Abstract
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 °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 °C (CADD) from meteorological stations, and CSDF was strongly associated with CADD (n = 52, R2 > 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.
Highlights
Lyme disease, caused by bacteria of the Borrelia burgdorferi sensu lato complex, is the most common vector-borne disease in the temperate zone of the northern hemisphere.In eastern North America, the vector is the tick Ixodes scapularis, which is expanding its geographic range northward into and through southeastern and south-central Canada [1,2].Lyme disease cases in Canada are increasing commensurate with northward expansion of the range of the tick into three main zones—southern Manitoba and adjacent northwesternOntario, southern Ontario and Quebec, and the maritime provinces of New Brunswick andNova Scotia [2,3,4,5]
Here, we explore the use of Earth observation (EO) data for public health purposes to identify how environmental suitability for the Lyme disease vector I. scapularis has changed over a 16-year timescale when it is thought that a warming climate has driven the range expansion of the tick and Lyme disease risk into Canada
From the 235 meteorological stations on the study area, 63 were rejected for missing data, while 52 located in dominant vegetation areas, with an average of percent vegetation cover (PVC) higher than 0.85 and a percent forest cover higher than 50% in the 3 km buffer around meteorological station, were used for the validation
Summary
Lyme disease, caused by bacteria of the Borrelia burgdorferi sensu lato complex, is the most common vector-borne disease in the temperate zone of the northern hemisphere.In eastern North America, the vector is the tick Ixodes scapularis, which is expanding its geographic range northward into and through southeastern and south-central Canada [1,2].Lyme disease cases in Canada are increasing commensurate with northward expansion of the range of the tick into three main zones—southern Manitoba and adjacent northwesternOntario, southern Ontario and Quebec, and the maritime provinces of New Brunswick andNova Scotia [2,3,4,5]. In eastern North America, the vector is the tick Ixodes scapularis, which is expanding its geographic range northward into and through southeastern and south-central Canada [1,2]. Lyme disease cases in Canada are increasing commensurate with northward expansion of the range of the tick into three main zones—southern Manitoba and adjacent northwestern. There is compelling evidence that recent climate warming in southern. Canada has facilitated range expansion of the tick [6]. Future projected climate change is expected to drive further range expansion of I. scapularis within Canada and thereby to be accompanied by an increase in the human population exposed to ticks and an increase in the number of human cases of Lyme disease [7,8]. If a person contracts Lyme disease, those with an early
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