Towards the elimination of the bioko form of simulium Yahense from Bioko: Planning and insecticide trials

Onchocerciasis on Bioko island is transmitted by the endemic Bioko form of Simulium yahense. After collection of baseline data on the fly's breeding sites, its insecticide susceptibility and infection rates with Onchocerca volvulus, a ground-based insecticide trial was planned and executed in the northern two-thirds of the island. The first round of five consecutive weekly treatments was conducted during the week beginning 12 February 2001, using knapsack sprayers to dispense 21 litres of a 20% EC formulation of temephos (Abate) at a dose of 0.065 ppm at 92 locations in 30 rivers with discharges >0.05 m3s-1. The treatments were mostly successful, but failures on three rivers were attributable to the inaccessibility of sites upstream of the highest accessible treatment points. The results showed that an aerial campaign could eliminate the vector from the island and this optimism was vindicated by the success of a subsequent helicopter-based campaign completed in 2005.