RabiesVirus in Small RuminantsCONSOLINI IRENE USAMVBT V YEAR 20192020 [621714]

RabiesVirus in Small RuminantsCONSOLINI IRENE USAMVBT V YEAR 2019/2020

INTRODUCTIONuRabiesiscausedby a rhabdovirusof the genusLyssavirus. The virus isexcretedin the saliva of infectedraccoons, skunks, foxes, and bats, aswellasdomesticdogs and cats. Elsewherein the world, the mongooseand vampire batare importantvectors, althoughbatsprobablypresentlessof a riskto sheepand goatsthando rabidcarnivores. The virus isrelativelyfragile and easilyinactivatedby exposureto ultravioletlight or common disinfectants.

INCIDENCE OF INFECTIONuMore than55,000 peopledie of rabieseachyear, mostlyin Asia and Africa.uFor the last 11 years, the averagenumberof annualconfirmedcasesof rabiesin sheepand goatshasbeen11, while7 infectedcamelidsin totalhavebeenreportedduringthisperiod. Obviously, the trueincidenceof diseaseislikelyto be higher, asthe diagnosiswillbe potentiallymissedin manyanimalsfor lackof testing.

INCUBATION PERIODuThe incubationperiodbetweenexposureand developmentof clinicalsignswilldependin part on the location of the bitewoundon the body. The virus ascendsnervesto reachthe brain and inoculationin the musclesof the head willbe more rapidlyfatalthana biteto a distalhindlimb. Accordingto Fowler, 20 alpacasfrom a herdof 160 werebittenby a rabiddog in Peru. Thirteendiedor wereeuthanizedin extremis, with incubationperiodsvaryingfrom 15 to 34 days. Affectedanimalsdied6 to 8 daysafterdevelopmentof clinicalsigns. Similarincubationperiodshavebeenreportedin sheepand goatsafterexperimentalinfectionor observedattackby a rabidanimal.

PATHOGENIC CHARACTERISTICS

EARLY SIGNS uEarlysignsof rabiesin llamasand alpacasmayinclude lameness, ataxia, or posteriorparesis. Similarprodromalsignsalongwith inappetenceand/or fine muscletremorsare reportedin sheepand goats. Bothfuriousand paralyticformshavebeenobservedin small ruminantsand camelidswith rabies. Anyneurologicsignsare possible, includingdysphagia, salivation, teethgrinding, bleating, voice change, and aggression, eitherhead buttingor tryingto bite. Pruritusatthe scarof the bitewoundisreportedinconsistently. Woolpullingissometimesnoted. Somewhatuniqueto small ruminantsisan occasionalmarkedincreasein sexualactivity. For instance, a femalegoatwith rabiesmighttryto mountand breedherdmatesor a tirein itsenclosure.

DIAGNOSISuRabiesisa fataldisease, usuallybutnotalwayswithin10 daysof the first clinicalsigns. Ifthe animalwith suspectneurologicalsignsdiesor iseuthanized, itisidealto submitthe entirecarcassto the diagnosticlaboratoryfor a complete necropsyexamination, so thata diagnosiscan be made evenifrabiesisnotpresent. Ifthatisnotpossible, eitherthe head or appropriate portionsof the brain shouldbe submittedto the state laboratoryfor testing. uTo removeadequatesamplesthroughthe foramenmagnum, first disarticulatethe skullfrom the spine atthe atlanto-occipitaljoint and placethe head dorsalside down on a flatsurface. In additionto wearinggloves, use a face shieldto avoidsplashof CSF intothe eyes. Inserta knifewith a long thinbladeinside the dura and usingan apple-coringmotion, free the brain stemfrom the meninges. Pull on the brainstemwith forcepsand severitinside the foramenmagnum with the knife. A long-handledspoonor spatula-likeinstrumentcan thenbe usedto separate the cerebellumfrom the cerebellarpedunclesand coaxitout throughthe foramenmagnum

MORE INFOS REGARDING THE COLLECTION COULD BE FIND HERE: https://www.wadsworth.org/programs/id/rabies/animal-specimen-testing

uIfthe fluorescentantibodytest (FAT) ispositive, the laboratorywillconfirmthe diagnosisby virus isolationin cellculture, ratherthanthe oldermouse inoculationtest. The viralstraininvolvedcan be furtheridentifiedusinga monoclonalantibodypanel. Occasionallyhistologyisdoneon a brain thatwasnotpreviouslysubmittedfor rabiestesting. A nonsuppurativeencephalitiswith mononuclearcellperivascularcuffswillbe presentifthe animaldiedof rabies. Negri bodiesmaybe seen, whichare eosinophilicinclusionsin the cytoplasmof neuronsin the hippocampusand in Purkinjecells. Theyare a classicfindingin animalswith rabiesand oftendescribedasbeingpathognomic, butin factspecificityislessthan100%. Accordingto the CDC the presenceof Negri bodieshasa sensitivityof about50% whencomparedwith FAT for the diagnosisof knownrabidanimals

uA newerRapidRabiesEnzymeImmuno-Diagnostictest (RREID) usesbiotinylatedantibodies, streptavidinconjugateand monospecificpolyclonalantibodiesagainstlyssaviruses. Thistest isspecificbutnotquiteassensitive asthe FAT . Itisveryusefulfor epidemiologicstudiesand in situationssuchasthirdworld countrieswhereequipmentfor fluorescentantibodytestingislacking

