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Malaria, Anopheles stephensi, Horn of Africa, Range expansion, climate change, climate attribution
Abstract:
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 mosquito species originating in Asia and well-adapted to urban environments. The World Health Organization subsequently issued a vector alert, urging increased mosquito surveillance in the affected areas. Here, we analyse 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 implement a boosted regression tree approach to train ecological niche models and investigate changes in the distribution of areas ecologically suitable for An. stephensi. We compare estimates derived from climate data spanning 1901 to 2019 with those from a counterfactual baseline in which climate trends have been removed for the same period. Overall, our results suggest that factors other than climate change may have 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, in order to inform targeted and effective malaria control strategies.
