Equine Herpesvirus (EHV): What It Is and How to Spot It in Your Horses

In recent weeks, multiple states across the U.S. have reported cases of Equine Herpesvirus-1 (EHV-1), including the neurologic form known as Equine Herpes Myeloencephalopathy (EHM). Many of these cases have been traced to large barrel racing and rodeo events, prompting arena closures, event cancellations, and new movement requirements for horses.

Understandably, this has owners, trainers, and veterinarians on high alert. This post explains what EHV is, what to watch for, and practical steps you can take to help protect horses in your care.

Equine herpesvirus (EHV), sometimes called equine rhinopneumonitis, is a family of highly contagious viruses that circulate in horse populations worldwide. Of the nine known equine herpesviruses, the ones that matter most for everyday horse health are:

• EHV-1 – can cause:
  • Respiratory disease
  • Abortion in pregnant mares
  • Neurologic disease (EHM)
• EHV-4 – primarily causes respiratory disease, especially in younger horses
  

Like other herpesviruses, EHV can establish latency, meaning a horse can be infected, recover, and then carry the virus silently. Under stress (travel, competition, illness), the virus can reactivate and shed, even if the horse doesn’t look sick.

EHV spreads efficiently wherever horses commingle, including at shows, sales, rodeos, boarding barns, and training facilities. The virus is transmitted by:

• Direct horse-to-horse contact, especially nose-to-nose
• Respiratory droplets from coughing or snorting in close quarters
• Contaminated equipment and environments, including:
  • Shared water buckets and feed tubs
  • Tack, grooming tools, lead ropes, and halters
  • Trailers, stalls, and fences
• People and vehicles acting as mechanical carriers via hands, clothing, boots, and surfaces

The virus can survive in the environment for a limited time, especially in cool, damp conditions, but it is readily inactivated by common disinfectants when used correctly.

EHV infection can look very different from horse to horse. Broadly, we think of three major clinical presentations:

1. Respiratory Form (EHV-1 & EHV-4)

• Both EHV-1 and EHV-4 commonly cause a respiratory syndrome that can range from mild to severe. Typical signs include:
  • Fever (often the earliest sign)
  • Lethargy and decreased appetite
  • Watery to thick nasal discharge
  • Cough
  • Swollen lymph nodes under the jaw
• During outbreaks, state and veterinary officials often recommend checking temperatures twice daily on exposed horses and treating any fever (commonly greater than 101.5°F / 38.6°C) as a red flag that warrants a call to your veterinarian.

2. Neurologic Form – Equine Herpes Myeloencephalopathy (EHM)

• EHM is a neurologic syndrome primarily caused by EHV-1. In this form, the virus damages blood vessels in the spinal cord and brain, leading to neurologic signs that can progress quickly and may be fatal.
• Neurologic signs can include:
  • Sudden incoordination (ataxia), especially in the hind limbs
  • Weakness or “wobbly” gait
  • Horse standing in a “dog-sitting” posture
  • Tail weakness or loss of tail tone
  • Urine dribbling or inability to urinate normally
  • Difficulty rising or lying down and unable to get up
  • Severe cases may require intensive nursing care and can have a high mortality rate
• Not every horse with EHV-1 will develop EHM. In fact, neurologic cases are relatively rare compared to the number of horses exposed or infected; however, outbreaks can affect 20–50% of at-risk horses in a group once EHM appears.

3. Reproductive Form (Abortions & Neonatal Disease)

• EHV-1 is a well-known cause of abortion in pregnant mares and can also cause weak foals and neonatal death. Abortions most often occur in the last trimester, sometimes with minimal warning. 
• Mares may appear clinically normal before aborting, but can shed large amounts of virus, posing a risk to other pregnant mares and horses in the barn.

As of late November 2025, EHV-1 and EHM cases linked to large competition events have been confirmed in several states, including Texas and Oklahoma. These outbreaks have led to:

• Cancellations of major rodeo and barrel racing qualifiers
• Temporary closures of equestrian arenas in affected regions
• Issuance of animal health alerts and advisories by multiple state departments of agriculture
• Heightened monitoring of horses that traveled to specific events and surrounding shows

State animal health officials and organizations, including the Equine Disease Communication Center (EDCC), USDA APHIS, and AAEP, are providing ongoing updates and outbreak management guidance.

