Evaluating Transmission of Chronic Wasting Disease in the Environment

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Chronic wasting disease (CWD) is a fatal disease of deer, elk, and moose and has been spreading in North America for the past two decades. The disease is spread by infected body fluids. Animals can become infected by coming into direct contact with a CWD-infected animal, or an infected animal can leave behind fluids (e.g., saliva, urine) that an uninfected animal will come into contact later. Because there is no cure or vaccine, disease mitigation or prevention are the best options to combat CWD. This research evaluates the potential for salt licks to act as sites for CWD transmission.


Elk in Wyoming

Elk captured using a camera trap. Elk are susceptible to chronic wasting disease. (USGS, Public domain.)

Chronic wasting disease (CWD) is a fatal disease of deer, elk, and moose caused by improperly folded, infectious proteins called prions. CWD can be transmitted by infected animals or by  infected body fluids in the environment (e.g., infected saliva or urine on the soil). This disease has negatively affected the deer, elk, and moose populations in North America over the past 20 years, and there is no cure or vaccine for CWD, so wildlife and land managers are interested in developing strategies of disease mitigation and prevention. 

Understanding the importance of agricultural mineral licks (sometimes called salt licks) in CWD transmission will provide managers valuable disease mitigation and prevention information. Agricultural mineral licks are put out to provide supplemental minerals (e.g., sodium, magnesium) for cattle, but other animals like deer and elk also use them. The potential risk with mineral licks is two-fold. First, animals congregate at mineral licks because they are “hotspots” containing an uncommon, but necessary mineral resource. Therefore, if a CWD-infected individual is present, it can easily infect others through direct contact. Second, an animal can indirectly infected others by leaving infected saliva on the mineral licks to be picked up by uninfected animals later.     

Having the tools to quickly detect CWD in the field is also necessary in the fight to manage this disease. Unfortunately, a lack of powerful diagnostic tools has hampered the ability of researchers to collect and implement a relatively easily sampling protocol. There is an assay being developed called the real-time quaking induced conversion (RT-QuIC) that can detect CWD prions in tissues and body fluids. However, improvements need to be made to this assay for it to be more useful on fecal and soil samples.

Salt lick (right) and device to exclude wildlife from access to minerals (left)

Orange and black excluder device (left) will contain minerals, but intended to allow livestock access while excluding wildlife. Mineral block to the right of excluder device. (Credit: Paul Cross, USGS. Public domain.)


This research uses experimental sites across multiple regions of Wyoming to evaluate the potential for mineral licks to be CWD transmission sites. Randomly chosen sites will have excluders placed and elk and deer behavior will be monitored in a before-after-control-impact design with camera traps (i.e., remote cameras) and GPS collars. These excluders are intended to allow livestock to continue to access mineral licks while excluding wildlife. It is unknown how effective these excluders will be and how far wildlife may adjust their space use when excluded from mineral licks. Elk, mule deer, moose, and possibly whitetail deer will be studied. Camera traps and GPS collars will monitor animal behavior to access the degree of congregation that occurs at the sites, and samples will be taken at the mineral licks so they can be tested for CWD and assist in the optimized of the RT-QuIC assay.

USGS scientists, state partners, and landowners are working together to find how CWD moves through the environment and improve the tools to test for CWD.


For more information on NOROCK chronic wasting disease research, click here.