Update: Recent test results from the 2016 firearms deer season show two deer harvested by hunters in southeastern Minnesota were infected with chronic wasting disease. Read the latest news and learn more about CWD in Minnesota.

When they head into fields and woods this fall, Minnesota's half-million deer hunters will have the usual hunting concerns on their minds—such as weather conditions, safe handling of weapons, and placing deer stands in the right spots. Most won't give a second thought to whether the deer in their sights will be safe to eat.

That was not the case a few years ago. In January 2011 an adult female deer near Pine Island in southeastern Minnesota tested positive for chronic wasting disease. It was the first wild deer in Minnesota found with the fatal malady. When the Centers for Disease Control and Prevention advised against eating CWD-infected deer, hunters were left in the uncomfortable position of pulling the trigger or loosing an arrow on animals they shouldn't consume.

A neurological disease, CWD causes brain degeneration and certain death in deer, elk, moose, and reindeer. Animals with advanced infection tend to be emaciated and lethargic. They stumble, tremble, and salivate excessively before dying.

Scientists are unsure of the disease's origin, but they know abnormal proteins called prions cause CWD. Infected animals shed prions in saliva, feces, and urine. Prions can live for years in the environment. There's no scientific evidence CWD can be transmitted to humans. The pathogens are most commonly transmitted among deer by prions in feces or urine. The disease can also pass directly between animals—by touching noses, for example.

Minnesota's disease-free deer herd didn't happen by accident. For well over a decade, the DNR has been maintaining an aggressive surveillance effort that tested more than 50,000 wild deer, elk, and moose in the state. Widespread testing began after the 2002 discovery of a CWD-positive elk at a central Minnesota farm. Captive elk from three additional farms have tested positive, as have a white-tailed deer and a red deer at game farms. To date, just one wild deer has tested positive.

Hit It Hard. "We knew our only chance to do anything was to catch it early and be aggressive—hit it hard and hit it as early as possible. Otherwise, you're out of luck," says DNR wildlife research manager Lou Cornicelli, who was the big-game program leader when CWD turned up in 2011. That meant dramatically lowering deer numbers to reduce the risk of disease transmission and testing harvested deer to determine how widespread CWD might be.

The DNR aimed to prevent a situation like the one in Wisconsin, where more than 25 percent of deer in some areas have CWD. Wisconsin has spent millions of dollars to fight the disease since first discovering infected deer there in 2002. It implemented various herd-reduction methods but ended them following negative public reaction to liberal hunting regulations.

The disease now has become endemic—meaning it occurs regularly—in parts of Wisconsin and other states. While the exact ramifications of endemic CWD are unclear, "it is anticipated endemic CWD will depress cervid populations to some unknown level," according to the Wyoming Game and Fish Department's CWD management plan.

The DNR's protocol for CWD testing includes collecting samples from deer that appear to be sick, those that have been hit by vehicles, and those that hunters harvest in surveillance areas. Hunters must bring harvested deer to a check station. DNR biologists extract lymph nodes from the deer and send samples for screening at the University of Minnesota or Colorado State University. Any samples that appear to be positive go to the National Veterinary Services Laboratory in Ames, Iowa, for final testing.

The testing protocol worked as intended in the Pine Island area. The surveillance effort there had resulted from the 2009 discovery of CWD-infected elk at a game farm. In November 2010 when the archery hunter killed the adult doe about three miles southwest of that farm and brought it to a check station, he described the animal as thin but not exhibiting abnormal behavior. The doe's thinness "suggested she was probably sick for some time," said Michelle Carstensen, DNR wildlife health program leader.

One of 524 animals tested in the area that year, the doe was confirmed positive for CWD by late January 2011. "We had a response plan developed, so we could fall back on that," Carstensen said. "But really, we fell back on our bovine TB experience. We learned a lot from that disease."

