A mule deer buck shot in January north of Thief River Falls after Department of Natural Resources authorities determined its unusual behavior posed a safety risk has tested positive for brain worm infection.

Doug Franke, area wildlife manager for the DNR in Thief River Falls, said he received the diagnosis Thursday from DNR Wildlife Health experts.

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Tissue samples from the deer had been sent to the University of Minnesota's Veterinary Diagnostic Laboratory for testing, and lesions were "highly suggestive" of brain worm infection, according to the U of M diagnosis.

The mule deer also was tested for chronic wasting disease, and test results in early February came back negative.

"So, we can say with good confidence that brain worm was the cause of the mule deer's behavior," Franke said in an email.

Brain worm is caused by a parasite that works its way into the food chain through snails. According to the Natural Resources Research Institute in Duluth, white-tailed deer are natural hosts of the parasite but generally aren't infected.

Moose are the most susceptible to brain worm, but mule deer and elk also can be infected, Franke said.

DNR conservation officer Tony Elwell of Thief River Falls shot the mule deer buck Jan. 17 after DNR staff determined it was a liability to motorists along U.S. Highway 59. Mule deer aren't common in northwest Minnesota, but the 1½-year-old buck may have wandered into the state from western North Dakota, which has the closest resident mule deer population.

The buck showed no fear of humans, and there were reports of a motorist who had to physically shoo it off the road.

"The body condition was really good, its physical appearance was good, but its cognitive health was suspicious," Franke said in a January story. "It just didn't seem like it was all there, if you want to call it that."

The buck, which had a 2x3 rack, reportedly had been in the area north of Thief River Falls for some time.