bovine virus diarrhea and pi’s：牛病毒性腹泻和pi的

Bovine Virus Diarrhea and PIs,Brendan Kraus, DVMSpur Ridge Vet HospitalMarion, KS,What is BVD?,Bovine Virus Diarrhea2 Biotypes & 2 GenotypesA contagious disease transmitted in bodily fluidsCauses a wide range of clinical symptomsCause marked suppression of immune system,Biotypes of BVD (Type does not affect immune response!),CytopathicKills cells in tissue cultureArises from a virus mutationMost common strain in vaccines,NoncytopathicDoes not change culture cellsMost common biotype found in nature,Genotypes of BVD,Type 1Original strains of BVD that were isolatedIs included in all BVD vaccines *There is some cross protection with vaccines between types 1 & 2,Type 2This type was more recently discoveredHemorrhagic syndrome strainsIs included in most BVD vaccines now,BVD symptoms,70-90% of infections are subclinicalPneumoniaFeverRhinitisDiarrheaOral and GI ulcersImmune suppression,AbortionsStillbornsBirth Defects,Mycoplasma Joint,What is Persistent Infection?,A PI calf is born infected with the virusThis can happen if the dam is a PI animalThis can happen if the dam is transiently infected during pregnancy from another animal*The virus must be non-cytopathic*The calf must be infected between 40-100 days approximatelyDuring this time the calf has no immune system so it recognizes the virus as “self” and never clears itAfter this time, the calfs immune system is developed enough to fight the virus,Manifestations of Calves infected in utero,PI calf (Body does not recognize virus)Virus is always circulating in bodyMay die soon after birthMany are clinically normalThis is the natural reservoir of the virus,Infected in utero but not PI (infected around or after day 100)Congential defectsSkeletal problemsDome shaped headShortened lower jawEye abnormalitiesBrain defectsAbortionsClinically normal calvesCalves that are not killed can clear the virus and go on,PI Calves,PI calves are more likely to die than non-PI calves in the first yearPneumoniaDiarrheaPoor doerMany look and perform like a healthy calf,Pasteurella mult. Lungs,Mucosal Disease,This is Highly fatal syndrome in which the mucous membranes become ulceratedMouthStomachIntestineTeatsCoronary bands of hooves,Abomasal Ulcers,Mucosal Dz, cont,For mucosal disease to occur a PI calf (noncytopathic) must be superinfected with a cytopathic strain.The more closely related the viruses are genetically, the worse the diseaseWhen a noncytopathic virus found in nature mutates to cytopathic & the calf is exposedWhen the PI calfs own noncytopathic strain mutates,PI Calf Shedding,PI calves shed the virus their entire lifeSome periods they may shed a lot, and others not as muchVirus shed in saliva, tears, urine, feces, bloodThere is so much virus shed, that most vaccines cannot protect other cattle against a PIContinue to infect cow herds and create more PIs,PI Diagnosis,Ear Notch ElisaEar Notch ImmunohistochemistyPolymerase Chain ReactionVirus IsolationThese tests can be done at anytime in a PIs life and only need to be done once. If positive, will always be positive. If negative, can be infected with BVD but will not be a PIIf transiently infected, some tests may be positive, but the calf may need to be tested again in a month to confirm PI status,BVD Control& Prevention,Vaccination with a vaccine using Type 1 and Type 2 strainsModified live vaccine creates a stronger, more natural immunity, is cheaper, and less doses requiredNewer vaccines have label claims that if given to cow pre-breeding can successfully prevent PI in fetus,BVD Control & Prevention, cont