U.S. Department of the Interior

U.S. Geological Survey

USGS-NWHC Information Sheet 

October 2002

ment for CWD is known. The mode 

of transmission of CWD between 

animals is not known, although direct 

contact between infected and noninfected animals is the most likely 

route of transmission. Contamination 

of soil by excreta from infected animals is thought to be another route of 

transmission, particularly among captive herds of deer and elk. However, 

the role of environmental contamination in free-ranging animals is not 

clearly understood. Infected deer and 

elk can appear robust and healthy in 

the early stages of CWD; it may take 

several years before they show clinical signs, after which the disease is 

fatal. The clinical signs are not unique 

to the disease and can be due to other 

conditions such as malnutrition. Currently all testing for CWD requires the 

microscopic examination of a specific 

portion of the brain or lymph nodes. 

Recently, a biopsy technique for 

tonsilar tissues from 

live deer 

has been 

developed; 

however, 

this test 

seems to 

work for 

whitetailed deer 

and mule 

deer but 

not for elk. 

The spread 

of CWD 

in wild 

Chronic Wasting Disease

C hronic Wasting Disease (CWD) affects elk, 

white-tailed deer and mule deer, but is not 

known in livestock or humans. No treatment is 

known and the disease is fatal.

Chronic Wasting Disease (CWD) is 

one of a group of diseases known as 

transmissible spongiform encephalopathies (TSEs). TSEs include such 

diseases as scrapie in sheep, bovine 

spongiform encephalopathy (BSE) 

in cattle (Mad Cow Disease), and 

Creutzfeldt-Jakob disease in humans; 

all are diseases of the nervous system 

that result in distinctive lesions in 

the brain. The cause of all TSEs is 

unknown; however, these diseases are 

diagnosed by the presence of aberrant prion proteins. These modified 

proteins are typically found in nervous and lymphatic tissues, but recent 

experimental evidence shows prions 

can occur in muscle tissue of mice as 

well.

CWD is a disease of wildlife that 

affects elk, white-tailed deer, and mule 

deer. CWD has not been documented 

in livestock or humans. No treatanimals is of great concern. The 

disease was originally described 

in captive animals 35 years ago in 

Colorado. However, over the last five 

years, CWD has been detected in wild 

herds in several surrounding states and 

Canada. In 2002, CWD was detected 

in wild deer in South Dakota, Wisconsin and New Mexico. Researchers 

speculate that CWD could have been 

spread long distances as a result of 

interstate shipment of infected animals. 

The recent detection of CWD in 

the wild white-tailed deer herd in 

Wisconsin is of particular concern. 

White-tailed deer appear more susceptible than mule deer and elk to 

CWD with a greater percentage of the 

herd becoming infected. Until now, 

CWD was found in white-tailed deer 

herds in Colorado, Wyoming, and 

Nebraska where deer occur at densities 

of approximately 2-5 deer per square 

mile. In Wisconsin, deer are found at 

75+ animals per square mile (conservative estimate by Wisconsin Department of Natural Resources). No one 

knows how rapidly CWD will spread 

among white-tailed deer at these 

densities or what long term effect this 

disease will have on a herd of this size 

(approximately 1.5 million animals).

Infected mule deer. Photo courtesy of National 

Park Service.

For more information on Chronic 

Wasting Disease, please contact Dr. 

Scott Wright, USGS National Wildlife 

Health Center, (608) 270-2460, or Mr. 

Paul Slota, USGS National Wildlife 

Health Center, (608) 270-2420.
Printed on recycled paper

For additional information on this disease, please try some of the following 

websites:

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

US Department of Agricullture: Veterinary Services http://www.aphis.usda.gov/vs/nahps/cwd/index.html

Canadian Food Inspection Agency http://www.inspection.gc.ca/english/anima/heasan/ disemala/

 cwdmdce.shtml 

Colorado Division of Wildlife http://wildlife.state.co.us/CWD/index.asp

Montana Department of Livestock http://www.liv.state.mt.us/WASTINGDISEASE/CWD.HTM

Wisconsin Department of Natural Resources http://www.dnr.state.wi.us/org/land/wildlife/whealth/issues/cwd/

Wyoming Game and Fish Department http://gf.state.wy.us/HTML/hunting/chronicwast.htm

Highlights in understanding of Chronic Wasting Disease and related efforts in human medicine.

White-tailed deer. Photo courtesy of P.E. Johns. 

Research begun

on cause of

Creutzfeldt-Jakob

Dr. Stanley Prusiner wins

Nobel Prize in Medicine

for linking prions to TSEs

First cases of

CWD in captive

mule deer herd

First wild elk in

CO diagnosed

with CWD

CWD found in wild

herds in SD, NE, WI,

NM and Saskatchewan

First wild elk in

WY diagnosed

with CWD

Brain lesions

found in deer

with CWD

USDA begins testing

of captive western

deer herds under

emergency rule

Chronic

Wasting

Disease

Creutzfeldt

-Jakob

Disease

1960 1980 1990 2000 2010 1970

TSEs linked

to prions