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Chronic wasting disease battle heats up in Minnesota

This emaciated deer in Iowa County, Wis., was later confirmed to have CWD. Most animals that carry the disease look healthy. It's only in the final stages where they become sickly looking. Wisconsin DNR photo. 1 / 3
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This captive elk was later found to carry chronic wasting disease, an always fatal brain ailment. Some scientists say they expect CWD to make the jump to humans, as did mad cow disease in the 1990s. Colorado Parks and Wildlife photo 3 / 3

With Minnesota wildlife officials scrambling this winter to slow the spread of chronic wasting disease among wild deer in southeastern counties, and 55 Wisconsin counties now identified as CWD sites, the impacts of the disease are hitting closer to the Northland.

CWD, now confirmed in 25 states and two provinces, is always fatal to cervids — whitetail and mule deer, moose and elk. Studies show that once it infects more than one-third of the population, entire herds may be decimated.

In parts of southern Wisconsin, more than 50 percent of the wild deer are now infected with CWD. So far, there is no antidote, no vaccine for deer, no way to get rid of it.

But it's not just deer populations that are at stake — it could be the future of deer hunting. Even if wild deer somehow persist on the landscape, it's unclear how many hunters would still want to hunt them if CWD remains a possible threat to people.

The disease has never been confirmed in people, but it's very similar to mad cow disease, which crossed species and killed humans.

CWD, caused by mutated proteins called prions, already has crossed species to macaque monkeys that were fed infected meat in laboratory tests. Dr. Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota and an expert on infectious diseases, puts the human danger bluntly.

"I do believe that it is not a matter of if, but when, CWD crosses to humans,'' Osterholm told the News Tribune.

"That's the biggest scare with this disease — what that would do" to deer hunting and wildlife management, said Michelle Carstensen, wildlife health program group leader for the Minnesota Department of Natural Resources.

CWD can be spread not just by infected live deer, but by contaminated feces, saliva and other bodily fluids and body parts from deer long dead. Predators that eat infected meat can move the mutated proteins around for miles. It can persist in soil for years, maybe indefinitely. It can even be taken up from soil by plants that healthy deer might eat.

"It's kind of like radioactivity. Once you have this stuff, it never really goes away,'' said Lindsay Thomas of the Quality Deer Management Association, a national deer hunting group based in Georgia. "So the goal is to keep it out as long as you possibly can. If you don't have it, you don't want it. Consider it like a front in a war where you do everything to keep it out. Deer hunters need to be at war with this disease."

In Wisconsin, wildlife officials have essentially given up trying to contain the disease by active management such as culling infected deer. While the state still tests some of the deer shot each year for CWD, public and political pressure years go ended efforts to reduce the disease by culling infected herds.

But in Minnesota, wildlife officials are battling the disease aggressively this winter, trying to keep CWD confined to a few captive deer farms and small areas of wild deer habitat. So far, only 32 wild deer in Minnesota have been confirmed with CWD, all in southeastern counties, compared to thousands in Wisconsin.

"By the time Wisconsin discovered they had CWD, in 2002, it was probably already on the landscape for a decade. They were already over 5 percent prevalence (of CWD among wild deer in infected areas.). So, the horse was already out of the barn,'' Carstensen said. "But we are at only 1 or 2 percent, even in our our core (CWD-infected area.) Is it realistic to say we can eliminate CWD in Minnesota? No, it's not possible. But we think we still have a chance to keep it in check."

Wisconsin woes

During the most recent hunting 2018 seasons the Wisconsin DNR tested 16,337 deer for CWD, a fraction of more than 250,000 harvested statewide in bow and gun seasons. Some 975 were positive for CWD, about 6 percent. But in some areas, such as Iowa County in the southwestern part of the state, more than half of all deer are carrying CWD, said Tami Ryan, chief of the Wisconsin DNR's wildlife health program.

Ryan said researchers are in the third year of a four-year study to determine if CWD in high prevalence areas is already impacting deer populations, as it has in Wyoming in both mule and whitetail deer. So far, no results available.

Ryan said the state has also no data on whether CWD is impacting license sales, whether fewer people are buying deer hunting licenses or eating venison because of CWD.

She said when it first was confirmed in Wisconsin, in 2002, there was about a 10 percent decline in license sales.

"But after that, the numbers went back up," Ryan said. "We really don't know if it's impacting the decline we're seeing more recently. We don't have that kind of recent behavioral data."

CWD timeline

January 1967

Chronic wasting disease first identified as a disease in captive mule deer at the Colorado Division of Wildlife Foothills Wildlife Research Facility in Fort Collins, Colo.

February 1978

CWD officially classified as a transmissible spongiform encephalopathy, like scrapie in sheep and goats, mad cow disease in cattle and Creutzfeldt-Jakob disease in humans.

September 1981

The Colorado Division of Wildlife identified CWD in a wild elk, marking the first documented case of CWD in a wild animal.

February 1996

CWD found for in a Saskatchewan farm elk — the first time outside of the Colorado/Wyoming CWD zone.

February 2001

South Dakota discovered CWD in wild white-tailed deer for the first time.

February 2002

First CWD confirmed in a Wisconsin wild whitetail deer.

August 2002

First CWD in Minnesota confirmed in an Aitkin County elk farm.

September 2005

First CWD confirmed in a wild moose in Colorado.

April 2006

University of Wisconsin researchers discover that CWD prions adhere to soil and can infect new animals for years, maybe forever.

October 2006

Colorado researchers find CWD prions can be transmitted through saliva and blood.

December 2008

Researchers find CWD prions are shed in the feces of early-stage CWD-infected deer.

December 2009

First CWD confirmed in a wild deer in southwestern North Dakota.

January 2011

Minnesota's first documented case of CWD in a wild deer in Olmsted County, near where a CWD-positive elk was found on a farm the year before. No other CWD-positive deer have been found since in that area.

January 2016

A CWD-positive deer confirmed at a Crow Wing County farm where all the deer eventually perished due to CWD. So far no wild deer have tested positive in the area.

July 2017

Canadian scientists reveal that CWD was transmitted to monkeys that were fed infected meat or brain tissue from CWD-infected deer and elk.

November 2018

CWD confirmed in a wild deer in Houston County, many miles from any other infected sites in Minnesota.

December 2018—February 2019

Minnesota DNR holds several special hunting season to cull and test more deer near where CWD positive deer have been confirmed. Federal sharpshooters called in to kill and test more deer in the area.

Sources: Minnesota DNR, Wisconsin DNR, Wildlife Management Institute,, Centers for Disease Control and Prevention, Quality Deer Management Association.