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

During the last decade, the Horn of Africa has experienced an unexpected surge in urban malaria cases, with annual outbreaks intensifying each year in some countries. The trend began in 2012 in Djibouti City, followed by outbreaks in 2016 in Ethiopia and Sudan. Research involving mosquito surveillance revealed the presence of Anopheles stephensi, a species originating in Asia and well-adapted to urban environments. The World Health Organisation subsequently issued a vector alert, urging increased mosquito surveillance in the affected areas. Here, we analysed a database of geo-referenced records of An. stephensi collected across its native range to explore whether the recent range expansion of this vector in the Horn of Africa could be attributed to climate change. To this end, we implemented a boosted regression tree approach to train ecological niche models and investigated changes in the distribution of areas ecologically suitable for An. stephensi. We compare estimates derived from climate data spanning 1901–2019 with those from a counterfactual baseline in which climate trends were removed for the same period. Overall, our results indicated that factors other than climate change likely contributed to the expansion range of An. stephensi on the African continent. The association between lower pasture density and higher ecological suitability points to a potential link with expanding urban environments, where this vector is known to thrive. These findings highlight the need for further investigation into the ecological and anthropogenic drivers shaping the spread of An. stephensi to inform targeted and effective malaria control strategies.