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Contagious equine metritis (CEM)

What is CEM?

Contagious equine metritis is a highly contagious venereal disease of horses. Infected stallions do not show clinical signs but can spread the infection to mares. Infected mares show variable clinical signs ranging from none to a severe and purulent inflammation of the uterus lining.

CEM is caused by a bacterium called Taylorella equigenitalis, often referred to as CEMO (contagious equine metritis organism).

There are two strains of T. equigenitalis. One is sensitive to streptomycin while the other is not.

Both strains are capable of producing epidemic venereal disease in susceptible mares. The second taylorella, T. asinigenitalis, was isolated from donkeys in the USA in the late 1990s.

CEM in the UK

CEM was first reported in England in 1977. Since then the disease has occurred in many countries. Suspicion of CEMO infection must be reported to Defra. The last recorded incident confirmed in Great Britain was in 2005. In recent years confirmed cases in Britain have been confined to non-thoroughbred horses, mainly involving or resulting from imported warmbloods.