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Contagious Equine Metritis

Contagious equine metritis (CEM) affects horses, donkeys, mules, zebras and other equidae and is passed on through sexual contact. It does not affect humans but is a notifiable disease. That means if you suspect it, you must tell the Animal and Plant Health Agency (APHA) immediately. Failure to do so is an offence.

Current Situation

The last outbreak of CEM in Great Britain was in 2012.

Clinical Signs

Contagious Equine Metritis (CEM) is a venereal infection of the genital tract of horses triggered by the Taylorella equigenitalis bacteria.

Stallions do not normally show clinical signs of the disease, but can be carriers of it. In mares you should look out for discharge from swollen genitals, especially 1-6 days after mating. Infected mares can also be temporarily infertile if they have contracted CEM, so if your mare is failing to get pregnant, ask your vet to examine her.

If you believe any of your equines have CEM then you should:

  • tell your vet immediately - they may take samples from your horse for lab testing

  • isolate any animals you think are affected
  • stop the suspect animals from mating
  • avoid using semen from stallions with suspected or confirmed infection

Biosecurity Guidance

The Government's policy on disease control is that prevention is better than cure. This approach works by reducing the chances of a disease entering the animal population, and if it does then it can be quickly spotted and dealt with through the preventative measures.

You can help prevent disease by practising strict biosecurity on your premises. Our equine biosecurity leaflet outlines practical, day-to-day actions that can be easily adopted in order to reduce the potential for the introduction or spread of disease-causing agents. You can also use the HBLB Code Of Practice to help prevent infection and to stop the disease spreading.

How CEM is spread

CEM is spread from horse to horse during mating, but it can also be spread when horses are artificially inseminated.


Control Strategy

Movement Controls & Tracings

If notifiable disease is confirmed, the premises becomes an Infected Premises (IP) and infected equine/s are immediately placed under movement restrictions and isolated from all other equine/s on site. Movement restrictions may also be imposed on other equines and/or items such as fodder, manure, bedding, vehicles or equipment.  The purpose of movement restrictions are to reduce the risk of the spread of disease, and some movements may be permitted under licence.

Tracings of the infected horse/s activity will be investigated to establish possible origins of disease and onward spread. Other equines at the infected premises or identified as a result of tracings may be subject to inspection or examination by a Veterinary Officer.

Further information on the control of infection is available in the HBLB Code Of Practice and the statutory requirements within Infectious Diseases of Horses Order 1987. Restrictions will remain in place until the investigation is complete and notifiable disease is ruled out.


There is no vaccination available for Contagious equine metritis (CEM).


Relevant Legislation

The main domestic legislation on CEM is the Infectious Diseases of Horses Order 1987.