Veterinary News:

AERC Recommendations on EHV-1 for Endurance Events – November 21, 2025

Equine herpesvirus 1 (EHV-1) is a highly infectious disease of horses that in its mildest form causes respiratory disease, and in its more severe forms results in abortion and neurologic disease. In the last several weeks, cases of EHV-1 neurologic disease have been reported across the United States originating from events in Texas and Oklahoma. Cases have now been identified in Texas, Oklahoma, Louisiana, Colorado and Maryland. The neurological form of disease is often fatal.

The virus is shed in nasal secretions and can be transmitted by nose-to-nose contact between horses, or by contact with fomites. Fomites are objects such buckets, trailers, grooming implements, or human hands that become contaminated with virus-laden respiratory secretions from an infected horse, and then transmit the virus to another horse.

EHV-1 infected horses display mainly respiratory symptoms. Signs include fever, anorexia, depression, and nasal discharge. The symptoms of the neurologic form of EHV-1 are more expansive. These horses exhibit not only the respiratory symptoms but also have difficulty in urinating or urine dribbling, ataxia (a weak and uncoordinated gait), and/or the inability to rise from recumbency. This form of the disease is known as equine herpes myeloencephalopathy (EHM) and is the dangerous form of EHV-1 infection.

Consult with your veterinarian on a proper vaccine schedule for your horse. Horses travelling to equestrian events are recommended to be vaccinated for influenza, EHV-1 and EHV-4. While currently available EHV-1 vaccines do not reliably prevent the neurologic form of disease, they can help decrease viral load and shedding, therefore reducing the risk of transmission.

If you are a rider or crew member planning to attend an endurance event, we recommend adherence to the following guidelines to minimize risk of contracting or spreading the disease:

Familiarize yourself with any special biosecurity measures put in place by ride management prior to arriving at the ride. Be aware that these may vary from ride to ride, and state to state, contingent upon reported cases in the local area.

Take your horse’s temperature PRIOR to departing for your event, ideally keep a temperature log, taking the temperature twice daily. Horses with temperatures above 101.5° F should be examined by a veterinarian and refrain from travel to the event. If your horse develops clinical signs at the ride, quarantine the horse and notify ride management and the head veterinarian. DO NOT walk the horse through camp to the veterinarians.

Do not share any implements with horses not from your home farm.

Avoid touching horses that are not from your group.

Common water troughs pose a high risk of transmission; avoid their use whenever possible. Consider the use of a collapsible bucket on trail. When common water is all that is available, avoid crowding of horses, and discourage horses from rubbing their heads on the sides of the troughs.

The following guidelines are recommended for ride managers contingent upon the risk in their area.

Keep up to date on reports of EHV-1 in your state, and any associated travel restrictions, and plan your biosecurity protocol accordingly. Check both your state’s department of agriculture and the EDCC (Equine Disease Communication Center) as these are the most reliable sources of current information. Seek assistance from your ride veterinarians as needed.

For horses arriving from in-state where a health certificate is not required by law, consider requiring a temperature log of twice daily temperature checks for three days prior to travel to the event. At the time of arrival at the ride no horse should be allowed into camp without having its temperature checked by the ride veterinarians or designated ride management personnel.

Consider increasing the number of water troughs and designating one trough “buckets only” to decrease the risk of transmission.

Allow for adequate spacing of horses in ride camp.

Design the flow of horses through the vetting areas to allow for distancing between horses. Consider posting signs to remind riders in this area to keep horses from contacting each other.

Have in place a plan for rapid notification of ride participants if a horse at the ride develops EHV-1 after returning home.

Ride veterinarians should be cognizant of the fact that their physical contact with all the horses makes them a high-risk fomite. The following guidelines are recommended.

Disinfect hands and stethoscopes between horses.

Consider asking the rider or crew member to raise the horse’s upper lip to inspect mucous membranes.

Bring appropriate PPE to the ride to allow safe examination and handling of a suspected EHV-1 case without the risk of transmission to other horses. This should include disposable gloves, boots and coveralls, as well as biosecurity bags in which to dispose of them.

The nature of our sport, held in remote areas and wide-open spaces, allows us a measure of safety over equestrian sports that take place in barns and enclosed venues to continue holding rides with appropriate precautions in place. Please take your role in this shared responsibility seriously so that we may protect the well-being of our equine athletes as we continue to enjoy our events.

Submitted by
Jay (Jeanette) Mero, DVM