Equine Herpes Virus (EHV) is also known as rhinopneumonitis and is a respiratory disease caused by a virus. Almost all horses have been infected with the virus at some point in their lives, often asymptomatically, and carry the virus in their bodies afterwards. Most of the time, horses are not actively shedding the virus, but stressful situations like travel or competition can prompt horses to begin shedding it again. At this point, they may or may not have symptoms of illness themselves and may infect others.

Strains: EHV-1 and EHV-4 are the most common forms of Equine Herpes Virus. EHV-1 is more severe and can cause respiratory illness and abortion. It can also become Equine Herpesvirus Myeloencephalopathy (EHM) which is characterized by neurological symptoms. EHV-4 is primarily a respiratory infection and has less frequent cases of abortion and neurologic signs. Vaccines are available for these diseases.

Incubation: The incubation period is the time from exposure to the virus to when a horse shows clinical signs of infection. For EHV, the incubation period is anywhere from two to ten days and horses will be actively shedding the virus during this period. Horses may shed virus prior to showing any clinical signs.
Transmission: Transmission occurs through direct contact (horses touching), indirect contact (contaminated equipment, vehicles, clothing, etc.) and can be spread through the air (nasal discharge particles).

Shedding period: Varies by horse and strain. Horses with clinical signs (nasal discharge, abortion, neurologic signs) should be considered contagious until cleared by their veterinarian through testing, quarantine, or both.

Clinical Signs: Clinical signs may include fever, enlarged lymph nodes, nasal discharge and possible neurologic symptoms such as hind limb ataxia, incoordination, lethargy, or head tilt.

Diagnostic testing: Nasal swabs and blood samples can be used to diagnose EHV.

Treatment: There is no specific treatment for EHV infection, but support treatments include NSAIDS (non-steroidal anti-inflammatory drugs) to control fever or other clinical signs. Antivirals may be of benefit early in the infection period.

Prevention: Vaccinations are available for prevention of the respiratory and abortive form of EHV-1 and EHV-4. There is currently no vaccine labeled for the prevention of the neurologic form (EHM). Management practices for preventing EHV-related disease includes maintaining current vaccinations on all horses on the property, practicing biosecurity while traveling and showing, and quarantining any new horses (or horses returning to a farm after travel) for at least 21 days before integration into the farm herd.