Geospatial modelling of dry season habitats of the malaria vector, Anopheles funestus, in south-eastern Tanzania

Abstract

Introduction: Anopheles funestus is a major malaria vector in east and southern Africa, and currently dominates transmission in many parts of Tanzania. Previous research has identified its preference for specific aquatic habitats, especially those that persist in dry months. This suggests the potential for targeted control through precise habitat mapping and characterization. In this study, we investigated the influence of habitat characteristics, land cover, and human population densities on An. funestus distribution during dry seasons, and subsequently developed a habitat suitability model for this vector species in southeastern Tanzania. Method:Eighteen villages in south-eastern Tanzania were surveyed during the dry season from September-December 2021. Water bodies were systematically inspected for mosquito larvae and characterized by their physio-chemical characteristics and surrounding environmental features. A generalized linear model was used to assess the presence of An. funestus larvae as a function of the physico-chemical characteristics, land use and human population densities. The results from this model were used to generate spatially explicit predictions of habitat suitability in the study districts. Results: Of 1,466 aquatic habitats surveyed, 440 were positive for An. funestus. River streams had the highest positivity (74%; n=322) followed by ground pools (15%; n=67). The final model had an 83% accuracy in predicting positive An. funestus habitats, with the most important characteristics being permanent waters, clear waters with or without vegetation or movement, and shading over the habitats. In addition, there was a positive association with forested areas and a negative association with built-up areas. Human population densities had no influence on An. funestus distribution. Conclusion: This study underscores the crucial role of both the specific habitat characteristics and key environmental factors, notably land-cover, in the distribution of An. funestus. In this study area, the species predominantly inhabits river streams and ground pools; and prefers clear, perennial waters with and shading. The strong positive association with more pristine environments with tree covers and the negative association with built-up areas underscore the importance of ecological transitions in vector distribution and malaria transmission risk. Such spatially explicit predictions could enable more precise interventions, particularly larval source management, to accelerate malaria control.