratoryKabete Nairobi to be tested for the presence of RVF virus-specific IgG and IgM antibodies

Besides sentinel serological surveillance other animals inthe neighbourhood were monitored for any clinical diseasesuggestive of RVF The case definition for RVF infection

was animals showing abortions mortality in lambs andkids high fever lymphadenitis nasal and ocular dischargesprofuse fetid diarrhoea severe prostration dysgalactia andjaundice In instances where some of these clinical signswere encountered EDTA blood (10mL) was collected andtransported frozen to the laboratory for analysis

24 Sample Collection Transportation and Processing Bloodwas collected aseptically from the jugular vein into 10mLEDTA vacutainers and into plain vacutainers precoated withserum activator The animal unique identification (id) on eartag was recorded to link the vacutainer code with the animalidentification The vacutainers for whole blood were placedin a cool box with dry ice and transported to the laboratoryfor aliquoting Later on they were aliquoted into 3 bar-coded cryotubes and samples were placed on dry ice readyfor transportation The blood for serum was slanted in theshade to prevent exposure to excessive temperatures Thesewere then taken to the refrigerator and placed vertically untilthe following day The tubes were carefully removed fromthe refrigerator and centrifuged the bungs were removedand clear serum was carefully pipetted off into sterile bar-coded cryovials The sample identification was then enteredand linked to the animal identification for accurate datamaintenance

25 Animal Data Capture and Storage A 10-inch HewlettPackard (HP) netbook a USB Bluetooth adapter (UD100)a USB GPS Dongle (ND100S) a 1-dimensional barcodescanner radio frequency identification (RFID) tags and ahand held RFID tag reader were used for animal data captureand storage in the field

Sentinel animals were ear tagged with radio frequency(RFID) chips (All flex USA) A Bluetooth enabled RFIDreader was used to capture the animal identity duringsampling and to transmit this information via Bluetooth toa netbook

In order to ensure error-free sample collection a softwaresystem (tarakibu) was developed using python html andJavaScript and MySQL to associate the animal id GPS-derived time and location at sampling time and to associatesample barcodes into a database The aliquoting processwas managed by a program (Ukasimu) which ensured thatbarcodes on aliquots were associated with the original col-lection data Further information on these systems includingsource code is available at httpsgithubcomilritarakibuand httpsgithubcomilriukasimu

26 Laboratory Analysis of Samples The serum samples wereanalyzed using the inhibition enzyme-linked immunoassaykit for the detection of antibody (both IgG and IgM) toRift Valley fever virus in humans and domestic and wildruminants (Special Pathogens Unit National Institute forCommunicable Diseases South Africa) [26] The positiveserum samples for RVFV virus-specific antibodies werethen tested for IgM antibodies using the IgM captureenzyme-linked immunoassay (BDSL Special PathogensUnit


Table 2 Number of RVF seropositive animals and number of replaced animals during the different sampling periods at Ijara district

Site Animal type Sampling periodSeptember 2009 October 2009 February 2010 May 10 June-July 2010 October-November 2010 June 2012

KotileSheep (119899) 2 (17) 3 (17) 0 (17) 3 (17) 3 (17)Goat (119899) 1 (139) 0 (139) 0 (139) 0 (139) 1 (139)

Number replaced 36 12 49 13

SangailuSheep (119899) 2 (25) 2 (25) 25 (25) 2 (25) 9 (25)Goat (119899) 1 (31) 0 (31) 14 (31) 6 (31) 18 (31)

Number replaced 1 56

GedelunSheep (119899) 0 (50) 7 (50) 1 (50)Goat (119899) mdash mdash mdash

Number replaced 4 14Numbers in brackets (119899) indicate total number sampled for each animal per sampling period mdash shows data on animals not recruited

National Institute for communicable Diseases Johannes-burg South Africa) [27] The kits were used followingthe protocol of the manufacturer Whole blood from animalsthat tested positive on IgM capture ELISA was tested forRVFV antigen by quantitative real time RT-PCR (qRT-PCR)using RVF reagents from CDC Atlanta [28] and the AppliedBiosystems 7500 real time PCR equipment was used Theprimer and probe set used was RVFL-2912fwdGG (51015840-TGA-AAATTCCTGAGACACATGG-31015840) RVFL-2981revAC (51015840-ACTTCCTTGCATCATCTGATG-31015840) and RVFL-probe-2950 (51015840-CAATGTAAGGGGCCTGTGTGGACTTGTG-31015840)labeled at the 51015840 end with the reporter dye FAM and at the31015840 end with the quencher BHQ1 The target region was the Lsegment The samples that tested positive on RVF InhibitionELISA but tested negative on RVF IgM capture ELISA werepresumed to be positive for IgG antibodies The purpose wasto save on laboratory testing costs and only pick RVF IgMpositives that indicated current exposure of the animals toRVF virus

27 Data Analysis Thenumber of seropositive animals out ofthe total sampled for each period was analysed using a gener-alized linear model (GLM) with binomial error structure orquasibinomial error structure in case of overdispersion andlog link in R 2110 software [29] When any of the parameters(animal type site or sampling period) was significant theodds ratio (OR) and corresponding confidence interval (CI)were estimated against a reference category from each type

