Learn everything about Equine Viral Arteritis (EVA), its impact on reproductive health, and effective prevention strategies. Discover the importance of testing, vaccination schedules, and biosecurity measures to keep your herd safe. Consult with your veterinarian today to protect your horses from EVA.
As the new year begins, horse owners are entering the busy foaling and breeding season. For breeding facilities, this time of year means foal watching, frequent reproductive veterinary appointments and endless cups of coffee to survive the long days. Amid this controlled chaos, a silent and dangerous illness can spread quickly through breeding herds: Equine Viral Arteritis (EVA).
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Equine Viral Arteritis (EVA) is a non-zoonotic viral disease that affects all equine species. It spreads through direct contact with bodily secretions or indirectly via contaminated materials. Infected horses are most contagious seven to 14 days after the onset of illness. Additionally, aborted fetuses and placental tissues can transmit the virus if not handled with strict biosecurity protocols.
Colts and stallions serve as the primary reservoirs for the virus; approximately 30% to 60% of stallions carry EVA. Unvaccinated pregnant mares are the most vulnerable population, facing a high risk of abortion if infected. Young foals can also contract the virus, which may lead to fatal pneumonia.
Symptoms of EVA
Many horses infected with EVA are asymptomatic. When signs do occur, they typically emerge within two to 14 days of exposure. Common symptoms include:
- Vision Signs: Eye discharge, redness, swelling around the eye, light sensitivity (photophobia), or cloudiness.
- Respiratory Signs: Nasal discharge, coughing, and labored breathing.
- Reproductive Signs: Abortions in mares (typically between three and 10 months of gestation) and fertility issues in stallions.
- Systemic Signs: Fever, hives, colic, diarrhea, and edema (swelling), particularly in the scrotum, mammary glands, or midventral area.
- Gait Changes: Stiff movement or lack of muscle coordination (ataxia).
Risk Factors
While all horses are at risk—especially during breeding season or at horse shows—the danger is significantly higher for:
- Unvaccinated horses.
- Very young or aged horses.
- Immunocompromised animals or those with underlying health issues.
Diagnosis and Reporting
Diagnosing EVA is challenging because it mimics other equine diseases. Veterinarians use clinical signs alongside lab tests, including blood work, nasal swabs, and semen evaluation.
The gold standard for diagnosis is virus isolation. Samples must be collected as soon as symptoms begin, as the virus often becomes undetectable after 28 days. In cases of severe disease or fetal loss, post-mortem tissue exams are conducted.
Important: EVA is a reportable disease. If a horse tests positive, you must notify your veterinarian or state animal health agency immediately to help monitor and control the spread.
Most horses recover from EVA without complications through supportive care. However, severe cases may require:
- Anti-inflammatory drugs.
- Diuretics to reduce swelling.
- Nutritional support.
- For stallions: Because stallions can become chronic carriers, castration is often the only way to eliminate the viral shed.
Prevention: Vaccination and Biosecurity
The most effective way to prevent an outbreak is through vaccination. Because vaccine availability can be limited, work with a veterinarian to create an individualized plan.
- Breeding Stallions: Test for EVA at least 60 days before breeding. Negative stallions should be vaccinated, quarantined for 28 days, and receive annual boosters. Positive stallions should only be bred to vaccinated or positive mares.
- Broodmares: Negative mares should be vaccinated and isolated for 21 days before breeding. Pregnant mares are typically vaccinated three months prior to foaling.
- Foals: Foals from immune mares generally carry maternal antibodies; they are typically vaccinated at 6 months of age.
Conclusion
EVA is a significant threat to equine reproductive health, particularly due to the risk of abortion in mares and chronic shedding in stallions. With no specific antiviral treatment available, rigorous testing, annual vaccinations, and strict biosecurity during travel are the best defenses for your herd. Always consult your veterinarian to ensure your vaccination schedule is up to date.
