Page 29 - MDWFP CWD Response Plan
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wildlife research facilities in Colorado in the late 1960s, but it was not identified as a TSE
                   until the 1970s.
                   Scrapie, a TSE of domestic sheep, has been recognized in the United States since 1947, and it
                   is possible that CWD was derived from scrapie. It is possible, though never proven, that deer
                   came into contact with scrapie-infected sheep either on shared pastures or in captivity
                   somewhere along the front range of the Rocky Mountains, where high levels of sheep
                   grazing occurred in the early 1900s.
                   It may be possible that CWD is a spontaneous TSE that arose in deer in the wild or in
                   captivity and has biological features promoting transmission to other deer and elk.

                   How does CWD spread?
                   It is not known exactly how CWD is transmitted. The infectious agent may be passed in
                   feces, urine or saliva. Transmission is thought to be lateral (from animal to animal). The
                   minimal incubation period between infection and development of clinical disease appears to
                   be approximately 16 months. The maximal incubation period is unknown, as is the point at
                   which shedding of the CWD agent begins during the prolonged course of infection.
                   Because CWD infectious agents are extremely resistant in the environment, transmission
                   may be both direct and indirect. Concentrating deer and elk in captivity or by artificial
                   feeding probably increases the likelihood of both direct and indirect transmission between
                   individuals. The movement of live animals is one of the greatest risk factors in spreading the
                   disease into new areas.

                   What are the symptoms of CWD?
                   The most obvious and consistent clinical sign is weight loss over time. CWD affected
                   animals continue to eat but amounts of feed consumed are reduced, leading to gradual loss of
                   body condition. Excessive drinking and urination are common in the terminal stages.
                   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. Excessive salivation, drooling and grinding of the teeth also are

                   How is CWD detected?
                   Clinical signs of CWD alone are not conclusive, and there is currently no practical live
                   animal test. Currently, the only conclusive diagnosis involves an examination of the brain,
                   tonsils or lymph nodes performed after death.

                   Why are we concerned about CWD?
                   CWD poses serious problems for wildlife managers, and the implications for free-ranging
                   deer are significant:
                       -  Ongoing surveillance programs are expensive and draw resources from other wildlife
                          management needs.
                       -  Impacts of CWD on population dynamics of deer and elk are presently unknown.
                          Computer modeling suggests that CWD could substantially reduce infected cervid
                          populations by lowering adult survival rates and destabilizing long-term population
                       -  Where it occurs, CWD may alter the management of wild deer and elk populations,
                          and it has already begun to do so.

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