Background:A number of studies have assessed possible climate change impacts on the Lyme disease vector, Ixodes scapularis. However, most have used surface air temperature from only one climate model simulation and/or one emission scenario, representing only one possible climate future.Objectives:We quantified effects of different Representative Concentration Pathway (RCP) and climate model outputs on the projected future changes in the basic reproduction number (normalR0) of I. scapularis to explore uncertainties in future normalR0 estimates.Methods:We used surface air temperature generated by a complete set of General Circulation Models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) to hindcast historical (1971–2000), and to forecast future effects of climate change on the normalR0 of I. scapularis for the periods 2011–2040 and 2041–2070.Results:Increases in the multimodel mean normalR0 values estimated for both future periods, relative to 1971–2000, were statistically significant under all RCP scenarios for all of Nova Scotia, areas of New Brunswick and Quebec, Ontario south of 47°N, and Manitoba south of 52°N. When comparing RCP scenarios, only the estimated normalR0 mean values between RCP6.0 and RCP8.5 showed statistically significant differences for any future time period.Conclusion:Our results highlight the potential for climate change to have an effect on future Lyme disease risk in Canada even if the Paris Agreement’s goal to keep global warming below 2°C is achieved, although mitigation reducing emissions from RCP8.5 levels to those of RCP6.0 or less would be expected to slow tick invasion after the 2030s. https://doi.org/10.1289/EHP57
Larvae of winter ticks, Dermacentor albipictus (Packard), ascend vegetation in autumn and form clumps that attach to passing ungulate hosts. We tested the hypothesis that vegetation height determines the height of clumps. During the vegetation-to-ungulate transmission period (early September to mid-November), larvae were released at the base of simulated vegetation (nylon rods 245 cm tall) in outdoor and laboratory trials and in the absence of host cues. Rod height exceeded the height of the tallest ungulate host, which is the moose, Alces alces (L.). Most larvae stopped climbing and formed clumps 50-190 cm above ground, which coincided with torso heights of moose; elk, Cervus elaphus L.; and deer, Odocoileus spp. Rafinesque. More clumps formed in outdoor trials than in laboratory trials and clump heights tended to increase over the course of the experiment, but clump number, size, and height did not correlate with weather conditions. Winter tick larvae appear to determine their height above ground in the absence of external cues, but this mechanism may be modified by external conditions.
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