Country-level operational implementation of the Global Plan for Insecticide Resistance Management

Abstract

Malaria control is reliant on the use of long-lasting pyrethroid-impregnated nets and/or indoor residual spraying (IRS) of insecticide. The rapid selection and spread of operationally significant pyrethroid resistance in African malaria vectors threatens our ability to sustain malaria control. Establishing whether resistance is operationally significant is technically challenging. Routine monitoring by bioassay is inadequate, and there are limited data linking resistance selection with changes in disease transmission. The default is to switch insecticides when resistance is detected, but limited insecticide options and resistance to multiple insecticides in numerous locations make this approach unsustainable. Detailed analysis of the resistance situation in Anopheles gambiae on Bioko Island after pyrethroid resistance was detected in this species in 2004, and the IRS program switched to carbamate bendiocarb, has now been undertaken. The pyrethroid resistance selected is a target-site knock-down resistance kdr-form, on a background of generally elevated metabolic activity, compared with insecticide-susceptible A. gambiae, but the major cytochrome P450-based metabolic pyrethroid resistance mechanisms are not present. The available evidence from bioassays and infection data suggests that the pyrethroid resistance mechanisms in Bioko malaria vectors are not operationally significant, and on this basis, a different, long-lasting pyrethroid formulation is now being reintroduced for IRS in a rotational insecticide resistance management program. This will allow control efforts to be sustained in a cost-effective manner while reducing the selection pressure for resistance to nonpyrethroid insecticides. The methods used provide a template for evidence-based insecticide resistance management by malaria control programs.

Fig. 1.

Numbers of Anopheles caught in domestic window traps in Bioko in 2004–2005, disaggregated to show the effect of house spraying. (A) Graph reproduced from ref. . (B) The same data from Sharp et al., 2007, disaggregated into window-trap nights prespraying (green) and window trap nights postspraying (blue). The spray round was carried out between February and July 2004.

Fig. 2.

The sporozoite rates in A. gambiae before and at different time intervals after spraying.

Fig. 3.

Whole-genome reciprocal dye swap pairwise microarray comparisons of A. gambiae populations collected from Bioko, unexposed or exposed to insecticides with a susceptible West African A. gambiae population.