Chronic Wasting Disease: Status, Science, and Management 

Support by the U.S. Geological Survey

CWD in free-ranging populations

Known distribution prior to 2000 

(free-ranging)

CWD in captive facilities (depopulated)

CWD in captive facilities (current)

EXPLANATION

Chronic Wasting Disease: Status, Science, and Management 

Support by the U.S. Geological Survey

By Christina M. Carlson, M. Camille Hopkins, Natalie T. Nguyen, Bryan J. Richards, Daniel P. Walsh, and W. David Walter

Background and Significance

Chronic wasting disease (CWD) is an emerging infectious 

disease that is fatal to free-ranging and captive animals in Cervidae (the deer family; referred to as “cervids”). Affected animals 

include some Odocoileus, Cervus, and Muntiacus species (deer), 

Cervus canadensis (elk), Alces alces (moose), and Rangifer tarandus (reindeer). Once an animal is infected, CWD typically causes 

neurological damage that grows more severe until the host animal 

dies. Originally identified in 1967, to date (early 2018), the disease 

has been found in 24 States as well as Canada, South Korea, and 

Norway. It continues to spread across North America through 

new and ongoing outbreaks (fig. 1). In addition, the proportion 

of CWD-infected animals is increasing in many areas where the 

disease is already established. For example, the proportion of 

adult male and female Odocoileus virginianus (white-tailed deer) 

in north-central Iowa County, Wisconsin, that tested positive for 

CWD has more than doubled during a 6-year period (2011–16). 

Approximately 40–50 percent of the adult male population and 

20-30 percent of the adult female population was infected by 

2016, making north-central Iowa County one of the most heavily affected regions in the United States (Wisconsin Department 

of Natural Resources, 2017). In some heavily affected areas, total 

cervid numbers have decreased over time due to CWD, which 

suggests that these cervid populations may not be sustainable in 

the long-term (Miller and others, 2008; Almberg and others, 2011; 

Monello and others, 2014; Geremia and others, 2015; Edmunds and 

others, 2016; DeVivo and others, 2017). In east-central Wyoming, 

the number of wild white-tailed deer in a study population declined 

10.4 percent annually between 2003 and 2010. Moreover, deer that 

tested positive for the causative CWD agent were 4.5 times more 

likely to die each year than deer that tested negative (Edmunds 

and others, 2016). In sympatric mule deer, the population declined 

by 21 percent annually during a 5-year study, and researchers 

concluded that CWD was a significant causative factor in this 

decline (DeVivo and others, 2017). In addition to CWD’s effects 

on free-ranging cervids, the disease also directly impacts captive 

herds. CWD has been identified in over 175 North American captive cervid facilities (fig. 1) where infection rates have approached 

80 percent (Keane and others, 2008) and have resulted in the 

destruction of all individual deer within most of these facilities 

and costly government compensation associated with this animal 

depopulation. Current evidence strongly suggests CWD has been 

transmitted between captive and free-ranging cervids and that the 

movement of cervids, through both natural and human-assisted 

means, is one of the greatest risk factors in spreading CWD to new 

areas (Bollinger and others, 2004; Haley and Hoover, 2014). 

Figure 1. Reported distribution of 

chronic wasting disease (CWD) in 

North America in 2018: 24 States and 

2 Canadian Provinces have reported 

the disease in free-ranging and captive 

cervids. An online version of this map is 

updated when CWD is detected in new 

locations in North America and is on 

the web, at http://www.nwhc.usgs.gov/

disease_information/chronic_wasting_

disease/index.jsp.

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2017–1138

March 2018
In addition to direct disease impacts on cervids, CWD may 

also impart economic, social, and ecological effects, and complicate cervid management. For example, the State of Wisconsin 

spent $32.3 million on CWD surveillance and management from 

2001 to 2006 to address the disease and monitor its spread (Wisconsin Legislative Audit Bureau, 2006). In the United States, big 

game hunting is enjoyed by 11.6 million hunters, and it provides 

212 million person-days (the amount of recreation time in days 

contributed by all participating persons) of hunting recreation and 

contributes approximately $170 billion to the nation’s economy 

each year (2011 figures; U.S. Fish and Wildlife Service and 

U.S. Census Bureau, 2014). Surveys of deer hunters suggest nearly 

half would stop hunting if approximately 50 percent of wild deer 

became infected with the CWD agent or if a human-health risk 

from CWD was identified (Needham and others, 2004; Vaske 

and Lyon, 2011). Decline in hunter participation results in loss of 

hunting-related revenue (including travel, equipment, and license 

sales) that supports the economic stability of many local communities and directly funds wildlife management and conservation 

efforts (Needham and others, 2004). In addition to local communities, the movement of CWD presents a threat to tribal culture and a 

traditional tribal food source (Great Lakes Indian Fish and Wildlife 

Commission, 2018). Hunting is a primary tool for managing and 

controlling cervid populations; overabundant cervid populations 

facilitate spread of some cervid diseases and lead to ecologic and 

economic damage (Côté and others, 2004). For example, overbrowsing and foraging by deer can inflict major economic losses on 

forestry and agriculture and negatively impact the abundance and 

diversity of forest vegetation and wildlife (Côté and others, 2004).

