ANTIGENIC DIVERSITY OF BOVINE VIRAL DIARRHEA VIRAL ISOLATES CONTRADICTS THE CONCEPT OF HERD SPECIFIC STRAIN

In the epidemiology of bovine viral diarrhoea (BVD), immunotolerant - persistently infected animals (IPI) appear to be major sources of cont amination. These animals produce large quantities of replicating virus and have therefore been proposed as being responsible for generating antigenic variability. However, limited studies have failed to detect antigenic or genetic changes in viruses isolated at different times fr om IPI. An hypothesis is that the immunotolerance of IPI against their homologous strain is accompanied by immune elimination of antigenic v ariants. The presence of an IPI in a herd could therefore limit antige nic variation, eventually leading to the existence of herd specific st rains. To verify this hypothesis we characterized, against a panel of monoclonal antibodies, 37 BVD virus strains isolated from IPI of 12 he rds in Eastern Belgium. Intra-herd antigenic variation was compared to inter-herd variation. Antigenic variation within herds was found to b e surprisingly high but, nevertheless, significantly lower than variat ion between herds.