Equine Viral Arteritis in Horses: Respiratory Signs, Testing, and Control

Quick Answer
  • Equine viral arteritis, or EVA, is a contagious viral disease that can cause fever, nasal discharge, cough, red eyes, limb swelling, and abortion in pregnant mares.
  • Some horses have mild signs or no obvious signs at all, so lab testing is important when there is a breeding, travel, or outbreak concern.
  • Stallions can become long-term carriers and shed virus in semen, which makes breeding management a major part of control.
  • Your vet may recommend isolation, PCR or virus testing on nasal secretions, blood, or semen, and paired blood tests depending on the situation.
  • Typical diagnostic cost range in the US is about $200-$800 for an exam, sample collection, and basic lab testing, with higher costs if semen testing, repeated testing, or farm biosecurity planning is needed.
Estimated cost: $200–$800

What Is Equine Viral Arteritis in Horses?

Equine viral arteritis (EVA) is a contagious disease caused by equine arteritis virus. It can affect the respiratory tract and blood vessels, which is why horses may develop fever, nasal discharge, cough, red eyes, swelling, and sometimes more widespread illness. In pregnant mares, the virus can also cause abortion.

One tricky part of EVA is that signs vary a lot. Some horses look mildly sick for a few days, while others show more obvious swelling, eye irritation, or reproductive problems. Some infected horses may have very subtle signs, which means the disease can spread before anyone realizes it is present.

EVA also matters because of breeding. After natural infection, some stallions can become persistent carriers and continue shedding virus in semen even after they look normal. That carrier state plays a major role in how the virus stays in horse populations, so your vet may focus not only on the sick horse in front of you, but also on breeding history, semen exposure, and herd-level control.

Symptoms of Equine Viral Arteritis in Horses

  • Fever
  • Clear nasal discharge
  • Cough
  • Red eyes, tearing, or conjunctivitis
  • Swollen eyelids or puffiness around the eyes
  • Swelling of the limbs, underside, or scrotum/prepuce
  • Depression or low energy
  • Abortion in pregnant mares

Call your vet promptly if your horse has fever plus respiratory signs, eye redness, unusual swelling, or any reproductive concern. EVA can look like other infectious diseases, so testing matters. See your vet immediately if a pregnant mare aborts, if several horses on the property become sick around the same time, or if a breeding stallion may have been exposed.

What Causes Equine Viral Arteritis in Horses?

EVA is caused by equine arteritis virus, an RNA virus spread through respiratory secretions and through semen from infected carrier stallions. Horses can become infected by close contact with a horse that is actively shedding virus from the respiratory tract, or through breeding exposure by natural service or artificial insemination.

Respiratory spread tends to matter most during outbreaks where horses are housed, transported, shown, sold, or hospitalized together. The virus can also move indirectly on contaminated hands, clothing, tack, breeding equipment, or other fomites when biosecurity is poor.

For breeding farms, the biggest long-term risk is the carrier stallion. A stallion may recover from infection but continue shedding virus in semen for months, years, or longer. That is why your vet may recommend blood testing first and then semen testing in antibody-positive, nonvaccinated stallions.

Not every exposed horse becomes seriously ill, and not every horse needs the same response. The right plan depends on age, pregnancy status, breeding role, vaccination history, travel history, and whether the concern is a single sick horse or a herd-level exposure.

How Is Equine Viral Arteritis in Horses Diagnosed?

EVA cannot be confirmed by signs alone. Your vet usually starts with a history and exam, then chooses samples based on why EVA is suspected. Testing may include PCR or virus detection from nasal secretions, blood, semen, or reproductive and fetal tissues, along with serology to look for antibodies.

In a horse with recent fever and respiratory signs, your vet may collect nasal swabs or secretions and blood. In a pregnant mare that aborts, placental and fetal tissues can be important. In breeding stallions, the workup often begins with a blood test for antibodies. If an unvaccinated stallion is antibody-positive, semen testing is typically needed to determine whether he is a carrier.

Your vet may also recommend paired blood samples taken weeks apart if the first results are unclear or if timing of infection matters. Because EVA can resemble other equine infectious diseases, your vet may test for additional causes of respiratory illness or reproductive loss at the same time.

Turnaround time and total cost depend on the lab, shipping, and how many horses need testing. If there is a breeding or movement issue, your vet may also coordinate with state or federal animal health officials and breed registry requirements.

