MINNEAPOLIS — Nearly 100 cases of chronic wasting disease were documented in Minnesota deer last year, the highest number on record and surpassing the previous high by about a third.

Since the first case of the neurodegenerative disease was confirmed here in 2002, about 400 deer have been catalogued with CWD, according to the Minnesota Department of Natural Resources and Board of Animal Health. About six cases have been documented so far in 2025.

The increase comes as the firearm deer season opened amid a reported resurgence in the whitetail population after two mild winters.

Still, Minnesota’s level of CWD pales in comparison to Wisconsin’s.

Wisconsin reports hundreds of cases — primarily in their southwestern counties — every year, according to the data from the Wisconsin Department of Natural Resources and Department of Agriculture, Trade and Consumer Protection.

All told, they’ve seen several thousand CWD cases over nearly 25 years, compared to Minnesota’s few hundred.

The data shows CWD has mostly been found in Minnesota’s southeastern counties, although it has jumped to northern counties in small numbers. The figures include both wild and captive animals.

Meanwhile, the epicenter of the Wisconsin cases is in Iowa County, where more than 4,500 cases have been documented since 2002.

Disease signs

Chronic wasting disease, a neurodegenerative disease that affects deer and other hooved mammals like elk, causes lethargy and weight loss. It is always fatal.

Infected animals spread prions, the infectious agent, through saliva, urine, feces, blood, antler velvet and from the carcass after death, but the spread is not fully understood. Prions are resistant to heat, disinfectants and decomposition.

One recent study by Minnesota and Wisconsin researchers suggested that infected deer ticks swallowed by deer during social grooming may be one way that the disease jumps from animal to animal, according to a 2023 Minnesota Star Tribune report.

Although the disease is fatal for the animals, there have been no documented cases of CWD in humans. Still, the possibility is always there, according to Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota School of Public Health.

Monitoring the herd

The first case of CWD in Minnesota was in a farmed elk in 2002 in Aitkin County. Incidents of the disease began appearing in wild whitetail deer in 2010.

The Minnesota DNR’s deer permit areas govern rules on tracking CWD into two types of zones, designed to track the progression of the disease in deer herds.

In management zones, CWD has been found in wild deer, and testing is mandatory during the opening weekend of the firearms season. Strict restrictions on moving carcasses, a deer feeding ban and increased hunting opportunities with liberalized bag limits help mitigate disease spread.

In surveillance zones, CWD has not been found in wild deer, but they are considered at risk for disease transmission from adjacent areas.

The DNR provides hunters with guidance on CWD testing. New this year will be reduced availability of head boxes in CWD zones. Previously, the boxes were available for much of the season for hunters to drop off the heads of harvested deer for processing and CWD testing by the DNR. But this year, those drop-off boxes were only available from opening weekend through Tuesday.

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Tony Kennedy of the Minnesota Star Tribune contributed to this report.

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