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New insecticide-coated bed net battles malaria

Innovation could help in fight against rising rates of insecticide resistance

Mark Gould

Thursday, 12 April 2018

New bed nets coated with a long-lasting chemical called piperonyl butoxide (PBO) and combined with pyrethroid insecticide are delivering significant reductions in rates of infection amongst children.

In tests the new nets reduced incidence rates in children by 44% over one year, and 33% over two years, compared to the bed nets currently used, according to a randomised controlled trial* published in The Lancet.

Based on this evidence, the World Health Organisation (WHO) recommends increasing coverage of PBO bed nets in areas where resistance to pyrethroids is developing.

Progress in malaria control is under threat by wide-scale resistance to the pyrethroid insecticide class currently used in indoor spraying and on current bed nets. This has resulted in a need for new types of insecticide for nets and indoor spraying.

“Our study is the first randomised control trial to report that PBO nets were more effective than standard nets against malaria infection and transmission by pyrethroid resistant mosquitoes. It also provides the strongest evidence so far of the effect of pyrethroid resistance on the use and efficacy of standard nets,” says lead author Dr Natacha Protopopoff, from the London School of Hygiene and Tropical Medicine.

“For areas where malaria is showing heightened levels of pyrethroid resistance, replacing standard nets with PBO nets will be an important way to reduce prevalence of the infection in children. The change in WHO guidance to reflect this will affect many areas of Africa where malaria is endemic, and currently standard nets are provided.”

In this study, the authors compared standard and PBO bed nets and indoor spraying of another insecticide – called pirimiphos-methyl – in 40 villages in Muleba (Tanzania). The PBO chemical is expected to last for up to two years when applied to nets, while pirimiphos-methyl indoor spraying lasts for approximately one year.

The randomised trial included four groups: households either received a PBO net with no indoor spraying, a PBO net and indoor spraying, a standard net with no indoor spraying, or a standard net and indoor spraying. Previously, there was inadequate evidence to justify swapping from standard nets to PBO nets across all areas, and concerns that the PBO chemical could interact and reduce the benefits of pirimiphos-methyl indoor spraying.

After nine months, malaria infection was 44% lower in the group receiving PBO nets alone than in the group receiving standard nets alone (31% [275/883] children infected in the PBO net group vs 55% [515/9329] of children in the standard nets group). This effect was sustained after 21 months where there were 33% fewer infections in children using the PBO nets (46% of children in the PBO nets group were infected with malaria vs 68% of children using standard nets).

In addition, at nine months, malaria prevalence in the group who received indoor spraying and standard nets (29% [252/877] children infected) was 48% lower than in the standard net group who did not receive spraying (55% children infected).

However, there was limited additional benefit gained from combining the PBO nets and indoor spraying. The addition of indoor spraying did not significantly improve protection over the PBO nets alone. However, the authors also note that in areas where indoor spraying with pirimiphos-methyl already occurs, substituting PBO nets for standard nets would provide no additional benefit.


*Effectiveness of a long-lasting piperonyl butoxide-treated insecticidal net and indoor residual spray interventions, separately and together, against malaria transmitted by pyrethroid-resistant mosquitoes: a cluster, randomised controlled, two-by-two factorial design trial. The Lancet, 11 April 2018.

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