Habitat drivers and predicted distribution shifts of Anopheles coluzzii under climate change: Results from the systematic review

The two main Afrotropical malaria vectors - Anopheles coluzzii and An. gambiae, formerly known as M and S molecular forms - play a crucial role in malaria transmission in Sub-Saharan Africa. Despite their recent divergence, they exhibit distinct larval habitat preferences and micro-geographic distribution in West and Middle Africa. We performed a systematic literature review to retrieve studies that report counts of An. coluzzii and An. gambiae in their sympatric range since 2001, the year of the first description of the molecular forms. The review yielded 255 papers, leading to a dataset of 211,580 individuals from 2118 sampling sites. Combining these records with high resolution geographical and eco-climatic satellite data by spatial statistical model highlighted predominance of An. gambiae in most of the range with particular reference to Middle Africa and to all areas above 100 m asl. Anopheles coluzzii shows relative frequencies ranging from 58 % to 71 % in most of a 100 km wide coastal ribbon and in the western part of the northernmost range. Between these two extremes the species are found in sympatry, with An. coluzzii frequencies <6 % in Sudan savannahs areas. Areas suitable for An. coluzzii in East Africa are predicted based on the current probability of the species occurrence and are expected to increase under future climate change scenarios. The possible spread of An. coluzzii in this region may impact on malaria transmission and pose a new challenge for innovative species-specific control activities, such as the gene-drive system, highlighting the need of specific surveillance by implementation appropriate diagnostic approaches.