June 30, 2021
December 8, 2020

Disease Spotlight: EHV Type 1

Learn the signs of EHV-1 so you know how to protect your horse in the case of an outbreak.

Allison Armstrong Rehnborg

When was the last time you brushed up on barn biosecurity? Just like using hand sanitizer and personal protective gear are helpful measures for people during a global pandemic, practicing good hygiene and biosecurity at the barn and at horse shows can help protect your horse from contagious diseases like equine herpesvirus-1 (EHV-1). Outbreaks of EHV-1 can occur at any time, so it’s important to stay current on the latest news regarding this disease in areas where you plan to travel with your horses.


EHV-1 is a contagious respiratory disease that can spread quickly through nasal secretions from infected horses and contaminated equipment. It’s also an extremely common disease in the equine population, according to Gisela Hussey, DVM, Ph.D., professor of pathobiology and diagnostic investigation at Michigan State University in East Lansing, Michigan.

“Most adult horses are infected with EHV-1 throughout their lifespan, and establishment of lifelong latency is detected in up to 70% of infected horses,” Hussey said.

EHV-1 affects horses in multiple ways, including respiratory symptoms, neurological issues, abortion in pregnant mares and death in newborn foals. Common symptoms include:

  • Fever
  • Depression
  • Anorexia
  • Coughing
  • Nasal and eye discharge

Some horses who become infected with EHV-1 may also develop equine herpesvirus myeloencephalopathy (EHM), which is a severe neurological form of the disease.

“While most horses become infected with EHV-1 throughout their life, typically only around 10% of infected horses show clinical signs of EHM except for older horses, whose risk of EHM is higher,” Hussey explained.

There are many factors involved in why some horses develop EHM while others don’t, but some strains of the virus are more likely to cause EHM than others. According to the American Association of Equine Practitioners (AAEP), the onset of neurologic disease is typically sudden and progresses rapidly. Symptoms include weakness in the hind limbs, loss of tail tone, head tilt, leaning against a fence or wall and an inability to rise. Any symptoms like these warrant an immediate call to your veterinarian.


While equine herpesvirus sounds scary, it’s important to remember that this disease can be prevented and managed by using sound biosecurity protocols and acting quickly in the case of an outbreak. You can stay updated on disease outbreaks in your area by checking with your state’s agricultural department, but it’s a good idea to practice basic biosecurity with your horses all the time.

“Because the majority of horses are latently infected and vaccines don’t protect against the most severe forms of EHV-1, including EHM, good biosecurity at the barn and when going to horse shows is critical,” Hussey said. “For the barn, that means quarantine for new incoming horses or for horses returning from a show that become sick. At the show, avoid sharing buckets or other equipment that could be contaminated, wash your hands and keep your horse away from horses that are not from the same barn. These measures aren’t always practical, so do the best you can under the circumstances.”

If you think a horse may have been exposed, Hussey recommends following these AAEP guidelines:

  • Isolate potentially infected horses for 28 days after the last new infection
  • Look for clinical signs and perform twice-daily temperature checks
  • Keep out of the primary biosecurity perimeter
  • Wash your hands regularly
  • Don’t share equipment between infected and susceptible horses
  • Don’t move exposed horses

“It is important to realize that the majority of horses have been exposed to this virus and are likely latently infected and will re-activate throughout their life, so there is no sure way to prevent exposure,” Hussey explained. “On a day-to-day basis, enjoy your horse and don’t drive yourself crazy. If you go to a horse show, move barns or there are other scenarios that might increase the chance for re-activation or exposure, consider basic measures. If there is an outbreak in your barn or a horse returns from a place that reported an outbreak, communicate with the barn manager and the barn community, implement biosecurity measures and consult your veterinarian or experts for help in mitigating the outbreak.”

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