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A sixth deer in southeast Minnesota tested positive for chronic wasting disease (CWD), the Department of Natural Resources said Tuesday.

The animal, an adult doe, joins two other adult does and three adult bucks that have tested positive for CWD since November. The disease is carried in an animal’s saliva and other body fluids and is always fatal to moose, elk and deer.

The most recent infected animal was killed by a hunter during a special 16-day season that began Dec. 31 and ended Sunday. The season was established by the DNR to reduce the number of deer in a 371-square-mile disease management zone in the southeast and to determine the disease’s prevalence in the area. Live animals can’t be tested for CWD.

Wildlife managers had set an initial goal of 900 adult deer to be killed and tested during the special hunt and during a follow-on landowner hunt that began Monday.

Now, with six positive CWD hits among 640 adult deer tested, DNR lead wildlife researcher Lou Cornicelli said some larger number of deer will need to be killed to determine how widespread, or limited, the disease is.

More than 150 fawns also were killed in the special hunt. They weren’t tested because the CWD incubation period can be longer than one year.

Five of the diseased deer were killed within an approximately 5-square-mile area, with the sixth felled about 5 miles north of that cluster. The area is north and east of Preston.

“We will explore doing some genetic work on the six positives to see if the animals are in some way related,” Cornicelli said, adding, “We don’t know how the disease got here.”

The DNR has issued 270 landowner hunting permits, with no limit to the number of animals that can be killed. If the total harvest is insufficient to infer a disease prevalence probability, federal sharpshooters might be brought in to add to the tally.

Researchers believe that once CWD infects a critical mass of animals in an area it can no longer be eradicated.

Such is the case in some parts of southern Wisconsin, where as many as half of adult bucks are infected with CWD. The Wisconsin Department of Natural Resources has effectively given up trying to stop the disease in that area.

Cornicelli said intensified deer harvesting may be necessary near where the five infected Minnesota deer were killed.

“The only chance you get to control this disease is on the front end,” he said.

A December aerial survey of the southeast Minnesota CWD zone yielded an estimated deer population of 24 animals per square mile, a figure that likely was closer to 30 before last fall’s hunting seasons. Both figures are high compared to most regions of the state.

The whitetail population in the disease zone can rebound quickly, even with the intensified harvest, wildlife officials said, assuming the disease is contained.