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