Serological characterization of viruses isolated from experimental mucosal disease.

Four cattle persistently infected with non-cytopathogenic bovine viral diarrhoea-mucosal disease (BVD-MD) virus and 3 normal controls were challenge exposed to cytopathogenic BVD-MD viruses that are antigenically different from the persistent viruses. Two of the persistently infected cattle developed mucosal disease and became moribund on postinoculation days (PID) 28 and 14, respectively; one developed severe and chronic diarrhoea and became moribund on PID 32; and the other remained healthy until the end of the experiment (PID 150). All control cattle showed transient fever, but no diarrhoea, and recovered from infection. Cytopathogenic viruses were isolated from blood of all cattle early in infection (PID 5-10) and from carcasses at necropsy. The former viruses were antigenically identical with the challenge viruses. On the other hand, the antigenicity of the cytopathogenic viruses isolated from carcasses at necropsy were different from that of the challenge viruses but similar to that of the non-cytopathogenic persistent viruses. Three of 4 persistently infected cattle, but not the calf which became moribund on PID 14, produced serum neutralizing (SN) antibodies to the challenge viruses, but not to the persistent viruses and the cytopathogenic viruses isolated from carcasses at necropsy. Control cattle produced SN antibodies to both the challenge and persistent viruses.