Congenital abnormalities in newborn lambs after infection of pregnant sheep with Akabane virus

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Abstract
Akabane virus (a Bunyavirus) was associated with epizootics of congenital deformities in cattle, sheep and goats. Experimental studies using mouse-adapted virus inoculated i.v. into pregnant sheep gave an inapparent infection. Neutralizing antibodies were detected on day 5, and peaks in the titer were seen at days 10 and 48. Ewes infected at day 30-36 of pregnancy produced 5 (31% incidence) deformed lambs. Sera from 4 of these possessed neutralizing antibodies to Akabane virus before ingesting colostrum. Two lambs had arthrogryposis, hydranencephaly, kyphosis, scoliosis and brachygnathia; 1 had micrencephaly; and the other 2 had porencephaly. The 2 lambs with arthrogryposis and hydranencephaly had extensive lesions in other tissues. In the spinal cord there was a marked decrease in the number of ventral horn neurons and a depletion of myelin. Skeletal muscles showed marked atrophy. The medulla of the thymus possessed large Hassall''s corpuscles and a reduced number of thymocytes in the cortex. Apparently the pathogenic effects of Akabane virus are related to the gestational age (30-36 days) at which the fetus is infected. Akabane virus can now be included in the growing list of teratogenic viruses and provides an interesting system for studying such congenital diseases.