What is Chronic Wasting Disease?

CWD is one member of a family of diseases called transmissible spongiform encephalopathies (TSEs), which includes 

scrapie in sheep and goats, bovine spongiform encephalopathy 

(commonly called “mad cow disease”) in cattle, and CreutzfeldtJakob disease in humans. CWD is the only TSE known to affect 

free-ranging wildlife. The causative agents of TSEs are thought 

to be prions (pronounced PREE-ons) (Prusiner, 1982). Prions 

are unconventional pathogenic agents that are comprised mostly, 

if not entirely, of a misfolded, infectious form of a normally 

occurring host protein. Prion proteins are found most abundantly 

in mammalian brain and central nervous system tissues. Prions 

are unique when compared to all other known pathogens, in part 

because they do not have a nucleic acid genome, such as DNA. 

Other known pathogens, such as viruses and bacteria, need DNA 

or RNA to replicate, while prions do not. Additionally, prions 

exhibit an extraordinary resistance to common treatments used 

to stop other infectious agents, such as ultraviolet and ionizing 

radiation, exposure to chemical disinfectants, and heat treatments (Colby and Prusiner, 2011). Prions typically infect hosts 

in a species-specific manner, and CWD prions can be passed via 

direct transmission between susceptible cervids and by indirect 

transmission through contact with contaminated materials in the 

environment (Miller and others, 2004). Following a protracted 

incubation period during which there are no outward signs of 

disease, CWD-positive animals suffer progressive neurological 

degeneration that causes physiological and behavioral changes 

(listlessness, excessive drinking and urination, lowering of head, 

weight loss) and, ultimately, death (Williams and Young, 1980). 

A white-tailed deer displaying clinical signs of chronic 

wasting disease including weight loss, poor body condition, 

and hypersalivation. (Photo by Warden Micheal Hopper, 

Kansas Department of Wildlife, Parks and Tourism.)

Light microscopy images of A, healthy deer lymphoid tissue. B, CWD-infected 

deer lymphoid tissue. CWD prion protein deposition in lymphoid follicles is 

indicated by red staining. Staining for disease-associated prion protein in brain 

or lymphoid tissues is the primary method used for diagnostic testing to confirm 

a CWD diagnosis. (Photo from USGS National Wildlife Health Center files.)

B

A
Current Status of Chronic Wasting Disease

The disease is currently spreading geographically and has 

recently been detected in additional cervid species. CWD was 

first detected outside North America when infected Canadian elk 

were exported to South Korea between 1994 and 1997, and the 

disease spread between captive cervids (Sohn and others, 2002; 

Kim and others, 2005,). In 2016, the disease was detected for the 

first time in free-ranging reindeer, moose, and Cervus elaphus 

atlanticus (red deer) in Norway (Benestad, 2016; Norwegian 

Veterinary Institute, 2017).

The extraordinary stability of the CWD prion allows it to 

remain infectious in the environment for years, posing longterm potential risks to agricultural, wildlife, and public health 

(Miller and others, 2004). Noncervid species may be directly 

or indirectly exposed to CWD prions on the landscape through 

urinary, salivary, or fecal shedding from infected animals or 

decomposition of diseased carcasses. Although the risks of 

CWD transmission between species are not completely characterized, infection of noncervid species with CWD prions has 

not been reported under natural conditions. However, rodents 

(voles, mice, and hamsters), carnivores (ferrets, mink, and cats), 

livestock (cattle, sheep, goats, and pigs), and primates (squirrel 

monkeys and cynomologus macaques) have been experimentally infected. Some of these experiments use natural routes of 

exposure, such as feeding of prion-infected meat (Haley and 

Hoover, 2014; Moore and others, 2017; Czub and others, 2017). 

Although there are no current reported cases of natural CWD 

prion infection in humans, the successful experimental infection 

of two species of nonhuman primates raises concern over the 

potential for CWD to be transmitted to humans. Consistent with 

this concern, the Centers for Disease Control and Prevention 

(2015), the World Health Organization (2012), and many local 

public health departments advise against human consumption of 

CWD-infected animal parts or products.

