Spatial and seasonal dynamics of Simulium damnosum s.l. and entomological indicators of onchocercosis in the provinces of Huambo and Cuanza-Sul in Angola.

BACKGROUND: Onchocerciasis remains a public health problem in Angola. Despite the implementation of onchocerciasis control programs based on mass treatment with ivermectin, current entomological data remain limited, making it difficult to accurately assess the potential risk of transmission. Our objectives were to analyze the spatial and seasonal dynamics of Simulium damnosum s.l. and the main entomological indicators of onchocerciasis in the provinces of Huambo and Cuanza Sul, Angola, to assess the potential entomological risk of transmission. METHODS: We captured black flies using the human bait capture method for 48 days between July and October 2025. Analyses of entomological indicators included abundance, monthly bite rate (MBR), parity, seasonality, daily activity, and monthly transmission potential (MTP). Morphological identification of specimens was performed according to standard taxonomic keys. RESULTS: A total of 6.038 black flies were captured during the study period, including 3.615 in Huambo and 2.423 in Cuanza Sul. All black flies belonged to species of the savanna group. The average BMR was high (1.890 bites/person/month), with significant seasonal variations. The overall parity rate reached 59%, significantly higher in Cuanza Sul. No black flies infected with Onchocerca volvulus were found, resulting in a zero PMT at all study sites. CONCLUSION: Despite high vector density and relatively old black fly populations, the absence of transmission suggests a reduction in onchocerciasis transmission in the studied regions. These results demonstrate the importance of maintaining regular entomological surveillance to prevent potential transmission in an ecological context favorable to the vector.