There are at least 25 countries in the world where contagious equine metritis (CEM) exists, or has been known to exist sometime in the past, in the native equid population (meaning horses, mules, donkeys, etc.). These countries include England, Ireland, France, Germany, and other member states of the European Union. The United States is considered "free" of CEM, meaning the disease does not occur in the native equid population. However, some instances of CEM in what is considered "native" stock, as well as imported Warmblood stallions, have raised questions on whether we are doing enough to protect our animals from importing this highly contagious disease (see Viewpoint).

CEM is a highly contagious venereal infection of all equids caused by the bacterium Taylorella equigenitalis. It was first recognized as a previously undescribed disease in horses in 1977. That year, there was an outbreak of venereal disease in Thoroughbred breeding animals in the United Kingdom and Ireland. According to research published by Peter J. Timoney, FRCVS, PhD, former head of the Gluck Equine Research Center in Kentucky, since that first report in 1977, CEM has been recorded in various horse populations throughout the world, including those in many European countries, plus Japan, Australia, and North and South America.

"Contagious equine metritis continues to be the focus of considerable international concern, not only because of its potential to cause widespread, short-term infertility in broodmares, but also because of the ease with which the carrier state can be established in stallions and mares."
--Dr. Peter Timoney
"Contagious equine metritis continues to be the focus of considerable international concern, not only because of its potential to cause widespread, short-term infertility in broodmares, but also because of the ease with which the carrier state can be established in stallions and mares," reported Timoney.

CEM can cause short-term infertility in mares, frequently, but not always, associated with an endometritis and vaginal discharge. The infection rarely results in abortion. Foals born to mares infected with CEM can become infected while in the uterus (which is uncommon), and thus be contaminated with the bacterium at birth or at the time of parturition. Mares can become inapparent carriers of the bacterium, meaning they look and behave normally, but they harbor the organism in their reproductive tracts and can shed it into their environment and through breeding (naturally or by artificial insemination).

Stallions don't develop clinical signs of disease after becoming exposed to the organism that causes CEM. In the truest definition of the word, stallions don't become "infected" following exposure to Taylorella equigenitalis. They merely harbor the organism as a surface contaminant on their external genitalia.

CEM

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Past outbreaks of CEM have shown that the clinically inapparent carrier state can be established in a large percentage of exposed stallions. The stallion looks normal, but can infect the mare to which he is bred naturally or by AI. The mare then can be responsible for spreading the bacterium to other stallions or mares back at her home farm, and those horses then can spread it to other stallions and mares.

There is no vaccine against CEM, but there are ways to detect the organism's presence in the reproductive tract (where it is confined) and to rid stallions and mares of the bacterium.

Disease Basics

Spread of the Taylorella equigenitalis organism is by the venereal route, primarily through natural breeding or artificial insemination. However, the disease also can be spread through indirect, mechanical means--by contamination of barn equipment, insemination or breeding equipment, vaginal speculum, examination sleeves, or by grooms or handlers who fail to maintain proper hygiene when handling mares and stallions, especially during breeding. Timoney also mentioned the possibility of a carrier teaser stallion being a means of spreading the disease on a farm.

The disease can be spread through indirect, mechanical means--by contamination of barn equipment, insemination or breeding equipment, vaginal speculum, examination sleeves, or by grooms or handlers who fail to maintain proper hygiene when handling mares and stallions, especially during breeding.
As mentioned before, transplacental transmission of Taylorella equigenitalis can occur in pregnant mares. Timoney noted that currently there is no evidence that Taylorella equigenitalis is a free-living organism or that it is especially resistant to conventional disinfectants or various environmental factors (exposure to sunlight, heat, or cold).

The clinical response of a mare following exposure to Taylorella equigenitalis can vary from overt disease to subclinical (inapparent) infection. Disease is limited to the reproductive tract in mares, and there has been no evidence of systemic illness in affected animals.

The incubation period is from two to 12 days. Mares typically develop an odorless, grayish-white mucopurulent vulvar discharge of uterine origin. The discharge can vary in amount, and usually lasts approximately two weeks (occasionally longer).

"The discharge is associated with periods of endometritis, cervicitis, and vaginitis, and a return to estrus after a shortened diestrous period," noted Timoney. "In some mares, the extent and severity of the inflammatory response are not readily assessable unless the reproductive tract is examined with the aid of a speculum."

Whether or not the mare has outward clinical signs following infection, most will fail to conceive afterward. The infertility has been found to be short-lived, however, usually lasting only a few weeks. No long-term infertility problems have been reported in mares infected with Taylorella equigenitalis. Timoney noted that re-exposure of mares previously infected with Taylorella equigenitalis usually results in little or no clinical evidence of CEM.

