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."

Winter hunts and sharpshooters

This winter in and around southern Minnesota's Fillmore County efforts are underway to kill as many deer as possible in the core of the CWD-infected area to reduce the population and thus reducing the chance of spread. Special public and landowner hunts were held in December and early January. Later this month, U.S. Department of Agriculture sharpshooters will be called in to kill even more deer. Each deer will be tested for CWD.

Just east of that primary CWD zone, in Houston County in the southeast corner of the state, special public hunts will be held in coming weeks to kill and test more deer around where a single mature buck shot in November tested positive for CWD.

"We really want to know if that buck was an outlier, if he wandered in from somewhere else, or if we have CWD in that area,'' Carstensen said. The buck was 8 miles from a CWD-infected deer farm in Winona County, about 15 miles away from the nearest CWD-infected wild deer in Minnesota and about 20 miles from CWD-infected areas of Iowa and Wisconsin.

"We have no idea where that buck became infected," Carstensen said.

So far, landowners, hunters and Minnesota lawmakers have cooperated with the DNR's aggressive culling strategy, agreeing to see fewer deer in their favorite area - at least for a year or two until populations bounce back - in exchange for a chance at keeping CWD from spreading.

"We have a few people who can't see past the next hunting season and that big buck they want to shoot and don't want us taking more deer,'' Carstensen said. "But, for the most part, we have people who are thinking about the future, about whether their grandchildren will have deer hunting."

Craig Engwall, executive director of the Minnesota Deer Hunters Association, said his group continues to support the DNR's aggressive efforts. He said the approach is similar to battling against invasive species: You can't stop the spread of invaders like zebra mussels, he noted, but you can slow it down and keep them out as long as possible - until, maybe, scientists come up with a defense.

"We want Minnesota to take the aggressive approach so we don't end up like Wisconsin,'' Engwall said. "I think there's pretty good public support to go after this (CWD) while we still can."

Thomas said every state is handling CWD a little differently. But efforts to cull large numbers of deer in infected areas have worked well in New York, where a few CWD positive deer were eliminated and the disease so far hasn't returned, and in Illinois, which has aggressively culled deer in CWD areas and held infection rates to 2 percent or less.

"If Minnesota can keep it that way, it seems to work. It's a long, constant, expensive battle. But it beats the alternative of having CWD everywhere,'' he said.

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."

Slow the spread

CWD is spreading deer-to-deer as the animals move naturally in the wild. Mature bucks can travel many miles during the fall mating season, the rut, and move CWD from one county to another, even one state to another, often following habitat corridors like rivers.

But much of the spread of CWD has been blamed on deer and elk farms which raise, trade and transport cervids for food or for trophies to be hunted in so-called "canned" hunts in fenced preserves. Outbreak maps of wild CWD cases often seem to cluster around contaminated farms, and there have been calls for additional controls, if not outright bans, on such farms.

In Minnesota's Crow Wing County, near Brainerd, a dead deer farm buck was confirmed CWD positive in 2017. (The only reliable test for CWD is after death.)

The DNR instituted mandatory testing for wild deer shot in the area. So far, no wild deer have tested positive, but the DNR wants to keep testing in the area after a total of nine deer in the farm have perished from CWD. It's unknown how many of the 106 deer still on the farm have CWD.

There remains no requirement for farmers to depopulate a captive herd even when they test positive for CWD.

"We're really going to be watching the area around that farm going forward,'' Carstensen said.

Engwall said his group will continue to push for rules banning the interstate and intrastate transportation of captive deer and to require double fencing around deer and elk farms to keep wild deer away from potentially CWD-infected deer farms. The group opposes canned hunts.

Minnesota has some 398 licensed deer and elk farms, Wisconsin has 380. They are regulated under state agriculture departments and generally outside the purview of state natural resource agencies.

"If you look at the maps where there have been CWD (positive) farms and where it shows up in the wild, it's pretty clear what the problem is,'' Engwall said.

But hunters may also be to blame, unknowingly killing an infected animal and then bringing it back back home where parts of the animal are disposed of incorrectly, like tossing carcases or deer parts into the woods.

Because most infected animals look healthy (only at the end of their lives do infected deer begin to look like zombies, and most hunters wouldn't harvest such a sickly looking animal) most hunters don't have any clue the animal is infected, and most deer are never tested.

Last year, Thomas, of the Quality Deer Management Association, used public license data to find that hunters from 49 different states - every state except Delaware - killed more than 32,000 whitetails in just four Wisconsin counties with the highest incidence of CWD in the state - Dane, Iowa, Richland and Sauk. (Dozens of those hunters were from Minnesota, including several from the Duluth area.) Thomas said that means it's very possible, considering the high rate of infection in those counties, that some or even many of the non-resident hunters shot and then moved CWD contaminated deer.

Many states, including Minnesota, now have regulations against importing or moving deer carcass. But enforcement is sketchy and it's unclear how many hunters are complying.

"Even if you don't have CWD in your area ,you can't think of this as some far-off problem, because that's when it's going to show up your own backyard,'' Thomas said. "If you hunt deer in other states, near CWD areas, if you don't take precautions and follow the rules, you are just as likely to bring it home in a deer carcass as some deer farmer trucking a live deer across state lines."

What we know about CWD

It's a mutant protein

Chronic wasting disease is an always-fatal nervous system disease found in cervids - deer, elk and moose. There is no known cure. It is not a virus or bacteria.

CWD is one of a family of diseases called transmissible spongiform encephalopathies caused when a naturally occurring protein, called a prion, mutates and then resists being broken down by the body the way normal proteins are.

