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Mule Deer with Chronic Wasting Disease
Elk with Chronic Wasting Disease

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Chronic wasting disease (CWD) is a transmissible spongiform encephalopathy transmissible spongiform     encephalopathy (TSE) of deer and elk.  To date, this disease has been found only in cervids (members of the deer family).  First recognized as a clinical "wasting" syndrome in 1967 in mule deer in a wildlife research facility in northern Colorado, it was identified as a TSE in 1978.  CWD is typified by chronic weight loss leading to death.  There is no known relationship between CWD and any other TSE of animals or people.

                  In the mid-1980s, CWD was detected in free-ranging deer and elk in contiguous
                  portions of northeastern Colorado and southeastern Wyoming.  In May 2001, CWD
                  was also found in free-ranging deer in the southwestern corner of Nebraska (adjacent
                  to Colorado and Wyoming) and later in additional areas in western Nebraska.  The
                  limited  area of northern Colorado, southern Wyoming, and western Nebraska in which
                  free-ranging deer and/or elk positive for CWD have been found is referred to as the
                  endemic area.  Soon after diagnosis of the disease as a TSE, Colorado and Wyoming
                  wildlife management agencies stopped the movement of deer and elk from their
                  research facilities; wild cervids have not been translocated from the endemic area. In
                  2002, CWD also has been detected in wild deer in south-central Wisconsin,
                  southwestern South Dakota, the western slope of Colorado, southern New Mexico,
                  and northern Illinois.

                  CWD also has been diagnosed in farmed elk and deer herds in a number of States and
                  in two Canadian provinces.  The first positive farmed elk herd in the United States was
                  detected in 1997 in South Dakota. 

                  Since then, 25 additional positive elk herds and two positive farmed deer herds have
                  been found: South Dakota (7), Nebraska (4), Colorado (10), Oklahoma (1), Kansas (1),
                  Minnesota (1), Montana (1), and Wisconsin (2).  As of October 2002, three of these 27
                  positive herds remain under State quarantine.  Twenty-three of the herds have been
                  depopulated or have been slaughtered and tested, and the quarantine has been lifted
                  from one herd that underwent rigorous surveillance with no further evidence of disease. 
                  CWD also has been found in farmed elk in the Canadian provinces of Saskatchewan
                  and Alberta and in free-ranging mule deer in Saskatchewan.  For more information on
                  CWD in Canada, visit the Canadian Food Inspection Agency Web site at
                  www.inspection.gc.ca/english/anima/heasan/disemala/cwdmdce.shtml. 

                  Species that have been affected with CWD include Rocky Mountain elk, mule deer,
                  white-tailed deer, and black-tailed deer.  Other ruminant species, including wild
                  ruminants and domestic cattle, sheep, and goats, have been housed in wildlife
                  facilities in direct or indirect contact with CWD-affected deer and elk with no evidence
                  of disease transmission.  There is ongoing research to further explore the possibility of
                  transmission of CWD to other species.
 

               Causative Agent
                  The agent responsible for CWD (and other TSEs, such as scrapie and bovine
                  spongiform encephalopathy) has not been completely characterized.  There are three
                  main theories on the nature of the agent that causes CWD:  (1) the agent is a prion,
                  an abnormal form of a normal protein, known as cellular prion protein, most commonly
                  found in the central nervous system.  The abnormal prion protein “infects” the host
                  animal by promoting conversion of normal cellular prion protein to the abnormal form;
                  (2) the agent is an unconventional virus; (3) the agent is a virino, or “incomplete” virus
                  composed of nucleic acid protected by host proteins.  The CWD agent is smaller than
                  most viral particles and does not evoke any detectable immune response or
                  inflammatory reaction in the host animal.  Based on experience with other TSE
                  agents, the CWD agent is assumed to be resistant to enzymes and chemicals that
                  normally break down proteins, as well as resistant to heat and normal disinfection
                  procedures. 

