Influence of climate and heatwaves on dengue transmission in Sao Paulo and Natal, Brazil

PLOS One | https://doi.org/10.1371/journal.pone.0334838 October 24, 2025 2 / 13 Introduction Dengue, the most prevalent virus transmitted by mosquitoes and a major global health issue, impacts more than 126 nations and incurs yearly expenses amounting to billions of US dollars [1–3]. While vector control remains the most practical strategy for limiting dengue transmission, it has not been sufficient to stop the escalating fre- quency of arbovirus epidemics or the widening geographic range of endemic trans- mission [3]. This persistent expansion is largely fueled by well-documented factors, including increased air travel, intensified international trade, and growing urban over- crowding [4,5]. Growing attention from researchers and policymakers is now focused on the role of weather conditions in dengue outbreaks, particularly in the context of climate change [3,6,7]. Growing data from epidemiological and experimental studies suggests a rela- tionship between ambient temperature and dengue occurrence [8]. The correlation between temperature and dengue occurrence exhibits a bell-curve pattern, where the peak risk emerges at an ideal temperature, commonly known as the inflection thresh- old [9,10]. Although dengue occurrence demonstrates a distinct seasonal trend, prior research examining the short-term influence of temperature on dengue cases has generally encompassed all recorded instances within the study timeframe or peak transmission phases [9,10]. While the relationship between maximum temperatures

and dengue prevalence in tropical regions has been widely explored [10–14], inves- tigations into the effects of heatwaves remain scarce. Heatwaves, described as periods of extreme heat exceeding a specific threshold, may influence dengue distri- bution differently from isolated high-temperature events. For example, extreme heat during heatwaves has been shown to inhibit mosquito abundance [15]. Additionally, high temperatures can suppress viral replication and mosquito activity while prompt- ing human behavioral changes that reduce transmission risks – a pattern supported by a study [9] that demonstrated the inhibitive effect of heatwaves on mosquito popu- lations. In contrast, research by Cheng et al. [3] conducted in subtropical Hanoi, Viet- nam, indicated that heatwaves may contribute to more severe dengue outbreaks at a later time. This evidence indicates a potential association between heatwaves and dengue occurrence. As climate change accelerates in the 21st century, heatwaves are projected to become more frequent, intense, and prolonged [16], highlighting the urgent need to understand their impact on dengue outbreaks. Dengue is a growing global health threat, with cases rising by 85.5% from 1990 to 2019 – up from 30.7 million to 56.9 million – and deaths increasing from 28,151– 36,055 in the same period [17]. The Americas recorded a historic peak in 2023, with 4.5 million cases and over 2,300 deaths [18]. In Brazil, where dengue re-emerged in 1986 [19], transmission has intensified in recent years, fueled by the widespread

presence of mosquito vectors and the co-circulation of all four virus serotypes [20]. While temperature is a well-established factor in dengue transmission, the role of extreme heat events – particularly heatwaves – remains poorly understood. Unlike general warming trends, heatwaves represent short-term, intense spikes in tempera- ture that may uniquely influence mosquito behavior, virus replication, and human contribution to the research themes of the National Institute for Science and Technology - INCT Klimapolis, which is funded by the Brazilian Ministry of Science, Technology, and Innovation (MCTI), National Council for Scientific and Technological Development (CNPq) under project number 406728/2022- 4, as well as the initial German Brazilian Klimapolis Laboratory, funded by the German Federal Ministry of Education and Research (BMBF). A.G. thanks to FAPERJ for the Auxílio Cientista do Nosso Estado and CNPq for the Bolsa de Produtividade. C.L. thanks to FAPESP for the grant 2022/13367-9 and CNPq for the grant 153620/2024-2. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist.