Dourine, also known as covering sickness or genital glanders, is a serious condition that can result in mortality; the mortality rate is thought to be over 50%. No vaccine is available, therefore prevention is extremely important.
Dourine is a venereal disease caused by the protozoan parasite Trypanosoma eqiperdum. The infection is sexually transmitted, both during natural mating and by artificial insemination. Transmission from stallions to mares is more common, but mares can also transmit the disease to stallions. Rarely, infected mares pass the infection to their foals, possibly before birth or through colostrum and milk, and infections may also be acquired through mucous membranes, such as the conjunctivae.
The disease has been eradicated from many countries including the UK and USA, but is still seen in southern and eastern Europe, Asia, Africa, South America, Mexico and Russia. The latest reports were in June 2011 where it was found in Sicily and northern Italy.
Dourine is a notifiable disease in the USA, EU and is also notifiable by law in the UK under the Infectious Disease of Horses Order 1987. If you suspect your horse has dourine, the Department for Environment, Food and Rural Affairs (DEFRA) in the UK must be notified. State or federal authorities in the USA, must immediately be informed upon diagnosis or suspicion of the disease.
Clinical signs vary significantly, but in geldings and stallions the most obvious signs are inflammation of the penis (balanitis) or both the penis and prepuce (balanoposthitis). In some cases the horse may not be able to retract the penis back into the sheath at all (paraphimosis). Swelling may spread to the scrotum and as far as the ventral abdomen and chest where the affected skin may become depigmented. In breeding stallions, another sign of infection will be failure to achieve intromission when servicing mares.
In mares, signs include vaginal discharge and swelling of the vulva which can lead to vaginal prolapse and may extend along the perineum to the ventral abdomen and mammary glands and may result in depigmentation. In pregnant mares, abortion can occur with more virulent strains.
Other signs include discharge, skin plaques (raised patches 2-10 cm in diameter which last for 3-7 days) and neurological signs, but severity varies with the virulence of the parasite and the general condition of the horse. If neurological signs develop, there may be associated weakness, incoordination and paralysis. Paralysis of the facial muscles, which is generally one-sided, may be seen in some cases. Ocular disease may be the first signs of dourine, which means conjunctivitis and keratitis are common. Anaemia and fever may also be seen. Dourine also results in a steady loss of condition, even though appetite remains good.
All of these signs may develop over weeks to months, and may wax and wane with relapses, probably precipitated by stress. This can occur several times before the animal either dies or experiences an apparent recovery.
As well as considering your horses history and clinical signs, your vet will need to take some blood samples to test in the laboratory to confirm a diagnosis of dourine.
While waiting for confirmation of diagnosis, all breeding activities must be suspended, the horse should be isolated, and the relevant authority should be informed of the situation.
If it is confirmed that your horse is in fact infected, all further action will be controlled by the relevant authority. But it is certain that all breeding activities must stop and the premises in question will be subject to official movement restrictions.
Unfortunately there are currently no effective treatments for dourine. Euthanasia is the best option to eradicate the infection.
There is currently no vaccine available for dourine, therefore prevention is essential.
Essential methods to prevent transmission:
- Avoid natural mating or artificial insemination with infected horses.
- Ensure blood tests for dourine are used to ensure horses are free from infection before breeding.
- Isolate and blood test horses introduced from endemic areas. Horses in isolation must not be allowed to mate and semen must not be collected or used for AI until negative dourine test results are confirmed.
- Report positive test results and horses showing clinical signs to the relevant authority.
- Do not move infected mares or stallions from endemic areas without veterinary approval.