It´s a disease caused by a protozoan parasite Trypanosoma equiperdum, it´s sexually transmitted during natural mating or by artificial insemination with infected semen.
It appears to disappear from the genital tract periodically and the horse may become non-infectious for weeks to months. Mucous membrane transmission via the conjunctiva of the eyes may occur. Infected immature horses may transmit the organism following maturity.
Clinical signs are highly variable in appearance and severity like fever, loss of appetite, conjunctivitis, swelling of the genitalia and mammary glands and discharge from the urethra or vulva
Characteristic raised skin plaques appear on the neck, hips and lower parts of the abdomen. Abortion may occur in pregnant mares. Small pustules develop in waves on the penis and prepuce or vulva. They ulcerate and heal slowly leaving slightly elevated pink scars.
The disease progresses slowly and progressively. Neurological signs may then develop, with penile and generalized muscular paralysis, leading eventually to incoordination, emaciation and death.
Although the clinical signs may be characteristic, the diagnosis is confirmed serologically. Treatment is attempted but the organism may persist in symptomless carrier form and recovered stallions are unsafe for breeding purposes. There is no available vaccine for dourine.
This article is based in scientific veterinary literature.