This article by the CDC is relatively old, but worth reading if you haven't read it before.
http://wwwnc.cdc.gov/eid/article/18/3/11-0685_articleThe following passage is most applicable to this discussion:
CWD Zoonotic Potential, Species Barriers, and Strains
Current Understanding of the CWD Species Barrier Strong evidence of zoonotic transmission of BSE to humans has led to concerns about zoonotic transmission of CWD (2,3). As noted above, CWD prions are present nearly ubiquitously throughout diseased hosts, including in muscle, fat, various glands and organs, antler velvet, and peripheral and CNS tissue (2,14,15). Thus, the potential for
human exposure to CWD by handling and consumption of infectious cervid material is substantial and increases with
increased disease prevalence.
Interspecies transmission of prion diseases often yields a species-barrier effect, in which transmission is less efficient compared with intraspecies transmission, as shown by lower attack rates and extended incubation periods (3,28). The species barrier effect is associated with minor differences in PrPc sequence and structure between the host and target species (3). Prion strain (discussed below) and route of inoculation also affect the species barrier (3,28). For instance, interspecies transmission by intracerebral inoculation is often possible but oral challenge is completely ineffective (29).
Most epidemiologic studies and experimental work have suggested that the potential for CWD transmission to humans is low, and such transmission has not been documented through ongoing surveillance (2,3). In vitro prion replication assays report a relatively low efficiency of CWD PrPSc-directed conversion of human PrPc to PrPSc (30), and transgenic mice overexpressing human PrPc are
resistant to CWD infection (31); these fi ndings indicate low zoonotic potential. However, squirrel monkeys are susceptible to CWD by intracerebral and oral inoculation (32). Cynomolgus macaques, which are evolutionarily closer to humans than squirrel monkeys, are resistant to CWD infection (32). Regardless, the finding that a primate is orally susceptible to CWD is of concern.
Interspecies transmission of CWD to noncervids has not been observed under natural conditions. CWD infection of carcass scavengers such as raccoons, opossums, and coyotes was not observed in a recent study in Wisconsin (22). In addition, natural transmission of CWD to cattle has not been observed in experimentally controlled natural exposure studies or targeted surveillance (2). However, CWD has been experimentally transmitted to cattle, sheep, goats, mink, ferrets, voles, and mice by intracerebral
inoculation (2,29,33).
CWD is likely transmitted among mule, white-tailed deer, and elk without a major species barrier (1), and other members of the cervid family, including reindeer, caribou, and other species of deer worldwide, may be vulnerable
to CWD infection. Black-tailed deer (a subspecies of mule deer) and European red deer (Cervus elaphus) are susceptible to CWD by natural routes of infection (1,34). Fallow deer (Dama dama) are susceptible to CWD by intracerebral inoculation (35). Continued study of CWD susceptibility in other cervids is of considerable interest.
Reasons for Caution
There are several reasons for caution with respect to zoonotic and interspecies CWD transmission. First, there is strong evidence that distinct CWD strains exist (36). Prion strains are distinguished by varied incubation periods, clinical symptoms, PrPSc conformations, and CNS PrPSc depositions (3,32). Strains have been identified in other natural prion diseases, including scrapie, BSE, and CJD (3). Intraspecies and interspecies transmission of prions from CWD-positive deer and elk isolates resulted in identifi cation of >2 strains of CWD in rodent models (36), indicating that CWD strains likely exist in cervids. However, nothing is currently known about natural distribution and prevalence of CWD strains. Currently, host range and pathogenicity vary with prion strain (28,37). Therefore, zoonotic potential of CWD may also vary with CWD strain. In addition, diversity in host (cervid) and target (e.g., human) genotypes further complicates defi nitive fi ndings of zoonotic and interspecies transmission potentials of CWD.
Intraspecies and interspecies passage of the CWD agent may also increase the risk for zoonotic CWD transmission. The CWD prion agent is undergoing serial passage naturally as the disease continues to emerge. In vitro and in vivo intraspecies transmission of the CWD agent yields PrPSc with an increased capacity to convert human PrPc to PrPSc (30). Interspecies prion transmission
can alter CWD host range (38) and yield multiple novel prion strains (3,28). The potential for interspecies CWD transmission (by cohabitating mammals) will only increase as the disease spreads and CWD prions continue to be shed into the environment. This environmental passage itself may alter CWD prions or exert selective pressures on CWD strain mixtures by interactions with soil, which are known to vary with prion strain (25), or exposure to environmental or gut degradation.
Given that prion disease in humans can be difficult to diagnose and the asymptomatic incubation period can last decades, continued research, epidemiologic surveillance, and caution in handling risky material remain prudent as CWD continues to spread and the opportunity for interspecies transmission increases. Otherwise, similar to what occurred in the United Kingdom after detection of variant CJD and its subsequent link to BSE, years of prevention could be lost if zoonotic transmission of CWD
is subsequently identified.