Morphologic lesions in type 2 BVDV infections experimentally induced by strain BVDV2-1373 recovered from a field case

Widespread outbreaks of severe acute BVDV, some associated with hemorrhagic syndrome (HS), were reported in Quebec and Ontario in 1993. These outbreak s caused significant economic hardship in infected herds. In the Ontario ou tbreak 150 dairy, 600 beef and 100 milk and grain fed veal herds were affec ted with losses estimated at $40 000-$10 000 per herd in lost animals, milk production, abortions and genetics. Fever, pneumonia, diarrhea, and sudden death occurred in all age groups of cattle. Abortions were frequently obse rved in pregnant cattle. The viruses associated with this outbreak were det ermined to be noncytopathic BVDV from the type 2 genotype. All BVDV2 associ ated with these outbreaks were noncytopathic. One of the viruses isolated f rom the Ontario outbreak, BVDV2-1373, was used to experimentally induce HS in 5-6 weeks old colostrum deprived, seronegative calves. All animals devel oped leukopenia and thrombocytopenia within 6-10 days with some developing bloody diarrhea and becoming moribund. Animals were killed for necropsy bet ween 6 and 11 days postinfection. Histopathologically lesions were similar, but more severe, to those seen early on (within first 9 days after superin fection) in animals with experimentally induced mucosal disease (MD). There were no erosions and ulcerations present in the upper digestive tract. In hemorrhages in the mucosa, virus antigen (VA) was present in macrophages of both the lamina propria and the submucosa and in basal epithelial cells. C ells containing VA were vacuolated and separated from each other. The most severe lesions observed in the digestive tract were in the Peyers patches a nd were characterized by depletion of lymphocytes and proliferation of cryp t cells resulting in crypthyperplasia. Apoptotic cells were present in cryp ts and areas of lymph follicles where viral antigen was detected. Out of th e six animals, VA was present in four animals in the pancreas, three animal s in the pituitary and in two animals in the adrenal glands. The results su ggest that the pathology resulting from acute infection with a highly virul ent noncytopathic BVDV2 differs from the pathology observed in classic muco sal disease. Published by Elsevier Science B.V.