Investigating Chronic Wasting Disease in White Tailed-Deer in Illinois 2003-2020: A Retrospective Spatial Analysis

Chronic wasting disease (CWD), a transmissible spongiform encephalopathy, affects captive and free-ranging species of the family Cervidae (moose, deer, and elk). CWD is endemic in North America and has been detected in 26 states in the United States and three Canadian provinces. Disease surveillance is essential to understand the emergence, distribution, and spread of CWD cases. In Illinois, to evaluate CWD prevalence and identify areas with increased infection rates, the state uses annual CWD testing of hunter-harvested deer in a surveillance program. We analyzed CWD surveillance data within 16 CWDinfected northern and northcentral Illinois counties. Of the 42,541 samples tested for CWD from recreational hunter-harvested deer between 2008 and 2019, 359 (0.84%) tested positive for CWD. We assessed spatial and temporal patterns of CWD in the study area using a retrospective Poisson scan statistic model to identify CWD spacetime clusters with high infection rates. We detected a significant primary cluster C1 (area = 23.59 km) in the north-central part of the study area from 2010 to 2015, and a secondary significant cluster C2 (area = 9.27 km) occurring from 2014 to 2019 in the northwest part. We evaluated the effectiveness of targeted local culling, a focused disease management program conducted in areas with known positive CWD cases. Of the 14,661 deer removed, 325 (2.22 %) tested positive for CWD. We compared the proportion of CWD-positive deer removed from areas where at least one CWD case was detected in the previous years (L1) with the deer removed in the immediate neighboring one square mile section areas (L2L4). At L1 a higher proportion of CWD-positive deer was removed compared to their surrounding areas. Exploring CWD's spatial distribution and clustering among free-ranging white-tailed deer in Illinois can help wildlife conservation stakeholders to limit the spread of CWD.