Contagious equine metritis in horses

A stallion, that was diagnosed as having Contagious Equine Metritis Organism (CEMO), has now been successfully treated. Horses that were ‘at risk’ or that had come into contact with the stallion have also been traced and tested. Those tests were negative. Defra has now lifted restrictions on the Somerset premises where the stallion is kept, and the investigation has been concluded.

CEMO is a treatable venereal disease of horses, which poses no risks to human health. This case was detected in March this year through routine testing. Previous cases of CEMO have occurred in a stallion and a mare in 2002, and a mare in 2003. The Horserace Betting Levy Board’s Code of Practice is aimed at preventing and controlling CEMO. Defra advises those intending to use horses for breeding to follow the guidelines for disease prevention that are contained in the code.

CEM was first described as a disease in 1978. It is not prevalent worldwide, and outbreaks are sporadic. Since 1980 there have been no reported cases except in Europe and Japan. Numbers of reported cases annually are generally in single figures. The usual measures of control are surveillance, monitoring, screening and movement controls. The disease in the UK is notifiable. There are no EU rules on the control of CEMO. However some third countries require disease free status for CEMO for trade purposes. There were 14 UK cases in 1996, two in 1997, 2 cases in 2002, 1 case in 2003. After the last outbreak, the UK had regained disease free status.

The severity of disease caused by the CEMO organism varies. The main outward clinical sign in a mare is a mild to heavy discharge from the vulva, resulting from an inflammation of the uterus (endometritis). Occasionally mares will show no clinical signs. Whilst infected most mares will fail to conceive. There have been cases of abortion associated with CEMO. The incubation period is 2-12 days and the period of clinical infection lasts on average 2 weeks. Infected stallions do not usually show clinical signs of infection, but merely harbour the organism on their external genitalia.

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June 7, 2005

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