Chronic wasting disease (CWD) is a prion disease affecting captive and free-ranging cervids (white-tailed deer, mule deer, elk and moose). First described in captive deer in Wyoming in the late 1960's, the geographical range of CWD now includes Alberta and Saskatchewan as well as Colorado, Wyoming, Nebraska, Wisconsin, New York, Virginia, Texas in the United States. Due to the inadvertent importation of infected elk, Korea has also reported CWD in farm raised elk. Clinical signs of CWD include emaciation and a reduced fear of humans. The origin and mode of transmission of CWD is unknown, but the infection rates within a given captive population can be very high (>80% of all animals in residence at one facility).
CWD is highly contagious (to deer and other cervids) and is always fatal. Although the disease primarily affects the central nervous system (brain) of infected animals, the infectious agent (CWD prions) are shed in saliva, urine and feces. As with other prion diseases, the incubation period for CWD in cervids is long (years). Infected animals do not show any signs of disease until months to years after initial infection. During this long pre-clinical phase of the disease, the animals are, however, shedding the infectious agent.
A number of studies have demonstrated that prions entering the environment (i.e., from the saliva, feces, urine of infected deer), bind strongly to soil and are not easily degraded, persisting in the environment for years to decades. Soil-bound prions are more infectious than unbound prions. These data suggest that reducing the exposure of cervids to prions in the environment will be a challenging problem.
CWD is not readily transmitted, experimentally, to other species. Transmission does, however, occur. The natural transmission of CWD into other species (other than other cervids) has not been documented nor has transmission into humans. Although there is, to date, no evidence of CWD transmission to humans, caution in handling CWD-positive animals is strongly recommended.
CWD Surveillance Sites