Abstract
BackgroundMalaria control through use of long-lasting insecticidal nets (LN) is threatened by the selection of anopheline mosquitoes strongly resistant to pyrethroid insecticides. To sustain future effectiveness it is essential to identify and evaluate novel insecticides suitable for nets. Mixtures of two insecticides with contrasting mode of action have the potential to kill resistant vectors and restore transmission control provided the formulation can withstand regular washing over the net’s life span.MethodThe efficacy of a novel mixture LN, Interceptor® G2, that combines the pyrrole chlorfenapyr and pyrethroid alpha-cypermethrin was evaluated under controlled household conditions (experimental hut trial) and by laboratory bioassay against pyrethroid resistant An. gambiae in Benin before and after standardized washing. Comparison arms included standard alpha-cypermethrin LN, nets hand-treated with chlorfenapyr-only and untreated nets.ResultsThe chlorfenapyr-alphacypermethrin LN demonstrated improved efficacy and wash resistance compared to a standard alpha-cypermethrin LN against pyrethroid resistant mosquitoes (resistance ratio 207). In experimental hut trial alpha-cypermethrin LN killed only 20% (95% CI 15–26%) of host-seeking An. gambiae whilst mixture LN killed 71% (95% CI 65–77%). Mixture LN washed 20 times killed 65% (95% CI 58–71%), and thus intensive washing reduced efficacy by only 6% (95% CI 1.3–11%). The chlorfenapyr net killed 76% (95% CI 70–81%). Personal protection and blood feeding inhibition did not differ between mixture and pyrethroid LN; however, the mixture LN was 2.5 (95% CI: 2.1–3.1) times more protective than untreated nets. Standard WHO cone bioassays conducted during day time hours failed to anticipate field efficacy but overnight tunnel tests successfully predicted mixture LN and chlorfenapyr net efficacy in field trials.ConclusionInterceptor® G2 LN demonstrates the potential to control transmission and provide community protection over the normal lifespan of long lasting nets where standard pyrethroid LN show signs of failing due to resistance.
Highlights
Long-lasting insecticidal nets (LN) are the most widely used public health interventions for malaria prevention [1]
In experimental hut trial alpha-cypermethrin LN killed only 20% of host-seeking An. gambiae whilst mixture LN killed 71%
Personal protection and blood feeding inhibition did not differ between mixture and pyrethroid LN; the mixture LN was 2.5 times more protective than untreated nets
Summary
Long-lasting insecticidal nets (LN) are the most widely used public health interventions for malaria prevention [1]. Malaria infection prevalence among African children is estimated to have declined from 33% to 16% and under-5 all-cause mortality by 48% over the same period. While a negative epidemiological impact of pyrethroid resistance on malaria control has yet to be confirmed [1, 4], an increasing number of reports show that pyrethroid resistance is capable of reducing the effectiveness of LNs used against host seeking mosquitoes [5,6,7], and leading brands are giving less personal protection and reduced vector mortality rates compared to areas of pyrethroid susceptibility [8, 9]. Malaria control through use of long-lasting insecticidal nets (LN) is threatened by the selection of anopheline mosquitoes strongly resistant to pyrethroid insecticides. Mixtures of two insecticides with contrasting mode of action have the potential to kill resistant vectors and restore transmission control provided the formulation can withstand regular washing over the net’s life span
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