The technical basis for coordinated action against insecticide resistance: preserving the effectiveness of modern malaria vector control
Meeting report, Geneva, 4-6 May 2010
Modern malaria vector control is exceptionally dependent on a single class of molecule: the pyrethroids. For public health purposes, pyrethroids are probably the best insecticides ever developed. They are currently the only class of insecticide used on WHOPES-recommended nets, and are substantially less expensive and longer-lasting than almost all the alternatives for indoor residual spraying (IRS). According to the Roll Back Malaria Global Malaria Action Plan (RBM/GMAP), about 60% of the projected malaria control expenditure in 2010 will be used for vector control commodities and activities, mostly long-lasting insecticidal nets (LLINs) and IRS, where currently pyrethroids are the most commonly used chemical.
In the last few years, genes conferring resistance to pyrethroid insecticides have been spreading rapidly and are now widely distributed in the main African mosquito vectors of malaria. One type of resistance – kdr – has been spreading in Anopheles gambiae for several years and is now widespread in West and Central Africa. Metabolic forms of resistance have also been found in several widely scattered locations among both An. gambiae and An. funestus. These metabolic forms of resistance are more difficult to monitor and, alone or combined with kdr, may be a much greater threat. There is evidence that at least some of these genes have the potential to threaten the effectiveness of current vector control efforts. Carefully designed epidemiological trials to accurately assess the impact of different types of resistance, particularly on the efficacy of LLINs, are urgently needed.
In order to develop an appropriate and comprehensive response, the WHO Global Malaria Programme convened an informal expert consultation at which participants were asked to review the current status of insecticide resistance in malaria vectors, and to identify options for a resistance management strategy that could help to preserve insecticide susceptibility, slow down the evolution of resistance, and prolong the effectiveness of current vector control interventions.