Understanding Equine Herpesvirus and Protecting Your Horses
The 2025 Outbreak: A Wake-Up Call
In November 2025, the equine community was reminded just how quickly EHV-1 can spread. An outbreak traced to the WPRA World Finals and Elite Barrel Race in Waco, Texas (November 5–9, 2025) resulted in confirmed cases across multiple states, including Texas, Louisiana, Oklahoma, Pennsylvania, Maryland, and Colorado. The outbreak led to the cancellation of numerous rodeo and barrel racing events as horse owners and organizers worked to contain the virus.
Texas Agriculture Commissioner Sid Miller issued an alert urging horse owners who attended or were near the Waco event to monitor their animals closely. As Miller noted, "This virus can spread fast, it can be deadly, and the earliest signs are often so subtle they're easy to miss."
While this outbreak captured headlines, it's important to understand that EHV-1 is not a new virus—it's a well-studied pathogen that veterinarians have managed for decades. The key to protecting your horses lies in understanding how the virus works and implementing proper biosecurity measures.
EHV-1 Resources:
- Read the EHV-1 Fact Sheet
- AAEP Equine Herpesvirus (EHV-1 & EHV-4) Disease Guidelines
- AAEP Equine Herpesvirus FAQ
What Is EHV-1?
Equine herpesvirus type 1 (EHV-1) is one of nine known herpesviruses that affect horses. It's among the most common and most concerning, capable of causing respiratory disease (commonly called rhinopneumonitis), late-term abortion in pregnant mares, neonatal foal death, and neurologic disease known as equine herpesvirus myeloencephalopathy (EHM).
An estimated 60–70% of horses are exposed to EHV-1 by two years of age. After initial infection, the virus can become latent—meaning a horse can carry it for life without showing symptoms. Stress factors such as travel, competition, or illness can reactivate the dormant virus, potentially triggering an outbreak.
How EHV-1 Spreads
EHV-1 is highly contagious and spreads primarily through direct horse-to-horse contact, particularly nose-to-nose interaction. It can also spread through aerosolized droplets from coughing or sneezing, contaminated surfaces including shared water buckets, tack, halters, lead ropes, and grooming equipment, and indirect transmission via humans who handle infected horses and then touch other animals without proper hygiene.
Importantly, horses can begin shedding the virus before they show any outward signs of illness, making early detection and quarantine protocols critical.
Recognizing the Signs
The incubation period for EHV-1 is typically two to ten days. Clinical signs can vary significantly depending on which form of the disease develops.
Respiratory signs include fever (often exceeding 102°F), nasal discharge, mild cough, lethargy, and reddened mucous membranes.
Neurologic signs (EHM) typically appear 1–7 days after fever onset and may include hindlimb weakness or incoordination, swelling or "stocking up" of the limbs, difficulty urinating or urine dribbling, trouble rising or standing, reduced tail strength, and in severe cases, inability to stand or coma-like states.
Only about 10% of infected horses develop neurologic signs, but EHM can be life-threatening with mortality rates ranging from 30% to as high as 75% in severe cases.
Treatment Options
There is no cure for EHV-1—once infected, the virus remains in the horse's system for life. However, supportive care and early intervention can significantly improve outcomes.
Supportive care includes rest and isolation, anti-inflammatory medications (NSAIDs) such as flunixin meglumine to manage fever and inflammation, nursing care including hydration, nutrition, and bladder management for neurologic cases, and DMSO (dimethyl sulfoxide) to reduce swelling.
Antiviral therapy using valacyclovir has shown promise in reducing viral shedding and viremia, particularly when administered early—ideally before clinical signs appear. Current dosing protocols typically involve a loading dose of 27 mg/kg orally three times daily for the first two days, followed by a maintenance dose of 18 mg/kg twice daily for 7–14 days. Research indicates that valacyclovir is most effective when given prophylactically to horses at high risk of exposure, though it may still provide benefit when started after fever develops.
Most horses with mild to moderate cases can be managed on-farm as long as they remain ambulatory and can eat, drink, urinate, and defecate normally. Recumbent horses (unable to stand) require referral to facilities with specialized isolation and intensive care capabilities.
Vaccination: What You Need to Know
Vaccines against EHV-1 and EHV-4 are available and can help reduce respiratory symptoms and viral shedding. However, no vaccine currently carries a label claim for preventing the neurologic form (EHM). Modified-live virus vaccines such as Rhinomune® have shown promise in reducing viral shedding and fever duration.
Vaccination recommendations include routine vaccination for horses at shows, training facilities, or other venues where horses mingle, boosters every six months for high-risk horses, and pregnant mares should receive vaccines specifically licensed to prevent EHV-1 abortion.
Critical note: It is not recommended to vaccinate horses that have already been exposed during an active outbreak. For horses with no known exposure, a booster is appropriate if they haven't been vaccinated within the past three months. Consult your veterinarian to determine the best vaccination schedule for your horses.
Prevention: Your Best Defense
Biosecurity is by far the most effective way to protect your horses from EHV-1. Implement these practices at your facility and when traveling:
Limit contact with unfamiliar horses. Avoid nose-to-nose greetings and don't allow your horses to share water buckets, tack, or grooming equipment with horses whose health status is unknown.
Quarantine new arrivals and returning travelers. Isolate any horse that has attended a show, competition, or event for at least 21 days. Keep them at least 30 feet from other horses.
Monitor temperatures twice daily. Fever often appears before other clinical signs. Any temperature above 101.5°F warrants immediate isolation and veterinary consultation.
Practice proper hygiene. Wash hands or use disinfectant between handling different horses. Change clothes and footwear after contact with horses of unknown health status. Use dedicated equipment for each horse when possible.
Clean and disinfect trailers between loads, especially after transporting horses that have been at events.
Respect quarantines. Quarantines typically remain in place for 21 days after the last case is diagnosed. Do not move horses from quarantined premises, and follow all guidance from your state veterinarian.
What to Do If You Suspect EHV-1
If your horse shows any signs of illness—particularly fever, respiratory symptoms, or neurologic abnormalities—take these steps immediately:
- Isolate the affected horse from all other horses on the property.
- Contact your veterinarian right away. They can perform PCR testing on nasal swabs or blood to confirm diagnosis.
- Document temperatures and symptoms in a daily log.
- Follow your veterinarian's guidance regarding reporting to state animal health officials (EHM is a reportable disease in many states).
- Stay Informed
For the most current updates on EHV-1 outbreaks, consult the Equine Disease Communication Center (EDCC), your state veterinarian's office, and your local equine veterinarian. Reliable information is your best tool for protecting your horses and the broader equine community.
At Wire2Wire Vet Products, we're committed to supporting horse health and helping you keep your animals safe.