EHM Outbreak Continues to Spread Across Eight States

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The outbreak of Equine Herpesvirus Myeloencephalopathy (EHM), a severe neurologic condition caused by  Equine Herpesvirus-1 (EHV-1), linked to a major rodeo event in Texas has now spread to at least eight states, affecting 32 horses, prompting continued warnings from animal health officials. The Equine Disease Communication Center (EDCC) is providing EHM outbreak updates as cases are confirmed by PCR tests.

The total horse count across the states affected by the EHM outbreak, based on the reported cases, is as follows:

• Texas: 14 EHM cases
• Oklahoma: 1 EHV-1 case (no neurologic signs) + 4 EHM cases = 5 cases
• Louisiana: 3 EHM cases
• South Dakota: 1 EHM case
• Colorado: 1 EHM case
• New Mexico: 3 EHM cases
• Arizona: 3 EHV-1 cases (no clinical signs)
• Washington: 2 EHV-1 cases (no neurologic signs)

Recap: The outbreak originated at the Women’s Professional Rodeo Association (WPRA) World Finals and Elite Barrel Race, held from Nov. 5-9 in Waco. The neurologic equine disease, caused by Equine Herpesvirus-1 (EHV-1), has led to dozens of confirmed cases.

Update: As of Nov. 25, Texas has reported the highest number of cases with 14 horses testing positive for EHM (up from 11 from 11/24), which includes neurologic signs. Oklahoma has confirmed one case of EHV-1 with no neurologic symptoms and four cases of EHM. Other affected states include Louisiana with three EHM cases, New Mexico with three EHM cases, and both South Dakota and Colorado with one EHM case each.

Additionally, two horses in Washington have tested positive for EHV-1 without neurologic signs, and three horses in Arizona have tested positive for EHV-1 but are not showing clinical signs. Officials have confirmed that an EHM case reported in Maryland on Nov. 18 was not associated with the Texas event.

EHM is a serious condition that affects a horse's central nervous system. Common neurologic equine disease symptoms include fever, limb swelling, hindlimb weakness, and urine dribbling. In severe instances, horses may suffer from seizures, an inability to stand, and other signs of cranial nerve dysfunction.

While EHV-1 is a common virus that typically causes respiratory illness in horses, certain strains can lead to the more severe neurologic form, EHM. The disease damages blood vessels in the brain and spinal cord, disrupting blood flow.

Despite the severity of the illness, the EDCC notes that many horses can recover. In most EHM outbreaks, 60-70% of affected horses survive with supportive veterinary care. Horse owners are urged to seek immediate veterinary evaluation if they suspect exposure or see symptoms. Isolation of affected animals is critical for containment.

For horse owners seeking equine herpesvirus prevention tips, biosecurity measures are paramount. These include avoiding nose-to-nose contact with unfamiliar horses, not sharing equipment, and quarantining new or returning animals. Veterinarians are encouraged to report any suspected cases to state animal health officials and the EDCC to aid in tracking the outbreak.

Biosecurity: To contain the spread of the virus, experts urge barn managers and horse owners to implement strict biosecurity protocols. The virus spreads through direct horse-to-horse contact, contaminated equipment and human interaction.

The following comprehensive checklist details essential supplies and procedures recommended for barns during an outbreak.

Core Biosecurity Supplies

Barns should stock these essential items to maintain hygiene and prevent transmission:

• Disinfectant Mats: Place these at all entry and exit points to clean footwear.   (Example ) 
• Disinfectant Cleaners: Use hospital-grade cleaners for all surfaces and shared equipment.   (Example ) 

Personal Protective Equipment (PPE): Staff should wear disposable gear when handling potentially infected horses

• Disposable coveralls  ( Example ) 
• Long-sleeve aprons  ( Example ) 
• Nitrile gloves  ( Example ) 
• Disposable boot covers  ( Example ) 

Chlorhexidine Products: Use for cleaning and sanitizing horses and handlers.

• Solutions  ( Example ) 
• Shampoos  ( Example ) 
• Sprays  ( Example ) 

Sanitizing Products: Ensure hand sanitizer and sprays are readily available.

• Farm-size hand sanitizer  ( Example ) 
• Sanitizing spray  ( Example ) 

Horse-Specific Items: Do not share these items between horses.

• Individual thermometers  ( Example ) 
• Temperature logbooks  ( Example ) 
• Immune and gut support supplements  ( Immune Support ,  Gut Support ) 

Additional Recommendations

Beyond basic supplies, facility managers should consider these enhanced protocols:

1. Dedicate Tools for Each Stall: Assign separate   feed tubs ,  water buckets ,  pitchforks and   muck buckets  to each horse. Never share equipment between healthy and quarantined horses.
2. Establish Footbaths: Place shallow tubs filled with disinfectant solutions, such as Virkon S or Trifectant, at all barn entry and exit points.
3. Implement Laundry Protocols: Use   biohazard-marked bins  for contaminated items. Wash items in hot water with bleach or disinfectant detergent. Ideally, use a separate washing machine for quarantine items.
4. Post Clear Signage: Place signs at quarantine zones, such as “No Entry – Quarantine” and “PPE Required,” to limit access and ensure compliance.
5. Use Disposable Paper Products: Replace reusable cloth towels with   heavy-duty paper towels  and   single-use grooming wipes  to prevent cross-contamination.
6. Secure Trash Bins: Use   foot-pedal-operated trash bins  with lids for disposing of gloves, PPE and contaminated materials.
7. Mark Zones with Tape: Mark quarantine areas with red or yellow tape and label stalls clearly. Maintain a log for anyone entering the zone.
8. Isolate Medical Tools: Provide individual stethoscopes and grooming tools for each horse. Use nylon halters and lead ropes, which are easier to disinfect than leather.
9. Control Ventilation: Assign fans exclusively to quarantine areas and prevent shared airflow between healthy and quarantined horses.
10. Stock Emergency Supplies: Keep NSAIDs,   electrolytes  and fluids on hand as prescribed by a veterinarian.
11. Prepare Transport Kits: Have disposable trailer mats, tarps and post-transport disinfectants ready for moving horses under quarantine.

Preventing the Spread

Veterinarians emphasize that biosecurity remains the most effective tool to contain the outbreak. Barn managers should ensure all staff receive training in proper protocols. Regular monitoring of horses’ temperatures—twice daily—is critical, as fever is often the first sign of infection.

For the latest updates on case numbers and regional alerts, visit the   Equine Disease Communication Center .