Chronic wasting disease (CWD), a contagious prion disease affecting several members of the cervid family, can have a significant impact on host population viability.  As a result, it is likely that there are wide reaching ecological impacts beyond those observed in the host species populations.  Despite this prospect, the ecological consequences of prion disease epidemics in natural populations have received little consideration.   In order to examine the effects of Chronic wasting disease (CWD) on wild populations of mule deer (Odocoileus hemionus) and the associated ecological consequences, we examined CWD dynamics and predation of a mule deer herd residing in Southwestern Boulder, Colorado.   

Results/Conclusions We found that CWD prevalence was high (29%) and that prion infection dramatically lowered survival of free-ranging adult (>2-year-old) mule deer. CWD infection also increased nearly fourfold the rate of mountain lions (Puma concolor) preying on deer, suggesting that CWD may have altered predator-prey dynamics in this area by facilitating hunting success.  Over the study period, several adult and subadult mountain lions were removed from the study area, allowing us to examine the relationship between hunting pressure and CWD dynamics within the deer population.  We also found a marked decline in the deer population over a 20 year period, suggesting that CWD may pose a long-term threat to deer populations, predator populations, predator-prey dynamics and have other significant ecological impacts on ecosystems in which deer are the primary large herbivore.  Moreover, remarkably high infection rates sustained in the face of intense predation show that even seemingly complete ecosystems may offer little resistance to the spread and persistence of contagious prion diseases.