Equine Viral Arteritis (EVA) by a Vet – 2025 Guide to Symptoms, Transmission & Vaccination 🧬🐴
In this article
Equine Viral Arteritis (EVA) by a Vet – 2025 Guide to Symptoms, Transmission & Vaccination 🧬🐴
By Dr Duncan Houston, BVSc
Introduction
Equine Viral Arteritis (EVA) is a contagious viral disease of horses that poses significant challenges for breeding programs. While EVA is not usually fatal, it can cause abortions in mares, pneumonia in foals, and turn stallions into lifelong carriers. Understanding EVA's transmission, diagnosis, and proper vaccine timing is key to protecting horse health and bloodlines in 2025.
What Is EVA? 🧬
- A contagious viral disease of horses
- Caused by the equine arteritis virus (EAV)
- Infects the respiratory and reproductive tracts
Who’s at Risk? 🎯
- Pregnant mares: Risk of abortion or infected foals
- Foals: Can develop fatal pneumonia or enteritis
- Stallions: Can become persistent virus carriers via semen
- Breeding farms: Greatest risk due to venereal spread
How EVA Spreads 🔄
- Respiratory route: Direct contact, coughing, nasal secretions
- Venereal transmission: Semen from infected stallions
- Frozen and chilled semen: Virus survives and spreads via AI
Clinical Signs of EVA ⚠️
- Fever
- Depression
- Swollen limbs (especially rear legs)
- Swelling of scrotum or mammary glands
- Hives or skin rash
- Eye inflammation (conjunctivitis)
- Nasal discharge
In Pregnant Mares
- Abortion—especially if infection occurs mid-gestation
- If exposed late in pregnancy, may deliver infected foal
- Foals can develop severe pneumonia or intestinal disease
In Colts and Stallions
- Virus persists in the accessory sex glands
- Can shed virus through semen indefinitely
- Carrier status does not affect fertility, but affects biosecurity
Diagnosis 🧪
- Blood test (serology): Detects antibodies to EVA
- Virus isolation or PCR: Confirms active infection
- Semen testing: Determines if a stallion is a carrier
EVA Vaccination 💉
- Safe and effective vaccine is available
- Important for:
- Breeding stallions
- Mares before breeding
- Young colts before puberty (prevents carrier status)
Important Note:
- Vaccine induces antibodies—you will test positive on EVA blood tests
- Always test BEFORE vaccination to establish baseline
Vaccination Protocol
- Test first—ensure horse is EVA-negative
- Vaccinate colts before sexual maturity (ideally 6–12 months)
- Document EVA-negative status and vaccination history for breeding stallions
- Annual boosters for breeding animals or those traveling internationally
Managing an EVA Outbreak 🛑
- Isolate symptomatic horses immediately
- Test and trace all recent contacts
- Halt breeding activities until situation is controlled
- Work with a vet and testing lab for full disease containment
Case Example: EVA Outbreak in Quarter Horse Stallion
- In 2006, EVA spread across six states through AI semen from an infected Quarter Horse stallion
- Multiple mares aborted or delivered sick foals
- Stallion was found to be a carrier, though asymptomatic
- Outbreak highlighted the need for testing before breeding
FAQs About EVA
Q: Is EVA deadly?
A: Not usually in adult horses, but can be fatal for foals and cause abortions in mares.
Q: Can carrier stallions be cured?
A: No—there’s no treatment to eliminate virus from the reproductive tract. Carrier stallions must be managed carefully.
Q: Can EVA-positive horses be shown or transported?
A: Yes, but breeding facilities often require proof of negative status or controlled vaccination history.
Conclusion
Equine Viral Arteritis is a breeding-related disease that causes reproductive losses, especially in unvaccinated or untested herds. In 2025, test-before-vaccine protocols, routine surveillance, and controlled vaccination offer effective protection. If you breed, ship semen, or manage stallions, EVA prevention should be part of your biosecurity plan.
Need EVA vaccine guidance or carrier screening? Visit AskAVet.com or download our app 📱 to consult Dr Duncan Houston on EVA protocols for your breeding program. 🩺🐴
