Page 29 - MDWFP CWD Response Plan

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
observed.

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
dynamics.
- 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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