Assessment of the Probability of Autochthonous Transmission of Chikungunya Virus in Canada under Recent and Projected Climate Change

Background: Chikungunya virus (CHIKV) is a reemerging pathogen transmitted by Aedes aegypti and Aedes albopictus mosquitoes. The ongoing Caribbean outbreak is of concern due to the potential for infected travelers to spread the virus to countries where vectors are present and the population is susceptible. Although there has been no autochthonous transmission of CHIKV in Canada, there is concern that both Ae. albopictus and CHIKV will become established, particularly under projected climate change. We developed risk maps for autochthonous CHIKV transmission in Canada under recent (1981–2010) and projected climate (2011–2040 and 2041–2070). Methods: The risk for CHIKV transmission was the combination of the climatic suitability for CHIKV transmission potential and the climatic suitability for the presence of Ae. albopictus; the former was assessed using a stochastic model to calculate R0 and the latter was assessed by deriving a suitability indicator (SIG) that captures a set of climatic conditions known to influence the ecology of Ae. albopictus. R0 and SIG were calculated for each grid cell in Canada south of 60°N, for each time period and for two emission scenarios, and combined to produce overall risk categories that were mapped to identify areas suitable for transmission and the duration of transmissibility. Findings: The risk for autochthonous CHIKV transmission under recent climate is very low with all of Canada classified as unsuitable or rather unsuitable for transmission. Small parts of southern coastal British Columbia become progressively suitable with short-term and long-term projected climate; the duration of potential transmission is limited to 1–2 months of the year. Interpretation: Although the current risk for autochthonous CHIKV transmission in Canada is very low, our study could be further supported by the routine surveillance of Ae. albopictus in areas identified as potentially suitable for transmission given our uncertainty on the current distribution of this species in Canada. https://doi.org/10.1289/EHP669


Figure S2
Risk categories for autochthonous CHIKV transmission by Ae. albopictus in Canada derived from combining the climatic suitability for CHIKV transmission potential (R 0 ) with the climatic suitability for the presence of Ae. albopictus (SIG index) using the 75 th percentile value of R 0 distributed across temperature range 10°C to 40°C as the cut-off.

Figure S3
Risk maps for autochthonous CHIKV transmission in Canada based solely on CHIKV transmission potential (R 0 ) using the 75 th percentile value of R 0 distributed across temperature range of 10°C to 40°C as the cut-off.

Figure S4
Duration in months where mean R 0 >1.0 (mean monthly temperature between >22.8°C and 33.6°C) in Canada based solely on CHIKV transmission potential (R 0 ) using the

Figure S5
Risk maps for autochthonous CHIKV transmission in Canada combining the climatic suitability for CHIKV transmission potential (R 0 ) with the climatic suitability for the presence of Ae. albopictus (SIG index) using the 75 th percentile value of R 0 distributed across temperature range 10°C to 40°C as the cut-off.

Figure S6
Duration in months for potential autochthonous CHIKV transmission in Canada combining the climatic suitability for CHIKV transmission potential (R 0 ) with the climatic suitability for the presence of Ae. albopictus (SIG index) using the 75 th percentile value of R 0 distributed across temperature range 10°C to 40°C as the cut-off.
The figures in Figure S1 show the monthly mean of climate change for one month in winter (January) and the three summer months (June, July and August). We used two distinct future period (2011-2040) and (2041-2070) with respect to the historical reference period . The y-axis is for temperature and x-axis for total precipitation. For each RCM, climate change signal is computed by making the absolute difference between the future and the current climatological mean.

Figure S2
Risk categories for autochthonous CHIKV transmission by Ae. albopictus in Canada derived from combining the climatic suitability for CHIKV transmission potential (R 0 ) with the climatic suitability for the presence of Ae. albopictus (SIG index) using the 75 th percentile value of R 0 distributed across temperature range 10°C to 40°C as the cut-off.

Figure S3
Risk maps for autochthonous CHIKV transmission in Canada based solely on CHIKV transmission potential (R 0 ) using the 75 th percentile value of R 0 distributed across temperature range of 10°C to 40°C as the cut-off.

Figure S4
Duration in months where mean R 0 >1.0 (mean monthly temperature between >22.8°C and 33.6°C) in Canada based solely on CHIKV transmission potential (R 0 ) using the 75 th percentile value of R 0 distributed across temperature range 10°C to 40°C as the cut-off.

Figure S5
Risk maps for autochthonous CHIKV transmission in Canada combining the climatic suitability for CHIKV transmission potential (R 0 ) with the climatic suitability for the presence of Ae. albopictus (SIG index) using the 75 th percentile value of R 0 distributed across temperature range 10°C to 40°C as the cut-off.

Figure S6
Duration in months for potential autochthonous CHIKV transmission in Canada combining the climatic suitability for CHIKV transmission potential (R 0 ) with the climatic suitability for the presence of Ae. albopictus (SIG index) using the 75 th percentile value of R 0 distributed across temperature range 10°C to 40°C as the cut-off.