'Pigeon Fever' - Corynebacterium pseudotuberculosis infection in Horses

摘要

Corynebacterium pseudotuberculosis is a gram-positive pleomorphic rod-shaped, intracellular, facultative anaerobe with worldwide distribution causing ulcerative lymphangitis, external subcutaneous abscesses, as well as internal infection in horses. InNorth America, disease is prevalent in the southwestern United States but cases of C. pseudotuberculosis infection have been reported throughout the USA. Infection has been reported in sheep, goats, cattle, buffalo, camelids, equids and humans. Corynebacterium pseudotuberculosis grows well at 36 °C on blood agar in 24 to 48 hours, and it forms small, pinpoint in diameter, whitish, opaque colonies that are surrounded by a weak zone of hemolysis. Because of the high content of lipids in the bacterial cell wall, particularly corynomycolic acid, the colonies spatter in a flame and can be pushed across the agar surface. The high content of lipids may facilitate survival of the organism in macrophages.2 Two species-specific biotypes of C. pseudotuberculosis have been identified based on differences in nitrate reduction, and DMA fingerprinting techniques have revealed multiple strains.Biotypes isolated from small ruminants are nitrate negative, while those from horses are nitrate positive. From the resultof DMA studies, the terms "biovar equi" for nitrate-positive and "biovar ovis" for nitrate-negative strains were proposed. Natural cross-species transmission does not seem to occur between sheep and horses, however cattle can have infection from either biotype.