The number of white-tailed deer that die from viruses in the Pacific Northwest has typically infected more animals during hot summers and periods of drought, experts say.
Deer get the virus after being bitten by mosquitoes, which thrive when the mud is exposed under dried-up waterholes where the insects live, according to the Northwest News Network.
And in dry periods, more deer gather around these holes in search of water and are more likely to be bitten by mosquitoes, experts say. The tiny insects can live in puddles of water as small as a deer’s hoofprint, according to the Oregon Department of Fish and Wildlife.
One virus is known as epizootic hemorrhagic disease, or EHD, and the other is known as bluetongue. They are not contagious to humans and cannot be transmitted from deer to deer. The spread usually stops after the first hard frost that kills the mosquitoes.
Increasing drought has made the viruses more prevalent this summer and fall, and this is worrying as climate change makes hot and dry conditions more common, said Kevin Snekvik of Washington State University’s Animal Disease Diagnostic Laboratory.
“Your population is starting to have more and more animals that are susceptible to the virus because they haven’t developed immunity,” Snekvik said.
Kristin Mansfield, a veterinarian in Washington state, said she was receiving reports of suspected cases in mid-August and slowly in late October.
“When I got the first report this summer, I looked at the calendar and it was August 16th. My thought was, ‘Oh boy. Here we go. Right on schedule, ‘”said Mansfield.
EHD affects white-tailed deer almost exclusively and can rarely affect domestic cattle. Bluetongue affects deer and bighorn and domestic sheep, she said.
Washington has received reports of sick deer from east of the Cascade Mountains, including Spokane Valley, Deer Park, Colfax and Davenport. Idaho Fish and Game reported that around 250 to 300 white-tailed deer died in the past month, including in the Kamiah and Clearwater areas.
Oregon is also seeing an increase in deer primarily infected with EHD, said Colin Gillin, an ODFW veterinarian.
Oregon ended the hunting season in the Blue Mountains last year because an estimated 2,000 deer died from the virus.
“There were no deer there for hunters to go out and spend their time,” said Gillin. “You just have to keep an eye on it and try to follow it. There is nothing you can do about that. “
That year the department also had reports of diseased black-tailed deer in central Oregon, which is a little unusual, Gillin said. The viruses are more common in white-tailed deer, he said.
“We have seen it more and more over the past 10 years, the more drought conditions we have,” said Gillin.
Snekvik said he was also concerned about the increase in other diseases such as the West Nile virus as summer conditions become more favorable for the mosquitoes that transmit the virus.
West Nile first arrived in the Columbia Basin. It has now been found in northern Idaho and near the Canadian border, he said.
“We see the virus moving further north over time, probably because the mosquitoes continue to carry it, because they can survive up there,” Snekvik said.