Dourine

Dourine is a sexually transmitted parasitic disease of equids, caused by flagellated protozoan, belonging to Trypanosoma equiperdum species.

Various strains with variable pathogenicity were described in the past. However, the protozoan has not been isolated since 1982. Recent studies based on molecular biology suggest that T. equiperdum and T. evansi are subspecies of T. brucei.

According to some theories, the disease is not caused directly by T. equiperdum but originates from an autoimmune process.

Dourine is the only trypanosomosis not transmitted by an invertebrate vector. Occasionally, transmission from the infected mother to foal at parturition or during milking has been described. The resulting infected foals, when sexually mature may transmit the infection.

T.equiperdum mainly invades the tissues of the host, and is exceptionally detected in blood. Initially, parasites are found free on the surface of the mucosa or between the epithelial cells of a newly infected animal.

 Parasites then may pass into the blood, where they are carried to other parts of the body.

The disease can affect horses, mules and donkeys.

Mules and donkeys often develop subclinical forms, they could also act as a unapparent carrier, equids are the only natural reservoir known. Dogs, rabbits rats and mice, can be experimentally infected, rats and mice develop parasitemic infection and therefore they are used for the isolation of T.equiperdum and antigen production for diagnostic tests.

T. equiperdum can be detected in the vaginal secretions of infected mares and in the seminal fluid and mucous exudate of penis in infected stallions.

The parasites are not continually present in the genital tract throughout the course of the disease, therefore transmission of the infection does not necessarily take place at every copulation.

The infection occurs in most of Asia, Africa, Russia, parts of Middle East, South America and southeastern Europe (Figure 1).

The incubation period varies considerably and may last from one week to some months. Disease severity may vary considerably as well. It is often fatal, if recovery occurs, animals may become latent carriers.

Clinical diagnosis is usually confirmed by serology. The main clinical symptoms are:

• Fever
• Local oedema of genitalia and mammary glands
• Oedematous cutaneous eruptions
• Incoordination, paraplegia and unilateral facial paralysis
• Ocular lesions
• Anaemia
• Progressive weight loss, resulting in a cachectic status.
• Chronic or milder forms of the disease may persist for months and years. Sub-clinical forms are more frequent in mules and donkeys.

The main lesions are:

• Oedematous and urticarial skin plaques, up to 5-8 cm in diameter ("silver dollar plaques");
• Oedema and gelatinous infiltration of the tissues of vulva, vaginal mucosa, uterus, mammary glands in female, and scrotum, testicles and prepuce in male;
• Vaginal mucosa may show raised plaques;
• Depigmentation of skin and mucosa may be observed near genitalia, perineum and udder;
• Abdominal lymph nodes are usually hypertrophic and hemorrhagic in some cases;
• Spinal cord of paraplegic animal is often soft and discolored, particularly in lumbar and sacral tracts.

Case-fatality rate associated with acute disease may approach 50%.

Trypanosomes are present, even if in low numbers, in lymph nodes, oedematous fluids, external genitalia, in vaginal mucus and in fluid contents of plaques;. Preputial and vaginal washings allow the identification of the etiologic agent by PCR technology.

The number of trypanosomes in circulating blood is scanty, therefore a volume of 5-10 ml of blood with anticoagulant (EDTA) should be collected for PCR test.

Whole blood without anticoagulant is collected for serological tests.

Blood samples have to be stored at refrigeration temperature (+4 ° C) and sent promptly to the diagnostic laboratory.

The complement fixation test is the prescribed test by the OIE for international trade. Indirect immunofluorescence may also be performed for the detection of antibodies against disease T.equiperdum.

Dourine differential diagnosis is carried out in respect of:

• Equine coital exanthema
• Contagious equine metritis
• Surra
• Nagana  (Tse tse transmitted  african  trypanosomosis)
• Anthrax
• Equine viral arteritis
• Equine infectious anaemia
• Purpura hemorrhagica
• All other conditions of weight loss, such as malnutrition, dental pathologies, chronic infections, verminosis

No vaccines are at present available. The control of all stallions before coitus is the only effective preventive measure.