Ecological drivers and mosquito abundance suggest high Rift Valley fever risk in Eastern Ethiopia

Objectives: Rift Valley fever (RVF) virus is a mosquito-borne zoonosis of public health importance. High RVF virus immunoglobulin G seroprevalence has been reported among humans and livestock in Ethiopia. However, data on mosquito abundance and their infection status remain limited. This study assessed mosquito abundance, ecological drivers, and RVF virus infection status in Eastern Ethiopia. Methods: A community-based cross-sectional study was conducted in the Shinile District and Dire Dawa Administration, Eastern Ethiopia, from April 1 to September 30, 2023. Adult mosquitoes were collected indoors and outdoors using light traps and Prokopack aspirators. Larvae were collected from water-holding containers and reared to adulthood in a controlled insectary environment. Mosquitoes were identified to the genus/species level based on their morphological characteristics. Aedes, Culex, and Anopheles were the target mosquito genera. Female mosquitoes of these genera were pooled and screened for RVF virus RNA using reverse transcription–polymerase chain reaction. Results: Of the 12,773 mosquitoes collected, 7811 (61.2%) were the target genera. Of these, 4094 (52.4%) were females. Among the female mosquitoes of the target genera, Anopheles were the most abundant (2367, 30.3%), followed by Culex (1154, 14.8%) and Aedes (573, 7.3%). Mosquito abundance increased with rainfall (r = 0.53–0.68) and decreased with temperature. Among the 1760 water-holding containers inspected for the presence of larvae, 247 (14.0%) harbored larvae. Barrels 29 (3.7%) and birkads (large, cemented water tanks) 8 (3.3%) were the major Aedes breeding containers. All 168 pooled samples tested negative for RVF virus. Conclusions: Potential mosquito species were abundant despite the absence of detectable viral RNA. The increase in adult mosquitoes with rainfall poses an ecological risk for RVF virus emergence. Targeted elimination of mosquito breeding containers and longitudinal One Health–based surveillance are recommended to monitor and detect cryptic transmission.