Equine Dourine

Other Names

Dourine; covering sickness; mal de coit; Trypanosoma equiperdum infection; equine venereal trypanosomiasis.

What is Equine Dourine?

Equine Dourine is a serious venereal disease of equids caused by the protozoan parasite Trypanosoma equiperdum. It is a notifiable disease in the United Kingdom and across the European Union, meaning any suspected case must be reported immediately to the relevant authorities — in the UK, this is the Animal and Plant Health Agency (APHA). Dourine is a Listed disease with the World Organisation for Animal Health (WOAH, formerly OIE), reflecting its potential for international spread through equine movement.

Unlike most other trypanosomiases in animals, Dourine is transmitted directly between horses during mating rather than through an insect vector. The parasite replicates within the reproductive tract and gradually spreads systemically, causing progressive neurological deterioration, skin plaques, genital oedema, and eventual emaciation. If untreated, the disease can be fatal.

Dourine is currently rare in Western Europe but is enzootic in parts of Africa, Asia, the Middle East, and South America. The risk of introduction via imported breeding stallions is the primary concern in the UK, making pre-import testing and biosecurity essential for international breeding operations.

Causes

Dourine is caused by Trypanosoma equiperdum, a flagellate protozoan parasite. It is transmitted during sexual intercourse from infected to susceptible horses. Infected stallions shed the parasite in the semen, and infected mares shed it in vaginal secretions. The parasite is not transmitted by biting insects, which distinguishes it from Trypanosoma brucei (African sleeping sickness in animals) and Trypanosoma evansi (surra).

After initial infection in the genital mucosa, the parasite disseminates via the lymphatic and bloodstream to affect the central nervous system, skin, and other organs. Donkeys and mules can also be infected and may act as carriers with subclinical infection, making them a potential reservoir in enzootic regions.

Symptoms and Signs

The clinical course of Dourine is typically chronic and progressive over months to years. Signs appear in three overlapping stages:

Stage 1 — Genital oedema:

Oedema of the vulva, vagina, or prepuce and penis
Mucopurulent discharge from the genitalia
Urticarial plaques on the genital skin

Stage 2 — Skin plaques:

Characteristic oedematous skin plaques (oedema plaques) over the body, especially the flanks, neck, and hindquarters
Plaques appear and disappear over hours to days — their transient nature is highly characteristic of Dourine
Progressive weight loss and poor condition

Stage 3 — Neurological deterioration:

Progressive hindlimb weakness, ataxia, and paresis
Facial nerve paralysis — drooping of the ear, lip, or eyelid
Wasting of hindquarter muscles
Depression and loss of condition
Terminal recumbency and death in untreated advanced cases

Diagnosis

Diagnosis is challenging, particularly in chronic or low-level infections. Direct detection of the parasite in smears or biopsies from genital lesions is possible in acute cases but often unreliable in chronic infections. Serological testing — the complement fixation test (CFT) is the reference method for international trade purposes — is the primary tool, though false positives and false negatives occur. PCR testing is increasingly used to improve sensitivity and specificity.

If Dourine is suspected in the UK, you must contact the APHA immediately and do not attempt to test or treat without official veterinary oversight. The horse must be isolated pending official testing, and the holding premises will be placed under movement restrictions.

Treatment

In the UK and the EU, there is no licensed treatment for Dourine, and affected animals are subject to slaughter under disease control legislation. Treatment with trypanocidal drugs (such as diminazene aceturate) is practised in some enzootic regions but does not reliably eliminate the organism and can produce carrier animals that continue to spread the disease.

The official response in the UK is culling of confirmed positive animals to prevent onward spread and to protect the national equine industry.

Prevention

Prevention in the UK centres on:

Pre-import testing of all equids arriving from countries where Dourine is enzootic — complement fixation testing (CFT) is required for international trade
Quarantine of imported horses before introduction to existing herds
Avoiding use of imported stallions from enzootic regions in natural cover programmes without appropriate testing and certification
Reporting any genital oedema, transient skin plaques, or progressive neurological signs in horses with an international movement history

The APHA and BEVA publish guidance on import requirements and testing protocols for equids entering the UK.

Prognosis

In countries where treatment is practised, the prognosis for individual animals is poor without treatment, and guarded even with treatment due to the risk of subclinical carriage. In the UK, the disease is notifiable and affected horses are culled — prognosis in the welfare and epidemiological sense is managed by the state response rather than by individual clinical management.

When to Call the Vet

Contact your vet immediately if a horse with a history of import from an at-risk country develops genital oedema, transient skin plaques, or progressive hindlimb weakness and ataxia. Do not wait for other signs to develop. This is a notifiable disease — your vet is legally required to report it and so are you as the keeper. Delaying notification risks wider spread and legal consequences.

Frequently Asked Questions

Is Dourine present in the UK?

Dourine is not currently enzootic in the UK. It is classified as an exotic disease, and any confirmed case would trigger an official disease response including movement restrictions and slaughter of affected animals. The UK’s freedom from Dourine is maintained through stringent import testing requirements.

Can Dourine spread through casual horse-to-horse contact?

No. Unlike most contagious diseases, Dourine is transmitted almost exclusively through direct sexual contact during mating. It is not spread by contact, shared water or feed, or insect vectors. This makes strict control of breeding activity in at-risk populations the primary tool for preventing transmission.

What should I do if I suspect Dourine?

Isolate the horse immediately, cease any breeding activity, and contact your vet and the APHA emergency line. Do not move any horses on or off the premises until official guidance has been received. Dourine is a statutory notifiable disease — failure to report it is a criminal offence.

Can donkeys or mules carry Dourine?

Yes. Donkeys and mules can be infected with Trypanosoma equiperdum and may show few or no clinical signs while remaining infectious. This subclinical carriage in donkeys is a significant concern in enzootic regions and supports the importance of testing all equids — not just horses — before importation.

For official information and reporting requirements, contact the Animal and Plant Health Agency (APHA) or consult the British Equine Veterinary Association (BEVA).