April 17th, 2018
New bed net to combat insecticide resistance recommended by the World Health Organization
By Scott Tytheridge
Research at the London School of Hygiene and Tropical Medicine (LSHTM) has revealed a new class of long-lasting insecticidal net (LLIN) that prevents mosquitoes from resisting pyrethroid insecticides. When used in a community randomised trial amongst children in Tanzania, the new nets were shown to significantly reduce malaria prevalence by 44% and 33% in the first and second year of the trial, respectively.
The novel LLIN is treated with an additional chemical known as PBO (piperonyl butoxide) which acts as a synergist – inhibiting the natural defence mechanism of the resistant mosquito, which normally breaks down the insecticide – and allowing the pyrethroid insecticide to work.
When the PBO LLIN was combined with indoor residual spraying (IRS), using a different type of insecticide in the organophosphate class, malaria prevalence was considerably lower (28.7%, 252/877) compared with the standard LLIN alone (55.3%, 515/932).
Professor Mark Rowland from LSHTM and principal investigator on the project, explains: “This project is a game-changer. The trial is the first clear evidence that nets treated with PBO can significantly improve personal and community protection from malaria compared to standard pyrethroid-only nets in areas where there is high pyrethroid resistance. It also demonstrated that pyrethroid resistance is now a significant problem in some areas and standard LLIN are less effective than before, and that the new IRS controlled malaria for an entire year before needing to be re-sprayed.”
As a result of the trial, the World Health Organization has issued an interim policy recommendation for PBO LLINs to be a new and effective class of LLIN. It has also recommended the new PBO LLINs should be issued in malaria endemic regions where pyrethroid-resistant mosquitoes are present.
 Natacha Protopopoff, Jacklin F. Mosha, Eliud Lukole, Jacques D. Charlwood, Alexandra Wright, Charles D. Mwalimu, Alphaxard Manjurano, Franklin W. Mosha, William Kisinza, Immo Kleinschmidt, Mark Rowland. (2018). Effectiveness of a long-lasting PBO treated insecticidal net and indoor residual spray interventions, separately and together, against malaria transmitted by pyrethroid resistant mosquitoes: A community randomised factorial design trial. The Lancet. DOI: 10.1016/S0140-6736(18)30427-6
 World Health Organisation (2018). Pyrethroid-PBO nets can provide children with greater protection against malaria. Available at http://www.who.int/malaria/news/2018/pbo-nets-lancet/en/.