"Persistence of the organism in the reproductive tract of the chronically infected mare will not, in the majority of cases, interfere with the maintenance of a normal pregnancy," he reported. "Abortion is a rare sequel to infection in the pregnant mare. In two reported cases of abortion ascribed to Taylorella equigenitalis, the bacterium was recovered not only from the placenta, but also from several sites in the aborted fetus."

Diagnosis

Diagnosis of CEM cannot be based on clinical signs alone, noted Timoney, because of similarity of the disease with other, more frequently encountered bacterial infections of the reproductive tract in mares (i.e.,Streptococcus zooepidemicus, Klebsiella pneumonia, and Pseudomonas aeruginosa). Isolation of the Taylorella equigenitalis bacterium in culture long has been regarded as the only definitive means of establishing a diagnosis of CEM in the mare or confirmation of the carrier state in the stallion, reported Timoney. He added that a recently developed polymerase chain reaction (PCR) assay for this organism might provide an equally sensitive and more rapid means of confirming infection. "The latter would be especially useful in instances where major difficulties are encountered in culturing Taylorella equigenitalis from sites heavily contaminated with other gram-negative or gram-positive bacteria, " wrote Timoney.

The sites usually sampled to culture for Taylorella equigenitalis in the mare include the uterus, cervix, clitoral sinuses, and clitoral fossa. He noted that care should be taken to use swabs that are small enough to sample the clitoral sinuses effectively.

"Endometrial/cervical swabs should be taken during early estrus," reported Timoney. "Swabbing of pregnant mares is restricted to sampling the clitoral sinuses and fossa. Vaginal exudate, if present, should also be cultured."

In stallions, swabs should be taken from the urethral fossa and sinus, distal urethra, external surface of the penis, and the prepuce. A sample of the pre-ejaculatory fluid also should be sampled. The penis should be fully extruded and erect to ensure effective sampling of these sites, noted Timoney.

"Aside from culture, stallions can also be screened for presence of the carrier state by test breeding to two mares, bacteriologically negative and serologically negative for antibodies to Taylorella equigenitalis," wrote Timoney. "Confirmation of the carrier state in a stallion is based on demonstration of Taylorella equigenitalis in the reproductive tract of the test mares and/or development of antibodies to the organism within 21-40 days after breeding."

He added that it is important that veterinarians obtain the swabs to insure that the appropriate sites in mares or stallions are reliably sampled. Three sets of swabs from these sites optimally should be obtained at intervals of no less than seven days. (If an animal has been treated, the initial swabbing should not occur within seven days after completion of treatment.)

Each sample must be placed in an individual file or tube in an antibiotic-free transport medium immediately after collection, and preferably be refrigerated for transportation to a recognized USDA-approved CEM testing laboratory. Samples should be cultured within 48 hours of being taken to maximize the chances of isolating the organism.

Treatment

No one treatment will guarantee resolution of clinical signs (if present) and clearance of the organism. Timoney noted, "It remains to be established whether it is even beneficial to treat the acutely affected mare, since there is some evidence that treatment may enhance the likelihood of persistence of T. equigenitalis in the clitoral region after it has been cleared from the proximal reproductive tract."

No one treatment will guarantee resolution of clinical signs (if present) and clearance of the organism.
Treatment for mares and stallions calls for removal of any smegma-type material from affected areas. In mares, the clitoral sinuses and fossa are thoroughly irrigated with a 4% solution of chlorhexidine and are packed with a 0.2% nitrofurazone ointment or equivalent. This regimen is repeated for five consecutive days. Some mares might require several courses of treatment before the organism is eliminated. Surgical removal of the clitoral sinuses may have to be resorted to in some of these mares to eliminate the carrier state.

For males contaminated with the organism, all smegma is removed from the external genitalia while the penis is fully extruded. The urethral fossa and sinus, prepuce, and penis are thoroughly cleansed with a 2% solution of chlorhexidine. After drying, 0.2% nitrofurazone ointment or its equivalent is liberally applied to the external genitalia. Treatment is repeated daily for five days. One course of treatment usually is adequate to eliminate the organism from the reproductive tract of the stallion.

Codes of Practice have been developed by several countries to provide guidelines for veterinarians, horse owners, and breeders for the prevention and control of CEM. These Codes of Practice are based on comprehensive bacteriological examination of the stallion, and test breeding the stallion to two susceptible mares to check for transmission of T. equigenitalis. Mares imported into CEM-free countries should be "rigorously screened, both bacteriologically and serologically" for evidence of infection with T. equigenitalis before being released into the country out of quarantine.

Any mares or stallions confirmed positive for CEM should be quarantined and isolated until treatment has proven successful and the animal is proven free of the organism.

"Where rigorously implemented over a period of years, well-formulated programs for the control of CEM have been successful in preventing and in some cases eradicating this disease from certain countries," noted Timoney.

About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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