Equine viral arteritis is a contagious disease of equids caused by equine arteritis virus. Equine arteritis virus can cause abortion in pregnant mares and establishment of a long-term carrier state in breeding stallions.

Transmission may occur through direct nose-to-nose contact with a horse that is shedding virus in respiratory secretions or by venereal transmission through virus-infected fresh, cooled, or frozen semen.

Clinical signs, if they occur, typically develop 3 to 13 days post exposure and may include fever, depression, lethargy, anorexia, dependent edema, urticaria, supra or periorbital edema, conjunctivitis, or serous to mucoid nasal discharge. Abortion can occur from 2 months to term after virus exposure in unvaccinated pregnant mares.

A carrier state can develop following equine arteritis virus infection in the post-pubertal colt or stallion. The virus can persist in the accessary sex glands of the reproductive tract for many years and may result in a lifelong infection. The carrier stallion is the natural reservoir of equine arteritis virus.

Diagnosis is based on clinical signs and laboratory testing for exposure to the virus in an unvaccinated horse by serologic testing of a blood sample for presence of antibodies and for the presence of virus in semen by virus isolation and/or PCR testing.

Vaccination of all seronegative stallions is recommended to protect stallions against infection and subsequent development of the carrier state. Seronegative mares should be vaccinated before being bred with equine arteritis virus-infective semen.


  1. All unvaccinated stallions should be evaluated for natural exposure to equine arteritis virus by serologic testing of a blood sample.
  2. All seronegative stallions should be vaccinated annually.
  3. Seropositive stallions that have not been vaccinated should have semen evaluated for presence of the virus (i.e. carrier/shedder status).
  4. Mares may be vaccinated upon owner request.