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    • Second the uncertainty in the vector and human parameters af

    2018-10-23

    Second, the uncertainty in the vector and human parameters affect the value of DEP through VC and the threshold value for intensity. All six vector parameters depend on temperature. The female vector-to-human population ratio depends on temperature the same way as longevity (Brady et al., 2014). The rest five of them with relationships obtained from field and laboratory experimental studies (Liu-Helmersson et al., 2014). These relationships may vary depending on the environmental conditions of the study location/laboratory/design, vector and virus types. The uncertainty of each parameter and its temperature dependent relation were not available. Thus, a Monte Carlo simulation was used to estimate the uncertainty for each parameter and their effect on VC, from which the seasonality for the 10 European cities - see Supplementary information (Section S6.1–S6.2) for details. In addition, although we chose the threshold value more conservatively (0.2day within the range of 0.1–0.25day corresponding to infectious potassium channel of 4 to 10days), the estimated intensity and duration for DEP should be viewed with caution. If different threshold values were used, the general trend and order of cities that would go over the threshold will hold, but the exact decade when the DEP goes over the threshold could change. However, using the threshold of 0.2day in the analysis of both the outbreak in Madeira in 2012 and the 2014 dengue outbreak in Japan, we found that this threshold corresponded spatially and temporally with the novel transmission events (Quam et al., 2016). See Supplementary information (Section S6.3) for more discussion. Third, for Ae. albopictus, only two parameters with temperature dependent relations were available in the literature (Delatte et al., 2009). The remaining parameters were assumed to have the same temperature dependent relationships as Ae. aegypti, although they were adjusted to the level of Ae. albopictus based on a literature review (Lambrechts et al., 2010). This would limit the accuracy of the estimated value of DEP for Ae. albopictus. See Supplementary information (Section S4) for more discussion. Finally, the temperature data used from CRU and CMIP5 are monthly averages over gridded area of 0.5×0.5°. While the daily datasets from E-OBS for the maps in Fig. 1 have finer resolution (0.25×0.25°, daily), coarser resolutions (CRU and CMIP5) may underestimate DEP during the summer and overestimate during the winter for cities located along the costal lines. This accounts for the differences observed between Fig. 1 and Fig. 2 for major cities. Much of our analyses were based on outputs from the coarser temperature data sets (CRU and CMIP5). Therefore, the conclusions drawn are more conservative for the summer and overestimates for the winter (Fig. 5 intensity). See Supplementary Information (Sections S1 & S2) for more discussion.
    Conclusion We identified past, present, and future high-risk cities and time periods for potential dengue transmission in Europe based on temperature and daily temperature variation. Compared to countries where dengue is endemic, Europe showed strong seasonality in dengue epidemic potential (DEP) without possibility of year-round epidemic transmission. Compared over two centuries, we found a slow increase in intensity and duration of dengue transmission over the past century and more rapidly changing trajectories projected in the 21st century with the rate of change depending on the level of greenhouse gas emissions. Although Europe currently does not have a sufficiently high DEP year round, increasing periods with higher temperatures and greater temperature variation in the future due to climate change could elevate DEP along a south to north gradient. By the end of this century, DEP for Ae. aegypti, could expand to Northern Europe (all 10 cities studied) and up to eight months in Southern Europe under the highest emission pathway (RCP 8.5). Under the lowest emission pathway (RCP 2.6), it could expand to Nice and Paris for Ae. aegypti from the current three Southern European cities. For Ae. albopictus DEP could expand to all of the Central Europe (7 cities) under RCP 8.5; however, it would remain nearly as it is now under RCP 2.6 (three Southern Europe cities). Therefore, climate change mitigation (or lack thereof) could have a large impact on the seasonal window and geographic range for dengue transmission potential in Europe. Under the higher emission scenarios, increasingly larger parts of Europe would have the potential for autochthonous dengue transmission should Ae. aegypti be introduced and established. Such concerns were substantiated by the dengue outbreak in Madeira in 2012. The same concern extends to Ae. albopictus if higher greenhouse gas emissions than RCP2.6 would be realized.