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.
Quarantined horse isolated in stall.
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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.
Stallions show no signs of infection and become disease carriers. Mares typically clear infection without treatment but can also become carriers.
In mares, symptoms usually appear 10–14 days after infection and include:
- Vaginal discharge (in up to 40 percent of affected mares)
- Infertility
- Abortion
CEM has been 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.
Controlling Contagious Equine Metritis
May 2024
Case Count as of 6/27/2024: Two pony stallions, one pony mare, and one pony gelding on a single premises in Orange County, Florida, have been confirmed positive for Taylorella equigenitalis.
On May 23, 2024, the National Veterinary Services Laboratories (NVSL) in Ames, Iowa, reported confirmation by bacterial culture a positive case of Taylorella equigenitalis, the causative agent of contagious equine metritis (CEM), in an 11-year-old domestic pony mare in central Florida. The mare had been bred by live cover on May 10th to a 3-year-old pony stallion. After breeding, the mare had retained free fluid in her uterus and was treated by uterine lavage on May 13th. The uterine fluid was collected and sent for routine bacterial culture, which ultimately yielded the confirmed positive results for T. equigenitalis.
On May 31, 2024, NVSL confirmed the 3-year-old pony stallion positive for T. equigenitalis on bacterial culture. Banked serum samples were used to conduct pre- and post-exposure complement fixation testing (CFT) on the positive pony mare which confirm the pony stallion as the source of her infection.
On June 12, 2024, NVSL confirmed a 6-year-old pony stallion on the index premises in Florida as positive for T. equigenitalis by bacterial culture. This stallion and the first positive stallion were collected using shared semen collection equipment one day apart in May 2024.
On June 27, 2024, NVSL confirmed a 6-year-old pony gelding on the index premises in Florida as positive for T. equigenitalis by bacterial culture. The gelding is the turn-out companion of the 3-year-old infected pony stallion and was likely exposed through routine sheath cleaning practices on the farm.
All 4 affected ponies are being held under state quarantine in Florida. The affected mare and both affected stallions have completed treatment for T. equigenitalis and will wait 21 days before they undergo retesting. The affected gelding is being scheduled for treatment. There are a total of 35 ponies on the premises (4 stallions, 18 geldings, 13 mares). Eight directly exposed ponies on the premises (2 stallions, 4 mares, 2 geldings) have been sampled for testing at NVSL. One mare has completed testing with all negative results and the other 7 exposed ponies have results pending.
The first positive stallion has been traced back to a farm of origin in Polk County, Missouri, where he was foaled in 2021 and remained until August 2023. His dam, a pony mare, is the only potentially exposed horse on the premises and is currently undergoing testing. The second positive stallion has been traced back to a farm of origin in Gallatin County, Kentucky, where he was born into an owned, but essentially feral herd of about a dozen domestic ponies and donkeys which were dispersed in 2022. Traceback and epidemiological investigation is ongoing and additional updates will be posted as they become available.
Genomic sequencing of the Taylorella equigenitalis isolates from this incident have indicated close correlation between the infected ponies on the index farm in Florida. The isolates do not match any T. equigenitalis isolates from previous U.S. outbreaks. The current isolates fall within the same clade as two previously obtained international isolates, but they are not closely related.
Press release by USDA