Bovine viral diarrhoea virus antigenic diversity: impact on disease and vaccination programmes.

Bovine viral diarrhoea virus (BVDV) infections in cattle are associated with a variety or "diverse" clinical forms. These include digestive tract, respiratory, foetal (varied, dependent on foetal age), haemorrhagic and systemic diseases such as mucosal disease, and immunosuppression and inapparent infections. The BVDV isolates themselves are "diverse" with genotype differences based on nucleotide sequences, antigenic variability and biotypes (presence or absence of cytopathology in cell culture). Two predominant genotypes are present in the US, BVDV1 and BVDV2. There are subtypes of BVDV1, namely BVDV1a and BVDV1b. Examination of BVDV isolates from cattle derived from diagnostic laboratory submissions indicates that BVDV1b subtype isolates were as prevalent if not more prevalent than BVDV1a isolates. There was an almost equal distribution of BVDV1b and BVDV1a isolates from cattle with history of respiratory disease, and more isolates, 6 versus 2, of BVDV1b than for BVDV1a in necropsy cases of pneumonia. There were significant antibody titre differences in sera from calves receiving modified live virus vaccines containing BVDV1a, with the BVDV1b antibody titres being significantly lower. A survey of the US licensed and marketed BVDV vaccines indicates that only one vaccine contains BVDV1b with the others containing BVDV1a or undesignated BVDV1.