Contagious Equine Metritis
Basic Information 
Epidemiology
Risk Factors
• Direct or indirect venereal contact with T. equigenitalis
• Occurrence of the carrier state in the stallion and the mare
• International or national movement of stallions and mares and shipment of semen
• Certain management practices (eg, “vanning in” or “walking-in” of mares to be bred naturally or by artificial insemination [AI])
• Failure to observe appropriate sanitary measures when breeding stallions naturally or when collecting semen for AI
Contagion and Zoonosis
• Transmission of CEM occurs primarily by the venereal route through:
• Transplacental infection of the fetus
• Contact of the external genitalia of the foal with a T. equigenitalis–positive placenta or clitoral area of an infected mare at the time of foaling
• Exposure of the external genitalia of postpartum foal to bedding or pasture contaminated with T. equigenitalis infective placental fluids or vaginal discharge
• Transmission between stallions and colts through the use of common sponges or cloths contaminated with T. equigenitalis to wash the external genitalia
Geography and Seasonality
• CEM has been reported to have occurred in some 29 countries worldwide since the disease was initially recognized in 1977. In countries where it is currently known or believed to occur, the infection is endemic largely in non-Thoroughbred breeds.
• Outbreaks of CEM and infection with T. equigenitalis invariably occur during the breeding season, whether in the Northern or Southern Hemispheres. On the other hand, carrier stallions or mares can be detected at any time either when undergoing pre- or post-entry testing required by an importing country or as part of a pre-breeding season screening program to identify carrier animals.
Clinical Presentation
Disease Forms/Subtypes
• CEM is an acute venereally transmissible disease that is restricted to the reproductive tract in mares. It is a non–life-threatening infection that is characterized by short-term infertility and very rarely, abortion around 7 months’ gestation.
• The clinical outcome after primary exposure in a mare can vary considerably from overt disease to asymptomatic infection. T. equigenitalis exists as a commensal on the external genitalia of the stallion, causing neither a local nor systemic inflammatory reaction.
History, Chief Complaint
• After an incubation period of 2 to 13 days, typically affected mares may present with an odorless, greyish-white, mucopurulent vulvar discharge of uterine origin. This can vary in amount and may persist for 2 weeks or longer. The discharge is accompanied by an endometritis, cervicitis, and vaginitis of varying severity.
• Irrespective of the presence or absence of clinical signs of infection, most mares fail to conceive after primary exposure to T. equigenitalis and return to estrus after a shortened diestrus period. The resultant infertility is short term with no long-term adverse effects on a mare’s fertility. Persistence of T. equigenitalis in the reproductive tract of the mare need not compromise the maintenance of a normal pregnancy and birth of a healthy foal.
Physical Exam Findings
• Clinical signs of the disease are only found in mares, with stallions being asymptomatic carriers of the organism. In clinical cases of infection, affected mares develop a severe, diffuse acute endometritis along with inflammation of the cervix and vagina.
• Acutely or chronically infected mares are afebrile without displaying any clinical signs of systemic illness. Typical cases of CEM have a mucopurulent vulvar discharge, which may be so profuse as to run down the hindquarters, wetting the entire perineal area and inside the thighs and matting the tail hairs. In contrast, other mares may merely have a bead of discharge at the lower commissure of the vulva. Intrauterine fluid accumulation can often be detected on ultrasonographic examination of affected mares. On vaginoscopic examination, discharge can be observed seeping between the folds of the external os of the cervix and accumulating on the floor of the vagina. Affected mares have a concomitant cervicitis and vaginitis, which may be more severe than seen in other bacterial infections of the reproductive tract in the mare.
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