3 Results

31 RVFV Seroconversion in Ijara In Kotile the percentseropositivity of the animals oscillated between 0ndash25 dur-ing the period of study On every visit animal replacementswere more frequent because at this site animals wererecruited from 5 different livestock owners and challenges topresent the animals for sampling by some owners resultedin missed sampling opportunities and the need for replace-ment (Table 2) In Sangailu animals were recruited fromone livestock owner and replacement was mostly due toseroconversion

There was a slight decrease in seropositivity (from 53to 36) between September and October 2009 but whenthe animals were sampled in early February 2010 39 out of56 (696) animals had antibodies against RVFV with only17 testing negative Only one animal was replaced duringthis period Samples collected during targeted surveillance inOctober 2010 from 2 goats that showed clinical signs of RVFinfection at a homestead in Marey (Ijara) were positive forIgM antibodies by ELISA and also antigen positive on realtime qRT-PCRThe owner of the Sangailu herd had removedall the ear tags from the animals on the subsequent visit assuch more animals were retagged and samples were collectedfor testing and eight were positive for RVFV antibodies dur-ing the sampling of May 2010 The next sampling carried outat the end of June and early July 2010 showed a seroconversionof 482 This necessitated the recruitment of another herd(Gedulun herd) in the same area in July 2010 of which 7 ofthe 50 animals had seroconverted when the second samplingwas carried out in October 2010 (Table 2)

Analyses of the combined data from Ijara showed thatthere was no significant difference in seropositivity betweenthe animal types (goat and sheep) (F

114= 2089 119875 = 0170)

and sampling period (F312

= 07806 119875 = 0527) Howeverthere was a significant difference in the level of virus exposurebetween the two sites (F

114= 13702 119875 = 0002) with

about 35-fold greater likelihood of exposure recorded inSangailu relative to Kotile (95 OR = 3371 CI = 18096ndash76686) Analyses of combined available data for Marigatdistrict during the sampling periods May 2009 November2009 January 2010 April 2010 May 2010 April 2011 August2011 and October 2011 showed no significant difference inexposure between the animal types goat and sheep (F

18=

2766 119875 = 0130) sites Ngrsquoambo and Salabani (F18

= 2766119875 = 0135) and sampling period (F

45= 2619 119875 = 0160)

We also analysed risk of RVF exposure for each siteindividually Our findings showed an overwhelmingly signif-icant difference in RVF exposure between the animal types(120594218

= 9322 119875 lt 0001) in Kotile with about a 51-foldrisk of infection recorded in sheep compared to goat (OR =5151 CI = 13507ndash337001) However there was no significantdifference recorded across the sampling periods (F

63= 0422

119875 = 0830) A converse pattern was observed in Sangailu


Table 3 Number of RVF seropositive animals and number of replaced animals during the different sampling periods in Naivasha

Animal type Sampling periodJanuary 2010 May 2010 June 2010 January 2011 July 2011 December 2011

Sheep (119899) 4 (59) 0 (59) 1 (59) 3 (59) 1 (59) 0 (59)Goat (119899) 1 (47) 0 (47) 0 (47) 1 (47) 1 (47) 1 (47)Number replaced 18 34 39 13 14 0Numbers in brackets indicate total number (119899) sampled for each animal per sampling period

where therewas no significant difference in exposure betweenthe animal types (F

18= 0109 119875 = 0749) and sampling

period (F45

= 46366 119875 = 00617) although with respectto sampling periods risk of RVF exposure was highest inFebruary-2010 in Sangailu as seen in Table 2

32 RVFV Seroconversion in Naivasha In Naivasha 106animals were recruited to the study (Table 1) and during thebaseline sampling only five animals had antibodies to RVFvirusThe subsequent samplings had zero one four two andone animals testing positive for RVF antibodies There werealways replacements during each visit (Table 3)

There was no significant difference in exposure betweenthe animal types (F

110= 09096 119875 = 0363) although there

was about a 2-fold higher likelihood of infection to occurin sheep when compared to goat (95 OR = 181 CI =0584ndash6749) Also the risk of exposure did not seem to differacross the sampling period (F

56= 3020 119875 = 0106)

33 RVFV Seroconversion in Marigat In Ngrsquoambo the live-stock owner had two types of herds goats that graze nearthe homestead in the Perkerra irrigation scheme and sheepthat left to graze around the shares of Lake Baringo Duringthe short rains period of November 2009 26 (265) werepositive in Ngrsquoambo and 8 (105) were positive in SalabaniThe next sampling carried out after six weeks revealed 24(244) positives in Ngrsquoambo and 11 (141) positives inSalabani During the sampling in January 2010 some of theanimals in Ngrsquoambo were not presented for sampling becausethey could not be traced in the expansive thickets of Prosopisjuliflora at the time

There was no significant difference in exposure due toanimal type both in Ngrsquoambo (F

112= 24491 119875 = 01176)

and Salabani (F114

= 0465 119875 = 050) Interestingly the riskof infection significantly differed across the sampling periodsat both sitesThehighest risk of exposurewas recordedduringthe periods of November 2009 and January 2010 at both sitesrelative to the others (Table 4)

