Mucosal disease of cattle: a late sequel to fetal infection.

The introduction of a heifer which was persistently infected with bovine virus diarrhoea-mucosal disease virus into groups of pregnant cattle resulted in abortion, neonatal death, persistent infection and, subsequently, mucosal disease in the surviving progeny. Cattle affected with mucosal disease were invariably seronegative at the time of investigation and subsequent cases occurred only in calves previously identified as seronegative and persistently infected. The detection of virus antigen by immunofluorescent staining of cells obtained from the nasopharynx was shown to be an efficient and rapid method for identifying persistently infected cattle, correlating perfectly with virus isolation.