The number of deer that test positive for chronic wasting disease in Missouri continues to climb at a slow and steady pace. That bad news is positive from the perspective that it could be worse.
Eleven new cases have been documented this fall in the same small area of Jefferson County where the disease has been detected 42 times since 2016. One positive test was reported last year near Ware, but all of the rest in the county have been in the triangle bounded by Interstate 55, Highway 67 and the Jefferson / Ste. Genevieve County line.
The largest number of samples submitted for testing each year are collected during the first two days of the November portion of the firearms hunting season. In 43 counties where the disease has been found in the past, hunters are required to have their deer tested during opening weekend. The results of those tests have been posted on the state Department of Conservation website.
More than 18,500 harvested deer were tested from opening weekend statewide. Combining all fall deer hunting seasons so far, almost 28,000 deer have been tested, and 98 news cases have been detected. That small percentage of positive tests – less than 0.3 percent – proves the rarity of CWD in the state, but it doesn’t diminish the danger of the deadly disease.
In locations like the Jefferson County triangle, the 42 positive results over the past eight years may have been from 1,000 tests from that area. That boosts the positivity rate over 4 percent. Several surrounding states have much higher incidence than Missouri, and places like Wisconsin have concentrated areas where 25 percent of adult bucks test positive for the disease. Resistance to testing or ignoring the possibility makes the spread of the disease worse.
More testing will be completed on deer harvested through the remaining archery hunting season. Deer will also be removed in post-season targeted culling efforts on properties where the disease has been detected.
The 11 cases in Jefferson County is among the highest totals this fall. Eight deer have tested positive in both Linn and Macon counties, which is where the disease was first detected in wild deer in Missouri in 2012. Somewhat surprisingly 10 cases have been reported in 2024 in Osage County where the first cases in that county were found last year.
Two other positive test reports are also notable for their locations. Texas County, one of the largest in the state geographically, regularly shows up among the top harvest counties in the state. Because the disease had not been detected there in the past, it has not been included in a CWD management zone, but it will be next year.
Callaway County also finishes among the top five in harvest totals consistently. It has been an island in mid-Missouri with CWD zone counties surrounding it. A positive test in Audrain County near its border with Callaway will likely mean mandatory testing in the future for that deer hunting mecca surrounding Fulton, Mo.
A little closer to home, Franklin County matched Jefferson with 11 new reported positive tests so far this year. Ste. Genevieve County, which has the highest number of positive tests in the state at 102, added 13 new cases. Perry County also has five new reports this year including one close enough to Cape Girardeau County for it to be added to surveillance efforts in the future.
“Hunters who provide samples from harvested deer play a critical role in efforts to monitor the spread of CWD and identify new areas of infection,” said Deb Hudman, supervisor for the state’s wildlife health program. “Finding CWD as early as possible provides us with the ability to work with landowners and hunters to effectively manage the disease to slow its spread and protect Missouri’s deer population.”
Similar to mad cow disease, CWD affects deer and other cervids. It is 100% fatal, and there is no vaccine or cure. The disease can be spread from direct deer-to-deer contact, through improper disposal of deer carcasses, and through the environment by deer contacting infectious material from other deer.
John Winkelman has been writing about outdoors news and issues in Jefferson County for more than 30 years and was the Associate Editor for Outdoor Guide Magazine.
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