EHV-1: What Are We Learning?

This potentially fatal infectious disease continues to challenge the horse industry, but our experiences are teaching us how to prevent its spread.

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EHV-1: What Are We Learning?
Events where horses commingle can be infectious disease breeding grounds, but in recent years many facilities have developed more comprehensive biosecurity measures to help prevent EHV-1 outbreaks. | Photo: Alexandra Beckstett/The Horse

There’s a life-threatening disease horses can harbor in their bodies without showing any signs of illness. But under stress—even inapparent stress—the horse can disperse the virus with every cough or sneeze, exposing nearby equids to the pathogen. All of this can happen undetected until, perhaps, a horse in the same barn turns up with a fever or another begins showing neurologic signs.

This nightmarish scenario can mark the start of an equine herpesvirus-1 (EHV-1) outbreak, which most frequently occurs where horses congregate, such as at horse shows, trail rides, or barns with transient populations.

In the past 15 years veterinarians have seen the number of EHV-1 cases and outbreaks in the United States rise. These scenarios have caused widespread worry and confusion among horse owners and brought equine transport and events to a screeching halt. The end result, however, has been increased awareness—particularly of the potentially fatal neurologic form, equine herpesvirus myeloencephalopathy (EHM)—and research funding to discover ways to prevent and treat the disease

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Written by:

Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey’s Guide to Raising Horses and Storey’s Guide to Training Horses. Besides having her own blog,, she writes a biweekly blog at that comes out on Tuesdays.

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