Equine Herpes Virus

Equine Herpes Virus is often times a mild disease in horses and is caused by EHV-1.  When this virus infects a horse, there is a time that the horse is often shedding the virus in nasal secretions with or without clinical signs.  If the horse gets a high viral load in the blood, then there is an increased chance that this horse will become neurological.  We say these horses have Equine Herpesvirus Myeloencephalopathy (EHM). Often times these horses are still shedding virus into the environment.  Non-neuropathic EHV-1 strain and Neuropathic EHV-1 strain classifications are somewhat confusing as both strains can lead to neurologic involvement.

This disease has broken out in 5 racetracks around the US.  There are also cases of showing up of horses that have been to rodeo type events here in Arizona as well as training facilities in Wyoming to name a few.

It is recommended that if your horse is showing signs of disease not to take it to an event and work with your veterinarian when it come to vaccinations for your equine companion.  Also think twice before sharing tack, buckets or grooming supplies as these can spread the virus.

Below is the press release for Turf Paradise Racetrack and further down is some more detailed information on EHM with thanks to the Equine Disease website.


NEWS RELEASE DATE: February 14, 2018

MEDIA CONTACT: Sharma Torrens, 602-542-3191, storrens@azda.gov

Quarantine in Place to Contain Equine Herpes Virus

Arizona Department of Agriculture (AZDA) Director Mark Killian ordered the quarantine of a barn at Turf Paradise Racetrack today in response to the reported case of a neurotropic form of Equine Herpes Virus – 1 (EHV-1) in one horse housed at the track.

Investigations are underway to identify any other horses that may have been exposed to EHV-1. The AZDA State Veterinarian and the Arizona Department of Gaming Division of Racing are working with officials at Turf Paradise to quarantine and monitor any other potentially exposed horses. Track management is also requiring strict biosecurity measures be practiced by all horse-owners and other personnel during this quarantine period.

Equine Herpes Virus -1 is highly contagious among horses but poses no threat to humans. The symptoms in horses may include a fever, nasal discharge, wobbly gait, hind-end weakness, dribbling of urine and diminished tail tone. The virus is easily spread by airborne transmission, horse-to-horse contact and by contact with nasal secretions on equipment, tack, feed and other surfaces. Caretakers can spread the virus to horses if their hands, clothing, shoes or vehicles are contaminated.

State Veterinarian, Dr. Peter Mundschenk, encourages Arizona horse-owners to contact their veterinarian for medical questions and to contact the State Veterinarian’s Office (602-542-4293) for quarantine questions and reminds Arizona veterinarians to report any horses exhibiting neurological signs to the State Veterinarian immediately.

Equine Herpesvirus Myeloencephalopathy

Disease Type: This disease is caused by the EHV1 virus which is common in the horse population. In extremely rare cases, EHV4 can develop into EHM.

Transmission: EHV1 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 such as stalls, water, feed, tack, and transport vehicles. Humans can spread the virus from horse to horse by contaminated hands and clothing.

Frequency: Although EHV1 and EHV4 are a relatively common cause of a mild respiratory disease, EHM, the neurologic form caused by either EHV1 or EHV4, is not common.

Incubation period: Ranges from 2 to 10 days. Horses can shed the virus during the incubation period.

Carrier status: Infected horses are carriers and can shed the virus even when showing no clinical signs.

Latency: EHV is a viral disease that most horses have been infected with at some point in their life. It is unknown why this virus produces the neurological form in some horses. Horses that have had EHV1 may be carriers and the virus may be latent and reoccur under periods of stress such as transport or a new activity.

Severity: EHM is life threatening.

Clinical signs:

FeverThis virus typically causes a biphasic (two phase) fever. The horse will have fever on day 1 or 2 and again on day 6 or 7. Neurological signs may not present until the second fever. Some horses may not develop a fever.

  • Nasal discharge
  • Depression
  • Incoordination
  • Hind limb weakness
  • Loss of tail tone
  • Loss of bladder toneurine dribbling or inability to urinate
  • Dog sitting position
  • Leaning against a fence or wall to maintain balance
  • Recumbencyinability to rise

Diagnosis: The diagnosis is made by having a veterinarian collect nasal swabs and whole blood collected from the horse. Horses with neurologic signs which test positive for EHV1 are considered positive for EHM.

Treatment: There is no cure for EHM. Supportive care is administered including the use of nonsteroidal antiinflammatory drugs (NSAIDS) such as phenylbutazone (Bute) or flunixin meglumine (Banamine) to reduce fever, inflammation, and pain. Corticosteroids have been used but there is no evidence of benefit. Antiviral drugs such as acyclovir and valacyclovir have been used but their value in horses with EHV infection is unknown.

Prognosis: Prognosis for horses who test positive for EHV and then develop neurologic signs of EHM is often poor with fatality as high as 30%. In rare cases, horses with neurologic signs can recover from the infection but may retain neurologic deficits.

Prevention: Currently, there is no USDA licensed EHV1 vaccine which is proven to protect against the neurological disease associated with EHV1. The best method of protection is always to maintain current EHV vaccinations on all horses on your property and to follow correct biosecurity protocol when bringing new horses onto your premises, when travelling, or during any activity where horses may come together.

Biosecurity: EHV1, and rarely EHV4, has the potential to cause EHM so biosecurity measures appropriate for EHV1 should be taken. EHV1 is spread via aerosol particles from nasal discharge or from contaminated surfaces including people, clothing, feed and water, implements, and stalls; isolation of affected or exposed horses is critical to preventing spread of the virus. Proper biosecurity measures include extensive cleaning and disinfection of surfaces and equipment that come in contact with affected horses. Individuals treating or coming into contact with infected horses need to follow appropriate disinfection protocols when handling multiple horses (Go To: http://equinediseasecc.org/biosecurity.aspx ).