Trail Talk

November 2025

Equine Herpesvirus-1 in the News

By Katie Delph Miller, DVM, MS, DACVIM
Clinical Associate Professor, Equine Internal Medicine

Many have probably heard the news and many rumors about Equine Herpesvirus-1 cases in the past couple of days. We want to provide an update of information and be a resource for finding answers.

What are the clinical signs of EHV-1 infection?

  1. Respiratory disease: Clinical signs include fever, nasal discharge, and cough along with non-specific signs of lethargy and decreased appetite.
    clinical sign of EHV-1, wobbly hind legs
    Figure 1
  2. Neurologic disease: Clinical signs include possible fever detection, incoordination and weakness of the limbs that are worse in the hind limbs (Figure 1), urine dribbling, decreased tail or anal tone, and possible progression to not being able to stand.This form of the disease is called Equine Herpesvirus Myeloencephalopathy (EHM).
  3. Reproductive disease: Clinical signs include abortion in late-term pregnant mares, still births, or birth of severely weak foals.

How is EHV-1 transmitted?

EHV-1 is contagious and spreads among horses through direct contact with respiratory secretions, inhalation of aerosolized respiratory droplets, or contact with contaminated equipment, tack, clothing (humans!), etc. Once infected, the incubation period before horses show clinical signs is typically 2-10 days but can be up to 14 days in some cases. Horses can be infectious via their respiratory secretions for 14-21 days or sometimes even longer.In the environment, outside of the horse, the virus can remain infective for 7-14 days.

If there is any concern of exposure to EHV-1, horses should be quarantined with biosecurity measures in place; and if any horses show clinical signs of disease associated with EHV-1, they need to be isolated from the rest of the herd and strict biosecurity used.

How is EHV-1 infection or EHM diagnosed?

clinical sign of EHV-1, nasal discharge
Figure 2

As with any concerns, your veterinarian will need to examine your horse. Be sure to tell your veterinarian of clinical findings (fever, nasal discharge, neurologic signs) as well as travel history and exposure to any other including sick horses when calling to make an appointment so that they can use appropriate personal protective equipment (PPE) when evaluating your horse. Based on clinical signs, your veterinarian may want to test for EHV-1 as well as perform other diagnostic tests to rule out other causes of disease. Definitive diagnosis for EHM is testing ideally both whole blood and nasal swab samples (Figure 2) via PCR. In other recent outbreaks, it was found that some horses had fever before their samples would test positive; therefore, if your horse tests negative, but is highly suspected of EHM or EHV-1 disease, testing may need to be repeated.

How can EHM be treated?

EHM is highly concerning disease because if the neurologic signs are severe, a horse can become recumbent, meaning that they can’t get up, or their neurologic signs may be long-lasting or residual affecting their performance. This outcome occurs in the minority of cases thankfully, but of course, we want to do everything we can to have complete recovery. Treatment principles are mostly supportive care with anti-inflammatories, anti-coagulant medications, or possibly antivirals. Some cases need a urinary catheter placed to ensure that they can empty their bladders, and some cases need help rising with a sling among other supportive measures. Anti-viral medications are best for prevention in exposed horses before the onset of clinical signs. Contact your veterinarian to discuss options for potentially exposed horses or, of course, if your horse is displaying clinical signs.

How can EHV-1 and EHM be prevented?

Good routine biosecurity practices are the best prevention:

  • Quarantine new horses to a property for 14-21 days
  • Quarantine or house horses that travel separate from the resident herd
  • Segregate old or young horses and pregnant horses from traveling horses
  • Have an isolation (separate air space is ideal) plan in case a horse develops signs of illness
  • Routine vaccination
  • Minimize stress
  • Quarantine any horses that may have been potentially exposed to EHV-1 or other infectious diseases
    biosecurity measures for EHV-1
    Figure 3
    • During quarantine, check and record temperatures twice daily.Contact your veterinarian if a temperature >101.5 °F or any other clinical signs of illness are observed.
    • Be sure to isolate further any horses displaying fever or clinical signs.
    • Use strict biosecurity measures including PPE (Figure 3) on exposed or ill horses.

Routine vaccination is important for all preventable diseases.For EHV-1, the American Association of Equine Practitioners (AAEP) considers EHV-1 a risk-based vaccination.This means that horses that travel or horses that are exposed to horses that travel should be vaccinated, and we typically recommend vaccination for EHV-1 every 6 months for prevention of respiratory disease.For pregnant mares, a high-antigen load vaccine is recommended at the 5th, 7th, and 9th month of gestation for prevention of reproductive disease.However, it is very important to note that none of the vaccines prevent the neurologic form of EHV-1.Contact your veterinarian to discuss vaccination options and set up a biosecurity plan for your farm.

What is the current situation?

On November 18, 2025, an officially-confirmed case of EHM was reported and was associated with the Women’s Professional Rodeo Association (WPRA) World Finals and Elite Barrel Race in Waco, TX that took place from November 5-9. Officially confirmed cases to date include 2 cases in TX, 2 cases in OK, and 3 cases in LA, as of Nov. 18, 2025. This is an evolving situation, and likely case numbers will continue to be updated. A good resource for current information is the Equine Disease Communication Center (EDCC). Any owners with horses that attended these events are requested by regulatory officials within each state, specifically the State Departments of Agriculture to isolate their potentially exposed horses, stop on-and-off movement on their farm, check temperatures twice daily, and use increased biosecurity measures on their farms.

Please contact your veterinarian or Equine Services at the K-State Veterinary Health Center (785-532-5700) with questions.

Additional resources for information: