Equine Herpesvirus (EHV-1 & EHV-4): What horse owners need to know

Equine herpesviruses (EHV) are widespread among horse populations, with EHV-1 and EHV-4 being the most clinically significant. EHV-1 can cause respiratory illness, abortion in mares, and a severe neurologic condition called equine herpesvirus myeloencephalopathy (EHM). EHV-4 primarily causes respiratory disease and rarely leads to abortion or neurologic signs.

Most horses are exposed early in life and may carry the virus in a latent state, which can reactivate during stress such as travel, illness, or competition. EHM occurs when EHV-1 infection leads to inflammation and damage to blood vessels in the brain and spinal cord, resulting in neurologic deficits. While only a small percentage of infected horses develop EHM, the condition can be life-threatening and often requires intensive care.

Transmission of EHV

Transmission occurs through direct horse-to-horse contact, aerosolized droplets from coughing or snorting, and indirect contact via contaminated surfaces such as stalls, trailers, tack, and water buckets. Humans can also act as mechanical carriers, spreading the virus on hands, clothing, and equipment. Horses may shed the virus during the incubation period, which ranges from 2 to 10 days, even before showing clinical signs.

Common signs of respiratory disease include fever above 101.5°F, nasal discharge, coughing, lethargy, and enlarged lymph nodes. Neurologic signs of EHM include hind limb weakness, incoordination, loss of tail tone, urine dribbling, leaning against walls, and, in severe cases, recumbency. Fever often precedes neurologic symptoms, but its absence does not rule out infection. Contact your local veterinarian immediately for care recommendations should your horse exhibit symptoms.

Limiting the spread of EHV

Effective biosecurity measures are essential to limiting the spread of EHV. The following practices can help lower the risk of transmission:

• Isolate horses returning from events or new arrivals for at least 14 to 21 days, monitor them twice daily for fever, and handle them last during chores.
• Avoid nose-to-nose contact and sharing of tack, grooming tools, or water sources, and disinfect all equipment thoroughly using an appropriate disinfectant, such as a bleach solution or accelerated peroxide.
• Clean trailers, stalls, and buckets of organic material like feces, bedding, and water before disinfection.
• Limit personnel contact with multiple horses, wear dedicated clothing, gloves, and boots when handling exposed animals, and wash hands thoroughly after contact.
• A vaccine is available but should be used with the advice of a veterinarian based on individual horse needs.
• Maintain accurate records of horse movements and exposure history for contact tracing if needed. Horses with fever or clinical signs should never be transported or brought to events.

Reporting cases of EHV

In Texas, EHV-1 is a reportable disease when it causes the neurologic condition. Veterinarians, laboratories, and horse owners and caretakers are required to report suspected or confirmed cases of the neurologic form to the Texas Animal Health Commission (TAHC) immediately. Prompt reporting enables TAHC to conduct disease investigations, provide movement and quarantine guidance, and issue official updates to the equine community. Current reporting information and regional contact numbers can be found on the TAHC website.

The American Association of Equine Practitioners (AAEP), the Equine Disease Communication Center (EDCC), and the TAHC emphasize that proactive biosecurity is the most effective way to prevent outbreaks. For real-time updates and official guidance, visit the EDCC and TAHC websites. Avoid relying on fear-based social media posts or unverified sources; instead, follow veterinary professionals and official agencies for accurate information.