Akabane disease in cattle: congenital abnormalities caused by viral infection. Experimental disease.

Nonpurulent encephalomyelitis and polymyositis were primary lesions of cattle and goats experimentally infected with Akabane virus. Two caprine fetuses, two months old, were infected placentally and examined 11 days after inoculation; twin caprine fetuses, three months old, were inoculated intramuscularly through the dam's uterus and examined nine days after inoculation. Both lesions were seen in each fetus. Reactive proliferation of immature endothelial cells was a significant encephalitic change. Myositic changes included parenchymal degeneration and cell infiltration in fetuses in the myotubule phase and the beginning of the myofiber phase. Only nonpurulent encephalomyelitis was seen in six calves 14 days to one year old, inoculated intracerebrally and examined six to 47 days after inoculation. Nerve-cell degeneration, neurological mobilization, and perivascular cuffs were typical encephalitic changes in the calves. Five fetuses were infected transplacentally and had polymyositis alone. The four bovine fetuses, two to six months old, were examined nine to 18 days after inoculation, and one caprine fetus, one month old, was examined 11 days after inoculation. Neither encephalomyelitis nor polymyositis was seen in four calves under one year old that were inoculated intravenously.