About CWD

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Chronic Wasting Disease
Chronic Wasting Disease
Mike Hopper, Kansas Department of Wildlife, Parks and Tourism

Chronic Wasting Disease

  • CWD is spread from deer to deer and kills all deer it infects.
  • The neurological disease infects deer and other members of the deer family (called cervids) by causing degeneration of brain tissue, which slowly leads to death.
  • CWD is caused by misshapen proteins called “prions.”
  • The disease has no vaccine or cure.
  • Based on current research, CWD remains relatively rare in the state at this time.

Why CWD is a Threat

  • CWD has the potential to greatly reduce deer numbers and deer hunting and watching over time for Missouri's nearly 520,000 deer hunters and almost two million wildlife watchers.
  • Missouri offers some of the best deer hunting in the country, and deer hunting is an important part of many Missourians' lives and family traditions.
  • Deer hunting is also an important economic driver in Missouri and gives a $1 billion annual boost to the state and local economies.

How CWD Spreads

  • CWD is spread from deer to deer through direct contact and through contact with soil, food, and water that have been contaminated through feces, urine, saliva, or carcasses of infected deer.
  • Potential for transmission increases when deer gather in larger, concentrated numbers.
  • Young bucks can also spread CWD to new areas as they search for territories and mates.
  • Moving carcasses out of the immediate area where harvested and improperly disposing of them can spread the disease.
  • It can take months or years for a deer infected with CWD to show symptoms. However, an infected deer can spread the disease to other deer and contaminate the environment while appearing healthy.

Signs of CWD

Deer infected with CWD do not always look sick. Symptoms include:

  • Excessive salivation
  • Drooping head/ears
  • Tremors
  • Emaciation
  • Change in behavior, such as a lack of fear of humans and a lack of coordination.

Differences between CWD and Hemorrhagic Disease (HD) or Blue-Tongue

  • CWD is new to the state with the first cases being detected in 2010 and 2011 in captive deer.
  • CWD is caused by misshapen proteins called “prions” that concentrate in the brain, lymph nodes, spine, and eye tissue of infected animals and lead to the slow death of all infected animals.
  • CWD is a 100-percent fatal disease that is spread from deer to deer through body fluids.
  • CWD symptoms include excessive salivation, drooping head/ears, tremors, emaciation, and change in behavior such as lack of fear of humans and lack of coordination.
  • CWD can take more than 18 months for an infected deer to show symptoms.
  • CWD has the long-term potential to significantly reduce deer numbers in the state over time.


  • HD has periodically affected deer in Missouri and other states for many decades with no long-term impacts to the overall deer population.
  • HD is caused by a naturally occurring virus spread by midge flies during the summer and fall and ends when cold weather kills the flies.
  • HD symptoms include fever, reduced activity, and swollen neck, tongue or eyelids. Because sick deer are feverish, they are often found near water.
  • HD-infected deer typically show symptoms within days of being infected and those that die do so within weeks of being infected. 
  • HD does not kill all deer it infects. Deer that survive HD develop antibodies for future immunity.
  • HD can have significant short-term impacts on a deer herd, but has never been shown to have long-term impacts on deer populations.

CWD Cannot Be Eliminated Once It’s Well Established

  • CWD remains relatively rare in the state at this time.
  • Research from other states that have had CWD much longer than Missouri shows that the disease has been impossible to eliminate once it has become well established in an area.
  • MDC will continue to focus on managing the levels of the disease where it has been found and reducing the risk of introducing the disease to new areas of the state.

CWD Has Not Always Been In Missouri

  • MDC has determined CWD was recently introduced to Missouri. This is based on the low current prevalence and limited distribution of CWD in Missouri.
  • Once well established, CWD increases in both prevalence and distribution over time. This means the number of cases of the disease present in a particular deer population in a particular area increases over time. It also means the disease spreads to many new areas over time.

Where CWD Came From

  • Researchers do not know the origin of CWD.
  • CWD was first found in captive mule deer at a research facility in Colorado in the 1960s.
  • It was first found in the wild in Colorado in the 1980s and has spread to almost two dozen states.
  • The first cases in Missouri were found at private big-game breeding and hunting facilities in 2010 and 2011.
  • The first cases in free-ranging deer were found in 2012 near the private breeding and hunting facilities.

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