Because requirements and risk levels change quickly during an outbreak, always check:

• Your state veterinarian or state animal health agency website
• The EDCC outbreak map and alerts
• Any event-specific health protocols if you plan to haul or compete

You can’t diagnose EHV in the barn aisle, but you can spot early warning signs and act quickly. Call your veterinarian promptly if you notice any of the following, especially if your horse has:

• Recently traveled to a competition, sale, or large equine event
• Been stabled near horses that have traveled
• Been notified as a potential contact of an affected facility

Red-Flag Signs to Watch For:

Monitor horses at risk at least twice daily for:

• Fever: ≥101.5°F (38.6°C)
• Respiratory changes:
  • New or worsening nasal discharge
  • Coughing
  • Rapid or labored breathing
• Behavior and appetite changes:
  • Lethargy, depression
  • Reduced appetite or not finishing feed
• Neurologic signs:
  • Stumbling, dragging toes, crossing hind legs
  • Difficulty turning or backing
  • Standing wide-based or in a dog-sitting position
  • Tail weakness, urine dribbling, or incontinence
  • Lying down and reluctant or unable to rise

How EHV Is Diagnosed:

• PCR testing on nasal swabs and/or blood samples to detect the virus
• Additional bloodwork or imaging to rule out other causes of neurologic disease
• Testing of aborted fetuses or placental tissue in reproductive cases

Only a veterinarian, working in conjunction with a diagnostic laboratory, can confirm an EHV infection.

Whether or not your barn has been directly exposed, strengthening day-to-day biosecurity is one of the best ways to protect horses and maintain business continuity during an outbreak. Recommendations from state and federal animal health agencies include:

Monitor and Record:

Take temperatures twice daily on exposed or high-risk horses and log them.

• Keep a simple chart with horse names, temps, and any clinical signs.
• Isolate and contact your veterinarian immediately for any horse exhibiting a fever or other concerning signs.

Isolate and Separate:

• Designate isolation stalls or areas for sick or exposed horses.
• Avoid nose-to-nose contact across stall fronts or over fences.
• Use separate equipment (buckets, feed tubs, pitchforks, muck carts) for each group, and clearly label them.
• Handle healthy horses first, then exposed or sick horses last.

Clean and Disinfect:

• Wash hands thoroughly between horses or wear disposable gloves.
• Regularly clean and disinfect:
  • Stalls (especially after a horse leaves)
  • Trailers
  • High-touch surfaces like door latches, cross-ties, and shared equipment
• Use an EPA-registered disinfectant labeled for enveloped viruses and follow the recommended contact times.

Manage Movement:

• Work with your veterinarian and state animal health officials before moving exposed horses.
• Follow any state quarantine or movement orders to the letter—EHV-1/EHM is a reportable disease in many states.
• Check current event and state-entry requirements for health certificates, test requirements, and additional declarations.

During fast-moving disease situations, requirements for horse movement and event participation can change quickly. While your veterinarian is your primary partner in clinical decisions, having accurate and up-to-date documentation when necessary is also crucial.

Through digital health certificates and integrated rule updates from regulatory authorities, platforms like GlobalVetLink help veterinarians:

• Stay aligned with current state and event requirements
• Reduce errors on certificates that could delay travel or entry
• Maintain clear, legible records during outbreak investigations

If you have any concerns about your horse’s health or possible exposure to EHV:

1. Contact your veterinarian immediately.
2. Isolate the horse from others while you wait for guidance.
3. Avoid hauling or attending events until you’ve discussed risk and requirements with your vet and, when appropriate, your state animal health official.

EHV outbreaks are stressful, but they are not new. With prompt recognition, strong biosecurity, and close collaboration between owners, trainers, veterinarians, and regulators, we can reduce spread, protect more horses, and keep the equine industry moving safely.