Evidence for biotype-specific effects of bovine viral diarrhoea virus on biological responses in acutely infected calves.

The relationship between the two biotypes of bovine viral diarrhoea virus (BVDV) and the biological responses they induce was studied in 3- to 6-month-old calves inoculated intranasally with a homologous pair of non-cytopathic and cytopathic strains. Marked differences in virological and serological events occurred following exposure to a specific BVDV strain. The non-cytopathic biotype was frequently recovered from nasal secretions and blood cells during the first 28 days post-inoculation whereas the cytopathic counterpart was detected infrequently in nasopharyngeal swabs only. There was no correlation of the recovery of infectious virus in vivo with the biotype-specific neutralizing humoral immune response. Furthermore, seroconversion did not correlate with resistance to reinfection as judged by the transient viraemia and/or shedding of virus observed in a challenge experiment.