Two Brazilian isolates of bovine viral diarrhea virus type 2 (BVDV-2) were inoculated in calves to evaluate their virulence and to study the pathogenesis of the infection. Previously to virus inoculation, the calves were immunossupressed with dexamethasone. Four 45 to 90-days-old calves (group A) were inoculated with isolate SV-260 (n=2) or LV-96 (n=2), and four 6 to 8-months-old calves (group B) were inoculated with isolate SV-260. Following virus inoculation, group A calves showed anorexia, depression, hyperthermia, signs of respiratory infection and profuse diarrhea, bloody in two cases. The respiratory and digestive signs progressed and the animals died or were euthanized in extremis between days 7 and 12 post-inoculation. Ulcers and erosions in the digestive tract (tongue, n=4; esophagus, n=1; rumen, n=1 and abomasum, n=3), edema of the lung (n=4) and abomasal mucosa (n=3); echimosis and suffusions in the spleen serosa (n=2), rumen, small intestine and ceccum (n=1), heart (n=1) and urinary bladder mucosa (n=1) and intestinal intussuseption (n=1) were the most prominent findings. Ulcerations and erosions accompanied by mononuclear cell infiltrates in the digestive tract mucosa and submucosa, and lymphoid depletion in lymph nodes and Peyer’s patches were frequently observed. Infectious virus was detected in several tissues and organs. Viral antigens were detected by immunohistochemistry mainly in epithelial cells of the digestive tract, in mononuclear cells of the perivascular and peribronchial spaces; in lymph node septae and capsule; and in lymphocytes and other mononuclear cells of the spleen and Peyer’s patches. Group B calves showed depression, hyperthermia, moderate signs of respiratory and digestive infection, small ulcerations in the tongue and recovered after a few days. These results demonstrate that the Brazilian BVDV-2 isolates were capable of producing an acute disease in calves upon experimental inoculation, and that the clinical and pathological consequences of the infection were more severe in young calves.
bovine viral diarrhea virus type 2; BVDV-2; experimental infection
