Precursor to Dengue: Projecting Effects of Climate Change on Mosquito Density in Southeast Asia

Closeup of three mosquito larvae in water.

The authors modeled seasonal variations of densities of Ae. aegypti and Ae. albopictus under current weather patterns and future climate scenarios (based on greenhouse gas emissions) over four periods: 2021-2040, 2041-2060, 2061-2080, and 2081-2100. The study area included the countries of Myanmar, Lao PDR, Thailand, Cambodia, and Vietnam, where dengue outbreaks occur frequently. 6 They used a compartmental process-based model that was validated using density data from entomological surveys in the cities of Phnom Penh (Cambodia) and Vientiane (Lao PDR).
Model estimates indicated that densities of both species would increase during the region's coolest months (December-February) under all climate scenarios. The warmest months (April-June) saw elevated population densities of Ae. aegypti throughout most of the region, whereas Ae. albopictus showed marked increases and decreases in densities in the northern and southern parts of the study area, respectively, for all years and climate scenarios. Model projections also suggested that Aedes densities are more likely to be affected by changes in temperature than precipitation.
Kristie Ebi, a Professor of Global Health and of Environmental and Occupational Health Sciences at the University of Washington, Changes in local temperature and precipitation patterns are affecting the geographic range and population densities of disease vectors such as Aedes aegypti (shown here) and Ae. albopictus mosquitoes, which spread dengue, Zika, and chikungunya. Image: © Cacio Murilo/stock.adobe.com.

131(3) March 2023
A Section 508-conformant HTML version of this article is available at https://doi.org/10.1289/EHP12772. explains that process-based models are built from equations describing the dynamics of disease origins. "They generally simulate the impact of weather variables on the health outcomes of interest using equations describing disease burdens at daily or weekly time steps," she says. In this case, the authors modeled mosquito densities without factoring in disease incidence or transmission. To do this, they simulated density variations of mosquitoes' different life stages based on development and mortality rates and their established dependency on temperature and precipitation. Future vector densities were modeled using climate projections based on nine climate models and four scenarios of greenhouse gas emissions. Ebi, who was not involved in the study, says the model could apply to other Aedes-borne diseases such as Zika and chikungunya.
Transmission of mosquito-borne diseases is a highly complex process. "For example, as temperature increases, the rate of virus development within the mosquito is increased, so it can take less time for the mosquito to be infectious, increasing transmission," says Simon Hales, a research professor in the Department of Public Health at the University of Otago, Wellington. "But the mortality rate of the mosquito also increases above a certain temperature, which reduces transmission." Although vector density is an important determinant of disease transmission, 7 Hales notes that very low density could be sufficient to maintain transmission if other conditions are right, "so a linear relationship with vector density is not expected." Hales was not involved in the new work.
Lead author Lucas Bonnin, a postdoctoral associate with the French National Research Institute for Sustainable Development working in Nouméa, New Caledonia, points to the model's usefulness for exploring the complexities of disease transmission. "The outputs of the model could be used to further investigate how vector density impacts disease dynamics," he says, "and to predict how climate change would affect those dynamics." Olayinka Osuolale, PhD, is an environmental health and microbiologist researcher and a senior lecturer at Elizade University, Ilara Mokin, Nigeria.