Apparent stability masks underlying change in a mule deer herd with unmanaged chronic wasting disease

Abstract

The contagious prion disease “chronic wasting disease” (CWD) infects mule deer ( Odocoileus hemionus) and related species. Unchecked epidemics raise ecological, socioeconomic, and public health concerns. Prion infection shortens a deer’s lifespan, and when prevalence (proportion of adults infected) becomes sufficiently high CWD can affect herd dynamics. Understanding population responses over time is key to forecasting long-term impacts. Here we describe unexpected stability in prevalence and abundance in a mule deer herd where CWD has been left unmanaged. High apparent prevalence (~30%) since at least 2005 likely drove observed changes in the proportion and age distribution of wild-type native prion protein ( PRNP) gene homozygotes among deer sampled. Predation by mountain lions ( Puma concolor) may be helping keep CWD in check. Despite stable appearances, prion disease nonetheless impairs adult survival and likely resilience in this deer herd, limiting its potential for growth despite refuge from hunter harvest and favorable habitat and winter conditions.

Abstract

Fischer and colleagues revisit the unmanaged Table Mesa mule deer herd to examine the impact and dynamics of chronic wasting disease. Their findings indicate that disease prevalence and deer abundance have been surprisingly stable overall since 2005, with the disease appearing to be kept naturally in check by predation from the local mountain lion population.