Equid alphaherpesvirus 1, also called Equine herpesvirus 1 (EHV-1), is a virus of the family Herpesviridae that causes abortion, respiratory disease and occasionally neonatal mortality in horses.

Initial spread of EHV-1 by a newly introduced horse through direct and indirect contact can lead to abortion and perinatal infection in up to 70 percent of a previously unexposed herd.

The outbreak lasted approximately two months, generating 90 confirmed cases of the disease, spread over 10 American states, and resulting in the deaths of 13 horses before it was declared contained by the US Department of Agriculture.

These conditions include high levels of stress, immunosuppression, transportation,[11] sale barns, competitions,[12] geological and management practices.

Latent infected horses do not shed EHV-1 through nasal secretions and therefore are not infectious and are called clinically normal.

[12] The signs that occur with EHV-1 and the EHM strain may include the following: decreased coordination, urine dribbling, fever, hind limb weakness, leaning against things to maintain balance, and lethargy.

Additional risk factors that vary depending on the type of EHV-1 strain present include the following: living quarters (confined or pastured), prevalence of other horses, unsterilized equipment shared between horses, transportation (hauling) and what time of year infection is present (winter or summer).

[12] The current diagnosis used for detecting EHV-1 involves PCR which amplifies a segment of DNA from the horse using specific primers that target EHV-1's genetic makeup.

This is common among horses that are latently infected where the virus is not actively replicating and therefore producing multiple copies of its genetic sequence.

If a horse is in fact infected with EHV-1, treatment options are limited with the use of anti-inflammatory drugs administered either orally or intravenously.

[11] Another facet of EHV-1 control is to be aware of the potential for spreading the virus via equipment, and transmission, via human contact, between horses.

As stated previously, stress will trigger a latent virus to reactivate, and it can allow an uninfected horse to be more easily infected.