Pestivirus fetopathogenicity in cattle: changing sequelae with fetal maturation.

The events which followed the introduction of a heifer into a dairy herd were consistent with the animal being persistently infected with bovine diarrhoea-mucosal disease virus. Obvious damage was limited to the progeny of cows which were in the first 168 days of gestation at that time. Only fetuses up to 81 days of gestation at the putative time of introduction of infection became persistently infected in calfhood and, although they exhibited body tremor, two such calves necropsied at three months of age lacked macroscopic or microscopic lesions in the central nervous system. In contrast calves which had been more advanced in gestation, at 146 and 153 days at the time of infection, had eliminated the infection and had lesions of cerebellar dysplasia and multifocal retinal atrophy.