Background Onchocerciasis (river blindness) is still endemic in parts of Africa, causing skin, eye, and brain disease. The cornerstone intervention for onchocerciasis control is community-directed treatment with ivermectin (CDTI), but therapeutic coverage remains sub-optimal in several endemic communities. The “Slash and Clear” (S&C) vector control technique has been proposed as an environmentally-friendly alternative tool to supplement CDTI.

Methods We conducted repeated cross-sectional entomological studies in Nachtigal, an onchocerciasis-endemic village located beside a fast-flowing segment of the Sanaga River in Cameroon. Blackfly breeding sites were mapped and monthly blackfly biting rates (BR) assessment, initiated at the Nachtigal riverbanks using the human landing-catch approach. Blackfly catching for BR measurements were done for three consecutive days (7:00 to 18:00 daily) every month, by the same two catchers, switching every hour. On March 1st 2023 (a timepoint marking the transition from dry to rainy season), we implemented the S&C intervention at the Nachtigal rapids. Physically-fit village volunteers were trained and supervised in the destruction of the breeding sites using machetes and the removal of potential substrates for blackfly breeding from the river. Post-intervention BR were assessed two weeks after the S&C, and changes in BR were calculated.

Results Following S&C, monthly BR went from 28,000 in February 2023 to 13,888 bites per person in March 2023 (50.4% reduction). In contrast, in the absence of S&C, BR were 31,108 in February 2022; rising to 36,053 in March 2022 (15.9% increase) with the returning rains. Therefore, compared to the natural evolution of blackfly abundance and nuisance, the S&C intervention engendered 50.4+15.9=66.3% decrease in the BR at the Nachtigal riverbanks.

Conclusion Our study demonstrates the significant impact of a community-based S&C vector control approach on blackfly biting rates. Coupled with good CDTI coverage, reducing the blackfly population would break the onchocerciasis transmission cycle and accelerate its elimination.