Serendipitous detection of invasive malaria vector Anopheles stephensi in Kisumu, Kenya in June 2022

Anopheles stephensi is an invasive malaria vector that has been rapidly spreading within Africa since it was first identified in Djibouti in 2012. As of 2025, it has been identified in eight other countries: Ethiopia, Sudan, Somaliland, Eritrea, Nigeria, Kenya, Ghana and Niger. We collected mosquitoes from an urban slaughterhouse in Kisumu City in western Kenya in mid-2022 for bloodmeal analyses. 19.6% (11/56) of the amplicon sequence variants (ASVs) assigned using the basic local alignment search tool (BLAST) returned matches for mosquito species, one of which was An. stephensi, from one pool of five mosquitoes that had been morphologically classified as An. gambiae s.l. Further analysis of the mitochondrial cytochrome c oxidase 1 (cox1) gene later confirmed the presence of An. stephensi, which were distributed across two well-supported clades. Some haplotypes grouped with others from northern Kenya (Wajir and Marsabit), while others clustered with haplotypes from Ethiopia and Sudan. This serendipitous detection of An. stephensi is the first report of the species South of the Equator. Therefore, we recommend continued entomological and malaria case surveillance in this area to evaluate how shifting vector dynamics and vector-livestock interactions may impact future control initiatives.