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Although CWD is a contagious fatal disease among deer and elk, research suggests that humans, cattle and other domestic livestock are resistant to natural transmission. While the possibility of human infection remains a concern, it is important to note there have been no verified cases of humans contracting CWD.
Transmission: Animal to Animal
Transmission of CWD is possible in species with closely related proteins, thereby being able to exchange prions and cause disease. It is not likely to jump the species barrier. There is no evidence at this time that CWD can be naturally transmitted to livestock or animals other than deer and elk. In deer and elk, the causal agent of CWD is transmissible from infected to uninfected individuals. Both circumstantial and experimental evidence implicates an animal to animal form of transmission. This occurs via horizontal or lateral (contact between adult animal and adult animal, contamination of feed or water sources with saliva, urine, and/or feces, or contact with an infected facility or area), and more rarely as vertical or maternal (adult animal (dam) to offspring via contact). Concentrating cervids in captivity and baiting or feeding animals can greatly increase the chances of disease spread.
Once natural transmission occurs, a minimum incubation period (the time from infection to observance of clinical signs) of 18 months is required between exposure to the causal agent and development of the disease. In captive cervid herds a minimal incubation period of 18 to 20 months for mule deer and 18 to 36 months for elk was observed. Some signs associated with CWD include: a decline in body conditioning, changes in behavior, tremors, reduced feed intake, and difficulty standing.
Transmission: Animal to Human
To date, there is no evidence that CWD can be naturally transmitted to humans or to animals other than deer and elk. There is no evidence that the agent that causes CWD occurs in the meat. CWD is not a food borne disease. Unlike BSE, CWD is not associated with being spread though the use of rendered meat or bone meal products. Proteins differ from one species to another therefore prions are unlikely to prosper in a new species. There is a "substantial barrier" to CWD transmission between animals and people.
The clinical course of CWD varies from a few days to approximately a year, with most animals surviving from a few weeks to several months. While a protracted clinical course is typical, occasionally acute death may occur; this may be more common in the wild than in the relative security of captivity. Aspiration pneumonia is a common finding at postmortem examination of terminal CWD cases and may confuse the diagnosis if the brain is not examined. Aspiration pneumonia presumably is due to difficulty swallowing, hypersalivation, and inhalation of foreign material into the lungs. Thus the brain should be examined for evidence of CWD on every prime age cervid that dies with pneumonia. Currently there is no clinical treatment available for CWD. Once the disease develops is perceived as fatal. Therefore, within captive facilities CWD management options are limited to quarantine or depopulation.