Identification of herd-specific bovine viral diarrhoea virus isolates from infected cattle and sheep

Thirteen pestiviruses isolated from ruminants on four different farms in Sweden were compared antigenically and genetically. On two farms, viruses were isolated from both cattle and sheep, a third farm contained only sheep and a fourth only cattle. Seven viruses were isolated from six different cattle and six viruses were isolated from five different sheep. Epitope conservation between the viruses was studied with a panel of 32 monoclonal antibodies, revealing that all of the isolates were BVDV-like. However, certain epitopes present in isolates from cattle were lost following virus transmission to sheep. In vitro amplification of the 5'-untranslated region of the 13 isolates by the polymerase chain reaction (PCR) and subsequent analyses of amplified products with restriction enzymes also indicated that all 13 isolates belong to the BVDV group of pestiviruses. A fragment of the E2 (gp53) gene of each virus was amplified by PCR and a comparison of the amplified sequence of 188 nucleotides separated the isolates into four groups each of which could be identified with a particular farm of origin. The 13 isolates were thus herd-specific rather than species-specific demonstrating that BVDV is readily transmitted between cattle and sheep.