Insecticide-treated materials, mosquito adaptation and mass effect: entomological observations after five years of vector control in Burkina Faso

Abstract

Insecticide-treated bednets and curtains have been shown to be successful in reducing malaria transmission and child mortality in Africa over periods of up to 2 years. A major concern relating to this approach is that, in time, it will be compromised by the selection of mosquito genotypes that are resistant at the biochemical or behavioural level. We report entomological data from a large area in Burkina Faso where insecticide-treated curtains have been in use for up to 5 years. Longitudinal indoor and outdoor CDC light-trap catches were performed in 4 sentinel villages. In addition cross-sectional surveys using indoor spray catches and outdoor CDC light-trap catches were performed each September in a larger number of villages, including 8 located outside the intervention area. We found no evidence of the selection of mosquito phenotypes that might compromise the intervention. Indoor and outdoor vector densities remained very low after 5 years of intervention, both compared with pre-intervention levels and with concurrent levels outside the intervention area. We found no evidence of a switch to outdoor rather than indoor biting. The proportion of blood meals taken on humans may have decreased but our data are inconclusive on this point. We observed higher vector densities and sporozoite rates at the periphery of the intervention zone than at the centre, which may reflect re-invasion of peripheral villages by mosquitoes from outside the intervention area. In 'real life' programmes, with perhaps patchy, less than optimal coverage, the protection against malaria transmission provided to individuals using insecticide-treated materials may be less than that achieved in the randomized controlled trials which demonstrated an impact of insecticide-treated materials on child mortality.

Insecticide-treated nets usage and malaria episodes among boarding students in Zaria, Northern Nigeria

“…Apart from providing physical barrier against mosquito bites, ITNs are known to have mass killing effects and to protect against a wide range of vector-borne diseases and reduce childhood mortality by about 20% in Africa. [11,[14][15][16] The cost of ITN, like cost of many public health goods continues to raise serious concern.…”

The Cost-Effectiveness of Permethrin-Treated Bed Nets in an Area of Intense Malaria Transmission in Western Kenya

“…[1][2][3][4] While there is a small but growing literature on the cost-effectiveness of ITNs, 3,[5][6][7] no information on cost-effectiveness in areas of intense, perennial malaria transmission is available. In addition, we know little about the extent to which the impact of ITNs on community members lacking ITNs (the mass effect 8 or community effect 9 ) influences estimates of cost-effectiveness. This economic evaluation is based upon the results of a community-based, group-randomized, controlled trial of ITNs in western Kenya conducted in an area of intense, perennial malaria transmission.…”

Collapse of Anopheles darlingi Populations in Suriname After Introduction of Insecticide-Treated Nets (ITNs); Malaria Down to Near Elimination Level

“…Decreased mosquito population densities and biting pressure have been found after use of insecticide-treated materials elsewhere, and (local) mass effects have been reported. 20,21 The fact that, in a small isolated village 100 km southwest of Drietabiki, An. darlingi can still be found, whereas along the much more populated Upper Marowijne River, the collectors return empty-handed rather supports the notion that a large-scale distribution of LLINs could have an impact on mosquito densities.…”