Since the outbreak of two deadly drought-related wildlife diseases in August, there have been more than 500 reports of sick or dead deer in Eastern Washington.

That number will likely grow, said Michael Atamian, the district biologist for the Washington Department of Fish and Wildlife, as more reports are cataloged by agency staff. A spate of cold weather, however, may mean the worst of the viral outbreak is over.

Both bluetongue and epizootic hemorrhagic disease are transmitted via biting Culicoides gnats. The disease cannot spread to humans, although wildlife officials recommend not eating animals that are obviously sick.

“We had a hard frost, at least at my house at Chewelah last night,” said Annemarie Prince, northeast district wildlife biologist on Friday. “I’m hoping that will stop it.”

In August, reports of dead or dying deer started coming in from across the region, Atamian said. WDFW biologists collected samples and confirmed the presence of both diseases.

Both bluetongue and EHD occur more frequently during drought years, possibly because deer concentrate around available water sources, which is also the breeding habitat for the gnats.

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White-tailed deer are most susceptible to these diseases and usually die within two to four days, but can survive up to two weeks, according to a WDFW statement. Mule deer do not typically die from these diseases, although there have been a handful of documented deaths this year.

There have also been reports of bluetongue outbreaks in bighorn sheep herds. As of late August, at least 20 bighorns had been found dead in British Columbia’s Grand Forks area and there have been reports of sick and dead bighorn sheep in the Okanogan region, Atamian said.

The last large outbreak occurred in 2015, and killed several hundred white-tailed deer in Eastern Washington.

It’s too soon to tell how this year’s outbreak compares to 2015, Atamian said, although geographically it’s just as widespread.

“What I’ve been telling most of our hunters, the geographic extent of this is pretty widespread in my district,” he said. “How severe it is in any of those places is not consistent.”

Tracking the extent of the disease is complicated by the fact that WDFW relies on citizen reports. This means that higher population areas, like around Spokane, receive more reports, Atamian said. At the same time, the public and the agency is more aware of the disease since the 2015 outbreak, possibly increasing the level of reporting.

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“We’ve done better, I’d have to say, and our public is more educated because of the 2015 outbreak,” Atamian said of tracking the disease.

As for any impacts on hunting, the agency will not change any seasons this year. Most general Washington deer hunting seasons open next weekend. In an email that will be sent to Eastern Washington hunters Monday, WDFW warned that hunting success may be impacted although there are “no further reductions in white-tailed deer seasons planned at this time.”

“From a hunter’s perspective is it going to make our hunting season harder? Yes,” Atamian said. “It means there will be less deer on the landscape.”

The 2015 outbreak had an outsized impact on white-tailed deer populations because it was followed by harsh winters in 2016 and 2017. Decreased harvest by hunters prompted the WDFW commission to eliminate antlerless deer hunting in District 1 in 2019 and then later throughout the region.

Biologists are hopeful those hunting reductions allow the white-tailed deer population to weather this outbreak better than the 2015 one.

“From a population standpoint, this is not the end of our whitetail deer,” Atamian said. “Yes, the population is taking a hit. This is horrible for the individual deer. But, the whitetail deer will bounce back from this eventually. Assuming we can avoid hard winters and massive droughts.”