Causal drivers of mosquito abundance in urban informal settlements

Urban informal settlement residents are vulnerable to mosquito-borne diseases, but little is known about the specific drivers of risk, or how they differ, within the diversity of informal settlements globally. Here we aimed to identify key drivers of mosquito abundance in different urban informal settlements to inform upgrading programs. We developed a causal framework of mosquito risk and tested it in two distinct geographic settings: Makassar, Indonesia and Suva, Fiji. Using longitudinal mosquito trapping surveys in 24 informal settlements between 2018 and 2024 (totalling 1534 successful trap sets in Makassar and 1216 in Suva), we fitted causal models to infer the relationships between climatic, environmental and socioeconomic drivers and the abundance of two dominant mosquito species: Aedes aegypti and Culex quinquefasciatus. Water supply and access, and variation in temperature and precipitation were key drivers of mosquito abundance in both informal settlement locations, but the direction of effects differed between vector species. Piped water supply in a settlement reduced the abundance of the dengue vector, Ae. aegypti but increased the abundance of Cx. quinquefasciatus. Higher temperature and precipitation were associated with more Ae. aegypti in both geographic locations. By identifying the pathways through which changes in informal settlement environments are likely to alter mosquito risk we provide essential information to guide upgrading and resilience programs.