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Animal and Plant Health Inspection Service
U.S. Department of Agriculture
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Contagious Equine Metritis (CEM)

Contagious Equine Metritis (CEM) is a venereal disease caused by the bacteria, Taylorella equigenitalis affecting only the equine species. It can have significant impacts on reproduction.  Treatment of CEM is usually successful.  CEM has not been shown to be zoonotic.  The United States is considered CEM free and therefore it is a Foreign Animal Disease reportable at both the Federal and State level.  Horses imported to the United States must meet certain import criteria or undergo CEM quarantine procedures at an approved facility to demonstrate freedom of CEM.

Prevention is based on screening of animals from endemic areas (in other words breeding only known negative animals) and proper precautions during breeding (biosecurity) to minimize contamination or transmission. There is no vaccine available. 

CEM is transmitted primarily through live cover breeding; with stallions as the major source of disease spread. Infection can occur during artificial insemination or be introduced via contaminated breeding or other equipment (fomites).

Stallions show no signs of disease and serve as carrier animals for spreading CEM.  Once the bacteria is introduced to a mare, clinical signs will usually appear 10 -14 days later. Clinical signs in mares may include:

  • Vaginal discharge in up to 40% of affected mares
  • Infertility
  • Abortion
In some cases mares may become carriers of the organism.  Foals born to infected/carrier mares may also become long term carriers of the organism.
Treatment consists of thorough washing of the external genitalia in stallions and mares using a disinfectant soap (e.g.  2% Clorhexidine) followed by thorough rinsing and application of a topical antibiotic (e.g. nitrofurazone or silver sulfadiazine). These steps are repeated for five consecutive days. Most horses will respond very well to a single series of treatment, however some may need retreatment. Stallions and mares from CEM affected countries are required to undergo CEM-quarantine upon arrival which includes testing for and treatment of CEM.

  1. It is recommended that active breeding stallions be cultured negative for Taylorella equigenitalis annually before entering the breeding shed.

  2. Maintain accurate and up to date breeding records including breeding date and stallion used to ensure quick identification of infection source and to limit spread.
  3. If you mares are exhibiting poor reproductive performance or have symptoms of CEM contact your local veterinarian.

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