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DOURINE

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Synonyms

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1. ETIOLOGY

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2. TRANSMISSION

Primary Route

• Venereal (coital) transmission - the organism's near-exclusive mode of spread
• Present in genital secretions (seminal fluid, vaginal secretions, urethral discharge) of infected animals
• Stallion to mare is more common, but mare to stallion transmission also occurs
• Can be present in semen before clinical signs appear (important epidemiologically)
• The parasite is shed in the mucous membranes and genital secretions at coitus and directly inoculated into the partner's mucous membranes

Other Routes (Rare)

• Conjunctival mucous membranes - occasional non-venereal infection
• Vertical transmission (mare to foal) - documented but uncommon; may occur transplacentally or during parturition
• Iatrogenic - contaminated equipment at artificial insemination could theoretically spread infection

Carrier State

• Donkeys and mules are commonly asymptomatic carriers and serve as a silent reservoir
• Periodically, the organism disappears from the genital tract for weeks to months - animals are non-infectious during these periods
• Parasitemia is intermittent and often undetectable in chronic stages

Incubation Period

• Ranges from a few weeks to several years (typically 1-4 weeks in experimental infections)

Geographic Distribution

• Endemic in Africa (Mediterranean coast, southern Africa, Ethiopia, Namibia)
• Middle East, Asia (Mongolia, Russia, Central Asia)
• South America (Argentina, Bolivia)
• Eastern and Southern Europe (outbreaks reported in Italy in 2011)
• OIE/WOAH-listed disease - notifiable internationally

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3. PATHOGENESIS

Pathogenesis Flowchart

Step-by-Step Pathogenesis

• T. equiperdum enters via genital mucous membranes during coitus
• Parasites establish in the subepithelial connective tissue of the genitalia
• Triggers a local inflammatory response: vasodilation, increased vascular permeability, perivascular infiltration of mononuclear cells
• Results in edema and tissue thickening of genital structures

• Local inflammatory mediators cause mucopurulent discharge, orchitis (stallions), vulvitis/vaginitis (mares)
• Ulcers and vesicles develop on genital mucosa; heal leaving leukodermic (depigmented) patches - white scars
• Edema can wax and wane; genitalia become progressively indurated

• Parasites breach local defenses and enter the bloodstream
• T. equiperdum undergoes antigenic variation of its variable surface glycoproteins (VSG), allowing it to periodically evade host antibody responses
• This leads to waves of parasitemia alternating with antibody-mediated clearance
• The host mounts antibody, complement, and cellular immune responses, but cannot clear the organism completely

• Hematogenous spread to skin, lymph nodes, peripheral nerves, and CNS
• Hypoalbuminemia develops from chronic inflammation and protein loss
• Anemia results from immune-mediated erythrocyte destruction and bone marrow suppression
• Protein-poor edema extends beyond genitalia (ventral edema, limb edema)

• Characteristic urticarial (trypanosomal) plaques appear on skin, particularly on neck, flanks, and thighs
• Plaques are 2-10 cm diameter, raised, depigmented, appear and disappear transiently
• These "dollar plaques" are considered pathognomonic for dourine
• Result from localized perivascular infiltration and immune complex deposition in the dermis

• CNS invasion causes meningoencephalitis and myelitis
• Peripheral neuritis contributes to motor deficits
• Demyelination in the lumbar/sacral spinal cord causes hindlimb ataxia and paresis
• Facial nerve palsy (unilateral), ptosis of lower lip
• Progressive weakness - hindlimbs > forelimbs

• Severe cachexia and progressive emaciation
• Profound hypoproteinemia with effusions (pleural, peritoneal, synovial)
• Recumbency, complete paralysis, death
• Untreated mortality: 50-70% (MSD Veterinary Manual)

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4. CLINICAL SIGNS

Stage I - Genital Stage

• Mucopurulent urethral discharge
• Edema and swelling of prepuce, glans penis, scrotum
• Orchitis and epididymitis
• Genital vesicles and ulcers → heal as white leukodermic scars
• Decreased libido or reluctance to breed

• Mucopurulent vaginal discharge
• Edema of vulva and mammary gland
• Vulvitis, vaginitis
• Thickened semi-transparent patches on vaginal mucosa
• Polyuria, signs of discomfort
• Abortion (with virulent strains)

