Histophilus ovis infection in sheep in Western Victoria

Organisms resembling Histophilus ovis were isolated from sheep in Western Victoria in association with synovitis, septicaemia and/or abscessation in 2 to 8 week old lambs. Histopathological lesions in these lambs were indicative of bacterial embolism with thrombosis. Similar organisms were also isolated from sheep in 2 flocks with a high neonatal mortality rate. These isolations were from vaginal swabs from the ewes, placentas and from one lamb which had meningitis, ependymitis, choroid plexitis, hepatic necrosis and focal myocarditis. The morphology, cultural characteristics and biochemical activity of the organisms are described and it is suggested that the organisms may be better classified in the genus Actinobacillus.