Equine Viral Arteritis is a contagious disease caused by the equine arteritis virus, an RNA virus that is found in many countries. While typically not life-threatening to otherwise healthy adult horses, EVA can cause abortion in pregnant mares, death in young foals, and establish a long-term carrier state in breeding stallions.

Incubation: The incubation period is the time from exposure to the virus to when a horse shows clinical signs of infection. For EVA, the incubation period is typically two to four days but can be as long as 14 days.

Carrier Status: Carrier stallions shed EVA constantly in semen, but not via the respiratory tract, urine, or blood. Only stallions and sexually mature colts can be carriers of EVA.

Transmission: Respiratory transmission is most common and spreads via droplets of respiratory secretions from acutely infected horses. Stress does not cause EVA, but can prompt carrier horses to begin shedding the virus, which can cause outbreaks. Stress in susceptible horses can worsen clinical signs and increase disease severity. Sexual transmission occurs through infected reproductive fluids (semen, uterine fluids, transferred embryos, or aborted materials). Indirect transmission occurs via objects (twitches, halters, hands of animal care personnel) contaminated with respiratory or reproductive secretions. Foals are infected prior to birth when their dam is infected in late pregnancy.

Shedding Period: Newly-infected animals (mares, geldings, foals) can shed the virus for up to 16 days.

Clinical Signs: Not all infected horses show clinical signs. Clinical signs are not specific for this infection and may be worse in young, old, or immunocompromised horse. Some of the non-specific clinical signs can include: fever (temperature up to 106ºF for two to nine days), swelling of limbs, abdomen, sheath/udder, stiffness when moving and runny nose. Abortion may occur any time after the second month of pregnancy.

Diagnostic Testing: Diagnosis is made by paired titers (two blood samples taken at a specific interval) in serum (a component of whole blood). It is important to note that titers cannot be used to differentiate animals who were vaccinated from those who were infected naturally. Stallions with positive serum titers should be further evaluated for persistent shedding (carrier) status.

Treatment: There is no specific treatment for Equine Viral Arteritis. Supportive care is administered in moderate to severe cases of disease, although most non-stallions clear the disease with no long-term side effects. There is no effective treatment for intact breeding stallions.

Prevention: Keep breeding horses that are at high risk for EVA up to date on vaccination. Consult a veterinarian for appropriate vaccination plan for the individual animal.