Survival and population growth of a free‐ranging elk population with a long history of exposure to chronic wasting disease

Abstract

Investigations of chronic wasting disease (CWD), a fatal, contagious prion disease of free‐ranging cervids, suggest the disease can cause long‐term population declines in deer (Odocoileus spp.). However, the implications of CWD for elk (Cervus elaphus nelsoni) populations are less certain. During 2008–2010, we used rectal biopsies and telemetry to observe disease transmission and survival in adult female elk from a high‐density herd in Rocky Mountain National Park (RMNP) that had been infected by CWD for over 25 years. We studied a cohort of 123 adult female elk that were determined to be free of CWD by rectal biopsy in 2008. Annual incidence of CWD was 0.08 [95% Bayesian credible interval (BCI) = 0.05, 0.12]. Annual survival probabilities of the cohort excluding harvest declined from 0.97 in 2008 (BCI = 0.93, 0.99) to 0.85 in 2010 (BCI = 0.75, 0.93). Declines in survival were attributed almost entirely to CWD; the proportion of radiocollared elk that died of CWD increased from 0.02 in 2008 (BCI = 0.00, 0.05) to 0.11 in 2010 (BCI = 0.04, 0.21). We attributed the increase to the time lag required for development of new CWD cases. We used survival rates of susceptible and infected elk to develop a projection matrix for a discrete time, female only model that estimated the intrinsic population growth rate (λ) of this elk herd to be 1.00 (BCI = 0.93, 1.05) using the prevalence of CWD (12.9%) and calf:cow ratios (24:100) observed during this study. Population declines were predicted to occur when prevalence of CWD exceeded 13% (BCI = 0, 35). However, this estimate was contingent on calf:cow ratios and harvest. Greater recruitment will offset some of the effects of CWD, whereas the inclusion of female harvest, which was excluded from this study, would likely result in lower λ values than those observed in this study. We conclude that CWD can exceed natural rates of mortality, reduce survival of adult females, and decrease population growth of elk herds. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Prion Amplification and Hierarchical Bayesian Modeling Refine Detection of Prion Infection

“…The higher overall prevalence estimate in this herd suggests previous measurements have been missing a large portion of PrP CWD -positive animals and that a long history of exposure to prions and decades of relatively high densities on the winter range may have led to increased prevalence194243. Further study is required to identify possible ecological differences in this herd compared to neighboring ones.…”

Chronic Wasting Disease Drives Population Decline of White-Tailed Deer

“…Therefore, as previously suggested [43], the best management strategy remains minimizing movement of CWD to new areas.…”

The demographic pattern of infection with chronic wasting disease in reindeer at an early epidemic stage

“…Interestingly, though the data published to date are limited, there appeared to be no sex bias in CWD infection in elk (Sargeant et al 2011, Monello et al 2014). The reasons for this are uncertain; however, one possible explanation is that environmental transmission may play a more important role in locations where sexual segregation is rather low and densities are high, such as winter ranges where elk may rut and spend the majority of the year (R. Monello, personal communication).…”

“…For CWD, absent or low infection prevalence in calves and markedly lower infection prevalence in yearlings compared to adults have been documented for mule deer (Miller and Conner 2005), white-tailed deer (Heisey et al 2010, Samuel andStorm 2016), and elk (Robinson et al 2012, Monello et al 2014, 2017. For CWD, absent or low infection prevalence in calves and markedly lower infection prevalence in yearlings compared to adults have been documented for mule deer (Miller and Conner 2005), white-tailed deer (Heisey et al 2010, Samuel andStorm 2016), and elk (Robinson et al 2012, Monello et al 2014, 2017.…”