Chronic Wasting Disease
Research at
the USGS-Wisconsin Cooperative Wildlife Research Unit
Background
Chronic
wasting disease (CWD) is a fatal neurodegenerative disease of mule deer
(Odocoileus
hemionus), white-tailed deer (O. virginianus), and elk (Cervus
elaphus) associated with the presence of transmissible protease
resistant
prion proteins (or prions). Although the transmission route of
CWD is
unknown, it may be transmitted among deer and elk by direct contact or
indirectly through the environment. Maternal transmission does not
appear to be
an important component of CWD epidemiology. Appearance of clinical
signs is
usually delayed, but symptoms typically appear within 18-24 months
after
experimental infections, and include weight loss, anorexia, repetitive
behaviors, hyperesthesia and intractability with progression to severe
emaciation, severe behavioral changes, excessive salivation, tremors,
and mild
ataxia. Pre-clinical disease can be detected in animal lymph node and
brain
tissues using a variety of diagnostic methods.
Historically,
CWD was believed occur only in the western United States, but it has recently been discovered in
the midwest
and eastern U.S. and in central Canada. The current
national distribution and extensive, peer-reviewed
descriptions of the
epidemiology of CWD are available (see here
and here).
An extensive bibliography
on CWD is available. The University of Wisconsin-Madison has a website devoted to CWD,
including a
list of CWD experts on campus and their research programs. The CWD
Alliance maintains an extensive website
on CWD news, scientific information, directory of experts, and many
other
resources related to CWD.
CWD was discovered in south-central Wisconsin in February 2002. Three adult male
deer
harvested within 5-km during the fall of 2001 (click here
for review) were diagnosed with CWD. Almost immediately following the
discovery
of CWD, an Interagency Health and Science team was convened to provide
scientific and management advice on CWD in Wisconsin. Various agencies were represented,
including
the Wisconsin Departments of Natural Resources, Health and Family
Services,
Agriculture Trade and Consumer Protection, the US Department of
Agriculture and
the US Geological Survey. Staff of the USGS-National
Wildlife Health Center (USGS-NWHC), the University
of Wisconsin-Madison Department of Wildlife Ecology, and the USGS-Wisconsin
Cooperative
Wildlife Research Unit (USGS-WCWRU) were asked to provide
quantitative,
epidemiological, and scientific support to assist in surveillance and
management of CWD in Wisconsin.
The current distribution
of CWD in Wisconsin is limited to an infected area in
south-central Wisconsin and an area of south-eastern Wisconsin continuing into northern Illinois.
An integrated research and management program has developed from this
collaboration including the USGS-NWHC, the Wisconsin
Department of Natural Resources (WDNR), and the
USGS-WCWRU. Research
studies at WCWRU have focused on understanding the epidemiology and
transmission of CWD in white-tailed deer, the landscape patterns
associated
with CWD distribution and spread, potential CWD transmission into other
wildlife species, and evaluation of CWD surveillance and management
actions.
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Introduction