34 Active RVFV Infection All the positive samples on RVFinhibition ELISA were tested using the IgM capture ELISAReal time qRT-PCR was carried out on the samples that werepositive on RVF IgM capture One sheep from the sentinelherd in Kotile was positive for RVF IgM antibodies andRVF antigen by qRT-PCR Two samples from opportunisticsampling were positive one from Ijara and the other fromMarigat both by IgM ELISA and qRT-PCR All the other

positive samples on RVF Inhibition ELISA were negative forIgM antibodies (Table 5)

4 Discussion

This study detected evidence of RVFV circulation duringthe IEP 2009 to 2012 in Ijara and Marigat (sites where RVFoutbreaks affecting livestock and humans were reported in200607) [30] with acute virus infections being detectedamong sentinel animals and among animals sampled oppor-tunistically within the vicinity There were no reports ofhuman RVF and no reports of increased abortion or sus-pected RVF outbreak by the veterinary and public healthauthorities in these areas Interepidemic transmission ofRVFVwas also demonstrated through seroconversion amongthe herds also in the absence of reports of clinical casesor reports of outbreaks among local animals and humanpopulations The observation of RVFV circulation amonglivestock in the IEP in Kenya is based on both detection ofinfection and seroconversion which would have escaped theknowledge of the veterinary and public health authoritiesraising concerns about capacity for alertness and prepared-ness in these hotspots and the need for improved detection ofRVFV activity among livestock

Animals from Ijara (mainly cattle) and Marigat (evensheep) move to the forest in Boni and around Lake Baringorespectively when pasture and water become scarce return-ing back to the normal grazing areasvillages when rainsreturn and pasture becomes available In both study sites theincrease in the seroprevalence was associated with floodingin the areas and animals migration back from the forest afterdry spells The forest ecosystem may be playing a role in theinterepizootic maintenance or amplification cycle for RVFin Kenya as postulated by Davies [2] who observed a smallpercentage of seroconversion in cattle that grazed in forestedareas and the role played by wildlife [20]

The observed RVFV activity in Baringo in this IEP (2009to 20012) suggests that the virus may have been establishedin the area earlier even though outbreaks were reported herefor the first time during the 200607 Kenya outbreak Thisgives credence to the argument that the virus may not havebeen introduced in the area in 200607 through movementof infected livestock from Northeastern Kenya during theoutbreak but rather occurred de novo in Baringo [10] Thismeans that the virus may have been here earlier than weknow


Table4Num

bero

fRVFseropo

sitivea

nimalsa

ndnu

mbero

freplacedanim

alsd

uringthed

ifferentsam

plingperio

dsatMarigatdistric

t

Site

Animaltype

Samplingperio

dMay

2009

Novem

ber2

009

Janu

ary2010

April

2010

May

2010

April

2011

August2011

Octob

er2011

March

2012

May

2012

Ngrsquoa

mbo

Sheep(119899)

11(50)

10(50)

1(60)

1(49)

12(50)

5(48)

3(54)

Goat(119899)

15(48)

14(48)

2(55)

1(49)

10(46)

5(52)

8(46)

Num

berreplaced

821

4222

24mdash

mdashmdash

Salabani

Sheep(119899)

1(51)

4(53)

7(53)

0(53)

0(53)

3(53)

0(53)

1(51)

Goat(119899)

0(25)

4(25)

4(25)

1(25)

0(25)

1(25)

0(25)

0(25)

Num

berreplaced

917

1514

27mdash

mdashmdash

Num

bersin

bracketsindicatetotaln

umber(119899)sam

pled

fore

achanim

alpersam

plingperio

d


Table 5 Animals with evidence of recent RVF infection (sentinel and targeted surveillance)

Animal ID Species Sample Location Sampling date Type IgM ELISA qRT-PCRAVD1002 Sheep Serum Marey Sangailu 281009 Targeted surveillance PositiveAVD1002 Sheep Whole blood MareySangailu 281009 Targeted surveillance PositiveAVD063 Sheep Serum Kotile 291009 Sentinel PositiveAVD063 Sheep Whole blood Kotile 291009 Sentinel PositiveAVD392 Goat Serum Salabani 51109 Targeted surveillance PositiveAVD392 Goat Whole blood Salabani 51109 Targeted surveillance Positive

Minimal virus circulation was detected in Naivasha herdover the monitoring period Naivasha was selected to repre-sent a site classified as endemic which experiences low levelvirus activity every rainy season and not explosive outbreakssuch as those reported in Ijara and Marigat in 199798 and200607 The herd was hosted by a farmer whose animals areconfined and do not migrate to forests in search of pastureand in addition the cattle were reported to receive RVFvaccination during periods of high risk which reduced therisk of exposure of our sentinel herds

The observed significant difference in risk of expo-sureinfections in sheep compared to goat in Kotile asopposed to Sangailu raises questions on differential risk levelsattributable to differences in animal speciesbreeds It hasoften been suggested that sheep are more susceptible toRVF than goats with more sheep being affected than otheranimals during outbreaks [31ndash34] However this indicatesdifferences in exposure risk between the sheep populationsfrom Kotile and Sangailu and further suggests difference invirus exposure risk between sheep breeds or populations

