2021 Case of Equine Herpesvirus Myeloencephalopathy (EHM) Identified in Vermont

May 3, 2021 | Montpelier, VT – In April 2021, the Vermont Agency of Agriculture (Agency) was notified that a horse exhibiting neurologic abnormalities tested positive for Equine Herpesvirus 1 (EHV-1), resulting in a case of Equine Herpesvirus Myeloencephalopathy (EHM). Due to the diligence of the owners and attending veterinarian, the disease was contained and did not spread. The Agency has released the quarantine and considers this incident closed. No equine movement linked this case to the outbreaks occurring in Florida or Europe, and it illustrates the importance of constant vigilance and good biosecurity.

EHV-1 is endemic in the US and most horses are infected with the respiratory form of the virus at some point in their lives. During periods of stress, previously infected horses can shed the virus and infect other horses through direct or indirect contact. In rare circumstances, that infection can manifest as EHM and be life-threatening.

Humans can also carry this virus and other disease-causing agents between equine populations on clothing, supplies and equipment. It is imperative that persons moving between horse populations, or from farm to farm, practice good hygiene, including regular hand washing and disinfection of equipment between uses.

The Agency is not planning to cancel or impose mandated restrictions on Vermont shows or other equine commingling events at this time. As always, horse owners/managers and equine event managers/employees are encouraged to implement biosecurity practices whenever horse(s) are moved away from or back to resident properties and/or commingled with horses from other properties.

As a precaution, Vermont horse owners should follow these basic biosecurity measures:

  • All newly-purchased horses or horses that return to Vermont from events should be immediately isolated from other horses and quarantined for at least three weeks;
  • All quarantined horses should be monitored for illness, including fever, cough, lack of appetite, nasal or ocular discharge, and/or swelling around the throat;
  • All quarantined horses should have a temperature taken twice a day during the isolation period, and have separate thermometers for each quarantined horse;
  • If a fever is recorded or signs of illness are noted, a veterinarian should be called immediately.

Remember to discuss vaccination protocols with your veterinarian that protect horses from EHV-1 and other contagious diseases! Anyone concerned about a potential EHV-1 case should contact their veterinarian immediately. 

For more information on equine biosecurity, review the Agency’s website here: https://agriculture.vermont.gov/animal-health/livestock-and-poultry-programs#equine.

Equine event managers, employees and superintendents can find additional biosecurity recommendations and event assessment forms and tools here: https://equinediseasecc.org/biosecurity/event.

Equine Herpesvirus Myeloencephalopathy (PDF): https://agriculture.vermont.gov/sites/agriculture/files/EHM_Guidance_Document%20for%20SAHO_Revised_2018.pdf

If you would like to be added to the Agency’s equine industry distribution list to receive equine-specific updates about this and other issues impacting the equine industry, please send a request to Kristin.haas@vermont.gov.

For questions, please contact:

Kaitlynn Levine, DVM (she/her/hers)

Assistant State Veterinarian

802-636-7144 | Kaitlynn.Levine@vermont.gov 


Contact Information

Agency of Agriculture, Food & Markets

116 State Street
Montpelier, Vt 05620-2901


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