CEM: An Insidious and Potentially Pervasive Disease

Contagious equine metritis (CEM) gives rise to considerable concern among horse breeders in many countries.

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Ever since initial reports of its discovery in England and Ireland in 1977, contagious equine metritis (CEM) has given rise to considerable concern among horse breeders in many countries. The contagiousness of the disease in breeding populations, ability to cause widespread short-term infertility in the mare, and the occurrence of the carrier state in both stallion and mare are all concerns about CEM, one of the most internationally regulated equine diseases.

The rediscovery of CEM in the United States in December 2008 reawakened awareness and concern about the disease and led to the most extensive epidemiologic tracing and diagnostic testing of any prior CEM event in the country. Several important findings were to emerge from these investigations.

Perhaps most disturbing was that the source of CEM was traced to a Warmblood stallion imported into the United States in late 2000, which had not been detected on pre- or post-entry quarantine and testing. On retrospective analysis, the causal agent of CEM, Taylorella equigenitalis, was found to have spread to 22 stallions, one gelding, and five mares, all of which were subsequently found to be carriers of the organism.

It should be emphasized that at no time over an eight-year period have there been any reports suggestive of CEM in mares following artificial insemination with semen from these stallions. Of major concern was the circumstantial evidence implicating indirect transmission of T. equigenitalis to the 22 stallions and one gelding through the use of contaminated fomites at different semen collection centers. Collectively, these findings serve to underscore the insidious and pervasive nature of CEM and the need for greatly improved biosecurity measures in facilities that engage in semen collection of stallions

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