EHD is a recurring disease and an unfortunate reality for Idaho’s white-tailed deer

Epizootic hemorrhagic disease occurs periodically in Idaho, typically during hot summers and during drought. It mostly affects white-tailed deer, but mule deer can also contract it. The disease is caused by a virus spread by gnats when deer are concentrated near ponds, reservoirs and other water sources with exposed mud and puddles that serve as a breeding ground for gnats.

"EHD is a naturally occurring, fast-acting viral disease, and our focus is on monitoring outbreaks," Fish and Game Wildlife Veterinarian Nicole Walrath said. "Unfortunately, there's no cure or available vaccine for EHD in white-tailed deer. EHD is often fatal once an animal develops symptoms, killing susceptible deer within 36 hours, but some deer will survive and develop immunity."

The severity of the outbreak and die offs is largely dependent on deer densities and the level of herd immunity. Because EHD is carried and transmitted by gnats, the only preventative would be significantly reducing the gnat population, which would be difficult, if not impossible. Vast areas would have to be treated with insecticide on public and private property in a very short span of time to head off an outbreak. Even if that was feasible, it would likely set up a larger die off later because the herd's immunity would be compromised.

Cooler weather tends to slow an EHD outbreak, and a hard frost typically ends it. There is no established human health risk associated with handling or eating animals infected with EHD.

Bottom line: EHD is unfortunately a disease that periodically hits whitetail herds in Clearwater and Panhandle Regions, and that's likely to continue in the future. Fortunately, most EHD breakouts affect a relatively small percentage of the deer population - although it can have a larger effect on local herds - but the effect is typically short lived.

After an EHD outbreak, whitetail herds usually rebound within 2-3 years, depending on the severity of the outbreak. The recoveries are often quick and predictable enough that Fish and Game rarely has to alter hunting seasons due to an outbreak.

"We certainly understand hunters' frustrations when they hear about another outbreak of EHD, which often occurs in August and September right before hunting season," Toby Boudreau, Fish and Game Deer/Elk Coordinator said. "We've been dealing with this disease for a long time while still maintaining very abundant whitetail herds. In most cases, the mortality is localized to lower-elevations areas. We know it can kill a portion of local herds, but that reduction is temporary."

Symptoms of EHD in deer include a loss of appetite and wariness, swelling around the head and neck, dehydration and weakness, increased respiration rate, excessive salivation, rosy or bluish color of mouth and tongue, blood flecks may occur in the urine and feces. In severe cases, a bloody diarrhea can develop.

Deer that are infected may show lameness and a tendency to avoid direct sunlight. An increase in body temperature can cause deer to seek cool places, such as in and around water.

For more information on EHD go to https://idfg.idaho.gov/conservation/wildlife-health/epizootic-hemorrhagic-disease .