High Incidence of Tick-Borne Disease in Midcoastal Maine and Possible Contributing Factors

Introduction: Since the 2010s, researchers and public health officials have noted that Maine’s midcoastal counties have higher incidences of Lyme disease, anaplasmosis, and babesiosis than elsewhere in the state. Methods: We examined available data to quantify geospatial clustering, (i.e., “hotspots”) of tick-borne disease incidence and hospitalizations for tick-borne illness. Passive tick surveillance entails collecting ticks found on people and pets, whereas active tick surveillance entails collecting ticks directly from the environment. Using both types of surveillance data, we searched for hotspots of higher blacklegged-tick abundance and pathogen prevalence in ticks. We qualitatively reviewed factors possibly related to tick exposure, such as landscape characteristics and human demographics. Results and Discussion: Lyme disease, anaplasmosis, and babesiosis incidence, as well as hospitalizations and tick-related emergency department visits clustered in Maine’s midcoastal counties. Data from passive tick surveillance indicated a midcoastal county cluster of blacklegged-tick submissions, whereas data from active tick surveillance indicated tick density was dispersed across regions. Passive surveillance is complicated by human behavior leading to human-tick encounters but has excellent spatial coverage. Active tick surveillance data is not confounded by human behavior but has sparse spatial coverage. The distribution of white-tailed deer did not align with the midcoastal hotspot. Climate was not more permissive in the midcoastal than south coastal counties. Conclusions: Residential-scale analysis is needed to understand how factors, such as landscape, age, lifestyle, and health-seeking behavior, elevate exposure to ticks in landscapes that superficially appear similar.