White-tailed deer, which are found throughout Northeast Oregon, are especially susceptible to the Epizootic Hemorrhagic Disease, which is spread by biting midges.

The insect-spread virus that killed an estimated 2,000 white-tailed deer in Umatilla County last fall has been detected elsewhere in Northeast Oregon, but it hasn’t caused any major die-offs in recent years, biologists said.

Epizootic Hemorrhagic Disease (EHD) is spread by the bite of midges that breed in stagnant water.

Deer can’t spread the virus, also known as blue tongue, to other deer or animals by direct contact. Midges carrying the virus can infect other animals, including mule deer, elk and cattle, but the mortality rate is much higher with white-tailed deer than with other species.

The virus poses no threat to people, cats or dogs. Nor can people become ill by eating the meat of a deer or other animal infected with EHD.

Biologists with the Oregon Department of Fish and Wildlife (ODFW) say EHD is responsible for the significant death toll among white-tailed deer last year in parts of Umatilla County.

There are herds of white-tailed deer in Baker, Union and Wallowa counties as well, and although biologists have confirmed cases of EHD in those counties over the years, they haven’t seen any losses comparable to what happened last year in Umatilla County.

The biggest recent die-off in Baker County happened during the late summer and early fall of 2015, said Brian Ratliff, district wildlife biologist at ODFW’s Baker City office.

Ratliff said ODFW didn’t compile an official death toll, but he believes many dozens of white-tailed deer died in the county in 2015.

Dead deer were found in Baker Valley and in Pine Valley.

There haven’t been any widespread outbreaks in white-tailed deer since 2015, and their population is rebounding in Baker County, Ratliff said.

White-tailed deer have expanded their range throughout much of Wallowa County, but biologists have confirmed only an occasional case of EHD in white-tails, said Pat Matthews, ODFW’s district wildlife biologist in Enterprise.

“We haven’t had any significant losses that we’re aware of up here,” Matthews said.

When EHD is prevalent it’s difficult to miss given the high mortality rate among white-tailed deer, he said.

“You’d notice if there was any significant number of deer dying,” Matthews said.

In Wallowa County white-tailed deer populations are highest in the Wenaha and Sled Springs units, with smaller numbers in the Snake River, Imnaha and Chesnimnus units, Matthews said.

Matt Keenan, ODFW’s district wildlife biologist in Union County, said biologists examined some white-tailed deer carcasses last year, but they weren’t able to get tissue samples fresh enough to have lab tests confirm EHD.

“But we think it’s likely” that the virus killed at least some of those deer, Keenan said.

He said it’s also possible that EHD killed two pronghorn antelope in Union County last year.

Ratliff said the only confirmed case of EHD over the past year in Baker County was in a mule deer that was living within the Baker City limits.

That deer had been showing neurological symptoms, he said.

Although infected mule deer are much more likely to survive than white-tailed deer are, Ratliff said the virus, which causes blood vessel constriction, can have severe and in some cases permanent effects on mule deer.

The vascular constriction can cause the testicles to shrivel and eventually fall off infected mule deer bucks, which renders them incapable of breeding, Ratliff said.

The loss of testicles also means the bucks can’t produce testosterone, the hormone that causes bucks to shed their antlers every year, generally in late winter.

When that happens the buck can have antlers for the rest of its life, and the antlers typically remain in the velvet stage constantly, Keenan said.

Ratliff said he has seen several mule deer bucks that apparently were infected with EHD in 2015, survived the virus but lost their testicles.

Ratliff and his colleagues, Matthews, Keenan and Phillip Perrine, assistant district biologist in Union County, all agreed that although white-tailed deer have been expanding their range in the region, they’re not responsible for declining populations in mule deer.

Mule deer declines have more to do with predators, the biologists said.