Missouri Shows Us How to Manage CWD in Deer for the Long Haul

April 22, 2024 By: Lindsay Thomas Jr.

The Missouri Department of Conservation recently released its 2023-24 chronic wasting disease testing results, and the report contains good news and a lesson for deer hunters in other states: If the disease is discovered early, active management can keep infection rates low. That means productive deer populations and sustainable hunter harvest for the long haul.

In the 12 years Missouri has been fighting CWD, the disease has spread slowly to 39 known counties, but none of them has a prevalence rate over 3%. Compare that to southwest Wisconsin where prevalence trends in many CWD areas are now climbing into the 20s, 30s, 40s and higher infection rates.

“Of all the positive counties we had in this last surveillance year, more than 75% of them have less than 1% sample prevalence, and more than 90% have less than 2% sample prevalence,” said wildlife biologist Jason Isabelle, Missouri’s deer program supervisor. “The information we have suggests that a couple of things are working in our favor. Early detection certainly, but also the localized management.”

Avoiding the CWD Curve 

From July 2023 to April 2024, MDC tested more than 37,000 deer from around the state, and only 162 tested positive. That’s a statewide prevalence rate of 0.4%. The trend is flat in the CWD management zone since 2012. Management efforts in localized areas within the zone, especially targeted removal by MDC and private landowners, is working to hold infection rates low.

With CWD, we can’t “flatten the curve” once prevalence rates climb high. We can only hold prevalence rates low and avoid the curve to begin with. For example, CWD had already infected high percentages of deer in outbreak areas by the time it was discovered in northwest Arkansas and western Tennessee. This is why early detection is critical. As deer hunters, we can help help with detection by participating in testing and monitoring programs.

A map of Missouri’s CWD management zone. Though the disease has slowly spread from multiple points to several counties around the state, CWD infection rates are below 1% in most areas.

As long as infection rates remain low, Missouri’s deer population can continue to thrive and support deer hunting. Until science finds a solution to the CWD problem, that’s the job of hunters and state wildlife agencies: Keep wild deer healthy even in the presence of CWD, and even when it continues to spread to new counties. Missouri is among the states that are showing us how it’s done.

Of course, some news outlets reported MDC’s data as bad news, because negative headlines drive clicks. These media outlets failed to provide the context that truly informs the public, and this continues to cause the most damage to the forces who are fighting CWD. The truth is, 162 positive deer out more than 37,000 tested is extremely good news, especially in a state that has been fighting CWD for 12 years.

Localized Management of CWD

Missouri deer hunters, landowners and MDC deserve credit for this good news, and MDC’s targeted removal effort stands out as a nationwide example of CWD management tactics that work. The state wildlife agency goes into known CWD areas where previous positives were discovered and – with landowner permission – kills an additional sample of deer after hunting season ends. MDC sets a removal goal in each area, shares it with landowners, and informs landowners when they meet the goal and are done for the year.

Because MDC has intel on previous positives, they are fairly good at finding more with these surgical strikes. Deer removed during MDC’s targeted removal effort this past year accounted for only 12% of all deer tested. However, those samples represented over 30% of the total CWD positive deer detected last year.

This removes a few more positive deer from the landscape that would have otherwise remained in the woods at least until the next deer season, continuing to spread CWD prions to other deer. Targeted removal also helps to reduce deer densities in these localized areas, which helps to slow the spread of the disease. It is one of the primary techniques for maintaining low prevalence, but the number of deer removed is very low compared to hunter harvest. Targeted removal accounted for 4,600 deer statewide, spread out over more than 30 core areas around the state, when hunter harvest last year exceeded 326,000 deer.

A Missouri hunter points to a map to show MDC staff where he killed his deer. If the deer ultimately tests positive, its location will help guide targeted management efforts that are keeping Missouri deer populations healthy.

In addition to targeted removal accounting for a disproportionate number of CWD-positive deer, low prevalence in the areas where the removals are conducted is another indication it is working. “When you remove deer within about 1 to 2 miles of earlier positives and only about 1% of them test positive, that’s a testament to the effectiveness of early detection and the localized management approach,” said Jason Isabelle.

Because targeted removal is not a countywide sweep but a focused strike near previous CWD positives, landowner permission and support are key. Unfortunately, not every landowner agrees to assist in the CWD fight. 

Intervention Must Start Early and Continue

MDC met with landowners in CWD areas to learn why they do or do not support targeted removal. Many non-supporters said they didn’t think CWD was a big enough problem yet to justify that type of response. However, if you wait until CWD prevalence rates are higher, it’s too late for targeted removal to be effective.

“With the prevalence rates being as low as they are in Missouri, landowners rarely see sick deer in the clinical stage of CWD, so some feel there isn’t a call to action yet,” said Jason. “A number indicated if they were seeing sick deer they would consider participating in targeted removal. Unfortunately, by the time that is happening, the window of opportunity to slow the progression of the disease is rapidly closing or has already closed.”

If you’re a landowner in any state or area that is fighting CWD, and you are asked to assist with extended deer harvest or targeted removal, I strongly urge you to support the effort. CWD is a creeping poison that doesn’t call attention to itself. If you wait until CWD is so prevalent that sick deer are noticeable, it’s too late.

We can live with CWD and continue to enjoy deer hunting and healthy deer populations as long as we actively manage the disease where it occurs – and hopefully science finds a better solution while we hold this defensive position. But early detection is essential. We know how to keep prevalence rates low. We don’t know how to reduce them once they are high. Some states missed their opportunity for early intervention, and hunters in those areas can only watch now as infection rates climb.

No matter where you hunt, you can help by being actively engaged in protecting deer. Follow carcass transportation guidelines. Report sick deer to your state wildlife agency to ensure early detection if the cause is CWD. Participate in voluntary CWD testing of your harvested deer when asked to help with monitoring. Help achieve target doe-harvest goals to maintain healthy herds where you hunt, even if CWD is not an issue there. Through these and other contributions, each of us can do our part in the fight against CWD.

About Lindsay Thomas Jr.:

Lindsay Thomas Jr. is NDA's Chief Communications Officer. He has been a member of the staff since 2003. Prior to that, Lindsay was an editor at a Georgia hunting and fishing news magazine for nine years. Throughout his career as an editor, he has written and published numerous articles on deer management and hunting. He earned his journalism degree at the University of Georgia.