THE DEVELOPMENT OF EARLY VS LATE-ONSET MUCOSAL DISEASE IS A CONSEQUENCE OF 2 DIFFERENT PATHOGENIC MECHANISMS

Bovine viral diarrhea (BVD) virus is the causative agent of fatal muco sal disease (MD) of cattle. Experimental induction of MD can be achiev ed by superinfection of calves persistently viremic with a noncytopath ic (ncp) BVD virus using an antigenically similar cytopathic (cp) BVD virus. Here we describe the characterisation of BVD viruses isolated f rom three cases of experimentally induced MD. One animal developed cli nical symptoms two weeks after superinfection (early onset MD), while the onset of disease in the other two cases occurred with a delay of m onths (Late onset MD). Antigenic characterisation of the viruses was p erformed using a panel of monoclonal antibodies against the E2 glycopr otein. For genetic analysis, RT-PCR was applied to amplify specific in sertions and duplications in the NS2-3 genomic region of the cp BVD vi ruses. In addition, these amplicons and fragments of the viral E2 gene s were sequenced. The results showed that in the case of early onset M D the cp BVD virus isolated after begin of disease was identical to th e one used for superinfection. In contrast, the cp BVD viruses isolate d from the two animals with late onset MD were obviously the result of genetic recombinations between the persistent ncp and the superinfect ing cp BVD viruses. We conclude that early, and late onset MD are the consequence of different pathogenic mechanisms.