Chronic wasting disease (CWD) is a unique transmissible spongiform 
encephalopathy (TSE) of mule deer (Odocoileus hemionus), white-tailed deer (O. 
virginianus), and Rocky Mountain elk (Cervus elaphus nelsoni). The natural 
history of CWD is incompletely understood, but it differs from scrapie and 
bovine spongiform encephalopathy (BSE) by virtue of its occurrence in 
nondomestic and free-ranging species. CWD has many features in common with 
scrapie, including early widespread distribution of disease-associated prion 
protein (PrP(d)) in lymphoid tissues, with later involvement of central nervous 
system (CNS) and peripheral tissues. This distribution likely contributes to 
apparent efficiency of horizontal transmission and, in this, is similar to 
scrapie and differs from BSE. Clinical features and lesions of CWD are 
qualitatively similar to the other animal TSEs. Microscopically, marked 
spongiform lesions occur in the central nervous system (CNS) after a prolonged 
incubation period and variable course of clinical disease. During incubation, 
PrP(d) can be identified in tissues by antibody-based detection systems. 
Although CWD can be transmitted by intracerebral inoculation to cattle, sheep, 
and goats, ongoing studies have not demonstrated that domestic livestock are 
susceptible via oral exposure, the presumed natural route of exposure to TSEs. 
Surveillance efforts for CWD in captive and free-ranging cervids will continue 
in concert with similar activities for scrapie and BSE. Eradication of CWD in 
farmed cervids is the goal of state, federal, and industry programs, but 
eradication of CWD from free-ranging populations of cervids is unlikely with 
currently available management techniques.