Spatiotemporal distribution of Anopheles stephensi in different eco-epidemiological settings in Ethiopia

Abstract

Abstract Background Malaria is a major public health concern in Ethiopia, and its incidence could worsen following the invasion of Anopheles stephensi. This study aimed to provide updates on the distribution of An. stephensi and likely household exposure in Ethiopia. Methods Entomological surveillance was performed in 26 urban settings from 2021 to 2023. A kilometer-by-kilometer quadrant was set per town and approximately 20 structures per quadrant were surveyed every three months. More intensive sampling was conducted in 50 randomly selected structures in 4 urban centers in 2022 and 2023 to assess household exposure to An. stephensi. Prokopack aspirators, and Centers for Disease Control and Prevention Light Traps (CDC LTs) were used to collect adult mosquitoes and standard dippers were used to collect immatures. Morphological keys and molecular methods were used for species identification. Polymerase chain reaction (PCR) assays were used to assess Plasmodium infection and mosquito blood meal source. Results Catches of adult An. stephensi were generally low (0.15 per trap), and the species was detected in 8 of the 26 study sites, including Assosa: the first collection in this area of western Ethiopia. Anopheles stephensi was the predominant species in 4 of the 8 positive sites, with 75–100% relative abundance. Household-level exposure, defined as the percentage of houses with a peridomestic infestation with An. stephensi, ranged from 18% in Metehara to 30% in Danan. At most collection sites, An. arabiensis was the predominant species, which accounted for 42.9–100% of the Anopheles catches in 20 of the 26 study sites. The bovine blood index (BBI), ovine blood index (OBI), and human blood index (HBI) for An. stephensi was 69.2%, 32.3%, and 24.6%, respectively, and for An. arabiensis 65.4%, 46.7%, and 35.8%, respectively. None of the 194 An. stephensi were positive for Plasmodium, whilst of 1434 An. arabiensis, 62 were positive, 10 for P. falciparum and 52 for P. vivax. Conclusions Anopheles stephensi showed widespread distribution across Ethiopia. Strongly zoophagic behavior coupled with low adult catches, might explain the absence of Plasmodium infection. Level of household exposure varied across positive sites. Further research is needed to better understand its bionomics and contribution for malaria transmission.