A community-based vector control intervention “Slash and Clear” implemented in two onchocerciasis-endemic foci in South Sudan

There was only limited reduction in blackfly biting rates after one round of "slash and clear" in Mundri and Mvolo.

Despite several rounds of ivermectin treatment, onchocerciasis transmission persists in Mvolo and Mundri West Counties (Western Equatoria State, South Sudan). A community-based "Slash and clear" (S&C) vector control method was recently introduced, but its effectiveness remains unclear.

Between October 2023 and November 2024, entomological studies mapped blackfly breeding sites along River Naam (Mvolo County) and River Yei (Mundri West County). Following baseline assessment of daily biting rates, one round of S&C was implemented at selected intervention sites, and monthly biting rates were monitored over a follow-up period of 8–14 months, compared between intervention and control sites.

Thirteen breeding sites of Simulium damnosum were found on the Naam and Yei Rivers. Biting rates were consistently higher during the rainy season than the dry season across both counties. Reductions in biting rates at intervention sites were not statistically significant on either river, and seasonality was the only significant predictor of biting rates. A single round of S&C did not result in significant reductions in blackfly biting.

Blackfly biting rates in Mvolo and Mundri West Counties are strongly influenced by seasonal variations, peaking during the rainy season. A single round of S&C is insufficient to reduce blackfly biting in the medium term. Repeated and strategically timed annual implementation of S&C is likely required to achieve significant and lasting vector control impacts.

This publication relates to R2HC funded study: Innovative approaches to reduce the burden of disease caused by onchocerciasis

‍