Climate Change

Abstract

Background
 The most common vector-borne disease in the United States is Lyme disease. Its causative bacterium Borrelia burgdorferi uses the blacklegged tick as its vector. Each stage of the tick’s lifecycle is dependent on ambient temperature and relative humidity. Indicators of climate change such as increasing temperature, rainfall, and extreme weather events may impact tick prevalence, leading to downstream changes in LD incidence. Prior national analyses have confirmed an association between climatic variables and LD incidence, but those analyses have yet to be repeated at the state level in Michigan. This study uses 20 years of county-level data to determine if increasing LD incidence in MI is associated with climate change.
 Methods
 Fixed-effects, longitudinal panel regression is used to model the relationship between LD and average temperatures, rainfall, and extreme weather events, using publicly available county-level data for MI. 
 Results
 Higher population counties in MI have an inverted U-shaped positive relationship with average temperature and incidence, in line with national analyses. Counties with lower populations had significant positive relationships with incidence and extreme precipitation events. The state as a whole shows a significant negative relationship between extreme heat days and LD (p<0.001).
 Conclusions
 Increasing tick-borne illness is a significant public health concern, and results from this report support further analysis into climate change impacts on tick abundance, and tickborne illness incidence. Better understandings of these relationships will inform LD interventions targeted towards communities most impacted by climate change.