Nonlinear impacts of climate change on dengue transmission

Dengue is a re-emerging mosquito-borne disease that infects hundreds of millions each year—a burden that is expected to increase with climate change. However, the precise relationship between dengue transmission and changing temperature is nuanced: previous research has shown that warmer temperatures can increase, decrease, or not affect dengue transmission, and has identified thermal optima ranging from 29-35ºC. Taking a trait-based approach, we characterized the effect of temperature on dengue transmission using data from laboratory experiments on Aedes aegypti mosquito vectors and dengue virus. We found that R₀ peaks at 29ºC, and that the mechanistic model predicts the occurrence and incidence of dengue across Latin American countries. We then asked whether a mechanistic, temperature-dependent model could predict the dynamics of outbreaks over time in two geographically distinct regions: Kenya and Ecuador. Forcing an susceptible, exposed, infectious, recovered (SEIR) model with climate dynamics, we found that the model could capture the number and timing of outbreaks but not their magnitude. We hypothesized that climate interacts with host susceptibility to determine epidemic magnitude. To test this hypothesis, we used a 20-year dengue and climate time series in San Juan, Puerto Rico and empirical dynamic modeling. We showed that dengue dynamics are highly predictable and depend on nonlinear, interactive effects of temperature, rainfall, and the availability of susceptible hosts. Finally, we used a meta-analysis ask whether the predicted nonlinear relationship between dengue transmission and temperature from the mechanistic R₀ model can explain apparent discrepancies in the measured effects of temperature on dengue in field studies from across Latin America and Asia. We found that temperature – dengue correlations were most strongly positive at 25ºC, where the slope of R₀(T) is steepest, and decline to below zero as temperatures approach the predicted thermal optimum of 29ºC. Together, this work demonstrates that temperature is an important, nonlinear driver of dengue dynamics and that climate warming is poised to expand dengue transmission beyond its current, already expanding burden.