Diversity, Distribution, and Plasmodium falciparum Sporozoite Infectivity of Anopheles Mosquitoes in Flood-Prone Communities of Kasese District, Western Uganda: A Cross- Sectional Household Entomological Study

Background Malaria poses an ongoing public health challenge for children in Uganda, especially in climate-vulnerable, flood-prone communities. Understanding malaria vector species diversity and transmission measures is vital to guide vector control in these unique environments. We sought to determine the vector species diversity, distribution, and Plasmodium falciparum sporozoite infectivity in flood-prone villages in the Kasese district, Uganda. Methods We conducted a cross-sectional study in which we collected adult mosquitoes indoors and outdoors from 154 consented sentinel households using unbaited CDC light traps. Mosquitoes were identified morphologically to genus and species. Adult female Anopheles spp. were tested for P . falciparum circumsporozoite antigen by ELISA. We estimated associations between entomological outcomes and covariates of interest, including place of residence, net ownership, household location and construction materials, and reported history of floods in the previous year. Results Between 19th February and 22nd May 2025, a total of 1,772 mosquitoes were collected in 136/154 (88.3%) households. Adult Anopheles mosquitoes were collected in 54/154 households (prevalence 35.1% (95% CI: 27.9–43.0)). The highest presence of Anopheles mosquitoes was in Karusandara (58%), and the lowest in the more urban municipality area (22%). We documented diversity in known malaria vectors, with Anopheles gambiae s.l. (73.7%), and An. funestus (9.4%) being most common, but also An. pretoriensis, An. rivulorum, An. mouchetti, An. nili, and An. marshalli were identified. Plasmodium falciparum circumsporozoite antigen was detected from three female An. funestus demonstrating a mosquito sporozoite infectivity rate of 1.49% (03/202) (95% CI: 0.48–4.53), and a household positivity rate of 1.95% (3/154) (95% CI: 0.62–5.91) across the study area. Conclusion The varied species diversity may sustain malaria transmission in this region of rapidly changing ecological conditions as a result of flooding. The sporozoite infectivity and household positivity emphasize ongoing transmission of malaria, albeit at a low levels, even during an atypically dry period. There is a need to strengthen implementation of targeted vector control interventions with a focus on flood-prone and low-altitude communities within Kasese District, western Uganda.