Equine Herpes Virus- 1 (EHV-1)

Dr. Casey Rabbe DVM
Faribault Veterinary Clinic

What is “Myeloencephalitis”?

Myeloencephalitis is a neurological disease that is caused by an equine herpes virus infection. Neurological diseases are those that are associated with problems in the brain and spinal cord. Equine Herpes Virus-1 (EHV-1) infection causes damage to the blood vessels that supply the brain and spinal cord of the horse. Without blood supply, these tissues are damaged, which leads to the symptoms associated with this disease. EHV-1 can also cause respiratory disease, abortions, and death in young foals. The neurological symptoms are most often due to a particular strain of this virus that has a mutation in its genes.

How common is this virus?

By 2 years of age, most horses have been exposed to the virus. Generally, exposure occurs through contact with the dam. The virus becomes inactive or “latent” in the horse’s body and causes no symptoms of disease. Stress, heavy work, transporting long distances, or weaning can cause the virus to reactivate and the horse to show symptoms of the disease. In recent years, there has been an increase in the number of cases reported around the country. Outbreaks have occurred at large horse shows, boarding facilities, and racetracks. Due to the large number of exposed horses and the serious consequences of this disease, an increased awareness of the neurological form of EHV-1 is a must.


Equine Herpes Virus handout 2015_html_m4b7a10baThe neurological form of EHV-1 can occur before or after the respiratory or abortion form of EHV-1. Neurological symptoms can occur alone. Signs of myeloencephalitis include:

  • Fever (4-10 days before signs below)
  • Decreased coordination
  • Dribbling urine
  • Loss of tail tone
  • Weakness in the hind limbs
  • Leaning on walls, fences etc.
  • Inability to stand, sitting like a dog


  • Swabs taken from the nostrils of a horse can be used to isolate the virus in the laboratory or used to run a test called a Polymerase Chain Reaction (PCR) which can detect virus in a sample.
  • A blood sample can be taken for laboratory virus isolation and PCR.
  • Two blood samples can be taken 2-3 weeks apart to determine if there has been an increase in antibodies to the EHV-1 virus, which would indicate exposure the virus.
  • Cerebral spinal fluid, fluid that surrounds the spinal cord, can be sampled for evidence of infection.Equine Herpes Virus handout 2015_html_13782e8e

**There are currently vaccines that control the respiratory and abortion forms of EHV-1, but the neurological form, myeloencephalitis, does NOT have a preventative vaccine.**

What to do if you suspect your horse has myeloencephalitis caused by EHV-1:

  • Call your veterinarian immediately. EHV-1 is a reportable disease! Immediate medical care is needed for your horse.
  • Isolate the infected horse from other horses and people. Move to a separate barn or paddock, or to a veterinary care facility.
  • Notify owners of other horses that were exposed to the infected horse in the last 10 days.
  • Isolate other exposed horses or sick horses.

Do not share equipment since the virus can be spread from contact with contaminated items.


As part of this work, we encourage horse owners to follow these equine biosecurity tips when traveling with their horse.

  1. It is always best to use your own trailer and equipment. If you must borrow, clean and disinfect items thoroughly before exposing your horse and again before returning.
  2. Don’t let your horse touch other horses, especially nose to nose.
  3. Never put the end of a shared hose in your horse’s water bucket without disinfecting first. Don’t hand-graze your horse where other horses have recently grazed.
  4. If you touch other horses, wash your hands with soap and water, and dry them well. Use disinfectant wipes or hand sanitizer if soap and water are not available. Don’t let strangers pet your horse.
  5. Clean and disinfect tack, boots, equipment, and grooming supplies before returning home. Make sure to clean off dirt and manure before disinfecting.
  6. Shower, blow your nose (germs can survive a long time in nasal secretions), and put on clean clothes and shoes upon your return.
  7. Keep returning horses separate from your other horses for up to 4 weeks. When doing feeding and chores, work with the returning horses last, wear boots and coveralls, and remove them before working with your other horses.
  8. Don’t forget to wash your hands.

Remember! Symptoms of this disease indicate an emergency.

Contact your veterinarian right away