Contagious Equine Metritis

"A Current Perspective"

Introduction and History:  Contagious Equine Metritis (CEM) is a transmissible venereal disease of equids caused by the gram negative bacterium, Taylorella equigenitalis.   CEM was first diagnosed in Europe in 1977 but, over the following year, several other countries including the United States (Kentucky) reported outbreaks.  Shortly thereafter, the disease was eradicated from the U.S. and, until December of 1998, was classified as a foreign animal disease.

Transmission:  Taylorella equigenitalis can be transmitted directly during breeding of a carrier stallion or mare or indirectly through artificial insemination or fomites.  The highly effective transmission of CEM can be attributed, at least in part, to unrecognized stallions carrying the bacteria on their external genitalia.  As such, multiple mares may become infected before the disease is even suspected.

Clinical Signs:  There are no reports of stallions infected with CEM showing clinical signs; however, clinical disease in mares is localized to the reproductive tract resulting in temporary infertility.  Mares can demonstrate three patterns of infection: acutely infected, chronically affected, or asymptomatic carriers.  Whereas acute infections present with copious, thick, gray vaginal discharge 10-14 days post breeding, chronic infections have less vaginal discharge and milder uterine inflammation, but are more difficult to eliminate.  After recovering from acute infections, mares can carry the bacterium asymptomatically for months.  CEM rarely causes permanent infertility or abortions.

Gross, Histological and Cytological Findings:  During the initial two to three weeks of infection, the endometrium and cervix are swollen, edematous, and covered with cloudy gray to white exudates.  The superficial (stratum compactum) and deep (stratum spongiosum) layers of the endometrium are thickened by edema and infiltrated by neutrophils and fewer eosinophils which transmigrate into the endometrial epithelium and uterine lumen.  By 14 days post-infection, the edema subsides and the inflammatory infiltrate consists of lymphocytes, plasma cells, and fewer neutrophils until day 21 when the inflammation becomes a mixed mononuclear cell population.  Inconsistent and less severe microscopic lesions include suppurative salpingitis and vaginitis.  No lesions are found in the clitoral fossa or clitoral sinus; however, organisms tend to persit in these locations for longer periods of time and are therefore common culture sites.

Diagnostics: Reproductive losses associated with CEM could significantly impact the economic status of the equine industry in the U.S.; therefore, great efforts have been taken to learn more about diagnosing CEM.  There are currently three tests used to determine if a horse is infected with T. equigenitalis. These include bacterial culture, serological testing, and test mating.

  Bacterial culture is the most reliable and accurate way to arrive at a diagnosis; however, challenges exist with respect to sample handling.  A swab of the genitourinary tract may be taken from the clitoral sinus, clitoral fossa, endometrium, and cervix, or the preputial folds, urethral fossa, urethra, skin of the penis, and pre-ejaculatory fluid of the mare and stallion, respectively.  Samples are then placed in liquid Amie's Charcoal medium and refrigerated until it is plated on chocolate agar.  False negatives occur if transit time is prolonged or the sample is warmed.  Despite its reliability, culture is time consuming and technically demanding, thus newer methods are being developed.

  Serological testing protocols have been surfacing since the emergence of CEM.  The most commonly implemented test at this time is complement fixation.  However, this test is limited to mares that have produced detectable antibodies to T. equigenitalis.  Polymerase chain reaction (PCR) tests are also used and have improved efficiency and reliability.  In addition, an Enzyme-Linked Immunosorbent  Assay (ELISA) has been designed for detection, but is less commonly employed.  Test mating combines technology from the tests detailed above.  In test mating, a stallion is bred to two CEM-negative mares.  The mares are then tested by culture and serology to check for infection.  The testing procedure requires 35 days before a stallion is declared negative.

  Current acceptable protocols for diagnosis include test mating with culture for stallions and culture combined with the complement fixation test for mares.

Current status: On December 15, 2008, a quarter horse stallion in central Kentucky was confirmed to be infected with T. equigenitalis. Fifteen days later, three stallions in Indiana also tested positive for the bacteria.  Epidemio-logical investigations have failed to identify the source of the outbreak.  As of April, 2009, 21 stallions and 5 mares in the United States have been confirmed positive for T. equigenitalis.  From these 26 positive animals, another 960 have been exposed making a total of 986 affected horses (270 exposed or positive stallions and 708 exposed or positive mares), covering a range of 48 states (Hawaii and Rhode Island have no links to the disease).  All of the positive and exposed horses were put in quarantine and underwent testing and treatment protocols.  Thus far, 823 (83.5%) of the 986 horses, including all horses from Indiana, completed testing and treatment protocols and were free of disease.

-by Seth Lundquist, Class of 2010

-edited by Dr. Chad Frank, ADDL Graduate Student

References:

1. Acland HM, Kenney RM: 1983.  Lesions of contagious equine metritis.  Veterinary Pathology 3:330-341.

2. Croxton-Smith P, Benson JA, Dawson FL, Powell DG: 1978.  A complement fixation test for the antibody to the contagious equine metritis organism.  The Veterinary Record 13: 275-278.

3. Duquesne F, Pronost S, Laugier C, Petry S: 2007.  Identification of Taylorella equigenitalis responsible for contagious equine metritis in equine genital swabs by direct polymerase chain reaction.  Research in Veterinary Science 1:47-49.

4. Katz JB, Evans LE, Hutto DL, Schroeder-Tucker LC, Carew AM, Donajue JM, Hirsch DC: 2000.  Clinical, bacteriologic, serologic, and pathologic features of infections with atypical Taylorella equigenitalis in mares.  Journal of the American Veterinary Medical Association 12: 1945-1948.

5. Katz J, Geer P: 2001. An enzyme-linked immunosorbent assay for the convenient serodiagnosis of contagious equine metritis in mares.  Journal of Veterinary Diagnostic Investigation 1:87-88.

6. McKinnon AO and Voss DL: 1993.  Equine Reproduction.  London: Lea and Febiger pp 846-848.

7. Timoney PJ: 1996.  Contagious Equine Metritis.  Comp Immun  Microbiol Infec Dis 3: 199-204.

8. http://www.aphis.usda/gov/newsroom/hot_issues/cem/index.shtml

9. http://www.aphis.usda.gov/publications/animal_health/content/printable_version/fs_ahcem.pdf