Treatment Options for Equine Viral Arteritis in Horses

Spectrum of Care means you have options. Here are treatment tiers at different price points.

Budget-Conscious Care

$300–$900
Best for: Mild, stable cases where the main goals are confirming risk, reducing spread, and supporting recovery without a large herd workup.
  • Farm call or clinic exam
  • Isolation from other horses
  • Temperature monitoring and rest
  • Targeted supportive care directed by your vet
  • Basic diagnostic sampling for the affected horse
  • Practical biosecurity steps for the barn
Expected outcome: Many nonpregnant horses recover well with supportive care, but the herd-level risk remains if testing and isolation are incomplete.
Consider: Lower upfront cost, but it may miss carrier or exposed horses on the property. This approach may be less useful for breeding farms, pregnant mares, or movement-related requirements.
Most Common

Recommended Standard Treatment

$900–$2,500
Best for: Most suspected EVA cases, especially when there are multiple horses on the property, breeding exposure, or a need to make safe return-to-barn decisions.
  • Complete veterinary exam and case history
  • PCR or virus testing plus serology as indicated
  • Isolation and written barn biosecurity plan
  • Follow-up testing for exposed horses when needed
  • Breeding-risk assessment for stallions and mares
  • Supportive medications or fluids if your vet feels they are appropriate
Expected outcome: Good for many adult horses with timely supportive care and strong infection-control steps. Reproductive losses and carrier-stallion issues can still have major consequences.
Consider: More complete and practical for real-world management, but costs rise with repeat visits, multiple horses, and laboratory follow-up.

Advanced / Critical Care

$2,500–$8,000
Best for: Severe illness, valuable breeding animals, abortion events, outbreak situations, or farms needing intensive diagnostics and control planning.
  • Hospitalization or intensive on-farm management
  • IV fluids and close monitoring
  • Expanded infectious disease testing
  • Repeated laboratory sampling for herd or breeding decisions
  • Consultation on stallion carrier status, semen management, and movement restrictions
  • Coordination with regulatory or breed-program requirements when applicable
Expected outcome: Often still favorable for the individual horse if complications are limited, but reproductive and business impacts may be substantial in breeding operations.
Consider: Most comprehensive option, but it requires more time, more testing, and a higher cost range. It may also involve stricter isolation and breeding restrictions.

Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.

Questions to Ask Your Vet About Equine Viral Arteritis in Horses

Bring these questions to your vet appointment to get the most out of your visit.

  1. Based on my horse's signs and history, how likely is EVA compared with other respiratory diseases?
  2. Which samples should we collect now: nasal secretions, blood, semen, or reproductive tissues?
  3. Does this horse need to be isolated, and for how long?
  4. Should other horses on the property be monitored or tested too?
  5. If this is a breeding stallion, do we need antibody testing first and then semen testing?
  6. What steps should we take right now to reduce spread through tack, clothing, trailers, and handlers?
  7. Is vaccination appropriate for any horses on this farm, and what timing matters before breeding?
  8. Are there state, federal, sales, show, or breed-registry rules we need to follow after a suspected or confirmed case?

How to Prevent Equine Viral Arteritis in Horses

Prevention starts with biosecurity and breeding management. New arrivals should be separated from resident horses for about 3 to 4 weeks when possible, and horses with fever or respiratory signs should be isolated promptly. Good hygiene matters too, including cleaning shared equipment and reducing indirect spread on hands, clothing, halters, and breeding tools.

For breeding programs, your vet may recommend routine EVA planning before the season starts. USDA guidance recommends blood-testing new breeding stallions for antibodies before each breeding season, and semen testing for antibody-positive, nonvaccinated stallions to identify carriers. Vaccination may be part of the plan for noncarrier breeding stallions and for mares before breeding in specific risk situations, but timing and documentation matter.

Vaccination is not a one-size-fits-all decision. Your vet may also need to consider state rules, breed registry expectations, travel requirements, and whether a horse has already been vaccinated or naturally exposed. On some farms, the best prevention plan focuses on testing and controlled breeding management rather than broad vaccination alone.

If your horse is part of a breeding program, ask your vet to help build a written EVA protocol before the season begins. That can include testing schedules, vaccine timing, isolation periods after first vaccination when required, and clear steps for handling semen, exposed mares, and any horse that develops fever or respiratory signs.

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