Earth Observation-Informed Risk Maps of the Lyme Disease Vector Ixodes scapularis in Central and Eastern Canada

Climate change is facilitating the geographic range expansion of populations of the tick vector of Lyme disease Ixodes scapularis in Canada. Here, we characterize and map the spatio-temporal variability of environments suitable for I. scapularis using Earth observation (EO) data. A simple algorithm for I. scapularis occurrence (cumulative degree-days and forest: CSDF) was developed by combining cumulative annual surface degree-days above 0 degrees C and forest cover. To map the environmental risk of I. scapularis (risk of I. scapularis: RIS) in central and eastern Canada from 2000 to 2015, CSDF was adjusted using data from an I. scapularis population model. CSDF was validated using cumulative annual degree days >0 degrees C (CADD) from meteorological stations, and CSDF was strongly associated with CADD (n = 52, R-2 > 0.86, p < 0.001). Data on field surveillance for I. scapularis ticks (2008 to 2018) were used to validate the risk maps. The presence of I. scapularis ticks was significantly associated with CSDF, and at a limit of 2800, sensitivity approached 100%. RIS increased over the study period, with the highest values in 2012 and the lowest in 2000. The RIS was on average higher in Ontario and Quebec compared to other provinces, and it was higher in the southern parts of the provinces. The proportion of the populated areas with a positive RIS increased on average in central and eastern Canada from 2000 to 2015. Predicted I. scapularis occurrence identifies areas with a more probable risk of tick bites, Lyme disease, and other I. scapularis-borne diseases, which can help guide targeted surveillance, prevention, and control interventions.

Automated summary

The study mapped the environmental risk of I. scapularis in central and eastern Canada from 2000 to 2015 using Earth observation data and population models. Results showed that the distribution of I. scapularis was closely associated with cumulative degree-days and forest cover, with risk increasing over time, especially in provinces like Ontario and Quebec.