Although the long-term effects of CWD on wildlife and 

ecosystems remain unclear, its documented and potential 

impacts make it a primary concern for natural resource management agencies in the United States and Canada. Effective 

vaccines and treatments do not currently exist and efforts to 

control or eradicate the disease from free-ranging cervid populations have been largely ineffective (Haley and others, 2014). 

Therefore, current management strategies include implementing 

strong preventative measures to reduce or disrupt CWD spread 

in cervids (Williams and others, 2002;DeVivo and others, 2017). 

Additional scientific studies could help provide a better understanding of the risks and disease dynamics of CWD, forecast 

short- and long-term impacts of the disease, and develop effective strategies for prevention and control.

William Miller prepares a DNA sample for genetic analysis. William is a graduate 

student at Pennsylvania State University studying the landscape genetics of white-tailed 

deer with the Pennsylvania Cooperative Fish and Wildlife Research Unit. His results will 

be used to inform spatial epidemiological models for chronic wasting disease in the 

eastern United States. (Photo by David Muñoz, Pennsylvania State University)
Northern 

Prairie Wildlife 

Research 

Center

Northern Rocky 

Mountain Science 

Center

National Wildlife 

Health Center

Wisconsin Cooperative 

Wildlife Research 

Unit Pennsylvania 

Cooperative 

Fish and Wildlife 

Research Unit

Pacific Region

Northwest Region

Southwest Region

Midwest Region

Southeast Region

Northeast

Region

Lorem ipsum

U.S. Geological Survey Science to Support Management of Chronic Wasting Disease

Figure 2. The U.S. Geological Survey science centers and cooperative 

research units conducting chronic wasting disease research and technical 

assistance for the United States. 

The U.S. Geological Survey 

(USGS) investigates CWD at 

multiple science centers and cooperative research units across the Nation 

(fig. 2) and supports the management of CWD through science-based 

strategies. CWD research conducted 

by USGS scientists has three strategies: (1) to understand the biology, 

ecology, and causes and distribution 

of CWD; (2) to assess and predict 

the spread and persistence of CWD 

in wildlife and the environment; 

and (3) to develop tools for early 

detection, diagnosis, surveillance, 

and control of CWD (table 1).

Table 1. U.S. Geological Survey Contributions to Understanding Chronic Wasting Disease.

[USGS, U.S. Geological Survey; CWD, chronic wasting disease]

Biology, ecology 

and epidemiology 

of CWD

USGS scientists work to:

•	 analyze the individual genetic characteristics that influence cervid risk of being infected with CWD.

•	 study how CWD prions change over time.

•	 study CWD transmission, spread, and prevention in free-ranging and captive cervids.

•	 assess the effect of CWD on cervid survival and long-term population growth.

•	 identify and investigate the species that harbor CWD and the ecological factors that may facilitate 

CWD transmission, including the potential roles of soil, plants, and wild rodents.

The USGS Northern 

Prairie Wildlife Research 

Center and the National 

Park Service are 

evaluating effects of 

elk density on survival 

and chronic wasting 

disease prevalence at 

Wind Cave National 

Park, South Dakota 

(Photo, immediately right, 

courtesy of the National 

Park Service, Wind Cave 

National Park).
WS_Requests\31622_Gude_CWDMap MAM 5/26/2016

Loc ShortestDist Drainage Via Drainage Dist

AB 28 mi Lodge Cr ~38 mi

SK 31 mi Frenchman Cr ~53 mi

WY1 7 mi Shoshone Rv ~10 mi

WY2 23 mi Big Horn Lake ~41 mi

WY3 24 mi Upper Tongue Rv ~ 25 mi

0 25 50 100

Miles

 

WY1 WY2 WY3

MT Hydrologic Units with CWD Locations

Scaled relative mule deer density 

(Max of summer and winter models, 

2015 population estimate)

High

Low

CWD 

Location

Buffers

CWD Locations Deer and Elk

AB

SK

20 miles

40 miles

60 miles

MT Hydrologic Units with CWD Locations

Scaled relative mule deer density

(Max of summer and winter models, 

2015 population estimate)

High

Low

AB

SK

WY1

WY2

WY3

20 miles

40 miles

60 miles

CWD 

Location 

Buffers

CWD Locations Deer and Elk 28 mi

31 mi

7 mi

23 mi

24 mi

Lodge Cr

Frenchman Cr

Shoshone Cr

Big Horn Cr

Upper Tongue Rv

~38 mi

~53 mi

~10 mi

~41 mi

~25 mi

Loc ShortestDist Drainage Via Drainage Dist

CWD risk 

assessment and 

modeling

USGS scientists have the capabilities to:

•	 identify risk factors for CWD prion infection and areas at high risk for CWD introduction.

