Modeled Impacts of Chronic Wasting Disease on White-Tailed Deer in a Semi-Arid Environment

Abstract

White-tailed deer are a culturally and economically important game species in North America, especially in South Texas. The recent discovery of chronic wasting disease (CWD) in captive deer facilities in Texas has increased concern about the potential emergence of CWD in free-ranging deer. The concern is exacerbated because much of the South Texas region is a semi-arid environment with variable rainfall, where precipitation is strongly correlated with fawn recruitment. Further, the marginally productive rangelands, in combination with erratic fawn recruitment, results in populations that are frequently density-independent, and thus sensitive to additive mortality. It is unknown how a deer population in semi-arid regions would respond to the presence of CWD. We used long-term empirical datasets from a lightly harvested (2% annual harvest) population in conjunction with 3 prevalence growth rates from CWD afflicted areas (0.26%, 0.83%, and 2.3% increases per year) via a multi-stage partially deterministic model to simulate a deer population for 25 years under four scenarios: 1) without CWD and without harvest, 2) with CWD and without harvest, 3) with CWD and male harvest only, and 4) with CWD and harvest of both sexes. The modeled populations without CWD and without harvest averaged a 1.43% annual increase over 25 years; incorporation of 2% annual harvest of both sexes resulted in a stable population. The model with slowest CWD prevalence rate growth (0.26% annually) without harvest resulted in stable populations but the addition of 1% harvest resulted in population declines. Further, the male age structure in CWD models became skewed to younger age classes. We incorporated fawn:doe ratios from three CWD afflicted areas in Wisconsin and Wyoming into the model with 0.26% annual increase in prevalence and populations did not begin to decline until ~10%, ~16%, and ~26% of deer were harvested annually. Deer populations in variable environments rely on high adult survivorship to buffer the low and erratic fawn recruitment rates. The increase in additive mortality rates for adults via CWD negatively impacted simulated population trends to the extent that hunter opportunity would be greatly reduced. Our results improve understanding of the potential influences of CWD on deer populations in semi-arid environments with implications for deer managers, disease ecologists, and policy makers.

Individual‐based model evaluation of using vaccinated hatchery fish to minimize disease spread in wild fish populations

“…Conversely, under the low infection probability scenario, period of infectiousness was longer, and therefore, there was more opportunity to expose susceptible individuals to the disease (Reno 1998). While unusual for VHS-like (viral hemorrhagic septicemia) diseases, high exposure mortality and low infection dynamics for pathogens can occur (e.g., chronic wasting disease, Foley et al 2016). This suggests that from a population perspective there can be benefits to a disease emerging rapidly and infecting a high proportion of the population very quickly rather than a disease emerging more slowly over the course of the year at least in cases where probability of death of infected individuals is based on virus exposure level.…”

Deterministic and stochastic analysis of an eco-epidemiological model

“…Keeping this in mind, we varied the infection rate β to observe different type of behavior of system (1). Suppose r = 14 5 , k = 7, μ = 1.5, a = 1, m = 1, ε = 1, τ = 1, d = 0.5, b = 1, our results show that the predator population will become extinct for the parametric values of β = 0.25 (see Fig. 1a).…”

“…Now if we choose, w 1 r K S * = w 2 βE * , w 2 βS * = w 3 , and w 2 a (14) it is easy to check that,…”

“…Research on CWD epidemics in captive deer and elk has shown that CWD prions can remain infectious in the environment for at least 2 years [11] and thus it has the potential to disrupt the ecosystems where deer occur in abundance. Recent works on CWD can be found in [12][13][14]. Through numerical simulations, Hobbs [15] suggested that CWD can be removed from an infected elk population allowing selective predation by wolves.…”

Study of a fractional‐order model of chronic wasting disease

“…In most of the cases, the disease spreads indirectly via environmental contamination, though some literature shows that the disease transmitted through direct transmission . There are several works on chronic wasting disease which may be found in . Other disease model studied in can be applicable to the chronic wasting disease for better understanding the system.…”