The disease is Contagious Equine Metritis or CEM and was assumed to have been eliminated from the United States until just recently. There have been many stories in the media over the past few weeks about CEM because there are now more than 370 horses in 42 states under federal quarantine, and the numbers are still climbing.

CEM affects only equids (horses, donkeys, etc.) and is not transmittable to humans or other farm animals. It is caused by the bacterium Taylorella equigenitalis.

This is a serious disease because it is highly contagious. It is difficult to detect and, therefore, to control. The bacteria lives in and on the reproductive tract and is a reproductive tract associated infection. Pleasure horses and all non-breeding horses are not at risk of being infected.

It is assumed to be primarily a venereal disease. The most likely route of spread in this current outbreak was the use of contaminated breeding equipment for artificial insemination and/or hands which were contaminated with the organism.

Initial exposure to the disease usually results in infertility. An infected mare may fail to conceive or she may spontaneously abort. Abortions related to CEM are considered rare; however, there has been one fully documented case.

Foals delivered by infected mares may become infected as they pass through the birth canal.

Stallions on the other hand exhibit no clinical signs but can carry the CEM bacteria on their external genitalia for years without ever developing antibodies in their blood.

If this current situation leads to CEM becoming established in the United States, the horse industry would suffer great economic losses. Already, Canada has placed restrictions on the importation of equines, equine semen, and equine embryos originating from specific areas and regions of the United States.

In Oklahoma, the State Veterinarian and their personnel are working with federal veterinarians to keep the Oklahoma horse population free of this disease. Should you or your veterinarian have further questions about regulations on CEM, more information is available through the State Veterinarian’s office.

If you are concerned about your breeding horses, your veterinarian or veterinarians at OSU’s Boren Veterinary Medical Teaching Hospital, can obtain the proper culture samples needed for a diagnosis. There are special requirements for sampling and for culturing this bacterium and these must be followed to achieve reliable results.

Treatments have been published for mares and stallions, however, all known infected horses and quarantined suspects must be placed under U.S. Department of Agriculture (USDA) regulated quarantine since this is a federally reportable disease. Therefore, all treatments and follow-up cultures must follow the prescribed protocol and oversight of the State Veterinarian office in conjunction with the USDA.
This column is provided by the faculty of the OSU Boren Veterinary Medical Teaching Hospital. The large volume of questions does not allow us to directly respond to specific email questions so please watch for your answer in the column. Email your questions for the column to This e-mail address is being protected from spambots. You need JavaScript enabled to view it and watch for your answer.

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