Environmental predictors of the seasonality of malaria transmission in Africa : The challenge

A description of malaria seasonality is important for planning and optimizing malaria control in both time and space, but adequate malariologic data are not available for many disease-endemic areas. We analyzed the relationship between seasonality in the entomologic inoculation rate (EIR) and environmental factors in sites across sub-Saharan Africa with the objective of predicting seasonality from environmental data. The degree of EIR seasonality in each site was quantified using an index previously used for rainfall. The results showed that seasonality of rainfall, minimum temperature, and irrigation are important determinants of seasonality in EIR. Model fit was poor in areas characterized by two rainfall peaks and by irrigation activities. Two rainfall peaks probably dampen seasonality and irrigation creates perennial breeding habitats for vectors independent of rainfall. This complex interplay between the seasonal dynamics of environmental determinants and malaria pose a great challenge and highlights the need for improved models of malaria seasonality.