Management of insecticide resistance in control of the Simulium damnosum complex by the Onchocerciasis Control Programme, West Africa: potential use of negative correlation between organophosphate resistance and pyrethroid susceptibility

Abstract

1. Resistance of some populations of the Simulium damnosum complex to temephos (100-fold at the LC50 level), with degrees of cross-resistance to chlorphoxim (14-fold) and other organophosphate insecticides, follows intensive larvicidal control of S. damnosum s.l. in West African river systems since 1975 by the WHO Onchocerciasis Control Programme. 2. Larvae of at least three sibling species of the S. damnosum complex have become organophosphate-resistant: these are the forest species S. sanctipauli Vajime & Dunbar and the savanna species S. sirbanum V. & D. and S. damnosum Theobald sensu stricto. 3. Organophosphate-resistant S. damnosum s.l. larvae show increased susceptibility to some organochlorine and pyrethroid insecticides, especially to permethrin (up to 11-fold) and OMS 3002 (up to 17-fold), as compared with organophosphate-susceptible populations. 4. This differential susceptibility is reflected by increased pyrethroid efficacy in operational use for river treatments against organophosphate-resistant field populations of S. damnosum s.l. larvae. Treatment of 100 km of the lower Bandama River in 1985 showed that permethrin at the highly selective dosage of 10 min exposure to 0.01 mg/l caused reversion towards organophosphate-susceptibility of the target population of S. sanctipauli. This effect was less pronounced when the Comoe River was treated at the lower dosage of 0.005 mg/l for 10 min. 5. To overcome temephos-resistance, it is proposed that the most rational usage of currently available larvicides would involve the following annual sequence of treatments: Bacillus thuringiensis serotype H-14 when river discharge is below 75 m3/s; chlorphoxim for about eight weekly treatment cycles after river discharge rises; permethrin (or alternative pyrethroid) for up to six treatment cycles--this should eliminate any incipient selection for chlorphoxim-resistance; resume chlorphoxim (or perhaps carbosulfan) treatments until river discharge falls below 75 m3/s permitting resumed use of B.t. H-14.

Trends in weekly reported net use by children during and after rainy season in central Tanzania

“…Within the households, use of insecticide-treated bed nets contributes to protection from mosquito bites for members of the household who do not have a net to sleep under [21-25] as well as for other members of the community [26-31]. Estimates of thresholds for community-level protection range from 35-65% from modeling [32] to 50% as described in Kenya [26].…”

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].…”

Susceptibility status of Anopheles gambiae sensu stricto (Diptera: Culicidae) to pyrethroid and carbamate insecticides in the Greater Accra region of Ghana, West Africa

“…The relationship between resistance to permethrin (pyrethroid) and the susceptibility to propoxur (carbamate) was shown by the observed phenomenon of negative correlation between the two insecticides. Comparable relationships have been reported for pyrethroid and organophosphate insecticides (Kurtak et al, 1987), giving rise to the hypothesis that negative correlation could be used for the management of resistance should the level of pyrethroid resistance become so high that they can no longer be used effectively. However, investigation of the phenomenon of negative cross resistance (Kolaczinski and Curtis, 2004) across different populations of Anopheles mosquitoes concluded that it is not a generalized phenomenon.…”