- Chronic Wasting Disease (CWD) is related to a group of
diseases known as transmissible spongiform encephalopathies (TSEs). TSEs
include such diseases as scrapie in sheep, bovine spongiform encephalopathy
(BSE) in cattle (aka Mad Cow Disease) and Creutzfeldt-Jakob disease of
humans and are diseases of the nervous system that result in distinctive
lesions in the brain. The causative agent is believed to be a modified
protein (prion). These modified proteins are typically found in nervous
and lymphatic tissues, but recent experimental evidence shows prions can
occur in muscle tissue of mice.
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- CWD infects elk, white-tailed deer, and mule deer, but
is not known to infect livestock or humans at the present time. No treatment
is known and the disease is typically fatal. The mode of transmission of
CWD between animals is not known, although direct contact between infected
and non-infected animals via saliva, urine and feces 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 implication 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 and may take many
years before they show clinical signs of the disease. 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. Recently, a biopsy technique for tonsilar
tissues from live deer has been developed; however, this test seems to
only work for white-tailed deer and mule deer but not for elk.
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- The incidence of CWD in wild animals 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 found in wild
herds in several surrounding states and Canada. In early 2002, CWD has
been detected in wild deer in South Dakota, Wisconsin and New Mexico. Researchers
speculate that CWD could have been transported long distance as a result
of interstate shipment of infected animals.
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- 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 contrast 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 infect
white-tailed deer at these densities or what long term affect this disease
will have on a herd of this size (approximately 1.6 million animals).
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- For more information on Chronic Wasting Disease Dr. Scott
Wright at 608-270-2460,
- or Paul Slota, at 608-270-2420, USGS, National Wildlife
Health Center
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- http://www.nwhc.usgs.gov/research/chronic_wasting/chronic_wasting.html
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