An ongoing outbreak of Equine Herpesvirus Type 1 (EHV-1), including its potentially fatal neurologic form, Equine Herpesvirus Myeloencephalopathy (EHM), has prompted a statewide alert for horse owners across the region. The current outbreak is linked to large equine events recently held in Texas and Oklahoma.

As confirmed by the Equine Disease Communication Center (EDCC), multiple EHV-1 cases have been confirmed across several states, including Oklahoma, linked to events like the World Championship Barrel Racing Finals in Waco, Texas, and the Barrel Futurities of America World Championship in Guthrie.

Horse owners are strongly urged to implement immediate biosecurity measures and monitor their animals closely.

The Threat: What is EHV-1 and EHM?

Equine Herpesvirus-1 (EHV-1) is a common virus, but certain strains can lead to severe complications.

The virus can manifest in three ways:

1. Respiratory Illness: Mild, flu-like symptoms, especially in young horses.

2. Reproductive Issues: Causes late-term abortions in pregnant mares.

3. Neurologic Disease (EHM): This is the most dangerous form, causing damage to the blood vessels in the brain and spinal cord and often leading to death or euthanasia.

There is currently no vaccine that reliably prevents the neurologic form (EHM).

Key clinical signs to watch for:

The first or only sign of EHV-1 infection is often a fever (temperature greater than 101.5 F) Neurologic signs typically appear 8 to 12 days after the fever begins.

Horse owners must immediately call a veterinarian if they observe any of the following signs:

• Fever (taken twice daily).

• Incoordination (ataxia), especially in the hind limbs, which may cause stumbling.

• Weakness, often causing the horse to lean against walls for balance.

• Loss of tail tone.

• Urine dribbling (inability to urinate normally).

• Lethargy or depression.

• Inability to stand (recumbency).

Immediate biosecurity and quarantine measures:

EHV-1 is highly contagious, spreading through direct horse-to-horse contact (respiratory secretions), aerosolized droplets (coughing), and indirect contact via contaminated equipment, clothing, and hands. The virus can remain viable on surfaces for up to 48 hours.

If your horse attended an event in an affected area (Texas or Oklahoma) or has commingled with exposed horses, the Oklahoma Department of Agriculture, Food and Forestry (ODAFF) advises following these guidelines immediately: 1. Isolation is Critical: Isolate the exposed horse for a minimum of 21 days from all other equines on the property, using separate equipment.

2. Monitor Temperature: Take and log your horse’s rectal temperature twice daily. Report any fever (greater than 101.5 F) to your veterinarian immediately.

3. Halt Movement: Do not move the exposed or sick horse and restrict the movement of any horses on the premises that have been in contact with the exposed animal.

4. Disinfection: Implement strict disinfection protocols. Clean and disinfect all trailers, tack, feed/water buckets, and grooming tools with a veterinarian-approved virucidal product (such as a 1:10 diluted bleach solution).

5. Personal Hygiene: Personnel caring for isolated horses must follow strict hygiene rules: wash hands, change clothing, and use disposable gloves before interacting with healthy horses. Veterinarians can utilize PCR testing on nasal swabs or blood to confirm the presence of EHV-1.

Treatment is primarily supportive care with anti-inflammatory drugs to manage fever and symptoms. Horse owners should contact their veterinarian immediately if they suspect exposure or notice any clinical signs.