Chronic Wasting Disease in Washington
Chronic Wasting Disease (CWD) is a lethal neurodegenerative disease affecting wild cervids (e.g., deer, moose, elk, caribou) in North America and Scandinavia. In the US, CWD has been detected in 35 states, and this August, the Washington Department of Fish and Wildlife (WDFW) announced the first detection of CWD in our home state, Washington.
CWD is caused by infectious misfolded proteins called prions that aggregate in tissues throughout an animal’s body. Prions are predominantly found in lymph and nervous system tissues, including the brain. These prion clusters (amyloids) essentially "swiss-cheese" the brain, causing the neurodegenerative symptoms indicative of this wasting disease. These clinical signs of disease appear in the last 6-8 weeks of a cervid’s life and include symptoms such as weight loss, lethargy, a splay-legged stance, drooping ears, and loss of fear.
.jpg "Chronic wasting disease affects cervid species, such as mule deer.") |
| Chronic wasting disease affects cervid species common to Washington, such as mule deer, pictured here. |
Prior to this late-stage of disease, animals can be infected with prions for anywhere between 16 months and 4 years. For much of this time, animals actively shed infectious prions through saliva, urine, feces, antler velvet, blood, and by way of decaying carcasses. Cervids become infected with CWD when they are exposed to prions either by coming into direct contact with an infected animal (e.g., sparing, grooming, touching noses) or indirectly when contacting areas of the environment where prions have been shed (e.g., concentrated areas where animals defecate, urinate, and feed).
It is unclear which form of transmission is more important for CWD disease dynamics given variability in CWD shedding patterns and the fact the prions can remain viable in the environment for long periods of time - perhaps decades! This uncertainty, paired with challenges associated with live testing cervids for disease (lymph and nervous system tissues are difficult to sample from a live animal) has made this disease particularly challenging to control.
In response to CWD detection in wild cervid populations, state agencies work to limit both the spread and overall prevalence (number of infected deer in the population) of the disease. In Washington, WDFW implement rule changes to aid in these efforts, including mandatory CWD testing in the vicinity of the first detection, banning baiting practices that artificially concentrate deer and increase risk for indirect transmission, and restricting the transport of harvested cervids to prevent geographic spread.
Rules such as those implemented by WDFW aim to address a variety of ecological, economic, and public health concerns broadly related to CWD. For example, CWD in mule deer is concerning in many areas from a herd-health perspective; mule deer populations have seen declines in much of the west in recent decades and it is unclear how much CWD might play a role in these declines. Further, revenue generated from excise taxes and fees closely tied to hunting are fundamental to wildlife conservation funding in the US; hence, there are economic concerns that reduction in cervid hunting interest and opportunities as a result of CWD could be detrimental to funding wildlife conservation in the US as a whole. And finally, while there is no direct evidence that CWD can infect humans, other prion diseases, such as mad-cow disease successfully crossed the human-animal barrier. As a result, the Center for Disease Control strongly recommends testing meat harvested from cervids for CWD prior to consumption, and not eating meat from an infected animal.
Working with your local state agency to test a harvested or salvaged cervid for CWD is a win-win situation, providing you with the information need to decide whether or not you want to eat the meat from a harvested animal and giving your state agency difficult-to-acquire information about CWD prevalence in your local area to aid in management efforts.
Becca Windell
Becca is co-founder of Home Range Wildlife Research and serves on the Board of Directors as Vice-President. She is currently working towards her PhD in Wildlife Biology at Colorado State University, where she studies chronic wasting disease in mule deer. Her research interests lie in applying animal behavior to disease, conflict, and other management challenges.
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| Becca performing a necropsy on a deer as part of her PhD research |