Bionomics of Anopheles stephensi across the urban-rural landscapes of Eastern Ethiopia.

Background: Invasion and spread of Anopheles stephensi in sub-Saharan Africa poses a threat to malaria control and elimination efforts in the continent. This study aimed to determine the distribution and bionomics of An. stephensi across the urban-rural landscapes of eastern Ethiopia.

Methods: Entomological surveillance was conducted in urban, peri-urban and rural settings of Dire Dawa and Awash Sebat Kilo from June to November 2022. Anopheles immature stages were collected using standard dippers. Adult mosquitoes were collected using CDC light traps, Prokopack aspirator and BG-pro traps. Mosquitoes were identified to species using morphological identification keys and polymerase chain reaction (PCR). Enzyme-linked immunosorbent assay was used to determine mosquito blood meal sources and Plasmodium sporozoite infection. The WHO tube bioassays were used to assess susceptibility of An. stephensi to pyrethroids, carbamates and organophosphates. Knockdown resistance (kdr) and acetyl cholinesterase (ace-1) target site mutations were analysed.

Results: A total of 16,135 Anopheles immature stages were collected. Anopheles stephensi comprised 95.3%, 79.0% and 47.8% of the Anopheles larvae collected from urban, peri-urban and rural settings, respectively. Anopheles stephensi was the predominant species (95.8%) in artificial habitats, followed by Anopheles arabiensis (4.0%). In natural habitats, An. arabiensis was predominant (82.7%), followed by An. stephensi (5.8%) and other species (11.5%). Among the 259 adult Anopheles mosquitoes collected, An. stephensi constituted 56.8%, An. arabiensis 42.9%, and Anopheles coustani 0.4%. The human, bovine, goat, chicken and dog blood indices of An. stephensi were 18.9%, 27.0%, 35.1%, 8.1% and 2.7%, respectively. The overall sporozoite rates were 2.0% for An. stephensi and 1.0% for An. arabiensis. Anopheles stephensi showed resistance to all tested insecticides, with a low frequency (< 0.4%) of kdr alleles and no ace-1 mutation detected.

Conclusion: Anopheles stephensi breeds in both artificial and natural habitats across urban, peri-urban and rural settings in eastern Ethiopia, with a preference for urban environments. It exhibits opportunistic feeding behaviour. The predominance of An. stephensi over the native vector, An. arabiensis, along with its susceptibility to Plasmodium infection, suggests that this species may contribute to the malaria resurgence in eastern Ethiopia. These findings will support malaria control programmes in planning vector control strategies that target the diverse larval habitats of An. stephensi. Further research is needed to develop innovative vector control and surveillance tools to address the challenge of insecticide resistance in An. stephensi and to effectively monitor its behaviour.