What is Contagious Equine Metritis?
Direct CEM import program inquiries to:
Dr. Emily Nietrzeba
Equine Staff Veterinarian
California Department of Food and Agriculture
Animal Health Branch
- Contagious Equine Metritis (CEM) is a sexually-transmitted disease of horses caused by the bacteria, Taylorella equigenitalis. Clinical signs in mares may include a mucopurulent vaginal discharge in up to 40% of affected mares, abortion and infertility. Stallions typically show no clinical signs. Both mares and stallions can become chronic CEM carriers and sources of infection for future outbreaks. The transmission rate is high with live cover breeding, but contaminated instruments and equipment may be an indirect means of infecting mares and stallions. The bacteria can also be spread in semen collected for artificial insemination. The United States is considered free of CEM; it is classified as a foreign animal disease in the U.S.
- What is the federal quarantine procedure for CEM?
- Mares and stallions (not geldings or horses under the age of 24 months) arriving in the United States at one of four ports of entry (Los Angeles, CA; Newburg, NY; Miami, FL; and Honolulu, HI) have been tested for CEM already in their country of origin. They are further tested at the port of entry for equine infectious anemia, dourine, glanders, and equine piroplasmosis. If the results are satisfactory, the horses are transported under seal to UC Davis; that is, after the completion of required testing, the horse is led into the transport trailer and a USDA agent places a numbered metal band over the door lock. Upon arrival at our CEM quarantine facility, the seal must be intact.
- What tests are available to diagnose CEM?
- There are two official validated diagnostic tests for CEM; bacterial culture and the serologic complement fixation (CF) test. Bacterial culture is the gold standard test to detect the organism from swabs collected from the genitalia of stallions and mares. Determination of a culture sample as positive or negative takes seven (7) days. The serologic CF test is used to assist in CEM diagnosis, but the value is limited to mares that have produced detectable antibodies to T. equigenitalis.
- Why is there a concern about CEM?
- CEM is a highly contagious reproductive disease. Depending on the severity and location of the infection(s), infected mares can experience temporary infertility for one or more breeding cycles. Since breeding of mares is limited to certain seasons, CEM can have a devastating effect on equine reproductive efficiency. The United States (U.S.) horse industry would suffer great economic losses if CEM were to become established in this country.
- What is done to prevent the entry of CEM into the U.S.?
- CEM is endemic in the horse populations in some countries that export horses to the U.S. The U.S. Department of Agriculture (USDA) has import requirements for CEM testing and treatment of mares and stallions over 731 days of age from those countries. Typically, stallions and mares will undergo post‐entry CEM testing and treatment at specially approved U.S. quarantine facilities before release for entry into the U.S.
- Is there a risk of introduction of CEM into the U.S.?
- Yes, there is a risk of introduction of CEM into the U.S. from horses originating in CEM‐affected countries. The USDA CEM testing protocols have successfully detected the CEM carrier state in a significant number of imported stallions and mares. All of these animals had been certified CEM‐ free based on negative pre‐export cultures on a single set of culture swabs before export to the U.S.
- What are the post‐arrival import testing requirements for a mare from a CEM‐affected country?
- Any mare over 731 days of age from a CEM‐affected country must complete the USDA post‐arrival CEM protocols. Once the mare has arrived in the approved state CEM quarantine facility, a CEM complement fixation test must be done and three (3) sets of culture specimens, at intervals, must be collected from the mucosal surfaces of the clitoral fossa and clitoral sinuses. In non‐pregnant mares, one set of specimens must include a swab from the surface of the distal cervix or endometrium. With receipt of all negative culture results, the mare must be treated for five (5) consecutive days with an ointment effective against the CEM organism. A mare may be released from state quarantine if the mare is CEM CF negative and all cultures performed on specimens taken from the mare are negative.
- Are there exemptions to the CEM post‐arrival import testing requirements for horses from a CEM‐affected country?
- Special provisions allow for the exemption of the following equids from post‐arrival import CEM testing and treatment protocols
- Wild zoo animals that are unlikely to have come in contact with domestic horses used for breeding.
- Spanish Purebred Horses imported for permanent entry from Spain.
- Thoroughbreds imported for permanent entry from France, Germany, Ireland or UK.
- Horses over 731 days imported for no more than 90 days of competition.
- Horses over 731 days of age imported for non‐competitive public exhibitions and entertainment purposes.
- What are the post‐arrival import testing requirements for a stallion from a CEM‐affected country?
- Any stallion over 731 days of age from a CEM‐affected country must complete the USDA post‐arrival CEM protocols. Once the stallion has arrived at the approved state CEM quarantine facility, one culture specimen shall be taken from each of the following sites on the stallion: the prepuce, the urethral sinus, the distal urethra, and the fossa glandis, including the diverticulum of the fossa glandis. With receipt of negative culture results, the stallion must be test bred to two (2) certified CEM‐negative test mares. Following the test breeding, the stallion must be treated for five (5) consecutive days with an ointment effective against the CEM organism. There are post‐test breeding testing protocols for the test bred mares. If all cultures and CF tests from the test bred mares are negative for CEM, the stallion has met the U.S. entry requirements and may be released from quarantine.
- Why is multiple sampling necessary for CEM quarantine testing?
- The identification of the CEM carrier animal, specifically stallions, has necessitated a multiple sampling protocol to address the challenges of CEM diagnosis. This is especially true for horses which have previously undergone treatment for the T. equigenitalis. Such animals can remain as a carrier and be difficult to detect on culture or PCR. Due to the need for multiple culture samplings, the confirmation of an animal’s freedom from the carrier state can be very time‐ consuming and costly.
- How does test breeding assist in the diagnosis of CEM?
- To maximize the chance of detecting CEM infection, stallions are required to be tested by both bacterial culture and test breeding. Test breeding will sometimes detect a T. equigenitalis infection that bacterial culturing of the stallion did not detect. Test breeding involves breeding a stallion to two (2) certified CEM‐negative mares. Following test breeding, the test mares are serially tested for CEM by bacterial culture and a serology test to determine if they are infected. It takes a minimum of thirty‐five (35) days after the test breeding to declare the stallion negative.
- Why is test breeding a requirement of import testing?
- Based on science, USDA concluded that the inherent risks of importing CEM into the U.S. can be mitigated by requiring stallions to be test bred to two mares as part of the post‐arrival quarantine and testing process. The decision was prompted by the difficulties experienced isolating the organism from heavily contaminated sampling sites, especially when dealing with streptomycin‐sensitive strains of T. equigenitalis.
- Has live cover/test breeding been proven to be an effective diagnostic tool?
- Yes. Of the twenty‐three (23) positive stallions detected during the 2009 United States CEM Outbreak investigation, three (3) stallions were confirmed by test breeding protocols. Difficulties in isolating the CEM organism from heavily contaminated sampling sites led to false negative cultures and the three (3) stallions were only confirmed positive after the live cover test breeding.
- Are there special considerations for shipping a pregnant mare?
- There are no specific welfare laws regulating transport of pregnant mares. Generally, mares should not be transported by air or over long distances if they are greater than 300 days of gestation/post service. It is recommended to ship pregnant mares between 120 days and six months of pregnancy. Mares should ideally be well settled into their foaling sites at least 4-6 weeks before the estimated due date in order to start developing immunity to local organisms.