Histophilus

Histophilus is a genus of Gram-negative bacteria belonging to the Pasteurellaceae family. The type species is Histophilus somni. Historically, Histophilus somni was classified as Haemophilus somnus, but genetic and phenotypic studies led to its reclassification into a new genus. These bacteria are facultative anaerobes and are commonly found as commensal organisms in the respiratory and reproductive tracts of a variety of animals, particularly cattle.

Histophilus somni is well-known for its role as a significant pathogen in livestock. It is a primary cause of infectious bovine keratoconjunctivitis, commonly known as pinkeye, which affects cattle worldwide and can lead to blindness and economic losses. Additionally, H. somni is implicated in a complex of diseases in cattle known as the "histophilosis complex" or "thromboembolic meningoencephalitis" (TME). This complex can manifest as respiratory disease, reproductive failure, and neurological signs, including fever, depression, incoordination, and paralysis.

The pathogenesis of Histophilus infections is often associated with its ability to induce inflammation and damage to host tissues. It can adhere to epithelial cells and evade the host immune system. Diagnosis typically involves isolation and identification of the bacteria from clinical samples, such as nasal swabs, eye swabs, or tissues from affected animals. Treatment usually involves antibiotics, and prevention strategies include vaccination and good husbandry practices.