Dourine in Horses: Venereal Trypanosome Infection Explained
- See your vet immediately if your horse has genital swelling, genital discharge, skin plaques, weakness, or neurologic changes after breeding exposure.
- Dourine is a contagious venereal disease of horses and other equids caused by the protozoan parasite Trypanosoma equiperdum.
- It spreads mainly during natural breeding, and infected horses may look normal early on while still posing a risk to breeding partners.
- Diagnosis usually relies on history, exam findings, and laboratory testing such as serology, with regulatory involvement because dourine is a reportable disease.
- Treatment decisions are complex and may be limited by state, federal, or import-export rules, so isolation and immediate veterinary guidance matter.
What Is Dourine in Horses?
Dourine is a venereal trypanosome infection of horses, donkeys, and mules caused by Trypanosoma equiperdum. Unlike many other trypanosome diseases, it is spread mainly during coitus, not by biting flies. That makes it especially important in breeding animals and in horses with recent import, export, or unknown breeding histories.
This disease can be acute or chronic. Early signs often involve the reproductive tract, such as swelling of the external genitalia or discharge. As the infection progresses, some horses develop raised skin plaques, weight loss, weakness, and sometimes neurologic problems. Untreated cases can be severe, and published veterinary references describe substantial mortality.
For pet parents in the United States, another key point is that dourine is considered a reportable equine disease concern. If your vet suspects it, they may need to involve state or federal animal health officials. That does not mean your horse definitely has dourine, but it does mean fast, careful evaluation is important.
Symptoms of Dourine in Horses
- Swelling of the penis, prepuce, vulva, or mammary area
- Mucous or mucopurulent genital discharge
- Raised circular skin plaques
- Weight loss and progressive muscle wasting
- Fever or general malaise
- Weakness, incoordination, or hind-end neurologic signs
- Reduced fertility or breeding problems
See your vet immediately if your horse develops genital swelling, discharge, skin plaques, weakness, or trouble walking, especially after recent breeding or movement across borders. These signs are not unique to dourine, and other conditions such as trauma, bacterial reproductive infections, contagious equine metritis, or neurologic disease can look similar.
The biggest concern is the combination of breeding exposure plus reproductive signs, or skin plaques plus weight loss or neurologic changes. Because dourine is a reportable disease concern, early isolation from breeding activity and prompt veterinary guidance help protect both your horse and other equids.
What Causes Dourine in Horses?
Dourine is caused by the protozoan parasite Trypanosoma equiperdum. The parasite is usually transmitted during natural breeding, when infected genital secretions pass from one equid to another. Horses, donkeys, and mules can be affected, and some animals may carry infection with few obvious signs early on.
This route of spread is what makes dourine different from many other trypanosome infections. In most cases, biting insects are not the main source of transmission. Instead, risk centers on breeding contact, exposure to infected semen or genital secretions, and movement of breeding animals from regions where the disease occurs.
In the United States, dourine is not considered endemic, so your vet may think about it most strongly in horses with import history, international travel, breeding exposure to imported animals, or regulatory screening findings. Because several reproductive and skin conditions can mimic dourine, laboratory confirmation is essential before any conclusions are made.
How Is Dourine in Horses Diagnosed?
Diagnosis starts with a careful history. Your vet will ask about recent breeding, travel, import status, contact with breeding animals, genital signs, skin plaques, and neurologic changes. A full physical and reproductive exam helps identify patterns that fit dourine, but signs alone are not enough to confirm it.
Laboratory testing is usually the next step. Veterinary references describe diagnosis using a combination of serology, clinical findings, and sometimes direct detection of the organism from genital discharges, skin plaques, or blood. Directly finding the parasite can be difficult, so negative direct tests do not always rule the disease out.
Because dourine is a reportable disease concern, your vet may coordinate with a state animal health official, USDA APHIS, or an approved laboratory. In some situations, horses may be isolated, quarantined, and retested if results are positive, suspect, or unclear. That process can feel stressful, but it is designed to protect the broader equine population while your vet works toward the most accurate answer.
Treatment Options for Dourine in Horses
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Immediate stop to breeding activity
- Physical exam and basic reproductive assessment
- Isolation from other breeding equids
- Initial reportable-disease consultation and sample collection
- Supportive care planning while awaiting official guidance
Recommended Standard Treatment
- Full veterinary exam with reproductive and neurologic assessment
- Official serologic testing and repeat sample submission as directed
- Quarantine or movement restriction planning
- Supportive care for pain, swelling, hydration, and nutrition as appropriate
- Case management with your vet plus state or federal animal health authorities
Advanced / Critical Care
- Referral-level evaluation or intensive on-farm management
- Expanded neurologic workup and broader rule-out testing
- Multiple rounds of official testing and documentation
- Aggressive supportive care for debilitated horses
- Transport, quarantine facility fees, and herd or contact-animal testing when required
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Dourine in Horses
Bring these questions to your vet appointment to get the most out of your visit.
- Do my horse's signs fit dourine, or are other reproductive or neurologic conditions more likely?
- Should this horse be isolated from breeding animals right away, and for how long?
- Which tests are being submitted, and what can those tests confirm or miss?
- Do state or federal animal health officials need to be notified in this case?
- What should I do about exposed mares, stallions, donkeys, mules, or pasturemates?
- What supportive care is appropriate while we wait for results?
- If results are suspect or inconclusive, what repeat testing timeline should I expect?
- How will this affect breeding plans, transport, sales, or import-export paperwork?
How to Prevent Dourine in Horses
Prevention focuses on breeding biosecurity. The most practical steps are to avoid breeding horses with unknown health status, review import and travel history carefully, and work with your vet before introducing a new stallion or mare into a breeding program. If a horse has genital discharge, swelling, skin plaques, or unexplained neurologic signs, breeding should stop until your vet says it is safe.
For breeding farms, a prevention plan may include pre-breeding exams, testing when indicated, careful recordkeeping, and immediate separation of horses with suspicious signs. Imported equids and semen programs may involve additional regulatory screening depending on origin and intended use.
There is no routine vaccine for dourine. In areas pursuing disease freedom, prevention may also involve official testing, movement controls, and removal of infected animals from breeding populations. Your vet can help tailor a realistic plan that protects your horse, your breeding program, and the wider equine community.