Histophilus somni

Unique Features, Pathogenesis and Lesions Update

Abstract

Haemophilus somnus has recently been renamed Histophilus somni and it has been proposed this name also includes Haemophilus agni and Histophilus ovis. The organism occurs in all management systems of the cattle industry, but the most serious losses occur in beef feedlots where co-mingling of cattle from numerous farms occurs. The disease in feedlots most often manifests as the septicemic form and is known as the Histophilus somni disease complex (HSDC), but pleuritis and bronchopneumonia are two other very common causes of disease or death. Despite effective vaccines and antibiotics,  sudden losses from 30 to 90 days after arrival at feedlots continue to occur in significant numbers, especially in certain geographical areas ofNorth America and Europe. There undoubtedly remains much to be learned about predisposing factors to histophilosis and how this organism avoids natural body defense mechanisms.