A study of some pathogenetic aspects of bovine viral diarrhea virus infection

The cytopathic (CP) TVM-2 strain of bovine viral diarrhea virus (BVDV) induced in calves a severe disease, characterized by the clinical picture which is usually reported for the acute primary infection observed under natural conditions. In contrast, the calves inoculated with a different biotype of BVDV, the non-cytopathic (NCP) New York-1 strain, remained clinically normal with the only evidence of virus replication in these calves being the recovery of the virus from their pharyngeal swabbings and blood and also the detection of specific neutralizing antibody in their serums. When calves were immunosuppressed with dexamethasone (DMS), they underwent an overt systemic disease of such a severity that in most of the cases it ended with the death of the animals. This result was obtained with either the CP and the NCP strain of BVDV. Finally, the mixed infection that was obtained in the calves with the CP and the NCP BVDV did not result in any particular unexpected pathological situation. It was speculated that the immunosuppressive activity of BVDV could be a property peculiar to certain isolates of the virus.