What is EHV-1

  • Contagious equine virus that can cause four clinical presentations: neurological disease, respiratory disease, neonatal death, and abortion.

Clinical Signs

  • Fever commonly precedes other clinical signs
  • Respiratory Disease
    • Fever, coughing, nasal discharge
    • Abortion
      • Usually occurs in late pregnancy (8+ months, but as early as 4 months) with no warning signs
      • Neurologic Disease – also known as Equine Herpesvirus Myeloencephalopathy (EHM)
        • Hind-end weakness and incoordination
        • Leaning against wall or fence to maintain balance
        • Urine dripping or inability to urinate
        • Down and unable to stand


  • Highly variable, incubation period may be as short as 24 hours, but is typically 4-6 days
  • When neurologic disease occurs, it is typically 8-12 days after fever begins

How is the virus spread?

  • The most common way to spread EHV-1 is by direct horse-to-horse contact
  • EHV-1 can also spread indirectly through contact with physical objects contaminated with virus
    • Tack, grooming equipment, feed and water buckets, people’s hands or clothing


  • Supportive care, anti-inflammatory drugs
  • Antiviral medications for horses with the neurologic form
  • Sling support for horses with severe weakness and in-coordination
  • Antibiotics may be given if your veterinarian is concerned about secondary bacterial infection
  • Isolate affected horses to prevent spread of infection


  • Vaccines are available to control the respiratory and abortion manifestations of EHV-1
  • Current vaccines do not reliably prevent development of the neurological form
  • Your veterinarian may recommend vaccination to help reduce spread of the virus
    • Calvenza
    • Pneumabort

Does EHV-1 affect other animals?

  • EHV-1 does not affect humans, dogs, cats, sheep, goats, cattle, pigs, or birds
  • Alpacas and llamas are susceptible to EHV-1

More information on EVH-1 and control measures that you can take are posted on the University of California Davis’s website.

Check out our blog post on ways that you can prevent the spread of EHV-1 by disinfecting your barn.

Please feel free to call the clinic at 763-441-3797 with any questions.


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  1. Pingback: Spring vaccines to protect your horse | Anoka Equine Blog

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