Clinical findings and pathological changes in Histophilus ovis infections of sheep

The Gram-negative pleomorphic bacterium Histophilus ovis was incriminated as the cause of natural cases of epididymitis in rams, polyarthritis in lambs, mastitis and abortion in ewes. Epididymitis was sporadic in occurrence, unilateral in distribution and varied from acute to chronic in degree. Polyarthritis affected recently born lambs and resulted in acute lameness and subsequent debility. Mastitis was rare in occurrence, unilateral in distribution, acute and gangrenous in type. Abortion was also rare and manifested by a specific haemorrhagic placentitis. These four conditions were reproduced experimentally. The clinical, pathological and histopathological changes associated with field and experimental cases are described.