Relationship Between Chronic Wasting Disease (CWD) Infection and Pregnancy Probability in Wild Female White-Tailed Deer (Odocoileus virginianus) in Northern Illinois, USA

Abstract

White-tailed deer (Odocoileus virginianus) are a cervid species native to the Americas with ecological, social, and economic significance. Managers must consider several factors when working to maintain the health and sustainability of these wild herds, including reproduction, particularly pregnancy and recruitment rates. White-tailed deer have a variable reproductive capacity, with age, health, and habitat influencing this variability. However, it is unknown whether chronic wasting disease (CWD) impacts reproduction and, more specifically, if CWD infection alters a female deer's probability of pregnancy. Our study addressed this question using data from 9783 female deer culled in northern Illinois between 2003 and 2023 as part of the Illinois Department of Natural Resources' ongoing CWD management program. Multilevel Bayesian logistic regression was employed to quantify the relationship between pregnancy probability and covariates like maternal age, deer population density, and date of culling. Maternal infection with CWD was found to have no significant effect on pregnancy probability, raising concerns that the equal ability of infected and non-infected females to reproduce could make breeding, which inherently involves close physical contact, an important source of disease transmission between males and females and females and their fawns. The results also identified that female fawns (<1 year old) are sensitive to county-level deer land cover utility (LCU) and deer population density, and that there was no significant difference in how yearlings (1-2 years old) and adult (2+ years old) responded to these variables.

Keywords: CWD; Cervidae; Odocoileus virginianus; TSE; cervid; chronic wasting disease; prion; reproduction; transmissible spongiform encephalopathy.

Figure 1

Maps of the study area in northern Illinois. (A) shows the counties included in the analysis, with the number of female deer that were culled and examined for pregnancy in parentheses beside the county name. (B) shows the cumulative number of chronic wasting disease (CWD) cases by TRS (township, range, and section) for all mortality sources between fiscal years 2003 and 2024 in the study area. (C) shows the total number of female deer included in this analysis by TRS. The fiscal year is the time between July 1st of one calendar year and June 30th of the next.