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.

Transmission
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.