Dourine is a contagious parasitic venereal disease of equines caused by the Trypanosoma equiperdum
protozoan. It is an OIE-listed
disease. Once widespread, Dourine has been eradicated from many countries but is still seen in Asia, Africa, South America, southern and eastern Europe, Mexico and Russia and was reported in June 2011 in Sicily and then just north of Naples, on the Italian mainland. A single case of dourine was reported in Germany in a mare in 2002.
The disease has three stages. Stage 1, which occurs typically 1-2 weeks after infection, some horse may experience genital swelling with varying severity. Stage 2 is marked by the temporary appearance of cutaneous "silver dollar" plaques and wheals along the horse's upper body. During stage 3 the horse demonstrates neurological signs such as ataxia, staggering, stiffness, weakened hind limbs, and can develop progressive anemia. 50% of horses die during this stage.
Unlike other trypanosomal
infections, dourine is transmitted almost exclusively through breeding. Transmission from stallions to mares is more common, but mares can also transmit the disease to stallions. T. equiperdum
can be found in the vaginal secretions of infected mares and the seminal fluid, mucous exudate of the penis, and sheath of stallions. Periodically, the parasites disappear from the genital tract and the animal becomes noninfectious for weeks to months. Noninfectious periods are more common late in the disease. Male donkeys can be asymptomatic carriers. Rarely, infected mares pass the infection to their foals, possibly before birth or through the milk. Infections are also thought to occur through mucous membranes such as the conjunctiva. Other means of transmission may also be possible; however, there is currently no evidence that arthropod vectors play any role in transmission. Sexually immature animals that become infected can transmit the organism when they mature.
The incubation period is a few weeks to several years.