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Equine Herpesvirus
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May 18th, 2011


Several cases of "neurologic rhino" have been reported in Arizona and nine other western states. All reported cases appear to stem from exposure to the equine herpes virus ("rhino") at a competition held in Ogden, Utah during the first week of May 2011. Some horses are recovering but others have been euthanized or have died.

Equine herpes virus ("rhino virus") has two strains, EVH-4 & EVH-1. EVH-1 usually causes respiratory disease. Sporadically, EVH-1 infection causes neurologic disease. The neurologic disease is a devastating illness that often ends in death or career limiting longterm damage. This virus only affects the equine species - horses, donkeys and mules. There is no danger to humans or other domestic animals.

There is no definitive treatment once animals become ill. Intravenous fluids, antiinflammatories, anti-viral medications ($$$) and nutritional support are all indicated but success of treatment is extremely variable.

Signs of infection with and illness from the neurologic form of EVH-1 include:

  • Incoordination of the hind legs (and occasionally front legs)
  • Urine dribbling - overflow from full bladder
  • Inability to stand or walk
  • Lethargy, fever and respiratory signs may be present before neurologic signs develop

Infected animals may shed the virus and cause infection in others before they appear ill. Monitoring temperatures will help detect infected animals earlier than waiting for other signs to develop. Horses with temperatures over 101F suspect for infection.

There is no commercially available vaccine that is labeled for prevention of equine herpesvirus myeloencephalopathy ("neurologic rhino"). However, there is evidence that vaccination with a good quality EVH-1 (rhino) product may help animals resist infection. Vaccination of at risk animals for EVH-1 is not known to lead to complications.

How to prevent the spread of EVH-1:
Probably the most important step in preventing spread of infection is limiting animals' exposure to the virus:

    Veterinarians are recommending that you try to keep horses at home for the next 14-21 days.
  • Isolate sick animals.
  • Do not share buckets, stalls, feeders, brushes, turnout areas, etc. between horses or groups of horses.
  • Do not borrow or lend equipment such as bridles and saddles.
  • Disinfect trailers between loads. Disinfect stalls if horses are being moved from one barn to another.
  • Wash or disinfect your hands between horses.
  • Disinfect your shoes before entering the barn area if you have been "off property".

The incubation period after exposure varies from 24 hours to as much as 21 days - the average time between exposure and illness is about 7 days. Infected animals should be kept isolated from others for one month after clinical recovery.

Information was provided by Laura M. Harris, DVM


Al Dunning's Encounter with EHV-1:
AQHA Professional Horseman recognized the symptoms of Equine Herpes Virus and was abl to save his three horses.


AAEP About the Outbreak and Additional Resources
AAEP List of State Vets
AAEP Fact Sheet
USDA Brochure on the Disease
Bio-security Tips