Quick Facts about Equine Herpesviruses (EHV and EHM)

Many questions were brought up when both Camelot Events and Langer Equestrian cancelled or moved their last shows of the season due to an outbreak of Equine Herpesviruses or EHV. While studying for the horsemastership quiz this year, we discussed EHV and the vaccinations required to prevent it, but I felt we didn’t have enough facts to understand why the quarantine was enforced and what can be done to prevent such outbreak in the future. I spent the next week researching the topic, so that I may share it with all of you.

According to a factsheet published by the Equine Disease Communication Center (EDCC), EHV is a common virus that is spread from horse to horse through contact with nasal discharge or spread as aerosol droplets. Horses can also contract the virus by coming into contact with contaminated surfaces, including people, clothing, tack, feed, water, and transportation vehicles. The virus can remain dormant for the lifespan of the horse but reactivation is possible from stress such as transport or new activity.

Clinical signs for both strains of the virus are the same and they include:

  • Fever
  • Nasal discharge
  • Lethargy/Depression
  • Neonatal Death
  • Neurologic disease

EHV usually causes a flu-like illness in the horse. Supportive care and rest are the main treatments. Non-steroidal anti-inflammatory medications, such as Bute or Banamine control fever, pain and inflammation.  In most cases, horses recover from EHV in a few weeks and once fully rested, they can gradually return to work. Some of the research suggests that older horses, with regular vaccinations, over time develop stronger immunity and can recover faster and easier than younger horses.

But in some cases, as Debra Sellon, DVM, reported in the Practical Horseman Magazine, the virus damages blood vessels in the brain and spinal cord, producing a deadly neurologic disease called Equine Herpesvirus Myeloencephalopathy or EHM. Neurologic signs may include lack of coordination, hind-end weakness, diminished tail tone or unwillingness to rise. Horses who remain able to stand usually recover. The outlook is not so good for those who go down and can’t rise.

There are few different strains of EHV as well.  EHV-1 and EHV-4 for instance are relatively common strains but the neurologic form of either EHV-1 or EHV-4, called Equine Herpesvirus Myeloencephalitis or EHM is very rare.

Currently vaccinations are available for prevention of EHV-1 and EHV-4 but as EDCC reports “there is no vaccine labeled for the prevention of the neurologic form or EHM”.

Since this virus can cause an epidemic in the facilities with multiple horses that have close contact, a quarantine of both horses and the facility is critical.  This is exactly what has been happening at LAEC since November 3rd.  It was found that a 5 year-old Saddlebred displaying severe neurologic signs and a 10 year-old Saddlebred in Los Angeles County displaying moderate neurologic signs were confirmed positive for the strain, EHV-1.  The two confirmed positive horses, along with four other horses, returned to California on October 30th from a horse show in Las Vegas, NV. Due to the severity of clinical signs, the 5-year-old horse was euthanized on November 3, 2016.

As of November 14th, 2016, 12 horses have been quarantined in total. To date, there have been seven confirmed cases of EHM.  Enhanced biosecurity measures are in place in all barns under quarantine and all horses’ temperatures are monitored twice daily. California Department of Food and Agriculture,CDFA, veterinarians, livestock inspectors and USDA animal health technicians continue to monitor the quarantine.

Elvenstar is very consistent about vaccinating for EHV twice a year, but will be taking extra precautions during this outbreak by not attending any further competitions until the California Dept. Of Food And Agriculture and the state veterinarians have declared the outbreak over and lifted all quarantines. This is the safest way to keep our horses at the lowest risk of infection.