Contagious Equine Metritis

Introduction

CEM is a venereally transmitted bacterial disease of horses. CEM was first reported in the UK in 1977. CEM still occurs in a number of other EU countries, including the Scandinavia countries, as well as in Morocco and Japan.

The following Code of Practice is reproduced by permission of the Horserace Betting Levy Board.

What are the causative agents of CEM?

Three species of bacteria are recognised as liable to cause outbreaks of infectious reproductive disease in the horse:

• Taylorella equigenitalis (the CEM Organism, or the CEMO)
• Klebsiella pneumoniae
• Pseudomonas aeruginosa

Infection with these bacteria can be highly contagious.

How does infection 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 artifical 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

Indirect infection is a significant risk for the transmission of the CEMO, and of Klebsiella pneumoniae and Pseudomonas aeruginosa between horses.

What are the clinical signs?

In the mare, the severity of disease caused by the CEMO varies. The main outward clinical sign is a discharge from the vulva, resulting from inflammation of the uterus, usually 1 to 6 days after infection at mating. There are 3 states of infection:

In the acute state, there is active inflammation and obvious discharge, 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. Stallions pass the bacteria on to mares during mating. Bacteria may also pass to mares, directly or indirectly, from infected teasers.

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 infection prevented and controlled?

You are advised to consult the Industry Common Code of Practice for the Prevention and Control of CEM.

The main ways of preventing infection are:

• check stallions, teasers and mares for infection before they are mated: this is done through swabbing
• if a horse proves to be infected, do not use it for mating until the infection has been successfully treated
• always exercise strict hygiene measures when handling mares, stallions and teasers
  
  The main ways of stopping the spread of infection if it does occur are to:
• stop mating by the infected horse(s)
• treat the infection and re-swab to check that the infection has cleared up before resuming mating
• exercise strict hygiene measures when handling the horses involved

NB: For non-Thoroughbreds, Artificial Insemination (AI) is a useful disease control measure. However, mare owners should only use semen collected from stallions proven free of infection at the time of semen collection.

CEM is a notifiable disease

In the UK, isolation of the CEM organism is notifiable by law, meaning that a suspicion or isolation of the organism must be reported to a Divisional Veterinary Manager (DVM) of the Department for Environment, Food and Rural Affairs (Defra).

This is a statutory requirement under the Infectious Diseases of Horses Order 1987. Copies of the Order (reference: 1987 No. 790) are obtainable from HMSO.

Hygiene

Owing to the risk of indirect infection, stud staff should be made aware that CEM, and disease caused by Klebsiella pneumoniae and Pseudomonas aeruginosa can be highly contagious. Staff should wear disposable gloves at all times when handling the genitalia of mares and stallions/teasers, and should change gloves between each horse.

Separate utensils should be used for each stallion/teaser.

If mares are infected when pregnant or foaling, hygiene is very important to prevent the transmission of infection through contaminated utensils or discharges from the mare.

Further information is available in Equine Veterinary Education 1996 Volume 8 (3) 166-170.

Controlling infection-recommendations

When infection is suspected or confirmed, mating, teasing, collection and insemination of semen must cease until treatment has taken place under veterinary direction and subsequent swabbing has proved that the infection has cleared up. The first swabs should be taken 7 or more days after the treatment has ended. Repeat clitoral and penile swabs should subsequently be taken at intervals of 7 or more days. Repeat endometrial swabs should ideally be collected during the next 3 oestrous periods.

In countries where CEM is notifiable, the government must be informed (for the UK, see Section 5 above). You should also inform your breeders' association.

If the CEM organism is suspected or confirmed in mares, stallions or teasers before mating, teasing or AI:
a. Seek veterinary advice and notify the Divisional Veterinary Manager (DVM) of Defra immediately.
b. Isolate the mares, stallions or teasers and treat as advised by the veterinary surgeon.

If the CEM organism is suspected or confirmed in mares, stallions or teasers after mating, teasing or AI:

• Seek veterinary advice and notify the DVM of Defra immediately.
• Stop mating/teasing and collecting and inseminating semen from the stallion/teaser.
• Isolate and treat the stallion/teaser under veterinary direction.
• Isolate and treat the infected mares as advised by the veterinary surgeon.
• Check and deal with any other mares implicated in the outbreak as advised by the veterinary surgeon; this may include blood tests.
• Notify all owners of mares booked to the stallion, including any which have already left the stud.
• Notify people to whom semen from the stallion has been sent.
• Notify the breeders' association.
• Do not resume mating, teasing or collecting and inseminating semen from the stallion/teaser until negative results from 3 full post-treatment sets of swabs have been obtained.
• Thereafter, the first 3 mares mated to him should be swabbed 3 times at intervals of at least 7 days.