•	 predict the risk of disease transmission among and between captive and free-ranging cervids.

•	 assess how different management approaches affect disease transmission, spread, persistence, and control. 

•	 investigate the potential for CWD transmission from cervids to other wildlife, domestic species, and humans. 

•	 develop tools or techniques for predicting CWD growth within free-ranging cervid populations and 

forecasting disease spread in regions of interest.

Figure, right, shows 

the measured and 

forecasted growth 

and spread of CWD in 

white-tailed deer in th

core area where CWD 

occurs in Wisconsin, 

USA. (Reference and 

image credit: Hefley 

and others 2017)

CWD surveillance 

and mitigation

USGS scientists are investigating new and improved methods to:

e 

•	 increase the efficiency of CWD surveillance programs.

•	 detect CWD prions in living and deceased animals and the environment.

•	 decontaminate natural and agricultural areas and disrupt disease transmission.

The USGS National 

Wildlife Health Center 

assisted Montana Fish, 

Wildlife & Parks to 

develop risk maps for 

CWD which helps inform 

the State’s surveillance 

program. To the right 

is a map including 

information from recent 

(2015) detections 

of CWD. (Reference and 

image credit: Russell 

and others, 2015)
Through a comprehensive, multidisciplinary research 

program, the USGS is providing cutting-edge science to help 

inform management of this challenging disease. USGS research 

has been instrumental in developing surveillance strategies for 

early detection of CWD in Montana and Shenandoah National 

Park in Virginia (Russell and others, 2015); identifying high 

risk areas for potential CWD transmission between wild and 

farmed deer in Pennsylvania (Carrollo, 2016); and identifying 

potential disease risks posed by CWD to noncervid species, such 

as bighorn sheep (Morawski and others, 2013). The benefits of 

USGS research on CWD extend beyond wildlife management. 

For example, USGS scientists identified a novel enzyme from 

lichens with the ability to breakdown infectious prion protein, 

which could be useful for decontaminating human hospital 

environments (Johnson and others, 2011). The USGS is committed to finding solutions to this challenging disease and providing 

research that has multiple benefits for wildlife health as well as 

environmental, agricultural, and, potentially, human health.

U.S. Geological Survey Web Links and Selected 

Publications

USGS Ecosystems CWD: 

https://www2.usgs.gov/ecosystems/disease/cwd.html

USGS National Wildlife Health Center: http://www.nwhc.usgs.gov/

USGS Northern Rocky Mountain Science Center: 

https://www.usgs.gov/centers/norock/

USGS Northern Prairie Wildlife Research Center: 

http://www.npwrc.usgs.gov/

Pennsylvania Cooperative Fish and Wildlife Research Unit: 

http://www.coopunits.org/Pennsylvania/

Wisconsin Cooperative Wildlife Research Unit: 

http://www.coopunits.org/Wisconsin_Wildlife/

USGS Publications Warehouse: https://pubs.er.usgs.gov/

Photo below. Research from the U.S. Geological Survey National 

Wildlife Health Center indicates that bighorn sheep could be 

vulnerable to CWD from either white-tailed deer or elk and to a 

domestic sheep prion disease known as scrapie (Morawski and 

others 2013). (Photo by Jim Peaco, U.S. National Parks Service 2004.)

Background photo. Scientists from the U.S. Geological Survey 

National Wildlife Health Center have identified an enzyme found 

in various species of lichens, including Parmelia sulcata, that are 

able to degrade infectious prion protein. Current research is focused 

on application of this lichen enzyme in decontamination of human 

hospital environments (Johnson and others 2011). (Photo by Christina 

Carlson, USGS, National Wildlife Health Center.)

Photo above. The U.S. Geological Survey is investigating prion 

contamination of plants, such as corn and other crops, to determine if 

they play a role in environmental prion transmission. (Photo by Christina 

Carlson, USGS National Wildlife Health Center.)
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For additional information contact:

Ecosystems Mission Area

12201 Sunrise Valley Drive

Reston, VA 20192

Director, USGS National Wildlife Health Center

6006 Schroeder Road 

Madison, WI 53711-6223

ISSN 0196-1497 (print)

ISSN 2332-1258 (online)

https://doi.org/10.3133/ofr20171138

Additional photographs by U.S. Fish and Wildlife Service. Banner—herd of mule deer by John Carr. Photographs pages 2 and 3—

elk ascending by Tony Hough; mule deer bedded down in frosty landscape, and mule deer on guard, by Tom Koerner; moose, by David Govatski.

Publishing support provided by the 

U.S. Geological Survey, 

Science Publishing Network, 

Madison Publishing Service Center