Confirmation of the presence of Anopheles stephensi among a conflict-affected host community in Aden City, Yemen

Background: Declines in global malaria cases and deaths since the millennium are currently challenged by multiple factors including funding limitations, limits of, and resistance to vector control tools, and also recent spread of the invasive vector species, Anopheles stephensi – especially into novel urban settings where malaria rates are typically low. Coupled with general increases in urbanisation and escalations in the number of conflicts creating rapid and unplanned population displacement into urban areas, particularly in the Middle East and sub-Saharan Africa, increased urban malaria is a major threat to control and elimination. Methods: Entomological monitoring surveys (targeting Aedes aegypti ) of water containers across urban areas hosting internally displaced people (IDP) communities in Aden city, Yemen, were performed by The MENTOR Initiative, a non-governmental organisation. As part of these surveys, in 2021 In 23 larvae collected and raised to adults were morphologically identified as An. stephensi . Twelve of the samples were sent to Liverpool School of Tropical Medicine for independent morphological assessment and genetic analysis by sequencing the ribosomal ITS2 region and the mitochondrial COI gene. Results: All twelve samples were confirmed morphologically and by sequence comparisons to the NCBI BLAST database as An. stephensi , with phylogenetic analysis of the COI sequences identifying a single haplotype with closest relationship to a haplotype found in Djibouti and Ethiopia. Conclusion: Our results confirm the presence of An. stephensi in Yemen. Discovery of the species in an urban community hosting thousands of IDPs living in temporary shelters with widescale dependency on open water containers is of particular concern due to the vulnerability of the population and abundance of favourable breeding sites for the vector. Proactive monitoring and targeted integrated vector management are required to limit impacts in this area of typically low malaria transmission, and to prevent further the spread of An. stephensi within the region.