Following up the sentinel herds from 2009 to 2012 itwas observed that the level of replacement was high in allthe study sites owing to loss of recruited animals throughdeath disappearance and seroconversion This greatly com-promised following up of individual animals making it acostly venture when at every visit animals had to be replacedand tagged In light of this challenge we recommend thatsentinel animals be followed up as a herd rather than atindividual level and criteria for selecting animals be sam-pled developed This could include sampling specific ageof animals whose history of vaccination against RVF isknown Following up a herd rather than an individual animalwould be more sustainable and cost effective compared tolongitudinal following up of individual animals There wasalso the challenge of livestock owners thinking that theywould be victimized when their animals were tagged Thiscaused some of them to remove the ear tags as the case was inSangailu which contributed to interruptions in the follow-up

Over the entire sampling period risk of exposure wassignificantly higher based on the sampling done in October2009 and January 2010 for Marigat (Ngrsquoambo and Salabani)and in February 2010 for Sangailu which may be attributedto the amounts of rainfall and flooding that occurred duringthese periods usually associated with short rains period inthe country It is worthy of note that most outbreaks havebeen associatedwith short rains which occur in above normalamounts [10 30 35ndash37]

From the observations made from following the herdsin Ijara (Sangailu Gedulum) and Marigat (Salabani andNgrsquoambo) it can be concluded that RVF virus activity occurseven in the absence of clinical infections in herds [35 37ndash39] Active surveillance is needed between epidemics to beable to detect transmission among livestock and possiblehuman exposure that may goundetected among remote ruralcommunities Most veterinary authorities depend on passivesurveillance to detect diseases that do not commonly occurThis is widely accepted because it has served the purpose thusfar Passive surveillance is not easy to detect in the currentcase of RVF virus circulation when animals are not showingclinical signs Active surveillance is recommended andwhereresources may not be available targeted surveillance in highrisk areas will help curb RVF outbreaks Isolation of viruscausing outbreaks is important in order to detect whetherthere are any variations [39 40]There is also a need to relookthe contingency plan used in response to RVF outbreaksbearing in mind that active transmission of the virus couldoccur in the absence of expected clinical events that havebeen relied on for a long time such as massive abortions inlivestock

Conflict of Interests

The authors declare that they have no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors acknowledge the AVID consortium memberinstitutions (icipe DVS KARI KWS ILRI and KEMRI)through their directors who were members of the ProjectManagement Committee for supporting the larger AVIDproject through the participation of their staff and the DVSstaff in Naivasha Ijara and Marigat (Dr Cheruiyot MrJonathan Rotich and Mr Omar Chatsi) and others forsupporting this work The authors express their immensegratitude to theVirology laboratory staff at CVL Kabete whoassisted in laboratory analysis of samples and the livestockowners in Marigat Ijara and Naivasha for their participationand use of their animals This project received full financialsupport from Googleorg the philanthropic arm of Google


References

[1] K J Linthicum F G Davies A Kairo and C L Bailey ldquoRiftValley fever virus (family Bunyaviridae genus Phlebovirus)Isolations from diptera collected during an inter-epizooticperiod in Kenyardquo Journal of Hygiene vol 95 no 1 pp 197ndash2091985

[2] F G Davies ldquoObservations on the epidemiology of Rift Valleyfever in Kenyardquo Journal of Hygiene vol 75 no 2 pp 219ndash2301975

[3] K J Linthicum ldquoRift valley feverrdquo in CRC Handbook Series inZoonoses section B Viral Zoonoses G W Beran Ed pp 125ndash138 CRC Press Boca Raton Fla USA 2nd edition 1994

[4] BMMcIntosh D Russell I Dos Santos and J H S Gear ldquoRiftValley fever in humans in South Africardquo South African MedicalJournal vol 58 no 20 pp 803ndash806 1980

[5] A M Seufi and F H Galal ldquoRole of culex and Anophelesmosquito species as potential vectors of rift valley fever virusin Sudan outbreakrdquo BMC Infectious Diseases vol 10 article 652010

[6] F G Davies and R B Highton ldquoPossible vectors of Rift Valleyfever in Kenyardquo Transactions of the Royal Society of TropicalMedicine and Hygiene vol 74 no 6 pp 815ndash816 1980

[7] D Fontenille M Traore-Lamizana H Zeller M Mondo MDiallo and J P Digoutte - ldquoShort report rift valley feverin Western Africa isolations from Aedes mosquitoes duringan interepizootic periodrdquo The American Journal of TropicalMedicine and Hygiene vol 52 no 5 pp 403ndash404 1995

[8] R Sang E Kioko J Lutomiah et al ldquoRift Valley fever virusepidemic in Kenya 20062007 the entomologic investigationsrdquoAmerican Journal of Tropical Medicine and Hygiene vol 83supplement 2 pp 28ndash37 2010

[9] I E Aradaib B R Erickson R M Elageb et al ldquoRift valleyfever Sudan 2007 and 2010rdquo Emerging Infectious Diseases vol19 no 2 pp 246ndash253 2013

[10] P Munyua R M Murithi S Wainwright et al ldquoRift Valleyfever outbreak in livestock in Kenya 2006-2007rdquoThe AmericanJournal of Tropical Medicine and Hygiene vol 83 no 2 pp 58ndash64 2010