Bovine tuberculosis, a chronic bacterial disease of cattle that can affect other animals, turned up in wild deer in northwestern Minnesota in 2005. The DNR immediately began to test hunter-harvested deer for the disease. When it began to find infected animals, the DNR instituted a number of management actions: reducing deer numbers, banning recreational feeding, and creating a management zone with special hunting regulations. It took four years, but the plan paid off—the last deer to test positive for bovine TB was in 2009.

Finding CWD in a wild deer always had been a possibility, which is why the DNR expended so much effort looking for it. "We had been testing for years," said Cornicelli, recalling the 2011 finding near the Pine Island game farm. "So we weren't blown out of the water that we had a positive, especially so close to the infected elk facility."

As managers plotted the fight against the disease, they stuck close to their CWD-response plan. They knew hunters wouldn't like the deer-density reductions. Folks who like to feed and watch deer recreationally wouldn't like the feeding ban.

"The discussion was never, 'Is the public going to be OK with what we're going to do?'" Cornicelli said. "The decision was that we were going to do it, and we're going to communicate to people what we're doing and hope we don't have to do it very long."

Decisive Actions. The agency created a new management zone that encompassed the area where the hunter had shot the diseased doe. In late January and early February of 2011, DNR conservation officers and biologists flew aerial surveys in the zone to determine deer densities and recreational-feeding locations. On Feb. 14, the DNR enacted a recreational feeding ban in Dodge, Goodhue, Olmsted, and Wabasha counties to limit unnatural concentrations of deer. Just before the ban went into effect, DNR conservation officers went from door to door to remind people to bring in their feed. In all but one instance, landowners had already taken the initiative to do so.

When it came time to kill deer to reduce densities and collect samples for testing, DNR officials decided against immediately bringing in U.S. Department of Agriculture sharpshooters, which had been controversial during the bovine TB fight. Instead, they first distributed permits that allowed landowners, or people designated by landowners, the opportunity to shoot deer on their property. Hunters weren't allowed to remove harvested deer from the management area until the animals tested negative.

"We had 491 deer submitted by landowners that first month," Carstensen said. "I still think one of the biggest successes was engaging landowners right off the bat with shooting permits. We empowered them to remove deer from their own land."

The landowner engagement effort extended beyond hunting permits. The DNR had rented a facility just north of Rochester as its base of operations for the fight, but DNR staffers planned to go to landowners who'd harvested deer. One of those landowners was Pine Island resident Josh Ruhnke, who had never hunted deer. He went into the woods behind his house and killed a doe that appeared 40 yards in front of him. Ruhnke informed the DNR of the kill. Shortly after he'd made the call, Erik Hildebrand, a DNR wildlife health specialist, arrived at Ruhnke's home to collect lymph node samples. Within three days, Ruhnke and other landowners knew whether the deer they'd killed had tested positive.

"We made it about as convenient for people as we could make it," Cornicelli said.

Between 2011 and 2013, the DNR sampled more than 4,000 deer within the CWD zone. All came back negative.

In 2014 the DNR sampled more than 400 deer in two southeastern deer permit areas, 348 and 349. That effort was the result of the discovery of CWD in Iowa's Allamakee County, which borders Minnesota. None of those animals tested positive, further bolstering DNR experts' view that CWD isn't present in the state or is present at such low levels as to be undetectable. The DNR plans further surveillance in the southeast this fall to ensure the disease hasn't spread from infections in wild deer in Wisconsin or Iowa.

Starting this fall, hunters may not bring whole carcasses of any member of the deer family into Minnesota from anywhere in North America.

Should CWD or another disease loom up in Minnesota deer, Cornicelli believes the agency has the blueprint in place for a successful fight. It may not be easy to implement restrictions and regulations that reduce the ways people enjoy wildlife, but it's necessary, he explains. "We have to make decisions that benefit the resource over the long term," Cornicelli says. "If you look at the population-level impact [on deer] in 50 or 100 years, we have to think about that. There's enough uncertainty about [CWD] and its long-term effects on the population, and that's more important than your deer hunting today."