Contagious Equine Metritis (CEM, CEMO) is a highly infectious disease of mares caused by Taylorella equigenitalis (previously called Hemophilus equigenitalis). The disease was first diagnosed in 1977 and subsequently spread to many nations. The disease was confirmed in the United States in 1978. Specific regulatory procedures for this disease have been established in the United States and 37 other countries.
The organism is carried on the external genitalia of stallions and transmitted at mating to mares, most of which are highly susceptible. The disease is self-limiting and usually clears with sexual rest after about 3 months. Some individuals may take longer to recover and require treatment, and others remain as carriers (harboring the organism but showing no symptoms) for years. Colt foals born to infected mares may be carriers and thus are capable of starting an epidemic by infecting mares during mating. The disease can be the cause of short-term infertility and, very rarely, abortion in mares.
There is genital inflammation, vaginal discharge and lowered fertility. Affected mares may return to heat unexpectedly, often with shortened interheat periods, but usually breed successfully once the infection has been eliminated. Stallions do not show clinical signs. Most cases resolve without treatment. However, infection appears to persist longer in older mares and recently foaled mares. Treatment is with antibiotics over a 7 to 10 period. Aggressive systemic antibiotic therapy accompanied by routine topical therapy might be required to treat some CEM-positive stallions.
Prevention and control of CEM is achievable through a comprehensive programme of breeding farm management that includes early detection and treatment of carrier mares and stallions.