Stage II - Cutaneous Stage

• Urticarial/trypanosomal plaques (2-10 cm diameter) - raised, circular, edematous
• Found on neck, flanks, back, thighs
• Appear and disappear within hours to days - pathognomonic
• Skin may show depigmented patches

Stage III - Neurological Stage

• Facial nerve palsy - usually unilateral
• Ptosis of the lower lip (very characteristic)
• Progressive hindlimb weakness, stiffness, and lameness
• Gait abnormalities: ataxia, stumbling, dragging of hind feet
• Inability to mount (detected only at mating in mild cases)
• Muscle atrophy and wasting
• Progressive paralysis leading to recumbency

Systemic Signs (Throughout)

• Progressive emaciation and weight loss
• Intermittent fever (corresponds with waves of parasitemia)
• Anemia (pale mucous membranes)
• Generalized lymphadenopathy
• Ventral edema
• General weakness and lethargy

Clinical Course Summary

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5. POST-MORTEM / PATHOLOGICAL LESIONS

• Edema and inflammation of genitalia; white leukodermic scars
• Perivascular mononuclear infiltration in skin, genitalia, nerves
• Demyelination in lumbar/sacral spinal cord
• Minimal internal organ lesions (inconsistent): pinpoint white hepatic foci, splenic congestion
• Increased synovial fluid in joints
• Yellowish fluid in thoracic and abdominal cavities (hypoproteinemia)
• Severe muscle atrophy and subcutaneous fat depletion

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6. DIAGNOSIS

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7. TREATMENT

Important note: It is uncertain whether any treatment can completely eliminate T. equiperdum. Long-term efficacy is unproven. Treatment may suppress clinical signs and parasitemia without achieving sterile cure, and relapse is well documented.

Drugs Used

Current Evidence (2025-2026)

• A 2025 study (PMID 39827514) identified 3'-deoxytubercidin as a potent candidate for treating surra and dourine
• A 2026 systematic review (PMID 41429593) - Raftery et al., Equine Vet J - reviewed equine trypanosomiasis disease management

Regulatory Consideration

• In many disease-free countries (e.g. USA, Western Europe), treatment is not permitted - infected animals are culled to protect disease-free status
• Treatment is only practiced in endemic regions as a control measure

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8. PREVENTION AND CONTROL

Individual Animal Level

1. Quarantine and testing of all new equids before introduction into a herd
2. Serological screening (CFT or ELISA) of breeding animals before use
3. Good hygiene at assisted matings and artificial insemination to prevent fomite-mediated spread
4. Avoid breeding animals with clinical signs

Herd and Regional Level

1. Prohibition on breeding in affected areas during outbreaks
2. Quarantine zones around infected premises
3. Serological surveillance to identify infected animals
4. Culling of positive animals - standard approach in disease-free countries
5. Identification and management of asymptomatic carriers (especially donkeys)

National/International Level

1. Movement controls - restrict movement of equids from endemic to disease-free areas
2. Import regulations - require negative CFT on imported equids
3. OIE/WOAH notification - dourine is a listed disease requiring immediate reporting
4. In the USA: notify state or federal veterinary authorities immediately upon suspicion

Vaccine

• No vaccine is available. Antigenic variation by T. equiperdum makes vaccine development extremely difficult.

Environmental Decontamination

• T. equiperdum is fragile in the environment and does not survive long outside a host
• Standard disinfectants effective against the closely related T. brucei include: 0.05% sodium hypochlorite, 70% ethanol, 2% formaldehyde, 2% TriGene, 0.05% glutaraldehyde
• Heat (50°C) kills 100% of T. brucei trypomastigotes

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Summary Table

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• CFSPH Iowa State Dourine Factsheet (Updated September 2024)
• MSD Veterinary Manual - Trypanosomiasis in Animals (Updated March 2026)
• Gizaw Y, Megersa M, Fayera T. Dourine: a neglected disease of equids. Trop Anim Health Prod. 2017;49(5):887-97. (Springer)
• Raftery AG, Gummery L, Garcia K. Equine trypanosomiasis, a systematic review: Disease management. Equine Vet J. 2026 Mar. PMID 41429593
• Gilbert RO. Dourine. In: Foreign Animal Diseases, 7th ed. USAHA; 2008. p. 231-6.