Demographic Patterns and Harvest Vulnerability of Chronic Wasting Disease Infected White-Tailed Deer in Wisconsin

Abstract

Chronic wasting disease (CWD) is a fatal disease of white‐tailed deer (Odocoileus virginianus) caused by transmissible protease‐resistant prions. Since the discovery of CWD in southern Wisconsin in 2001, more than 20,000 deer have been removed from a >2,500‐km2 disease eradication zone surrounding the three initial cases. Nearly all deer removed were tested for CWD infection and sex, age, and harvest location were recorded. Our analysis used data from a 310‐km2 core study area where disease prevalence was higher than surrounding areas. We found no difference in harvest rates between CWD infected and noninfected deer. Our results show that the probability of infection increased with age and that adult males were more likely to be infected than adult females. Six fawns tested positive for CWD, five fawns from the core study area, including the youngest (5 months) free‐ranging cervid to test positive. The increase in male prevalence with age is nearly twice the increase found in females. We concluded that CWD is not randomly distributed among deer and that differential transmission among sex and age classes is likely driving the observed patterns in disease prevalence. We discuss alternative hypotheses for CWD transmission and spread and, in addition, discuss several possible nonlinear relationships between prevalence and age. Understanding CWD transmission in free‐ranging cervid populations will be essential to the development of strategies to manage this disease in areas where CWD is found, as well as for surveillance strategies in areas where CWD threatens to spread.

A Weighted Surveillance Approach for Detecting Chronic Wasting Disease Foci

“…This assumes that probabilities of samples from the various strata entering the surveillance stream from other jurisdictions are similar to those we reported and that the effects and epidemiologic patterns of CWD are relatively constant between regions and across species, which seem reasonable, based on published observations (Miller et al, 2000;Miller and Wild, 2004;Miller and Conner, 2005;Joly et al, 2006;Grear et al, 2006) and on similarities between the weight values independently estimated for mule deer (Table 1) and for elk (D. Walsh, unpubl. data) using data from Colorado.…”

Epidemiology of Chronic Wasting Disease in Free-Ranging Mule Deer: Spatial, Temporal, and Demographic Influences on Observed Prevalence Patterns

“…comm. ), in white-tailed deer in Wisconsin (Grear et al, 2005), and in wapiti in northcentral Colorado (Miller and Conner, unpubl. ), suggesting that common transmission mechanisms and contact structures among the three natural host species may drive epidemic dynamics.…”

“…Based on previous analyses (Miller et al, 2000;Grear et al, 2005), we constructed four biologically reasonable models: Two models in which sex was either additive with ln(age) or multiplicative with ln(age) represented ''threshold'' models in which prevalence rose and then plateaued (Grear et al, 2005), and two models in which sex was either additive with age and age 2 or multiplicative with age and age 2 represented ''humped'' models in which prevalence rose and then declined (Miller et al, 2000). We compared these four models to a ''constant'' model in which prevalence remained unchanged across age groups; this last model represented a null model.…”

Deer density and disease prevalence influence transmission of chronic wasting disease in white‐tailed deer

“…The outbreak is west of Madison, WI and is centered in western Dane and eastern Iowa counties (Grear et al 2006, Joly et al 2006. We focused data collection and analysis within the Wisconsin Department of Natural Resources (WIDNR) designated 'western core area' which was 210 sections (544 km 2 ) and generally encompassed the areas of highest CWD prevalence (Joly et al 2006) in the outbreak.…”