Haemophilus somnus and reproductive disease in the cow: A review.

Haemophilus somnus causes inflammatory disease in the genital tract of cows as reported in several field surveys and experimental trials. This organism can also innocuously colonize the healthy genital mucosa of the cow, which indicates its dual relationship with the host, that of pathogen and commensal. Experimental data indicate embryocidal capability of this pathogen suggesting a possible role in early embryonic death. Haemophilus somnus also causes sporadic abortions after a bacteremia in the dam. Retrograde infection of the pregnant uterus from the lower genital tract appears unlikely; however, this process can account for post-parturient endometritis. Detection of high homologous IgG(2) serum antibody titers using an ELISA test may be useful for the diagnosis of current or recent genital inflammation. Experimental laboratory data indicate that a proportion of genital strains of H. somnus are pathogenic and capable of causing thrombotic meningoencephalitis and perhaps pneumonia. In vivo testing of the pathogenicity of genital strains remains to be conducted.