TREATMENTuThereisno effectivetreatment, so effortsshouldbe directedataddressingotherpossiblecausesof the clinicalsignssuchaspolioencephalomalacia, listeriosis, meningealworm, tickparalysis, and hepaticencephalopathyuLittle data isavailableconcerningthe probabilitythata small ruminantor camelidclinicallyillwith rabieswillexcretevirus in saliva, howevervirus hasbeenisolatedfrom 4.6% of salivaryglandsand 1.6% of saliva samplesfrom 87 cattlewith naturallyoccurringparalyticrabiesin Argentina. Transmissio nof rabiesfrom alpaca to alpaca asa resultof biteshasbeenreported. Fowlerreports thatcamelidswith rabiesare unableto regurgitateor spewstomachcontentsor saliva.

uRabiesvirus iswidelydistributedin tissuesof rabidanimals, and tissuesand productsfrom a rabidanimalshouldnotbe usedfor human or animalconsumptionor transplantation. Accordingto the National Associationof State Public HealthVeterinarians, pasteurizationand cookingwillinactivaterabiesvirus; therefore, inadvertentlydrinkingpasteurizedmilkor eatingthoroughlycookedanimalproductsdoesnotconstitutea rabiesexposure.

PREVENTIONuThereare severalbrandsof killedrabiesvaccine labeledfor sheepover 3 monthsof age. Defensor-3® (Zoetis) and Prorab-1® (Intervet) require2 ml IM, with annualboosters. Imrab® (Merial, 2 ml IM or SC) islabeledfor sheepwith boosters every3 years, afterthe initial1 yearbooster. No vaccinesare approvedfor goatsor camelids. Modifiedlive vaccinesshouldnotbe usedin anyof thesespecies.

uOfficialguidelinessaythatexposedunvaccinatedlivestockshouldbe euthanizedor slaughteredimmediately. Ifthe animalisnoteuthanized, itsbitewoundsshouldbe cleanedand disinfectedimmediatelyand itshouldbe observedand confinedon a caseby-case basisfor 6 months. Postexposurevaccinationof exposedlivestockhasbeenrecommendedin Texas and appearsto be generallyeffective. Vaccinationshouldbe repeatedin the 3rd and 8th weeks of the isolationperiod. Thisapproachisnotconsideredin the National Associationof State Public HealthVeterinariansCompendiumof RabiesPreventionand Control and maynotbe permittedby public healthofficialsin allstates.

ConclusionsuRabiesisa neurologicaldiseaseof mammalsthatisalmostinvariablyfatalonce the clinicalsignsdevelop. Allmammalsare susceptibleto rabies. Thereare manystrainsof the rabiesvirus; eachstrainismaintainedin particularreservoirhost(s). Importantmaintenancehostsinclude membersof the Canidae(dogs, jackals, coyotes, wolves, foxesand raccoondogs), Mustelidae(skunks, martens, weaselsand stoats), Viverridae(mongoosesand meerkats), and Procyonidae(raccoons), and the orderChiroptera(bats). Cat-adaptedrabiesvariantshavenotbeenseen, althoughcatsare ofteninfectedwith rabiesvirusesfrom otherhosts, and theycan readilytransmitthe virus. The importantreservoirhostsvarywith the area. In North America, maintenancehostsfor rabiesvirus include insectivorousbats, stripedskunks(Mephitismephitis), raccoons(Procyonlotor) coyotes (Canislatrans) and variousspeciesof foxes. Redfoxes(Vulpesvulpes), insectivorousbats, wolvesand raccoondogs (Nyctereutesprocyonoides) appearto be importanthostsin Europe. The canine rabiesvariantiswellcontrolledin the U.S., Canada and Europe, and itmayno longerbe circulatingor circulatesonlyatlowlevelsin some areas.

ReferencesuFowler, M.E.: Medicine and Surgeryof Camelids. 3rd edition. AmesIA, Wiley-Blackwell, 2010. National Associationof State Public HealthVeterinariansCompendiumof RabiesPreventionand ControluNational Associationof State Public HealthVeterinariansCompendiumof RabiesPreventionand ControluPugh, D.G.: Sheep& GoatMedicine, 2nd edition. Philadelphia PA, Saunders/Elsevier, 2011.uSmith, M.C. and Sherman, D.M.: GoatMedicine. 2nd edition. AmesIA, Wiley-Blackwell, 2009. uWilson, P .J. et al.: Evaluation of a postexposurerabiesprophylaxisprotocolfor domesticanimalsin Texas: 2000–2009. JAVMA 237:1395-1401, 2010.