BAKER CITY — An outbreak of an insect-spread disease has killed at least eight deer in Baker Valley in less than a week, and a state wildlife biologist fears this outbreak could be much worse than previous episodes.

The often-fatal illness is epizootic hemorrhagic disease, which is caused by a virus spread by the bite of midges that breed in stagnant water.

Brian Ratliff, district wildlife biologist at the Oregon Department of Fish and Wildlife’s Baker City office, said he received several calls over the weekend from residents who found dead deer on their properties in the Pine Creek and Ben Dier Lane area, at the western edge of Baker Valley about 12 miles northwest of Baker City.

Based on that cluster of cases, the disease seems to be spreading more rapidly than in previous outbreaks in the valley, Ratliff said.

EHD can kill white-tailed and mule deer — the first two carcasses Ratliff examined this weekend were mule deer — but whitetails are much more susceptible to the illness, he said.

An outbreak of EHD killed an estimated 2,000 white-tailed deer in Umatilla County during the fall of 2019.

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, pronghorn antelope, sheep and cattle, but the mortality rate is much higher with white-tailed deer than with other species, Ratliff said.

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.

The biggest recent outbreak in Baker County happened during the late summer and early fall of 2015, Ratliff said.

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

Ratliff said epizootic hemorrhagic disease outbreaks typically start later in the year, when water sources are more scarce, forcing deer to congregate in those places and making them more likely to either be infected by midges or, in the case of deer that already carry the virus, to spread it to midges that bite them.

The virus can spread in both ways, he said — from infected deer to midges, and from infected midges to deer.

That allows the illness to spread rapidly in certain conditions.

Ratliff said outbreaks usually dissipate once freezing temperatures have killed the year’s crop of midges.

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. That means bucks can’t produce testosterone, the hormone that causes bucks to shed their antlers every year. When that happens the buck can have antlers for the rest of its life, and the antlers typically remain in the velvet stage constantly.

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

White-tailed deer, which are found throughout Northeastern Oregon, are especially susceptible to the epizootic hemorrhagic disease, which is spread by biting midges.