Chronic wasting disease in Wisconsin remains centered in southern areas, offering a warning for the nation. Roughly 87% of Wisconsin's positive results come from the Southern Farmland zone. In the southwest, prevalence among adult bucks tops 30%. Wisconsin research spanning years places the threshold for a shrinking herd at about 29% prevalence among females. As infection creeps north, its advancing edge presents the risk ahead.
KEY FINDINGS
- Of Wisconsin's CWD detections, ~87% come from the Southern Farmland zone. During the 2025 hunting seasons, positive tests exceeded 2,000 deer. CWD first turned up in this area in 2002.
- Wisconsin DNR estimates for individual townships show CWD prevalence exceeding 30% among adult bucks in portions of the southwest core, including Grant, Iowa and Dane counties. Prevalence among adult males exceeds that among adult females.
- Researchers followed 766 deer wearing GPS collars and measured the survival toll: infected bucks had 17% annual survival, compared with 69% among uninfected bucks. For does, annual survival measured 41% with infection and 83% without it. Herd numbers start falling when prevalence among females rises above about 29%.
- CWD's advancing edge continues north from the farmland core. Clark and La Crosse counties recently recorded their first detections, while Wood, Oneida, and Portage recorded additional positives.
IA southern disease
The places carrying Wisconsin's CWD burden
CWD is spread unevenly across Wisconsin. The Southern Farmland zone, the fertile agricultural part of the south and southwest, accounts for the vast majority of the state's positive results, about 87%. CWD was first detected there in 2002 in Iowa, Dane, and Grant counties. Over two decades, intensive testing has followed the disease as it continues to saturate that core, while the northern forest zones remain relatively clean. A clear picture of Wisconsin's CWD situation centers on a few dozen counties in the south.
IIThe survival math
How infection changes a deer's survival chances
Prevalence matters because infected deer die more often. In a Wisconsin study spanning years, researchers placed GPS collars on 766 adult deer and followed survival according to infection status. The difference is sharp. An uninfected doe's chance of living through the year is about 83%, compared with 41% when infected. Bucks without infection have a 69% annual survival rate; with infection, that falls to just 17%. A buck's survival chance drops to roughly a quarter with infection. In these counties, describing CWD as a slow background loss misses the much higher death rates among infected animals. Survival over a year measures 41% among infected does and 17% among infected bucks, compared with 83% in uninfected does and 69% in uninfected bucks.
A healthy buck reaches another season two out of three times; an infected buck does so barely one out of six. That survival loss is why the share of deer carrying infection matters.
IIIThe 29% threshold
The prevalence threshold for a shrinking herd
The same research found a threshold: when CWD prevalence in adult females rises above roughly 29%, the herd is expected to lose its ability to replace itself and start shrinking. Reduced doe survival slows population growth, and the model predicts that the population will begin to decline above about 29% female prevalence. That threshold changes how the southwestern prevalence figures should be read. The 29% mark concerns female prevalence. Adult-buck prevalence above 30% alone does not establish that females have passed that mark. Prevalence is higher in adult males than in females, so the core could be close to the threshold. Local harvest and the number of young deer joining the herd also affect the outcome. Southwestern Wisconsin, where CWD was first detected in 2002, hosts an unusually large CWD study that has been running for many years. The area is also among the most thoroughly documented examples of CWD on a large scale.
IVThe front moving north
The ground to watch over the coming decade
Location defines the risk ahead. During recent seasons, the first case appeared in La Crosse County, and Clark County recorded its first detections among wild deer. Additional positives appeared in Wood, Portage, and Oneida. These counties lie along the farmland zone's central and northern margins, nearer the large forest tracts that have remained clean so far. Deer occur at lower densities in the northern forest, where additional detections are now being logged. For the 2030s, attention belongs on counties within the transition strip occupied by today's advancing edge.
VWhat it means
What southern herds and their hunters face
Hunters in southern Wisconsin are pursuing deer in herds where CWD is established. Across many southern units, the state offers generous opportunities to take antlerless deer as a management tool, together with testing and carcass regulations. When choosing where to spend a hunting season, differences in prevalence provide useful information. Nearer the southwest core, any individual deer is more likely to carry infection, and the herd faces greater mortality with a possibility of declining numbers. Wisconsin's farmland zone continues to have the state's strongest deer numbers. Follow state guidance for testing and handling carcasses, and understand rules aimed at reducing deer density as a response to the disease.
NOTES AND SOURCES
- Surveillance source: Wisconsin DNR. Its reporting for the 2025 hunting seasons supplies the positive-deer count and the Southern Farmland zone's concentration of positives (~87%). dnr.wisconsin.gov.
- Comparisons of healthy and infected deer survival, separated by sex, and the ~29% female-prevalence threshold for population decline come from Wisconsin's long-running CWD study using GPS collars. It followed 766 adult deer and 323 fawns. CWD was first detected in 2002 in Iowa, Dane, and Grant counties.
- Limits: prevalence differs greatly from place to place within zones and counties. These figures describe zones and regions rather than a census of each county, and they reflect recent Wisconsin DNR reporting.
Fully Drawn Research is an independent data analysis desk, not affiliated with any state wildlife agency, transportation agency, mapping provider or outfitter. Fully Drawn Research is independent and not affiliated with the Wisconsin DNR or any mapping provider. This paper reports disease surveillance data and is not medical, food-safety, or wildlife-management advice; hunters should follow Wisconsin DNR and public-health guidance on CWD testing and carcass handling. Figures current to recent-season Wisconsin DNR reporting.
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