Level of viral antigen in blood leucocytes from cattle acutely infected with bovine viral diarrhoea virus.

Blood samples from 24 calves undergoing experimental acute infection with a non-cytopathogenic bovine viral diarrhoea virus (BVDV) were examined for viral antigen in peripheral leucocytes with an enzyme-linked immunosorbent assay (ELISA), and for presence of virus in blood plasma in a cell culture assay. With the antigen ELISA, low positive values were detected in leucocytes sampled on days 3-4 from two of eight animals inoculated intranasally, and on days 11-13 from three of 16 animals inoculated intramuscularly. From 22 of the animals, low titres of BVDV were detected in blood plasma obtained 2-9 days after inoculation. All other samples, drawn between 2 and 21 days after inoculation, were negative for viral antigen. All animals seroconverted 3-4 weeks after inoculation, some after having shown mild and transient signs of disease.