Microbes increase thermal sensitivity in the mosquito Aedes aegypti, with the potential to change disease distributions

The mosquito Aedes aegypti is the primary vector of many disease-causing viruses, including dengue (DENV), Zika, chikungunya, and yellow fever. As consequences of climate change, we expect an increase in both global mean temperatures and extreme climatic events. When temperatures fluctuate, mosquito vectors will be increasingly exposed to temperatures beyond their upper thermal limits. Here, we examine how DENV infection alters Ae. aegypti thermotolerance by using a high-throughput physiological ‘knockdown’ assay modeled on studies in Drosophila. Such laboratory measures of thermal tolerance have previously been shown to accurately predict an insect’s distribution in the field. We show that DENV infection increases thermal sensitivity, an effect that may ultimately limit the geographic range of the virus. We also show that the endosymbiotic bacterium Wolbachia pipientis, which is currently being released globally as a biological control agent, has a similar impact on thermal sensitivity in Ae. aegypti. Surprisingly, in the coinfected state, Wolbachia did not provide protection against DENV-associated effects on thermal tolerance, nor were the effects of the two infections additive. The latter suggests that the microbes may act by similar means, potentially through activation of shared immune pathways or energetic tradeoffs. Models predicting future ranges of both virus transmission and Wolbachia’s efficacy following field release may wish to consider the effects these microbes have on host survival.

埃及伊蚊（Aedes aegypti）是登革病毒（DENV）、寨卡病毒、基孔肯雅病毒及黄热病等多种致病病毒的主要传播媒介。受气候变化影响，全球平均气温升高与极端气候事件频发的趋势均愈发显著。当温度出现波动时，蚊媒将愈发频繁地暴露于超出其高温耐受上限的温度环境中。本研究基于果蝇（Drosophila）相关研究构建的高通量生理「击倒」检测模型，探究登革病毒感染对埃及伊蚊热耐受能力的调控作用。既往研究已证实，实验室测得的热耐受指标可准确预测昆虫在野外的分布范围。本研究结果显示，登革病毒感染会提升宿主的热敏感性，该效应或最终限制该病毒的地理分布范围。此外，目前正在全球范围内作为生物防治制剂释放的内共生细菌沃尔巴克氏体（Wolbachia pipientis），对埃及伊蚊的热敏感性也具有类似影响。值得注意的是，在共感染状态下，沃尔巴克氏体并未对登革病毒相关的热耐受损伤起到保护作用，且两种感染的效应未呈叠加性。这一结果提示，两种微生物或通过相似机制发挥作用，例如激活共享的免疫通路或引发能量权衡。用于预测病毒传播未来分布范围以及野外释放后沃尔巴克氏体防控效能的模型，或可考虑纳入这些微生物对宿主存活的影响。