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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. The infectious agent may be passed in feces, urine or saliva.
In addition, hunters should take common sense precautions when field dressing and processing deer or elk taken in areas where CWD is found.CWD belongs to a group of diseases known as transmissible spongiform encephalopathies (TSEs).Within this family of diseases, there are several other variants that affect domestic animals: scrapie, which has been identified in domestic sheep and goats for more than 200 years, bovine spongiform encephalopathy (BSE) in cattle (also known as “mad cow disease”), and transmissible mink encephalopathy in farmed mink. Creutzfeldt-Jakob disease (CJD) occurs naturally in about one out of every one million people worldwide.Based on experience with other TSE agents, the CWD infectious agent is assumed to be resistant to enzymes and chemicals that normally break down proteins, as well as resistant to heat and normal disinfecting procedures.The origin of CWD is unknown, and it may never be possible to definitively determine how or when CWD arose.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.
Although maternal transmission (from mother to fetus) may occur, it appears to be relatively unimportant in maintaining epidemics.
The minimal incubation period between infection and development of clinical disease appears to be approximately 16 months.
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.
Variant Creutzfeldt-Jakob disease (v-CJD) has been associated with the large-scale outbreak of BSE in cattle herds in Great Britain.