Contagious Equine Metritis

Contagious Equine Metritis (CEM) is a venereally transmitted bacterial disease of horses. It is a notifiable disease under the Diseases of Animals (Northern Ireland) Order 1981 and any suspicious signs must be reported to a Divisional Veterinary Officer or their Private Veterinary Practioner (PVP).

What are the clinical signs?

In the mare, the severity of disease caused by the CEM organism varies. There are 3 states of infection:

  • in the acute state, there is active inflammation and obvious discharge from the vulva usually seen 1-6 days after infection at mating
  • in the chronic state, the signs may be less obvious but the infection is often deep seated and may be difficult to clear. Discharge may not be seen for up to 80 days after infection
  • there is also the carrier state. The bacteria have become established as part of the bacterial flora in the genital areas and there are no signs of infection. However, the mare is still infectious. Infected stallions and teasers are usually passive carriers, meaning that they do not show clinical signs of infection but have the bacteria colonised as part of the flora on their external genital organs. Although internal spread in the male is rare, the bacteria may occasionally invade the urethra and sex glands, causing pus and bacteria to contaminate the semen

How is CEM spread?

Infection spreads through direct transmission of bacteria from mare to stallion or teaser or from stallion or teaser to mare at the time of mating or teasing. It is also transmitted to mares if semen used in artificial insemination (AI) comes from infected stallions.
Indirect infection also occurs, for example:

  • through contaminated water, utensils and instruments
  • on the hands of staff and veterinary surgeons who handle the tail and genital area of the mare, or the penis of the stallion or teaser
  • genital to genital or nose to genital contact between stallions/teasers and mares

How is infection prevented and controlled?

The main ways of preventing infection are:

  • have stallions, teasers and mares checked for infection before they are mated: this is done through swabbing and testing at a laboratory
  • always exercise strict hygiene measures when handling mares, stallions andteasers

The main ways of stopping the spread of infection if it does occur are to:

  • stop mating by the infected horse(s)
  • seek veterinary advice immediately
  • isolate and treat the infected horse as advised by the attending veterinary surgeon
  • exercise strict hygiene measures when handling the horses involved
  • do not resume any breeding activity until freedom from CEM has been confirmed in all infected horses

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