An epidemiological framework for chronic wasting disease in multihost communities

Abstract

1. Many pathogens can infect several host species, which complicates the management of wildlife diseases. Even for generalist pathogens, hosts are not equally competent, and variable niche overlap between hosts leads to different exposure levels within hosts when compared with that between hosts. Hence, the processes determining spillover risk and the subsequent transmission dynamics within and between species differ. 2. Chronic wasting disease (CWD) is a contagious prion disease of the cervids detected across expanded geographic ranges over the last few decades. Multihost management has become topical with CWD detection among reindeer Rangifer tarandus in Europe, with an immediate spillover risk to sympatric species. Here, I argue for the use of a community epidemiological framework that distinguishes between- and within-host dynamics arising from host competence and exposure processes. 3. In CWD, host competence is mainly determined by how variants of the prion protein gene (PRNP) affect susceptibility. The exposure level is not only linked to the density of infected and susceptible hosts both within and between species but also to the spatiotemporal niche overlap between species and social organization within species. 4. Mule deer Odocoileus hemionus and white-tailed deer Odocoileus virginianus are highly susceptible and expected to show true multihost dynamics; however, mule deer have a higher CWD prevalence in sympatric areas, indicating only partially linked dynamics. Moose Alces alces are highly susceptible, but cases of CWD-infected moose are few and appear to be spillover events with subsequent epidemic die outs. Elk Cervus canadensis have less susceptible PRNP variants and low levels of prion shedding in lymphoid tissues, indicating lower contagiousness. CWD prevalence in elk is lower and appears to result from spillover and subsequent within-species emergence, which is partially independent of sympatric deer. 5. Synthesis and applications. Stronger awareness of the different expected CWD dynamics within and between species may facilitate effective surveillance and management. Surveillance should consider the potential lack of linked dynamics between species when designing sampling. Multihost management can target niche overlap at different scales to limit spillover risk: (1) geographic distribution ranges, (2) density reductions in overlap zones and (3) co-use of transmission hot spots.