CEM Outbreak Update
Contagious Equine Metritis (CEM), a highly transmissible venereal disease of horses, has recently returned to the United States. The outbreak has caused widespread concern that this previously eradicated disease will again become endemic in the US horse population. Although non-fatal and readily treatable, the disease is serious because of its negative effects on reproductive health and efficiency of broodmares, and the economic ramifications of such losses.
The disease was first described in England in 1977, and made its way to the United States by the spring of 1978, where it caused the US horse industry economic losses in the millions. The disease was eradicated from this country by the following year, although it remains endemic in several other countries.
CEM is a bacterial disease caused by Taylorella equigenitalis. Infected mares may develop a significant milky vaginal discharge within 2 weeks of breeding, and commonly do not become pregnant. Clinical signs are not seen in stallions, which makes accidental transmission of the disease quite easy. The bacteria lives on the skin of the stallion's external genitalia, where it can be transmitted to a mare during live cover, or included with semen collected for artificial insemination. Foals conceived by mares who are infected at that breeding can become chronically infected carriers.
CEM is diagnosed by blood testing and culture of the reproductive tract. Treatment involves cleaning and topical treatment of the external genitalia and systemic antibiotic therapy. Treatment is usually very successful, although more than one course of treatment may be needed in some horses.
United States import regulations require all sexually intact horses older than 731 days to be tested for CEM at an approved facility. Additionally, all semen shipments being frozen for export must be tested. This practice of testing semen led to the identification of the first known infected stallion in December 2008. Without such surveillance programs, it may have been much longer before the outbreak was discovered.
The original source of the disease in the US is not known, but transmission between stallions housed at the same farm was responsible for many additional infected animals. The disease most likely arrived in the US during 2005 or earlier, and then was transmitted from the infected stallion via contaminated semen collection equipment. At this time over 100 exposed stallions and 600 exposed mares in 45 states have been identified, quarantined, and subjected to testing. New York State is among those affected by the CEM outbreak, with 10 affected mares and 1 stallion.
Although some of the infected horses have been successfully treated and released from quarantine, the coast is not clear. There may still be undiagnosed infected horses in our breeding population. In order to avoid the serious economic losses associated with this disease, we must all work to avoid its spread. Practice good hygiene in the breeding shed: wear gloves, wash hands, clean and disinfect all collection equipment, use disposable plastic liners for wash buckets and insemination equipment. Find out the CEM status of prospective stallions or mares before accepting into your breeding program. Monitor mares for post-breeding discharge, and have any suspicious cases evaluated by a veterinarian.
