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A new study suggests that the risk of mosquito-borne illness in Brazil will rise significantly by the year 2080, but that climate action could help. Katherine Heath of the Burnet Institute, Melbourne, Australia, and colleagues present these September 18 in the open-access journal PLOS Neglected Tropical Diseases.

In many parts of the world, mosquitoes of the species Aedes aegypti transmit disease-causing viruses—such as dengue, Zika, and chikungunya—when they bite people to feed on blood. Prior research has linked climate change and urban growth to higher future risk of mosquito-borne disease. In Brazil, warmer temperatures and changing rainfall patterns already appear to be contributing to higher dengue rates.

However, predictions of future mosquito-borne disease risk are hampered by the difficulty of mathematically capturing the interplay between climate change, urbanization, and mosquito biology. To address that challenge, Heath and colleagues developed a new mathematical model that combines climate and anthropogenic factors with delay-differential equations describing Ae. aegypti survival and reproduction.

The model accounts for the impacts of temperature and rainfall on mosquito biology at different life-cycle stages, as well as the impacts of urban expansion and human-mosquito interaction on disease transmission and mosquito population growth.

The researchers used the model to predict future mosquito population density across Brazil from 2024 through 2080 under different Shared Socioeconomic Pathways, a set of plausible future climate and societal scenarios that include different levels of climate change mitigation, urban growth and greenhouse gas emissions.

The model predicts that, under the lowest emissions scenario, Brazil's overall Ae. aegypti density will be 11% higher by 2080 than in 2024. In the highest emissions scenario, density is predicted to increase 30% nationwide by 2080, but with hotspots in the South and Southeast where density will nearly double.

With rising Ae. aegypti density, dengue transmission is predicted to increase nationally—with the biggest increases in Southeast Brazil, where mosquito population growth is predicted to outpace human population growth.

These findings suggest that reducing emissions could reduce future disease risk. This study could also help inform national policies and local public health planning efforts.

The authors add, "Brazil already carries one of the world's highest burdens of mosquito-borne disease, and our results show these pressures could grow in the coming decades. Our model went beyond asking where mosquitoes might survive: it estimated how many there will be and what that means for future disease outbreaks.

"The difference between a high- and low-emissions future is stark: strong climate action could cut Brazil's projected mosquito density increases by two-thirds."