Local Landscape Change, Personal Practices, and Lyme Disease Risk in Ottawa, Ontario

Abstract

In Canada, Lyme disease is an emerging tick-borne illness with a number and extent of risk areas that continue to expand due to the effects of climate change. Nationally, the incidence of Lyme disease increased more than 17-fold since its designation as a notifiable disease in 2009. While Ontario's incidence rate is one of the highest among Canadian provinces, Ottawa was declared an at-risk region for the first time in 2017. Amidst the emergence of reproducing blacklegged tick populations and continued urban expansion of new communities into natural areas throughout this municipal region, the local incidence of Lyme disease has more than tripled.

Using the municipal region of Ottawa as a study setting, the objective of my thesis was to examine local Lyme disease risk as a function of environmental hazard and population-level vulnerability. I achieved this by (1) exploring socioeconomic and landscape factors associated with local Lyme disease risk at the neighbourhood scale, (2) identifying population-level characteristics associated with high knowledge and protective behaviour adoption, and (3) examining the Lyme disease transmission risk across a gradient of residential to woodland land use.

Count models of Lyme disease cases arising from exposures within patients' home neighbourhoods highlighted associations between forested landscape configurations and elevated local risk. Analysis of survey results identified population-level characteristics and high levels of both knowledge regarding Lyme disease and adoption of preventive and protective behaviours, from which several dynamics among population and exposure risk subgroups emerged. Finally, an analysis of environmental hazard along the residential-woodland gradient in western Ottawa neighbourhoods identified significant risk in the shared ecotone. Together, the results present strong evidence for factors associated with increased potential for human-tick encounters in fine-scale local settings and opportunities for targeted Lyme disease prevention efforts.