Impact of CWD on Fetal Growth and Pregnancy Rates in Illinois White-tailed Deer

A major concern with chronic wasting disease (CWD) in white-tailed deer (Odocoileus virginianus) is the potential for this disease to cause population declines through negative effects on reproduction. CWD is caused by a misfolded protein called a “prion,”—putting this disease of deer in the same family as “mad cow disease” and Creutzfeldt-Jakob disease, which affects humans. Though transmission of CWD from deer to their offspring during pregnancy has not yet been documented in white-tailed deer, it has been detected in other cervid species (Nalls et al., 2013), and transmission to fetuses has been documented in other prion diseases (Table 1) (Gallardo and Fernando, 2021).

Even if transmission during pregnancy does not occur in white-tailed deer, it is essential to know the effects of CWD on reproduction to maintain healthy deer herds. To investigate these potential effects, two modeling studies were done to evaluate the relationship between CWD infection in female deer, their pregnancy probability, and the growth of their fetuses. The data use information from female deer and their fetuses collected by the Illinois Department of Natural Resources (IDNR) as part of their localized focused culling program (Green et al., 2017; Varga et al., 2021), which was analyzed at the Wildlife Veterinary Epidemiology Laboratory at INHS-PRI. The data includes counties with CWD in northern Illinois in all years between the 2002-2003 and 2019-2020 management seasons.

In one study (currently under review), we identified that CWD-infected female deer in northern Illinois are just as likely to get pregnant as CWD-negative deer (Figure 1). This raises concerns about the transmission of CWD to males during the mating season or to fawns in the weeks after birth through high doe-fawn contact activities such as grooming and nursing (Figure 2).

Another study published in Theriogenology Wild (Mori et al., 2022) looked at the impact of maternal CWD infection on fetal weight and length. The study found that fetuses of CWD-positive deer weighed 1 percent less than fetuses of CWD-negative deer in Illinois (Figure 1). Since this modeling effort only includes fetuses in the second trimester of development, this difference in body mass could have been even larger at birth. It is known that fawn body weight is crucial to survival, especially in the first few weeks of life, so any consistent mechanism that reduces fetal weight threatens fawn health and survival (Carstensen et al., 2010). There was no relationship between fetal length and maternal CWD infection, and the fetal sex ratio remained around 1:1 regardless of infection status.

The breeding success of CWD-positive females and the negative impact of maternal CWD infection on fetal weight further emphasize the importance of removing infected deer from the landscape, either through regulated recreational hunting or targeted culling efforts. Eliminating sources of CWD infection helps to interrupt the chain of transmission, which is crucial for controlling CWD spread and prevalence, and maintaining healthy fawns and a healthy and stable wild white-tailed deer herd.

References

1. Nalls, Amy V., et al. “Mother to offspring transmission of chronic wasting disease in reeves’ muntjac deer.” PloS one 8.8 (2013): e71844.
2. Gallardo, Mauro Julián, and Fernando Oscar Delgado. “Animal prion diseases: A review of intraspecies transmission.” Open Veterinary Journal 11.4 (2021): 707-723.
3. Green, Michelle L., et al. “Reproductive characteristics of female white-tailed deer (Odocoileus virginianus) in the Midwestern USA.” Theriogenology 94 (2017): 71-78.
4. Varga, Csaba, et al. “Evaluating the ability of a locally focused culling program in removing chronic wasting disease infected free‐ranging white‐tailed deer in Illinois, USA, 2003–2020.” Transboundary and Emerging Diseases 69.5 (2022): 2867-2878.
5. Mori, Jameson, et al. “The impact of maternal infection with chronic wasting disease on fetal characteristics in wild white-tailed deer (Odocoileus virginianus) in Illinois, USA.” Theriogenology Wild 1 (2022): 100010.
6. Carstensen, Michelle, et al. “Survival, birth characteristics, and cause‐specific mortality of white‐tailed deer neonates.” The Journal of Wildlife Management 73.2 (2009): 175-183.
7. Tian, T., Halsey, S.J., Rivera, N.A., Brown, W.M., Novakofski, J.E. and Mateus-Pinilla, N.E., 2022. Impact of landcover composition and density of localized deer culling sites on chronic wasting disease prevalence. Preventive Veterinary Medicine, p.105774.

Dr. Jameson Mori is a postdoctoral researcher with the Mateus & Novakofski Chronic Wasting Disease Collaborative Labs. Their research focuses on using data and modeling to determine the impact of chronic wasting disease on white-tailed deer in Illinois and the effectiveness of management efforts to control the disease. They earned their B.S. at the University of Massachusetts Dartmouth and Ph.D. from the University of Illinois Urbana-Champaign.

Dr. Nelda Rivera‘s research focuses on the ecology and evolution of new and re-emerging infectious diseases and the epidemiology of infectious diseases, disease surveillance, and reservoir hosts’ determination. She is a member of the Wildlife Veterinary Epidemiology Laboratory and the Novakofski & Mateus Chronic Wasting Disease Collaborative Labs. She earned her M.S. at the University of Illinois at Urbana-Champaign and D.V.M at the University of Panamá, Republic of Panamá.

Peter Schlichting is the Deer Project Manager with the Illinois Department of Natural Resources’ Division of Wildlife Resources.

Dr. Jan Novakofski studies prion diseases or infectious agents composed entirely of protein in animals such as “mad cow disease” and scrapie. His efforts are contributing to better understanding the genetics and transmission of these types of diseases to protect the health of animals and humans. He earned his B.S., M.S. and PhD from the University of Wisconsin, Madison.

Dr. Nohra Mateus-Pinilla is a veterinary Epidemiologist working in wildlife diseases, conservation, and zoonoses. She studies Chronic Wasting Disease (CWD) transmission and control strategies to protect the free-ranging deer herd’s health. Dr. Mateus works at the Illinois Natural History Survey- University of Illinois. She earned her M.S. and Ph.D. from the University of Illinois Urbana-Champaign.