Newsdate: March 12, 2025 11:30 am
Location: WASHINGTON, DC

Contagious equine metritis (CEM) is a venereal disease of horses caused by the bacteria Taylorella equigenitalis. It can impact fertility in both mares and stallions. The United States is considered to be CEM-free. Therefore, CEM is a foreign animal disease that is reportable at both the Federal and State level. The U.S. horse industry could suffer significant economic losses if the disease became established here.

Mare and foal in green pasture.

Latest update from the USDA details the spread of the disease from pony stallions on a Florida facility to horses of other breeds around USA.
© 2016 by kyslynskaha New window.

CEM is spread during breeding or through contact with contaminated objects. It is highly contagious among horses and can be difficult to detect and control. Signs of illness in infected mares may not be obvious, and stallions carry the bacteria without showing any signs at all. In some cases, mares may also become carriers. Foals born to infected/carrier mares can also become long-term carriers of the bacteria.

Signs in mares may include

• Mild to heavy discharge from the vulva resulting from inflammation of the uterus 10 to 14 days post breeding
• Return to estrus after a shortened cycle
• Presence of lesions in the uterus

Stallions are asymptomatic and the disease is usually identified only after several mares become infected after being bred to the same stallion.

CEM has been detected sporadically in the United States, most recently in 2024. USDA oversees quarantine, testing, and treatment programs for CEM. We have eradicated the disease from the U.S. equine population after each previous detection and are responding to the current incident.

As of 3/10/2025:  Total of 52 cases, including 18 domestic ponies (2 stallions, 1 mare, 15 geldings), 18 riding horses of various breeds (all geldings), and 16 draft horses (all geldings) confirmed Taylorella equigenitalis-positive and connected to a single farm in Orange County, Florida.  Forty-one (41) of the positive horses are located on the index farm in Florida and 11 positive geldings are trace outs from the index farm which have been quarantined on 5 other farms in Florida, 1 farm in Iowa, 1 farm in Maine, 1 farm in Maryland, 1 farm in North Carolina, and 1 farm in South Carolina.

Veterinarians work with State or Federal animal health officials to test any horse suspected of having CEM or any horse exposed to a CEM-positive animal. You may also need to test for CEM to meet requirements for exporting horses, semen, or embryos to another country or as part of a routine breeding soundness examination. There are three ways to test for CEM: bacterial culture, blood testing, and test breeding.

Bacterial culture tests look for the bacteria that cause CEM. Veterinarians collect swabs and send them to approved laboratories. They require special handling and must be processed within 48 hours of collection. It takes 7 days to get a result. Typically, the veterinarians will collect three sets of swabs for culturing during a 7- to 12-day period.

Blood testing looks for an immune response to CEM, which helps determine if a horse has recently been exposed to the disease. This complement fixation test can only be used in mares because stallions do not develop an immune response to CEM.

Test breeding is used to detect CEM in stallions under certain circumstances. Test breeding is not normally required to export stallions or semen to another country. Mares are tested with bacterial culture and blood tests.

Report Signs of Animal Disease

Producers or owners who suspect an animal disease should contact their veterinarian to evaluate the animal or herd. Find an accredited veterinarian.
Animal health professionals (veterinarians; diagnostic laboratories; public health, zoo, or wildlife personnel; and others) report diagnosed or suspected cases of nationally listed reportable animal diseases to APHIS Area Veterinarians in Charge and to the State animal health official as applicable under State reporting regulations.

Animal health officials investigate each detection to identify, test, and treat all infected or exposed horses. Affected horses are quarantined and treated with antimicrobials to eliminate T. equigenitalis. They are retested and not cleared for release from quarantine until results are negative. After treatment, fertility appears to return to normal in recovered horses.

Treatment is performed in quarantine under the supervision of regulatory animal health officials. Personnel thoroughly wash the external genitalia in stallions and mares using a disinfectant soap (for example, 2% Chlorhexidine). After thoroughly rinsing the area, they apply a topical antibiotic (for example, nitrofurazone or silver sulfadiazine). Steps need to be repeated for 5 consecutive days. Most horses respond very well to one 5-day treatment; however, some may need to be retreated.

Press release by USDA Animal And Plant Health Inspection Service