PREVALENCE AND DISTRIBUTION OF ZOONOTIC PATHOGENS AND PARASITES IN RACCOONS (PROCYON LOTOR) OF NORTHERN ILLINOIS

Author

• Ashley McDonald, Southern Illinois University CarbondaleFollow

Date of Award

5-1-2026

Degree Name

Doctor of Philosophy

Department

Zoology

First Advisor

Jimenez, F. Agustin

Second Advisor

Nielsen, Clayton

Abstract

Raccoons (Procyon lotor) are widely distributed across North America and readily adapt to anthropogenic environments, often reaching high population densities in urban and suburban areas. The growing abundance of raccoons has led to heightened concern regarding disease transfer between raccoons, other wildlife, and humans. As synanthropic mesopredators, raccoons serve as a reservoir host for a variety of zoonotic parasites and tick-borne pathogens. Despite their ecological and public health importance, few regional studies in the Midwest have examined how urbanization and raccoon population size influence pathogen prevalence and multi-pathogen dynamics. I collected and necropsied 280 raccoons from five study sites across a rural-suburban gradient in northern Illinois during April-June 2022-2024. I used helminth recovery, qPCR, spatial data layers in GIS, and statistical modeling to quantify raccoon roundworm prevalence, zoonotic tick-borne pathogen prevalence, and patterns of coinfection and pathogen richness. I detected Baylisascaris procyonis (raccoon roundworm) in 106 raccoons (38%). Raccoon roundworm prevalence varied among sites (25-49%) but was not associated with percentage developed land cover or raccoon density. However, raccoon abundance had a significant negative effect on raccoon roundworm prevalence, suggesting that higher raccoon abundance may be associated with lower individual infection probability, potentially due to parasite aggregation dynamics. These findings suggest that raccoon population reduction alone may not effectively reduce environmental contamination or public health risk associated with raccoon roundworm. Of the 280 raccoons tested for pathogens, 278 (99.3%) tested positive for at least one pathogen. Two raccoons (0.71%) tested positive for Borrelia burgdorferi, one (0.35%) for Rickettsia rickettsii, 99 (35.4%) for Anaplasma phagocytophilum, and 276 (98.6%) for Babesia microti-like, while Ehrlichia chaffeensis was not detected. Prevalence of A. phagocytophilum and B. burgdorferi declined with increasing developed land cover, whereas raccoon density and abundance did not significantly influence prevalence of any pathogen. The exceptionally high prevalence of B. microti-like and moderate prevalence of A. phagocytophilum highlights raccoons as important reservoir hosts for both wildlife and human pathogens in northern Illinois and suggests landscape structure, rather than raccoon population size alone, may play a greater role in shaping tick-borne pathogen dynamics. I also examined patterns of coinfection and pathogen richness across the rural-suburban gradient. Fifty-nine percent of pathogen-positive raccoons were coinfected with multiple pathogens, including 38 triple infections and one quadruple infection. However, hierarchical multivariate models and permutation-based null models revealed no strongly supported positive or negative pairwise pathogen associations after accounting for environmental covariates. Observed coinfection frequencies did not differ from random expectations, indicating that shared exposure rather than consistent within-host facilitation or antagonism likely drives coinfection patterns in northern Illinois raccoons. Percentage developed land cover had a significant negative effect on pathogen richness, with raccoons in more developed landscapes carrying fewer pathogens. Raccoon abundance, however, did not influence pathogen richness. Overall, my study demonstrates that urbanization acts as a filter on pathogen communities in raccoons, reducing pathogen richness without consistently altering individual pathogen prevalence or pairwise coinfection structure. Raccoon population size alone was not a reliable predictor of zoonotic pathogen dynamics. These findings underscore the importance of landscape-level processes, vector ecology, and multi-host community interactions in shaping disease risk to both wildlife and humans. These findings also highlight raccoons as valuable sentinel species for zoonotic pathogen surveillance in urban areas.