               Clinical Signs
                  Most cases of CWD occur in adult animals.  The disease is progressive and always
                  fatal.  The most obvious and consistent clinical sign of CWD is weight loss over time. 
                  Behavioral changes also occur in the majority of cases, including decreased
                  interactions with other animals, listlessness, lowering of the head, blank facial
                  expression, and repetitive walking in set patterns.  In elk, behavioral changes may also
                  include hyperexcitability and nervousness.  Affected animals continue to eat grain but
                  may show decreased interest in hay.  Excessive salivation and grinding of the teeth
                  also are observed.  Most deer show increased drinking and urination. 

               Diagnosis
                  Research is being conducted to develop live-animal diagnostic tests for CWD. 
                  Currently, definitive diagnosis is based on postmortem examination (necropsy) and
                  testing.  Gross lesions seen at necropsy reflect the clinical signs of CWD, primarily
                  emaciation.  Aspiration pneumonia, which may be the actual cause of death, also is a
                  common finding in animals affected with CWD.  On microscopic examination, lesions
                  of CWD in the central nervous system resemble those of other TSEs.  In addition,
                  scientists use a technique called immunohistochemistry to test brain tissue for the
                  presence of the abnormal prion protein to diagnose CWD.

               Epidemiology
                  The origin and mode of transmission of CWD is unknown.  Animals born in captivity
                  and those born in the wild have been affected with the disease.  Based on
                  epidemiology, transmission of CWD is thought to be lateral or from animal to animal;
                  although maternal transmission may occur, it appears to be relatively unimportant in
                  maintaining epidemics.
 

               Surveillance
                  Surveillance for CWD in free-ranging deer and elk in Colorado and Wyoming has been
                  ongoing since 1983 and has helped define the core endemic areas for the disease in
                  those States.  CWD in free-ranging deer in Nebraska was detected in 2000/2001; more
                  intensive surveillance to better define the prevalence and distribution of the disease in
                  free-ranging deer in Nebraska is underway.  In addition, an extensive nationwide
                  surveillance effort was started in 1997-98 to better define the geographic distribution of
                  CWD in free-ranging cervids in the United States.  This surveillance effort is a
                  two-pronged approach consisting of hunter-harvest cervid surveys conducted in many
                  States, as well as surveillance throughout the entire country targeting deer and elk
                  exhibiting clinical signs suggestive of CWD.  Over 15,000 harvested free-ranging deer
                  and elk have been tested to date, including over 13,000 animals harvested from outside
                  of the endemic area.  The recent finding of CWD in wild deer in areas far removed from
                  the known endemic area has resulted in the development of plans for intensive
                  surveillance in the 2002-2003 hunting season to better define distribution of the
                  disease in wildlife in the United States.

                  Surveillance for CWD in farmed elk began in 1997 and has been a cooperative effort
                  involving State agriculture and wildlife agencies and the U.S. Department of
                  Agriculture’s (USDA) Animal and Plant Health Inspection Service (APHIS).  Farmed
                  cervid surveillance has been increasing each year since 1997 and will be an integral
                  part of the USDA program to eliminate CWD from farmed elk. 

               Management
                  In each State where CWD has been detected in wildlife, State wildlife agencies have
                  enacted response and/or management plans.  APHIS has provided assistance to
                  State officials in diagnosing CWD and in monitoring international and interstate
                  movements of animals to help prevent further spread of CWD.  Also, APHIS is
                  developing a program to eliminate CWD from farmed elk.  In addition, many State
                  animal health regulatory agencies have instituted CWD programs for farmed elk.  All of
                  these agencies are committed to limiting the distribution of the disease in free-ranging
                  deer and elk to the current localized area and decreasing its occurrence in both the
                  free-ranging and farmed deer and elk populations.

               National CWD Program
                  In May 2002, Congress requested that USDA and the Department of Interior develop a
                  plan to assist State wildlife management and agriculture agencies with CWD
                  management. A CWD task force was formed to ensure that Federal and State
                  agencies cooperate in the development and implementation of an effective national
                  CWD program. The task force delivered the Plan for Assisting States, Federal
                  Agencies, and Tribes in Managing Chronic Wasting Disease in Wild and Captive
                  Cervids to Congress in June 2002 and is currently developing an implementation
                  document for the plan. The plan addresses CWD diagnostics, communication,
                  information dissemination, management, research, and surveillance.