Mapping hotspots of malaria transmission from pre-existing hydrology, geology and geomorphology data in the pre-elimination context of Zanzibar, United Republic of Tanzania

Abstract

AbstractBackgroundLarval source management strategies can play an important role in malaria eliminationprogrammes, especially for tackling outdoor biting species and for eliminating parasite andvector populations when they are most vulnerable during the dry season. Effective larvalsource management requires tools for identifying geographic foci of vector proliferation andmalaria transmission where these efforts may be concentrated. Previous studies have reliedon surface topographic wetness to indicate hydrological potential for vector breeding sites,but this is unsuitable for karst (limestone) landscapes such as Zanzibar where water flow,especially in the dry season, is subterranean and not controlled by surface topography.MethodsWe examine the relationship between dry and wet season spatial patterns of diagnosticpositivity rates of malaria infection amongst patients reporting to health facilities on Unguja,Zanzibar, with the physical geography of the island, including land cover, elevation, slopeangle, hydrology, geology and geomorphology in order to identify transmission hot spotsusing Boosted Regression Trees (BRT) analysis.ResultsThe distribution of both wet and dry season malaria infection rates can be predicted usingfreely available static data, such as elevation and geology. Specifically, high infection rates inthe central and southeast regions of the island coincide with outcrops of hard dense limestonewhich cause locally elevated water tables and the location of dolines (shallow depressionsplugged with fine-grained material promoting the persistence of shallow water bodies).ConclusionsThis analysis provides a tractable tool for the identification of malaria hotspots whichincorporates subterranean hydrology, which can be used to target larval source managementstrategies