[11] C Sindato E Karimuribo and L E G Mboera ldquoThe epi-demiology and socio-economic impact of Rift Valley fever inTanzania a reviewrdquo Tanzania Journal of Health Research vol13 no 5 pp 1ndash16 2011

[12] R Lancelot J P Gonzalez B Le Guenno B C Diallo YGandega and M Guillaud ldquoDescriptive epidemiology of RiftValley fever in small ruminants in SouthernMauritania after the1988 rainy seasonrdquo Revue drsquoElevage et de Medecine Veterinairedes pays Tropicaux vol 42 no 4 pp 485ndash491 1990

[13] T Lernout E Cardinale M Jego et al ldquoRift valley fever inhumans and animals in Mayotte an endemic situationrdquo PLoSONE vol 8 no 9 Article ID e74192 2013

[14] V Racloz C Griot and K D Stark ldquoSentinel surveillancesystems with special focus on vector-borne diseasesrdquo AnimalHealth Research Reviews vol 7 no 1-2 pp 71ndash79 2006

[15] R D Sumaye E Geubbels EMbeyela andD Berkvens ldquoInter-epidemic transmission of rift valley fever in livestock in theKilombero river valley Tanzania a cross-sectional surveyrdquoPLoSNeglected Tropical Diseases vol 7 no 8 Article ID e2356 2013

[16] HM Kariithi Y S BinepalW CWilson R K Soi L O Ateyaand A A Oriko ldquoSero-surveillance of Rift Valley fever in sheepand goat flocks in high risk areas in KenyardquoKenya Veterinarianvol 34 2010

[17] B Soumare S Tempia V Cagnolati A Mohamoud G vanHuylenbroeck andD Berkvens ldquoScreening for RiftValley feverinfection in northern Somalia a GIS based survey method toovercome the lack of sampling framerdquo Veterinary Microbiologyvol 121 no 3-4 pp 249ndash256 2007

[18] J W Magona T Galiwango J Walubengo and G MukiibildquoRift Valley fever in Uganda seroprevalence and risk factorsurveillance vis-a-vis mosquito vectors anti-RVF virus IgG andRVF virus neutralizing antibodies in goatsrdquo Small RuminantResearch vol 114 no 1 pp 176ndash181 2013

[19] V Chevalier T Rakotondrafara M Jourdan et al ldquoAn unex-pected recurrent transmission of rift valley fever virus in cattlein a temperate and mountainous area of madagascarrdquo PLoSNeglected Tropical Diseases vol 5 no 12 Article ID e1423 2011

[20] S C Britch Y S Binepal M G Ruder et al ldquoRift Valley feverrisk map model and seroprevalence in selected wild ungulatesand camels from Kenyardquo PLoS ONE vol 8 no 6 Article IDe66626 2013

[21] J Gachohi B Bernard F Hansen and P Kitala ldquo spatially-explicit simulation model of Rift Valley fever transmissionrdquoAfrican Journal of Pharmacology and Therapeutics vol 1 no 42012

[22] AG Al-Qabati andA I Al-Afaleq ldquoCross-sectional longitudi-nal and prospective epidemiological studies of rift valley fever inAl-Hasa Oasis Saudi Arabiardquo Journal of Animal and VeterinaryAdvances vol 9 no 2 pp 258ndash265 2010

[23] H G Zeller D Fontenille M Traore-Lamizana Y Thionganeand J Digoutte ldquoEnzootic activity of rift valley fever virusin Senegalrdquo The American Journal of Tropical Medicine andHygiene vol 56 no 3 pp 265ndash272 1997

[24] F G Davies T M Logan Y Binepal and P Jessen ldquoRift Valleyfever virus activity in EastAfrica in 1989rdquoVeterinary Record vol130 no 12 pp 247ndash249 1992

[25] World Health Organization ldquoJoint FAO-WHO experts consul-tation on Rift Valley fever outbreak forecasting models FAOheadquarters Rome September-October 2008rdquo Report NoWHOHSEGARBDP20092 2009

[26] J T Paweska E Mortimer P A Leman and R SwanepoelldquoAn inhibition enzyme-linked immunosorbent assay for thedetection of antibody to Rift Valley fever virus in humansdomestic and wild ruminantsrdquo Journal of Virological Methodsvol 127 no 1 pp 10ndash18 2005

[27] J T Paweska F J Burt F Anthony et al ldquoIgG-sandwichand IgM-capture enzyme-linked immunosorbent assay for thedetection of antibody to Rift Valley fever virus in domesticruminantsrdquo Journal of Virological Methods vol 113 no 2 pp103ndash112 2003

[28] B H Bird D A Bawiec T G Ksiazek T R Shoemaker andS T Nichol ldquoHighly sensitive and broadly reactive quantitativereverse transcription-PCR assay for high-throughput detectionof Rift Valley fever virusrdquo Journal of Clinical Microbiology vol45 no 11 pp 3506ndash3513 2007

[29] RDevelopment Core Team R A Language and Environment forStatistical Computing R Foundation for Statistical ComputingVienna Austria 2010

[30] C W Woods A M Karpati T Grein et al ldquoAn outbreakof rift valley fever in Northeastern Kenya 1997ndash98rdquo EmergingInfectious Diseases vol 8 no 2 2002

