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 8 / 13 Discussion This research offers new perspectives on how heatwaves and meteorological factors influence dengue infections in two Brazilian cities, adding to the expanding body of knowledge regarding the effects of global warming on arboviruses. A key finding of this study is the negative correlation between heatwaves and dengue cases. Heatwaves can influence dengue transmission in diverse ways, depending on their intensity, duration, and timing during the transmission season. Milder or short-term heatwaves may temporarily reduce mosquito activity or hinder viral replication due to thermal stress, which may help explain the decreased transmission observed in our findings. In contrast, longer or more intense heat- waves can produce more complex outcomes. From an environmental perspective, extended periods of high temperature can cause shallow water sources to evaporate, limiting mosquito breeding habitats. On a physiological level, extreme heat may induce a synchronized emergence of adult mosquitoes, followed by high mortality rates if the heat persists beyond their tolerance limits. Additionally, larvae exposed to very high temperatures (e.g., 39°C) show a reduced expres- sion of heat shock protein genes, which are vital for surviving thermal stress – suggesting a potential vulnerability under extreme conditions [33]. These multifaceted effects indicate that the relationship between heatwaves and dengue is not

straightforward and may vary by region. Therefore, we emphasize the need for localized studies to better define and understand heatwave events in different contexts, especially as mosquito populations may adapt over time to changing climate conditions [15,34]. Temperature’s effect on dengue transmission occurs through various complex mechanisms [35–38], including its impact on the female mosquito’s reproductive cycle, feeding behavior, and the virus’s incubation period in both mosquitoes and humans [39,40]. A study examining how temperature influences the virus’s incubation period revealed that as the tem- perature increased from 25ºC to 30ºC, the incubation period shortened from an average of 15 days to 6.5 days [27]. Other studies have further clarified this relationship; for example, Damtew et al. [6] reported a 13% increase in dengue risk for every 1°C rise in high temperatures above baseline values. Optimal temperature ranges for dengue transmission have been identified as 14.8°C for minimum temperature [37] and 32–33°C for maximum temperature [36]. The temperature ranges used in the referenced studies correspond to those influencing the biology of the Aedes mosquito and dengue virus, which likely explains the observed relationship between temperature and dengue risk in the present study. Viral rep- lication reaches its peak at around 35ºC, a temperature higher than the threshold at which mosquito survival and feeding Fig 5. Exposure-response curve of São Paulo/SP, Brazil, showing overall cumulative effect of the total number of heatwave days in the week,

with reference to no heatwave days in the week. Shaded areas represent 95% confidence intervals. https://doi.org/10.1371/journal.pone.0334838.g005