Background Although “Slash and Clear” has proven effective in reducing blackfly densities in low transmission foci, the impact of this strategy in high transmission settings with large rivers and important vector densities remains to be demonstrated.

Methods A controlled before-and-after community-based intervention comprising two arms (Bayomen as control site and Biatsota as intervention site) was carried out in the Mbam Valley (Centre Region, Cameroon). In each arm, baseline blackfly densities were collected over one year using the human landing method. The intervention consisted of destroying the trailing vegetation where blackflies breed. Blackfly densities were collected post-intervention to assess the impact of the intervention. Before the intervention, a total of 36,273 and 29,041 blackflies were collected in Bayomen and Biatsota, respectively.

Results After the intervention period, the total blackfly density in the intervention site decreased from 29,041 to 20,011 (31.1% reduction), while an increase of 2·7% was observed in the control site (from 36,273 to 37,248). The Poisson mixed regression model shows that the reduction was significantly greater in the intervention site than in the control site (p<0.0005).

Conclusion This study showed that “Slash and Clear” approach is feasible and has a significant impact on vector densities in a high transmission setting. Further studies are needed to investigate the long-term impact of this vector control approach, and how this promising strategy can be scaled-up and sustained until elimination of onchocerciasis.