Chronic wasting disease (CWD) has emerged as an important disease of wildlife in 
North America. The disease is a unique member of the transmissible spongiform 
encephalopathies (TSEs) or prion diseases, which naturally affect only a few 
species. Of the TSEs, CWD is the only one found in free-ranging species. 
However, interest in CWD has recently grown, by association with the 
better-known TSEs such as variant Creutzfeldt-Jakob disease of humans and bovine 
spongiform encephalopathy. Knowledge of the geographic distribution of CWD, 
though still limited, has greatly improved since the mid-1990s as a result of 
surveillance in free-ranging deer and elk and in commercially owned Rocky 
Mountain elk (Cervus elaphus nelsoni), and the disease has now been found in 
multiple areas of the plains and Rocky Mountain foothills of western North 
America. Studies of the biology and natural history of CWD over recent years 
have resulted in a better understanding of the pathogenesis and epidemiology of 
the disease. Early involvement of the lymphoid tissues of the alimentary tract 
during the incubation period of CWD suggests plausible routes for agent exit 
from an infected individual, such as in faeces or saliva. Chronic wasting 
disease is laterally transmitted and environmental contamination may play an 
important role in local maintenance of the disease. Studies on the epidemiology 
of CWD have led to the development of models to help explain the history of CWD 
and to simulate future impacts on deer and elk populations. Diagnostic tests 
have been improved, allowing diagnosis early in the incubation period, long 
before the appearance of clinical disease. Surveillance techniques and 
programmes have been developed and instituted by wildlife management agencies 
for free-ranging deer and elk and by state and federal agricultural agencies for 
privately-owned elk. During the 1990s, perceptions of TSEs have altered 
dramatically; perhaps most remarkably, the goal of global eradication of all 
prion diseases is now being discussed.