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Equine Viral Arteritis


Equine viral arteritis (EVA) is an acute, contagious, viral disease of both horses and donkeys.


Where the Disease Occurs 

The virus is present in horse and donkey populations in many countries throughout the world.


Symptoms in Horses

Exposure to EVA virus may or may not result in clinical disease. When clinical signs occur they may range from fever, depression, respiratory symptoms, swelling of the legs (especially the hind legs), swelling of scrotum, prepuce and mammary glands,  conjunctivitis and nasal discharge. Symptoms are similar to several other diseases such as influenza and rhinopneumonitis.  The virus causes damage to the smaller blood vessels resulting in edema and hemorrhage in many tissues and organs. Some strains of the virus cause abortion and death in young foals.


How the Disease Spreads

  • Respiratory secretions
  • Breeding with infected stallions using fresh, cooled or frozen semen
  • Contaminated equipment-tack, equipment
  • Urine and feces
  • Mare to foal across placenta

Outbreaks of EVA are usually linked to the movement of animals or the shipment of semen. Viral transmission can be widespread at racetracks or on breeding farms.


Carrier stallions may be reservoirs of the virus without expressing any outward symptoms. These stallions are primarily responsible for persistence of the virus in different horse populations throughout the world.



Blood samples and nasopharyngeal and conjunctival swabs and semen may be collected for virus isolation and the detection of antibodies.


There is no specific treatment for EVA and most affected horses recover completely.


Control of the Disease in Animals

Most prevention and control programs are focused on preventing or curtailing dissemination of equine arteritis virus in breeding populations, minimizing the risk of virus-related abortion or death in young foals and establishment of the carrier state in stallions.


All Stallions should be tested for EVA. Positive stallions must be identified prior to breeding.


Breeding to a Positive EVA Stallion

Follow the advice of your veterinarian to institute a vaccination program for the mares to allow breeding with infected stallions.


Vaccination Programs

Follow the directions of your veterinarian in instituting a vaccination program for your farm.


Can People Get the Disease?

The disease only affects horses and donkeys.


Elisabeth J. Giedt, D.V.M. , M.B.A.

Director of Engagement, Continuing Education and Extension Center for Veterinary Health Sciences

002B Veterinary Medical Teaching Hospital

Oklahoma State University

Stillwater, OK 74078-2005



Elisabeth J. Giedt, D.V.M. , M.B.A.

Director of Engagement, Continuing Education and Extension

Center for Veterinary Health Sciences

Oklahoma State University

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