[31] M Eisa HM S Obeid and A S A El Saei ldquoRift Valley fever inthe Sudan I Results of field investigations of the first epizooticin Kosti Districtrdquo Bulletin of Animal Health and Production inAfrica vol 24 pp 343ndash347 1977


[32] European Food SafetyAuthority (EFSA) ldquoOpinion of the Scien-tific Panel on Animal Health andWelfare (AHAW) on a requestfrom the Commission related to ldquoThe risk of a Rift Valley feverincursion and its persistence within the communityrdquordquo EFSAJournal vol 3 no 10 pp 1ndash128 2005

[33] T G Ksiazek A Jouan J M Meegan et al ldquoRift Valley feveramong domestic animals in the recent West African outbreakrdquoResearch in Virology vol 140 no 1 pp 67ndash77 1989

[34] I Z E Imam R El-Karamany and M A Darwish ldquoAnepidemic of Rift valley fever in Egypt II Isolation of the virusfrom animalsrdquo Bulletin of the World Health Organization vol57 no 3 pp 441ndash443 1979

[35] J Fafetine L Neves P N Thompson J T Paweska V P M GRutten and J A W Coetzer ldquoSerological evidence of rift valleyfever virus circulation in sheep and goats in zambezia provincemozambiquerdquo PLoS Neglected Tropical Diseases vol 7 no 2Article ID e2065 2013

[36] J Gachohi F Hansen B Bett and P Kitala ldquoPersistence ofRift Valley fever virus in East Africardquo Geophysical ResearchAbstracts vol 14 EGU2012-8773-1 2012

[37] N Lagerqvist B Moiane L Mapaco J Fafetine S Vene andK I Falk ldquoAntibodies against rift valley fever virus in cattlemozambiquerdquo Emerging Infectious Diseases vol 19 no 7 pp1177ndash1179 2013

[38] FAO 2005 httpwwwfaoorgdocrep006y4611ey4611e00HTM

[39] B H Bird JW K Githinji J MMacharia et al ldquoMultiple viruslineages sharing recent common ancestrywere associatedwith alarge rift valley fever outbreak among livestock in Kenya during2006-2007rdquo Journal of Virology vol 82 no 22 pp 11152ndash111662008

[40] L Nderitu J S Lee J Omolo et al ldquoSequential rift valley feveroutbreaks in Eastern Africa caused by multiple lineages of thevirusrdquo Journal of Infectious Diseases vol 203 no 5 pp 655ndash6652011

Submit your manuscripts athttpwwwhindawicom

Veterinary MedicineJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Veterinary Medicine International



International Journal of

Microbiology


AnimalsJournal of

EcologyInternational Journal of


PsycheHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Evolutionary BiologyInternational Journal of


Hindawi Publishing Corporationhttpwwwhindawicom

Applied ampEnvironmentalSoil Science

Volume 2014

Biotechnology Research International


Agronomy




Journal of Parasitology Research

Hindawi Publishing Corporation httpwwwhindawicom


Volume 2014

Zoology

GenomicsInternational Journal of


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The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


VirusesJournal of

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Cell BiologyInternational Journal of



Case Reports in Veterinary Medicine


widely hypothesized that it is maintained through transo-varial transmission in the floodwater mosquitoes of theAedes genus [12ndash14] The unpredictable nature of outbreakshighlights the need for active surveillance to monitor cir-culation of the virus especially during the IEPs [4] toobtain an improved understanding of the mechanisms ofdisease transmission to ruminants and subsequent spilloverto humans which leads to outbreaksThere have been reportsof interepidemic circulation of RVFV in endemic countriesin Africa [15] in a number of Eastern Africa countriesSporadic cases of RVF that occur in such endemic zoneswith manifestation of abortions could easily be confused forother causes of abortion in livestock and be missed out [16]Circulation of RVFV in the absence of clinical disease amonglivestock has also been reported in some of the countries inthe region

Virus circulation occurring among apparently healthyanimals has also been observed in Somalia [17] Uganda [18]Mayotte [13] Tanzania [15] and Madagascar [19] and also inwild animals [20] RVF antibodies have also been detected inKenya in areas where the disease has never been reported [10]further confirming virus circulation without clinical diseaseUsingmodeling it has been shown that RVF virus can persistin an environment as long as the virus remains in a mosquitobreeding site once introduced [21]

Ruminants such as goats and sheep have been usedas sentinels for surveillance of RVF virus activity [12 2223] involving the detection of antibodies against the virusin sera In Kenya this approach has been mainly limitedto suspected sick or aborting animals [24] and the extentto which asymptomatic but viremic animals may act asreservoirs of infection is unknown Monitoring of infectionin susceptible hosts is therefore an important tool for riskassessment Furthermore data on species susceptibility andon animal demographics can provide useful information inidentifying RVF risk areas and variation [25]

This study reports on themonitoring of RVF virus activityin sentinel herds is comprised of sheep and goats Thiswork was conducted as part of a project geared towardsunderstanding the interepidemic circulation of the virus indiverse host systems and focusing on sites that were recentlyaffected by the RVF outbreaks in 20062007 We sought todetermine the degree and variation of RVF virus exposurein these herds including variation across the selected periodsand sites

