No abstract

A model is described for the validation of vaccines designed to protect the bovine fetus from bovine viral diarrhoea virus (BVDV). The fetopathic nature of the challenge strain of virus was confirmed and the method used to test a commercial vaccine (Bovidec) developed from a Compton prototype. Heifers were vaccinated two or three times about the time of impregnation and challenged when they were between 25 and 80 days of gestation. There was no evidence of a viraemia in the heifers after the challenge, or of infection with BVDV of 13 liveborn calves or two aborted fetuses.

Flow cytometry and two-colour immunofluorescence were used to detect cytoplasmic bovine viral diarrhoea virus (BVDV) antigen in ieukocytes from viraemic cattle. Monoclonal antibody to the p80 protein of BVDV, a non-structural viral antigen, was used to identify the subpopulations of leukocytes in which viral protein synthesis had occurred. Viral antigen was detected in 23 % of peripheral blood mononuclear cells. Monocytes were found to have the highest frequency of infection (35 %). A higher proportion ofCD2 + T cells (23 %) were infected, compared with B cells (11%) or WC1 + y6 T cells (11%). No significant differences in percentages of different leukocyte subpopulations in blood were detected in persistently viraemic animals compared with controls.