Rural-Urban Migration and Low-Transmission Endemicity of Malaria in Sub-Saharan Africa: A Statistical Inference Approach to Uncover Possible Mechanisms.

backgroundMalaria remains one of the most pressing public health challenges in Sub-Saharan Africa (SSA), which continues to shoulder over 90% of the global burden of malaria cases and deaths. Despite major investments in control and treatment, the region faces persistent transmission heterogeneity, with pockets of low but sustained incidence that often fuel larger seasonal outbreaks. Each year, during the hot and dry season, multiple low-transmission hotspots-ranging from 3 to 150 cases per 10,000 person-weeks-emerge in many peri-urban and rural-urban fringe zones in western SSA. These hotspots frequently precede widespread outbreaks that occur with the onset of the rainy season. While intensive malaria control programs have reduced incidence in many high-transmission areas, the persistence of such low-transmission hotspots throughout the dry months remains poorly understood.

methodsIn this study, we focus on Ouagadougou, the capital of Burkina Faso, where malaria incidence demonstrates striking spatiotemporal patterns. We hypothesize that seasonal rural-urban migration of labourers-driven largely by agricultural and economic cycles-plays a pivotal role in sustaining dry-season transmission, seeding subsequent rainy-season epidemics. To examine this hypothesis, we develop a data-driven malaria model and analyze with statistical inference methods to compare the impacts of seasonal, regular, and permanent migration patterns, using empirical incidence and mobility data.

resultsOur analysis indicates that seasonal migration most accurately explains the low-transmission endemicity in dry months and their amplification into widespread rainy-season outbreaks. High seasonal migration maintained a low but persistent level of transmission, preventing local fade-out, and significantly intensified transmission once favourable ecological conditions returned during the rains. These findings demonstrate how cyclical patterns of human mobility can drive malaria persistence even in periods otherwise unsuitable for transmission.

conclusionThese findings highlight the importance of incorporating human mobility, particularly seasonal labour migration, into malaria transmission models and control strategies. From a global health perspective, accounting for mobility-driven persistence mechanisms can strengthen malaria elimination programs across Sub-Saharan Africa, where seasonal migration is widespread. By integrating migration dynamics into intervention planning, policymakers can better anticipate epidemic risk and target resources to vulnerable communities, thereby moving closer to the long-term goal of malaria elimination.