Limited evidence for the impact of climate change on the range expansion of a malaria vector in the Horn of Africa

Published on March 30, 2026, by Diana Erazo

During the last decade, the Horn of Africa has experienced a worrying rise in urban malaria outbreaks, coinciding with the detection of Anopheles stephensi, an invasive malaria vector originally from Asia and well adapted to city environments. In this study, we investigated whether the recent spread of An. stephensi in the Horn of Africa could be attributed to climate change. To do so, we combined a database of geo-referenced occurrence records from across the species’ native and expanded range with ecological niche models based on boosted regression trees, and compared estimates obtained under observed historical climate conditions with those derived from a counterfactual climate baseline in which long-term climate trends were removed. Our results provide limited evidence that climate change has been a major driver of the recent expansion of An. stephensi in Africa. Instead, they suggest that large parts of the continent have likely been climatically suitable for this mosquito for a long time, and that its recent emergence is more likely linked to increased introduction pressure and anthropogenic drivers such as urban expansion. These findings highlight the need to look beyond climate alone when assessing the spread of invasive malaria vectors, and to strengthen surveillance and control strategies in rapidly changing urban environments. Read the whole study here.

Figure 1. Changes in the ecological suitability of Anopheles stephensi. Past distributions of ecological suitability were estimated using both reconstructions of historical climate (A) and (B) and a counterfactual baseline (D) and (E), and we also computed the difference between the distributions based on historical climate and distributions based on the counterfactual baseline (C). Ecological suitability values reported here were averaged over the estimates of 30 independent boosted regression tree (BRT) models considering three times more pseudo-absence than presence points, and which were trained on the ISIMIP3a reanalysis dataset GSWP3-W5E5.

Reference: Erazo D, Pietroiusti R, Ghisbain G, Colón-González FJ, Pironon S, Van Bortel W, Mengel M, Frieler K, Thiery W, Dellicour S (2026). Limited evidence for the impact of climate change on the recent range expansion of the malaria vector Anopheles stephensi in the Horn of Africa. Environmental Research Letters 21: 064028