2 Materials and Methods

21 Study Area This study was conducted between 2009and 2012 in Naivasha Ijara and Baringo Districts of KenyaThese sites were selected due to historic occurrence ofepizooticsepidemics of RVF in 19971998 and 20062007except for Naivasha where the disease is endemic Ijara andBaringo districts are both semiarid with low erratic rainfallbut prone to flooding in times of heavy persistent rainfallThey are home to predominantly pastoralist communitieswhich maintain large livestock herds However the regionsare geographically far apart in the North Eastern part of

0 50 100 200(km)

Figure 1

Kenya lying close to the Kenya-Somalia border to the NorthEast and Boni Forest and the Tana Delta to the Southwhile Baringo is in the Central Rift Valley of Kenya lyingat the shores of Lake Baringo Whereas RVF epizootics haverepeatedly occurred in Ijara an outbreak of RVFwas reportedfor the first time in Baring in 200607 Through the reviewof records at the district and guidance from the districtveterinary officer (DVO) and the medical officers of healthlocations which reported cases of RVF during the outbreaksin humans and animals were identified for the study Sentinelherds that had no history of RVF vaccination were set up inthe selected locations in the districts as indicated in Figure 1Three sites were identified to represent Ijara two towards theNorth of Boni forest area (Ijara (SangailuGedelun centeredon 13148∘S 407327∘E13837∘S 407133∘E)) and one towardsthe shores of the Tana Delta (Kotile 19658∘S 402063∘E)two in Baringo (Ngrsquoambo 04940∘N 360588∘E and Sala-bani 05507∘N 360501∘E) around Lake Baringo and one inNaivasha (07203∘S 364284∘E) at the base of the escarpment(Figure 1)

In villages at livestockwildlife interface and in closeproximity to forested areas around the lake Baringo wherepasture is available during dry season with livestock grazingin proximity to wild animals and returning to villages duringthe rains The herds identified had over 300 animals andthere was frequent contact between livestock and wildlifeaccording to information given by the local community






Total 254 290 544
























3 Results




114= 2089 119875 = 0170)



114= 13702 119875 = 0002) with


18=



45= 2619 119875 = 0160)



63= 0422







18= 0109 119875 = 0749) and sampling

period (F45




110= 09096 119875 = 0363) although there


56= 3020 119875 = 0106)



112= 24491 119875 = 01176)

and Salabani (F114




4 Discussion





Table4Num

bero

fRVFseropo

sitivea

nimalsa

ndnu

mbero

freplacedanim

alsd

uringthed

ifferentsam

plingperio

dsatMarigatdistric

t

Site

Animaltype

Samplingperio

dMay

2009

Novem

ber2

009

Janu

ary2010

April

2010

May

2010

April

2011

August2011

Octob

er2011

March

2012

May

2012

Ngrsquoa

mbo

Sheep(119899)

11(50)

10(50)

1(60)

1(49)

12(50)

5(48)

3(54)

Goat(119899)

15(48)

14(48)

2(55)

1(49)

10(46)

5(52)

8(46)

Num

berreplaced

821

4222

24mdash

mdashmdash

Salabani

Sheep(119899)

1(51)

4(53)

7(53)

0(53)

0(53)

3(53)

0(53)

1(51)

Goat(119899)

0(25)

4(25)

4(25)

1(25)

0(25)

1(25)

0(25)

0(25)

Num

berreplaced

917

1514

27mdash

mdashmdash

Num

bersin


umber(119899)sam

pled

fore

achanim

alpersam

plingperio

d











Acknowledgments



References

















































Microbiology


AnimalsJournal of








Volume 2014



Agronomy







Volume 2014

Zoology



InsectsJournal of




VirusesJournal of











Total 254 290 544
























3 Results




114= 2089 119875 = 0170)



114= 13702 119875 = 0002) with


18=



45= 2619 119875 = 0160)



63= 0422







18= 0109 119875 = 0749) and sampling

period (F45




110= 09096 119875 = 0363) although there


56= 3020 119875 = 0106)



112= 24491 119875 = 01176)

and Salabani (F114




4 Discussion





Table4Num

bero

fRVFseropo

sitivea

nimalsa

ndnu

mbero

freplacedanim

alsd

uringthed

ifferentsam

plingperio

dsatMarigatdistric

t

Site

Animaltype

Samplingperio

dMay

2009

Novem

ber2

009

Janu

ary2010

April

2010

May

2010

April

2011

August2011

Octob

er2011

March

2012

May

2012

Ngrsquoa

mbo

Sheep(119899)

11(50)

10(50)

1(60)

1(49)

12(50)

5(48)

3(54)

Goat(119899)

15(48)

14(48)

2(55)

1(49)

10(46)

5(52)

8(46)

Num

berreplaced

821

4222

24mdash

mdashmdash

Salabani

Sheep(119899)

1(51)

4(53)

7(53)

0(53)

0(53)

3(53)

0(53)

1(51)

Goat(119899)

0(25)

4(25)

4(25)

1(25)

0(25)

1(25)

0(25)

0(25)

Num

berreplaced

917

1514

27mdash

mdashmdash

Num

bersin


umber(119899)sam

pled

fore

achanim

alpersam

plingperio

d











Acknowledgments



References

















































Microbiology


AnimalsJournal of








Volume 2014



Agronomy







Volume 2014

Zoology



InsectsJournal of




VirusesJournal of

















3 Results




114= 2089 119875 = 0170)



