Bed net that ‘grounds’ mosquitoes cuts malaria cases

[NAIROBI] An innovative bed net that immobilises mosquitoes by making them unable to move or fly, has the potential to significantly reduce malaria infection in children, according to trial data analysis.

Malaria is a leading cause of illness and death in many developing countries, with young children and pregnant women most affected. In 2020 it killed 627,000 people, and 96 per cent of those deaths occurred in Africa, the World Health Organization (WHO) estimates.

While traditional insecticides kill the mosquito by poisoning its nervous system, a new net laced with chlorfenapyr insecticide causes wing muscle cramps which stop the mosquito from flying, meaning it starves to death, says the study published in The Lancet.

“By essentially ‘grounding’ the mosquito, our work on adding chlorfenapyr to standard pyrethroid nets has great potential to control malaria transmitted by resistant mosquitoes in Africa,” says Jacklin Mosha, a senior researcher at the National Institute for Medical Research in Mwanza, Tanzania, and lead author of the study.

“Based on this evidence, the national malaria control programme and the WHO can update current national malaria control strategies and include a new effective tool.”

Natacha Protopopoff, London School of Hygiene and Tropical Medicine

Insecticide-treated mosquito nets have been the main form of malaria prevention in the past decade in Sub-Saharan Africa, and the most effective, according to the WHO. It says they accounted for more than two thirds of an estimated 663 million malaria cases averted in the region between 2001 and 2015 as a result of key malaria control interventions.

But growing resistance to pyrethroids — the insecticide usually used to impregnate bed nets — in malaria vectors is threatening this achievement.

Our study shows that for the first time in over 40 years, another class of insecticide [chlorfenapyr] is safe to use on bed nets and more effective to prevent malaria, and halves malaria cases compared to current standard practice which is the pyrethroid insecticide mosquito nets,” said Mosha.

The researchers carried out a two-year randomised trial involving 39,000 households, in the Misungwi district of Tanzania’s Mwanza region where high levels of resistance to pyrethroids have been reported.

They enrolled 4,500 children aged six months to 14 years and divided them into four groups, with three groups receiving one of three new types of bed net and one group receiving standard mosquito nets. The children were then tested for malaria at the end of each rainy season.

“After 24 months, malaria infection was reduced by 37 per cent in children that received the chlorfenapyr insecticide nets compared to those receiving the standard pyrethroid nets,” Mosha told SciDev.Net.

She said that another bed net, treated with the chemical piperonyl butoxide to enhance the potency of pyrethroid, reduced malaria infection by 27 per cent over the first 12 months of the trial. But after two years, malaria infection in this group was similar to the standard net.

“This is likely due to it being used less regularly,” Mosha explained, with researchers having observed that holes appeared in these nets more quickly.

A third bed net, treated with pyrethroid and pyriproxyfen which sterilises female mosquitoes, was no more effective than the standard pyrethroid net, the researchers said.

Natacha Protopopoff, an associate professor in entomology at the London School of Hygiene and Tropical Medicine who led the research, stressed the need to use all tools available to tackle malaria, including mosquito nets, vaccines and treatments.

“Insecticide-treated bed nets that can kill resistant mosquitoes will be as important as ever for malaria control in the years to come,” she said.

She believes the findings could benefit all communities in Sub-Saharan Africa plagued by malaria.

“Based on this evidence, the national malaria control programme and the WHO can update current national malaria control strategies and include a new effective tool,” she said, adding: “It is essential, also, for funders and governments to fund these more effective tools.”

Peter Ofware, Kenya country director for the global health and human rights organisation HealthRight International, says such innovative tools for fighting malaria are welcome.

“We need all the help we can get to malaria, especially in endemic regions in Sub-Saharan Africa,” he said. “Such tools, if proved useful, should be quickly upscaled to most needy regions.”

He challenged governments and donor organisations to back such innovations with financial support in order for them to be successful.

This piece was produced by SciDev.Net’s Sub-Saharan Africa English desk.