When a deer become infected - from contact with contaminated soil or salvia, blood or feces of an infected animals - the bad prions multiply and damage the animal's nervous system. It can take up to two years for the symptoms to show.

It's spreading faster

In just 50 years, it's spread from a single known location, a wildlife research station in Colorado, to 25 states, two Canadian provinces, North Korea, Norway and Finland.

In Minnesota, CWD has been confirmed in wild deer in three southeastern counties: Houston, Olmstead and Filmore. It has been confirmed in deer on deer farms in Aitkin, Meeker, Crow Wing, Stearns, Lac Qui Parle, Olmstead and Winona counties.

In Wisconsin, 55 counties are labeled as CWD-impacted. Of those, 25 have had confirmed CWD in wild deer and 16 are within 10 miles of a wild CWD-positive deer. Another 14 counties have had CWD-positive deer in deer farms or are within 10 miles of those farms.

It's been found, but hasn't spread, in Northland

There have been two CWD cases in the Northand. One was a wild deer shot near Siren, Wis., in Washburn County, about 70 miles south of Superior, in 2012. So far, no other deer have tested positive in that area. That case is curious because the sickly deer was more than 100 miles away from the nearest CWD-positive location.

The other was an elk at an Aitkin County. Minn. deer farm in 2002. That was Minnesota's first-ever positive CWD hit and no wild deer in the area have tested positive since then.

It's similar to mad cow, Creutzfeldt-Jakob diseases

Creutzfeldt-Jakob is a rare but always fatal human brain disease. It is related to the form of mad cow disease that infected people, primarily in Great Britain, in the late 1990s and early 2000s, after they ate beef from infected cows. (Human mad cow disease is known as variant-Creutzfeldt-Jakob.) Both diseases attack the brain, and death usually occurs within a year.

Mad cow disease first occurred in cattle after they were given feed and bone meal from sheep, including some that had been infected with another prion disease called scrapie. Mad cow eventually changed to a strain of prions in cattle that could infect humans. It killed more than 200 people worldwide and 4.5 million cattle were euthanized.

The outbreak was traced to farmers chopping up unwanted cow parts and feeding them to other cows, spreading the infectious agent from cow to cow and eventually to humans. The FDA largely banned this practice in 1997.

It's spread to macaque monkeys, our closest relative

Health and especially wildlife officials have tried to stress that CWD is only a cervid, or deer family disease. They had been quick to note that, unlike mad cow disease, CWD had not jumped species. Only now it has.

A study in Canada led by a prion researcher with the Canadian Food Inspection Agency found that macaque monkeys had contracted chronic wasting disease after being fed meat from deer that tested positive for CWD.

Its potential impact on people is unknown

"To date, there is no strong evidence for the occurrence of CWD in people, and it is not known if people can get infected with CWD prions,'' the Centers for Disease Control and Prevention notes in their CWD advice. "Nevertheless, these experimental studies (with monkeys) raise the concern that CWD may pose a risk to people and suggest that it is important to prevent human exposures to CWD."

Studies continue to look at whether people who have contract with potentially CWD-infected meat are at increased risk for CWD-like diseases, the CDC notes, but, "because of the long time it takes before any symptoms of disease appear, scientists expect the study to take many years before they will determine what the risk, if any, of CWD is to people."

It can decimate wild deer herds

In September 2016, the scientific journal PLOS ONE published research the University of Wyoming that found a 10 percent annual reduction in a white tail population in parts of Wyoming. If that rate of decline continues, localized extinction will occur in less than 50 years.

Published models predict that CWD begins to reduce deer populations seriously when it hits 27 percent of the herd population. Some areas of southwestern Wisconsin have already hit 50 percent infection.

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

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.

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, Cwd-info.org, Centers for Disease Control and Prevention, Quality Deer Management Association.

Tips to limit exposure to CWD

• Do not shoot, handle or consume any animal that is acting abnormally or appears to be sick. Contact your state game and fish department if you see or harvest an animal that appears sick.

• Do not transport animal carcases from potentially infected areas to your home state. Minnesota already bans this practice, allowing no cervid carcases into the state. If you hunt out of state you must bring the animal meat back removed from the carcass. Carcass rules for most states can be found at ncwildlife.org/hunting/cervid-carcass-regulations.

• Wear latex or rubber gloves when field dressing your deer or elk.

• Fillet the meat off the bone from your animal. Don't saw through bone, and avoid cutting through the brain or spinal cord (backbone).

• Minimize the handling of brain and spinal tissues.

• Wash hands and instruments thoroughly after field dressing is completed.

• Avoid consuming brain, spinal cord, eyes, spleen, tonsils and lymph nodes of harvested animals. Normal field dressing coupled with boning out a carcass will remove most, if not all, of these body parts. Cutting away all fatty tissue will remove remaining lymph nodes.

• Have your deer tested if it comes from a potential CWD zone. Avoid consuming the meat from any animal that tests positive for the disease.

• If you have your deer or elk commercially processed, request that your animal is processed individually, without meat from other animals being added to meat from your animal.

• Stop baiting and feeding deer. Some groups are asking hunters to stop baiting and feeding deer because it brings them together where they can share saliva and other bodily fluids. Minnesota already bans bating, feeding and even use of deer scents in CWD-positive zones.

Sources: Minnesota DNR, Wisconsin DNR, Wildlife Management Institute, Cwd-info.org, centers for Disease Control and Prevention, Quality Deer Management Association.

CORRECTION: An earlier version of this story wrongly reported the location of a captive deer farm where all of the animals tested positve and died from CWD. That farm was in Winona County, not Crow Wing County.