Equine viral arteritis (EVA)

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Equine Viral Arteritis (EVA)

Equine viral arteritis (EVA) is a contagious respiratory and reproductive disease of equids, occurring as sporadic outbreaks in horses worldwide. It is considered to be a reportable disease in most countries worldwide. EVA is caused by the equine arteritis virus (EAV). EAV was first reported in the United States, when it was isolated from the lung tissue of aborted fetuses during an outbreak of respiratory disease and abortions in horses at a Standardbred breeding farm in Ohio.

EVA is of particular important to horse breeders as it causes abortion in mares, death in young foals, and can potentially cause a permanent carrier state in stallions. Export markets may deny entry to carrier stallions, virus infective semen, and any horse that is seropositive for EAV. Both vaccination and natural exposure are responsible for seropositive results. A carrier state develops in stallions that were sexually material at the time of initial EAV exposure and may result in persistant shedding of the EAV in semen. Stallions may remain carriers for weeks, months, years, or indefinitely. Carrier stallions shed the virus in their semen, but not in their urine or respiratory secretions.

The two most common routes for transmission of EVAV are through respiratory secretions of infected horses and semem carrier stallions. Transmission can also occur from fomites and vertical congenital infection of foals from utero. The virus can remain infectious for years in frozen semen.

Incubation Period
The incubation period for the virus is 2-14 days. Mares may abort anytime from 2 months of gestation to term in the acute phase or early in the convalescent stage of the infection. Abortion occurs within 1-3 weeks of respiratory transmission and not as a result of being bred to a carrier stallion.

If an Outbreak Occurs
During an outbreak of EVA, the primary control strategy should be isolation of horses suspected of being affected from other susceptible animals. Measures should be taken to disinfect possible fomites and vaccinate susceptible horses. All humans involved in an outbreak should be quarantined for at least 3 weeks after all active infections are resolved.


Loss of appetite
Edema (legs, ventral body, mammary glands, prepuce, scrotum, and around the eyes)
Excessive lacrimation
Petechial hemorrhage of mucus membranes
Stiff gait
Yellowing of mucus membranes
Urticaria (on the head and/or neck)
Rhinitis and nasal discharge


  • History
  • Clinical signs
  • Physical exam



Report diseaseEVA is a reportable disease, meaning that if you suspect that your horse has this disease, by law you need to report it to your veterinarian, or a state or federal veterinarian.
Supportive careStall rest, NSAID therapy, and diuretic to control edema.
Antimicrobial therapyMay be indicated in some horses to prevent secondary bacteria infections such as pneumonia or cellulitis which may result.


  • Vaccination of at risk horses
  • Blood samples for EAV testing should be collected before breeding and virus isolation should be performed on semen from seropositive stallions before use
  • Biosecurity
  • Carrier stallions should be bred only to mares that test seropositive for EAV, including those that have been properly vaccinated.
  • New horses that arrive on breeding farms, including those returning from being away at shoes, racetracks or other events, should be isolated for 3 to 4 weeks to prevent the spread of EVA and other infectious diseases.


Excellent, most affected animals recover completely.

Scientific Research

General Overviews

Risk Factors

  • Not conducting virus isolation testing pn all semen used to artificially inseminate susceptible mares.

Causative agent