CEM: An Insidious and Potentially Pervasive Disease

CEM: An Insidious and Potentially Pervasive Disease

The insidious and pervasive nature of CEM underscores the need for greatly improved biosecurity measures in facilities that engage in semen collection of stallions.

Photo: Anne M. Eberhardt/The Horse

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.

Of singular importance in preventing future CEM events in the United States or other CEM-free countries is the need for a highly reliable means of screening stallions and mares for the presence of the carrier state and sufficient monitoring to ensure the prescribed testing protocols are properly administered. Ideally, this should be an integral part of the pre-entry testing requirements implemented in the exporting country.

Experience over the years, however, has shown the need to complement pre-entry testing with additional post-entry quarantine and testing in the importing country. Had such a system not been in place in the United States, CEM would have been reintroduced multiple times, primarily through imported carrier stallions, the majority culture positive for streptomycin-sensitive strains of T. equigenitalis. This brings into question the reliability of the pre-entry testing performed on these and perhaps other imported stallions and mares.

Current pre-entry and post-entry quarantine and testing requirements for CEM, especially of stallions, are logistically burdensome and costly for owners and breeders. Accordingly, every effort should be made to develop more reliable means of detecting the carrier animal that are more sensitive, specific, and rapid than present testing procedures. The value of molecular-based tests, such as polymerase-based assays, need to be fully explored side by side with classical technologies.

CONTACT: Peter Timoney, FRCVS, PhD; 859/218-1094; ptimoney@uky.edu; Maxwell H. Gluck Equine Research Center; University of Kentucky; Lexington, Ky.
E.S. Rusty Ford; 502/564-3956, rusty1.ford@uky.edu; Equine Programs Manager; Kentucky Department of Agriculture; Frankfort, Ky.

This is an excerpt from Equine Disease Quarterly, funded by underwriters at Lloyd's, London, brokers, and their Kentucky agents.

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Equine Disease Quarterly

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