Larger mangrove forests carry lower and healthier ones higher malaria risk: the importance of integrating mangrove conservation with vector management at local scale

Malaria remains a major public health challenge causing an annual estimated 600,000 deaths and 250 million infections. While most malaria vector control efforts focus on freshwater mosquito species, saltwater-tolerant mosquitoes inhabiting coastal ecosystems like mangrove forests remain understudied. Historically, mangrove forests have been perceived as breeding grounds for malaria vectors, which is often a motivation for their destruction. However, mangroves provide crucial ecosystem services, and their impact on malaria transmission remains unresolved. This study presents the first African multi-country analysis linking mangrove forests to malaria prevalence. We employed piecewise structural equation models (SEMs) to examine the relationships among mangrove land cover and mangrove vegetation health across coastal settlements in 27 African countries. We combined satellite-derived land cover, vegetation, and weather data alongside malaria incidence records from 1996 to 2020. We found two key associations. First, increased mangrove land cover is associated with lower malaria prevalence at coarse spatial resolution, challenging the traditional view of mangroves as disease-promoting environments. This reduction may reflect ecological factors such as limited densities of saltwater mosquitoes, reduced larval development due to shading, or the presence of natural predators. Second, at fine and coarse spatial resolutions, healthier mangrove forests (i.e. more vegetation) are correlated with increased malaria prevalence. This trend may be driven by higher mosquito abundance and biodiversity in vegetatively rich mangrove areas, aligning with other studies showing vegetation as a positive predictor of mosquito population density. Our results suggest that mangrove forests generally carry a low risk of malaria transmission. From this low baseline, transmission is higher in healthier mangrove forests. How large this difference is will likely depend on the locality and configuration of the forests. These findings highlight the importance of integrating mangrove conservation with context-specific vector management strategies.