Effect of Climate Change on Lyme Disease Risk in North America

Abstract

An understanding of the influence of climate change on Ixodes scapularis, the main vector of Lyme disease in North America, is a fundamental component in assessing changes in the spatial distribution of human risk for the disease. We used a climate suitability model of I. scapularis to examine the potential effects of global climate change on future Lyme disease risk in North America. A climate-based logistic model was first used to explain the current distribution of I. scapularis in North America. Climate change scenarios were then applied to extrapolate the model in time and produce forecasts of vector establishment. The spatially modeled relationship between I. scapularis presence and large-scale environmental data generated the current pattern of I. scapularis across North America with an accuracy of 89% (p<0.0001). Extrapolation of the model revealed a significant expansion of I. scapularis north into Canada with an increase in suitable habitat of 213% by the 2080's. Climate change will also result in a retraction of the vector from southern United States, and movement into the central United States. This report predicts the effect of climate change on Lyme disease risk and specifically forecasts the emergence of a tick-borne infectious disease in Canada. Our modeling approach could thus be used to outline where future control strategies and prevention efforts need to be applied.

Figure 1

Distribution of climate-based habitat suitability for Ixodes scapularis, as predicted by the climate-based autologistic model. Suitable area (in yellow) represents 10.1% of North America and predicts the current distribution of I. scapularis (in red) with an accuracy of 89%. Non-overlapped yellow pixels represent suitable areas that have yet to be colonized. The blue line across Ontario represents the northern limit of habitat suitability predicted by Lindsay et. al., 1995.

Figure 2

Projected distribution of climate-based habitat suitability for Ixodes scapularis during three future time periods: the 2020’s, the 2050’s and the 2080’s. The simulation is based on climate change predictions using the Canadian Global Coupled Model (CGCM1) integration forced with anticipated increases in both greenhouse gas and sulfate aerosols. Areas of expansion and contraction from the current distribution of I. scapularis are displayed.

Figure 3

Change in county-based distribution of I. scapularis from present to the 2080s. The future distribution based on climate change data, which considers the effects of both greenhouse gas and sulfate aerosols, was overlaid on the current predicted distribution. The map reveals future suitable (in red) and unsuitable (in blue) counties. Counties that remain suitable over time (in pink) are also displayed.