Abstract
A total of 266 calves, 154 from areas with a history of the outbreaks of congenital anomalies caused by bovine viral diarrhea-mucosal disease (BVD-MD) virus and 112 from a clean area, were examined for persistent infection with BVD-MD virus. Non-cytopathogenic BVD-MD virus was isolated from sera and leukocytes obtained from 18 calves in the epidemic areas. The second blood samples were collected from 13 of 18 calves positive for virus isolation 1 to 2 months after the initial sampling, and the virus was again isolated from 12 calves, indicating that they were persistently infected with BVD-MD virus. Viral titers in sera and leukocytes of persistently infected calves ranged between 104.0 and 106.1 TCID50/ml. None of persistently infected calves has serum neutralizing antibody to BVD-MD virus. No persistently infected calves were found in the clean area. Antigenic properties of the viruses isolated from persistently infected calves were identical one another, but different from those of the No. 12, Nose and T-20 strains of BVD-MD virus, that had been isolated previously in Japan.
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