Chapter 2 Pyrethroid resistance in the African mosquito Anopheles gambiae and alternative insecticides for indoor residual spraying and use on mosquito nets

摘要

Resistance to pyrethroid insecticides has become widespread in Anopheles gambiae in West Africa. Whilst the kdr resistance in the An. gambiae S cytotype appears to have no operational importance, the resistance that has recently developed in the M cytotype of An. gambiae does appear to be protective and to threaten the future of pyrethroids at a time when coverage of insecticide treated nets and indoor residual spraying are being scaled up to great effect. There is an urgent need to develop alternative insecticides for vector control. No new class of chemistry has emerged for adult mosquito control since the pyrethroids. The primary characteristics required in an adulticide are contact activity, long residual activity and low mammalian toxicity. These criteria are less essential in agricultural insecticides where most R&D is focused. Two exceptions that may meet the vector control criteria are chlorfenapyr, a pyrrole, and indoxacarb, an oxadiazine used in crop protection. These compounds are unlikely to show cross-resistance to standard neurotoxic insecticides. Older chemistries such as the organophosphates have renewed potential in vector control. Advances in formulation technology mean that the residual activity of short lived insecticides may be extended to cover entire transmission seasons, reducing the need for costly, repeated applications. The problem of pyrethroid resistance in West Africa and the prospect of finding new compounds to supplement the pyrethroids are described. Such products will need to be evaluated in laboratory and field trials before they can be approved or taken up by malaria control programmes.