California Department of Food and Agriculture

Contagious Equine Metritis Information

March 19, 2013

California Department of Food and Agriculture, Animal Health Branch veterinarians are currently investigating Contagious Equine Metritis (CEM) infections in California. In January 2013, a private practitioner working up a 17 year old Lusitano mare for history of infertility, submitted samples to the California Animal Health and Food Safety Laboratory (CAHFS). The suspect sample cultured by CAHFS was confirmed positive for Taylorella equigenitalis the organism responsible for the foreign animal disease, CEM. During the 2012 breeding season, the index mare was bred by live cover and artificial insemination to a 20 year old Lusitano Stallion who was imported from Brazil in 2003. Testing of the Lusitano stallion confirmed CEM infection. Both mare and stallion are under quarantine for treatment and additional testing to ensure elimination of the organism.

Epidemiologic investigation requires identification of any mares or stallions potentially exposed to the positive stallion. During the 2012 breeding season, the positive Lusitano stallion was collected at a stallion station in California. Exposed stallion is defined as any stallion collected at the stallion station seven (7) days prior to the positive stallion and seven (7) days after the positive stallion. An exposed mare is defined as any mare bred by live cover or artificial insemination to the positive stallion. The initial epidemiologic investigation identified 11 exposed stallions and one exposed mare.

In addition, to the index mare and Lusitano stallion, one exposed stallion and one exposed mare have been confirmed positive for CEM and are under quarantine for treatment and additional testing. The new positive stallion is a domestic 25- year old Lipizzaner stallion that had semen collected at the same facility as the positive Lusitano stallion in 2012. The new positive mare is a domestic 13 year old Andalusian cross that was bred to the positive Lusitano by AI in 2012 and is currently pregnant. All positive animals are under quarantine for treatment and additional testing. The National Veterinary Services Laboratory has determined that the strain of the bacterium from all four positive horses does not match any T. equigenitalis strains ever found in the United States, indicating these cases are not related to any previous U.S. cases of CEM.

Nine (9) exposed stallions in California are under quarantine with regulatory testing protocols underway. One exposed stallion traced to Texas is under quarantine in Texas for testing at this time. Exposed stallion testing protocols include two sets of cultures and breeding of two qualified negative test mares. The test mares will be cultured on days 3, 6, 9 and 28 post breeding and bled for compliment fixation testing on day 21 post breeding. Stallions will be released from quarantine with negative pre breeding cultures, negative test mare cultures and negative test mare compliment fixation test. To date, all stallions have at least one set of negative cultures. Three exposed stallions have completed test breeding and are awaiting mare culture results. Six exposed stallions await test breeding. A thorough epidemiologic and diagnostic investigation is underway.

Disease Background

Contagious Equine Metritis (CEM) is a highly contagious venereal foreign animal disease of horses caused by the bacteria, Taylorella equigenitalis. Transmission occurs during natural cover or artificial insemination breeding. The disease is not known to affect humans or other species of livestock.

Most cases involve non-clinical mares with a mild uterine inflammation. However, an acute infection can cause active inflammation of the endometrium that results in a mucoid vulvar discharge 10-14 days post breeding. Abortions due to CEM are rare. Mares infected during pregnancy can produce subclinical carrier foals. Asymptomatic mares can be infectious and remain carriers for several months. Stallions exhibit no clinical signs but can carry the organism on their external genitalia for an extended period of time.

Carrier mares and stallions act as a reservoir of Taylorella. Undetected mares and stallions are the source of the infection for disease outbreaks. Detection of the carrier state relies on isolation of Taylorella equigenitalis from urogenital swabs of the mare and stallion. Due to the organism’s fastidious nature and slow growth characteristics, it is difficult to culture therefore requires multiple cultures over a period of one week. Serology is available to detect antibodies to CEM in mares. This test cannot be utilized in stallions, as detectable antibodies do not develop.

Mares and stallions with positive cultures for CEM can be successfully treated with appropriate antibiotics.


USDA Web Page

Contact us for more information:
California Department of Food and Agriculture
Animal Health and Food Safety Services, Animal Health Branch
1220 N Street
Sacramento, California 95814
Telephone: (916) 900-5002
Fax: (916) 900-5333
or send an email to: