Progress in controlling the reinvasion of windborne vectors into the western area of the Onchocerciasis Control Programme in West Africa

Abstract

Since vector control began in 1975, waves of Simulium sirbanum and S. damnosum s.str., the principal vectors of severe blinding onchocerciasis in the West African savannas, have reinvaded treated rivers inside the original boundaries of the Onchocerciasis Control Programme in West Africa. Larviciding of potential source breeding sites has shown that these 'savanna' species are capable of travelling and carrying Onchocerca infection for at least 500 km northeastwards with the monsoon winds in the early rainy season. Vector control has, therefore, been extended progressively westwards. In 1984 the Programme embarked on a major western extension into Guinea, Sierra Leone, western Mali, Senegal and Guinea-Bissau. The transmission resulting from the reinvasion of northern Côte d'Ivoire and Burkina Faso has been reduced by over 95%, but eastern Mali has proved more difficult to protect because of sources in both Guinea and Sierra Leone. Rivers in Sierra Leone were treated for the first time in 1989 and biting and transmission rates in Sierra Leone and Guinea fell by over 90%. Because of treatment problems in some complex rapids and mountainous areas, flies still reinvaded Mali, though biting rates were approximately 70% lower than those recorded before anti-reinvasion treatments started. It was concluded that transmission in eastern Mali has now been reduced to the levels required to control onchocerciasis.

Cytotaxonomy, morphology and molecular systematics of the Bioko form of Simulium yahense (Diptera: Simuliidae)

“…In other parts of West Africa, the available evidence suggests that line-squalls do not carry migrating S. damnosum s.l. (Garms et al, 1982), which usually move with the prevailing winds (Garms et al, 1979, 1982, Baker et al, 1990. In Benin, line-squalls are usually followed by a decrease in fly numbers .…”

Programme africain de lutte contre l’onchocercose (APOC) : transmission d’Onchocerca volvulusparSimulium damnosumS. l. dans deux régions de la République Centrafricaine

“…Ces caractères concernent la teinte des touffes de soies situées à la base des ailes (Kurtak et al, 1981) et la teinte relative des antennes, de la procoxa, du prosternum et du mesonotum (Dang & Peterson, 1980;Garms & Zillmann, 1984 ;Baker et al, 1990 ;Wilson & Baker, 1991 ;Wilson et al, 1993). …”

Factors affecting onchocerciasis transmission: lessons for infection control

“…In savannas controlled zones are liable to be reinfested by immigrants from afar, a phenomenon that afflicted the OCP [73,74,75,76] which was resolved by extending the treated zones. Another problem that affected OCP was the development in some cytoforms of resistance to the insecticides of choice that was circumvented partly by introducing alternative larvicides and partly by a policy of rotating the ones in use [77].…”