Pathology of ovine adenovirus type 4 infection in SPF lambs: pulmonary and hepatic lesions.

Seven lambs were challenged with an aerosol of OA4 virus. Four developed mild pulmonary oedema and a sparse accumulation of mononuclear cells around blood vessels similar to results reported previously. In addition, three had focal hepatic necrosis and one of these three had a non-suppurative occlusive cholangitis and portal tract lymphangitis and thrombosis. Basophilic intranuclear IB's were identified in many necrotic hepatocytes, in lymphatic endothelial cells involved in thrombi but in only one bile duct epithelial cell. Ultrastructurally, virions with the characteristics of adenovirus were seen in hepatocytes. Although only one IB was seen in the affected biliary system there was no evidence that it was caused by an agent other than OA4. Virus was considered to infect the respiratory system directly, be swallowed to infect the alimentary system and carried, possibly within cells, via a haematogeneous and/or lymphogenous route to the liver. The effect of naturally acquired virus on sheep is unknown but it is possible that it may predispose the host to more serious infections.