114= 13702 119875 = 0002) with


18=



45= 2619 119875 = 0160)



63= 0422







18= 0109 119875 = 0749) and sampling

period (F45




110= 09096 119875 = 0363) although there


56= 3020 119875 = 0106)



112= 24491 119875 = 01176)

and Salabani (F114




4 Discussion





Table4Num

bero

fRVFseropo

sitivea

nimalsa

ndnu

mbero

freplacedanim

alsd

uringthed

ifferentsam

plingperio

dsatMarigatdistric

t

Site

Animaltype

Samplingperio

dMay

2009

Novem

ber2

009

Janu

ary2010

April

2010

May

2010

April

2011

August2011

Octob

er2011

March

2012

May

2012

Ngrsquoa

mbo

Sheep(119899)

11(50)

10(50)

1(60)

1(49)

12(50)

5(48)

3(54)

Goat(119899)

15(48)

14(48)

2(55)

1(49)

10(46)

5(52)

8(46)

Num

berreplaced

821

4222

24mdash

mdashmdash

Salabani

Sheep(119899)

1(51)

4(53)

7(53)

0(53)

0(53)

3(53)

0(53)

1(51)

Goat(119899)

0(25)

4(25)

4(25)

1(25)

0(25)

1(25)

0(25)

0(25)

Num

berreplaced

917

1514

27mdash

mdashmdash

Num

bersin


umber(119899)sam

pled

fore

achanim

alpersam

plingperio

d











Acknowledgments



References

















































Microbiology


AnimalsJournal of








Volume 2014



Agronomy







Volume 2014

Zoology



InsectsJournal of




VirusesJournal of











18= 0109 119875 = 0749) and sampling

period (F45




110= 09096 119875 = 0363) although there


56= 3020 119875 = 0106)



112= 24491 119875 = 01176)

and Salabani (F114




4 Discussion





Table4Num

bero

fRVFseropo

sitivea

nimalsa

ndnu

mbero

freplacedanim

alsd

uringthed

ifferentsam

plingperio

dsatMarigatdistric

t

Site

Animaltype

Samplingperio

dMay

2009

Novem

ber2

009

Janu

ary2010

April

2010

May

2010

April

2011

August2011

Octob

er2011

March

2012

May

2012

Ngrsquoa

mbo

Sheep(119899)

11(50)

10(50)

1(60)

1(49)

12(50)

5(48)

3(54)

Goat(119899)

15(48)

14(48)

2(55)

1(49)

10(46)

5(52)

8(46)

Num

berreplaced

821

4222

24mdash

mdashmdash

Salabani

Sheep(119899)

1(51)

4(53)

7(53)

0(53)

0(53)

3(53)

0(53)

1(51)

Goat(119899)

0(25)

4(25)

4(25)

1(25)

0(25)

1(25)

0(25)

0(25)

Num

berreplaced

917

1514

27mdash

mdashmdash

Num

bersin


umber(119899)sam

pled

fore

achanim

alpersam

plingperio

d











Acknowledgments



References

















































Microbiology


AnimalsJournal of








Volume 2014



Agronomy







Volume 2014

Zoology



InsectsJournal of




VirusesJournal of







Table4Num

bero

fRVFseropo

sitivea

nimalsa

ndnu

mbero

freplacedanim

alsd

uringthed

ifferentsam

plingperio

dsatMarigatdistric

t

Site

Animaltype

Samplingperio

dMay

2009

Novem

ber2

009

Janu

ary2010

April

2010

May

2010

April

2011

August2011

Octob

er2011

March

2012

May

2012

Ngrsquoa

mbo

Sheep(119899)

11(50)

10(50)

1(60)

1(49)

12(50)

5(48)

3(54)

Goat(119899)

15(48)

14(48)

2(55)

1(49)

10(46)

5(52)

8(46)

Num

berreplaced

821

4222

24mdash

mdashmdash

Salabani

Sheep(119899)

1(51)

4(53)

7(53)

0(53)

0(53)

3(53)

0(53)

1(51)

Goat(119899)

0(25)

4(25)

4(25)

1(25)

0(25)

1(25)

0(25)

0(25)

Num

berreplaced

917

1514

27mdash

mdashmdash

Num

bersin


umber(119899)sam

pled

fore

achanim

alpersam

plingperio

d











Acknowledgments



References

















































Microbiology


AnimalsJournal of








Volume 2014



Agronomy







Volume 2014

Zoology



InsectsJournal of




VirusesJournal of
















Acknowledgments



References

















































Microbiology


AnimalsJournal of








Volume 2014



Agronomy







Volume 2014

Zoology



InsectsJournal of




VirusesJournal of







References

















































Microbiology


AnimalsJournal of








Volume 2014



Agronomy







Volume 2014

Zoology



InsectsJournal of




VirusesJournal of























Microbiology


AnimalsJournal of








Volume 2014



Agronomy







Volume 2014

Zoology



InsectsJournal of




VirusesJournal of













Microbiology


AnimalsJournal of








Volume 2014



Agronomy







Volume 2014

Zoology



InsectsJournal of




VirusesJournal of






Documents

Research Article Detection of Rift Valley Fever Virus