11/23/2025
IMPORTANT INFORMATION FOR HORSE OWNERS: Understanding EHV, How It Spreads, and How to Protect Your Herd
With recent EHV activity in several states and regions (Texas, Oklahoma, Louisiana, Colorado, Nevada, Arizona, Alberta, and spreading), this is a good time for horse owners to understand how Equine Herpesvirus works, why outbreaks happen suddenly, and what steps help keep horses safe.
🐴 What Is EHV?
Equine Herpesvirus (EHV) is a very common family of viruses in horses.
The two major types are:
EHV-1: Can cause fever, respiratory disease, abortions in pregnant mares, and the neurological form known as EHM (Equine Herpes Myeloencephalopathy).
EHV-4: Primarily causes respiratory illness.
According to the American Association of Equine Practitioners (AAEP), a large percentage of horses have already been exposed to EHV-1 or EHV-4 during their lifetime.
➡️ Source: AAEP Infectious Disease Guidelines (EHV-1)
https://aaep.org/guidelines/infectious-disease-control/equine-herpesvirus
🦠 Many Horses Carry EHV Quietly
Just like people can carry herpes viruses without active illness, horses can carry EHV in a latent (sleeping) state within their nerves or lymph tissue.
A horse may carry EHV for life without showing symptoms.
The virus stays dormant—until something triggers it.
⚠️ Stress Can Reactivate EHV
The Merck Veterinary Manual reports that stress is the most common trigger for reactivation.
Stress can include:
- Hauling or long trailer rides
- Being introduced to a new herd
- Weather extremes
- Illness
- Training, showing, or heavy exercise
- Weaning
- Overcrowding
- Poor nutrition or dehydration
When the virus reactivates, the horse begins shedding EHV even if it looks perfectly healthy.
Source: Merck Veterinary Manual – Equine Herpesvirus
https://www.merckvetmanual.com/horse-owners/viral-diseases-of-horses/equine-herpesvirus-infection-horses
📌 How EHV Spreads
EHV spreads very easily through:
- Direct Contact
- Nose-to-nose touching
- Coughing or sneezing droplets
Indirect Contact
- Shared water buckets
- Feed tubs
- Tack or grooming tools
- Stalls, trailers, fences
- People’s hands, clothes, and shoes
- Equipment or machinery moving between barns
The virus can survive hours to days on surfaces depending on temperature and humidity.
Source: Colorado State University Veterinary Teaching Hospital
https://csu-cvmbs.colostate.edu/vth/Pages/equine-herpesvirus.aspx
📈 How Common Is EHV?
There is no exact nationwide annual count, because EHV is not reportable in all states, but veterinary surveillance shows:
Mild respiratory EHV infections are very common every year.
Serious EHM outbreaks (neurological cases) occur 15–30 times per year in the U.S.
These outbreaks typically involve a handful to several dozen horses.
Source: USDA APHIS Equine Disease Events
https://www.equinediseasecc.org
🩺 Signs to Watch For
The earliest and most important sign is fever.
Other symptoms include:
- Nasal discharge
- Lethargy
- Loss of appetite
- Cough
- Hind-end weakness
- Stumbling or wobbliness
- Difficulty urinating
- Abortions in pregnant mares
Call a vet immediately if any horse has a fever or neurological signs.
🧪 Diagnosis & Treatment
Veterinarians use:
- Nasal swabs
- Blood samples
There is no cure, but supportive care—including fluids, anti-inflammatories, and NSAIDs—can help. Neurological cases may require hospitalization.
🛑 Biosecurity Is the Best Defense
Veterinary experts strongly recommend:
✔️ Isolate new or exposed horses for 21–28 days
✔️ Take temperatures twice daily
✔️ Do NOT share equipment
✔️ Disinfect buckets, stalls, and trailers
✔️ Limit hauling during outbreaks
✔️ Avoid visiting multiple barns
✔️ Wear clean clothes and wash hands between horses
These steps slow or stop nearly every outbreak.
Source: UC Davis Center for Equine Health
https://ceh.vetmed.ucdavis.edu/health-topics/equine-herpesvirus
💉 What About Vaccines?
Vaccines:
- Reduce viral shedding
- Help reduce spread
- Help with respiratory and abortion protection
But vaccines DO NOT prevent the neurological form (EHM).
Still, vaccination can slow outbreaks and reduce severity.
Source: AAEP Vaccination Guidelines
https://aaep.org/guidelines/vaccination-guidelines
🟢 Summary
Many horses carry EHV silently.
Stress can reactivate the virus.
A shedding horse can infect others before showing symptoms.
EHV spreads easily through direct and indirect contact.
Good biosecurity dramatically lowers risk.
Most cases are mild, but EHM is rare and serious.
Communication and quarantine save horses.
