Akabane virus infection in the pregnant ewe. 2. Pathology of the foetus

A strain of Akabane virus (CSIRO 16) isolated from Culicoides brevitarsis was given three different passage treatments in the laboratory and then inoculated into ewes that were 32 to 36 days pregnant. The foetuses from these ewes were examined between the 69th and 106th days of gestation. The 39 infected ewes produced 55 foetuses of which 44 (80%) had severe developmental defects. Arthrogryposis and agenesis of the brain or hydranencephaly, were present in 43 of the foetuses. Other gross defects affecting variable proportions of foetuses were porencephaly, brachygnathism, scoliosis, hypoplasia of the lungs and agenesis or hypoplasia of the spinal cord. Histopathological findings covered a wide spectrum of defects that have previously been considered to occur over an extended range of foetal ages. These defects included skeletal muscle atrophy and degeneration, and in the brain, particularly in the cerebrum, cystic areas and malacia, general oedema, subependymal gliosis, perivascular cuffing and mineralised plaques. Similar lesions were seen in the pons and cerebellum. Extensive lesions, with and without inflammation were seen in the spinal cord.