The expanding distribution of Ixodes scapularis and associated pathogens in the Chicago, IL metropolitan area

The distribution of the black-legged tick, Ixodes scapularis, and its associated pathogens, has expanded greatly in the Midwestern United States. While the spread of I. scapularis is cause for concern, the consequences are only epidemiologically significant if there is a corresponding increase in the distribution of a pathogen. The most medically-important pathogen transmitted by I. scapularis is Borrelia burgdorferi, the causative agent of Lyme disease, and human cases of this illness have been expanding in the Midwest as well. The forest preserves of Chicago, IL, present a unique opportunity to study the invasion ecology of I. scapularis and B. burgdorferi because this landscape offers limited habitat for both hosts and vectors. We sampled 41 different forest preserve sites over a span of four years (2011-2014), to determine variation in the density of I. scapularis and infection rates with pathogens, especially B. burgdorferi. To quantify variation in human land use, buffers were created around each of the sites to measure land cover composition using Arc GIS. Results suggest that abundance of I. scapularis and prevalence of B. burgdorferi are positively associated with forest cover and negatively associated with developed land cover. These findings indicate that within an urban landscape, there may be thresholds in the proportions of land cover types that limit the occurrence of both tick and pathogens. These associations may be used to develop predictive models concerning variation in tick-borne disease risk across a heterogeneous urban landscape.