New ‘mosquito grounding’ insecticide could revive stalling fight against malaria

A new insecticide which causes a mosquito’s wings to spasm and wither could revolutionise the stalling fight against malaria, scientists say.

The rollout of insecticide-treated bed nets has been central in efforts to reduce the spread of malaria, a mosquito-borne pathogen which remains one of the world’s deadliest infectious diseases.

But, despite a significant drop in fatalities in the last 20 years, rising insecticide resistance among mosquitos has hampered recent progress. In 2020 the disease killed 627,000 people – the highest annual death toll since 2011. 

Now, scientists believe a “mosquito-grounding” substance – the first new insecticide to be deemed safe and effective in roughly 40 years – could turn the tide against rising incidence. 

“These new nets are at the cutting-edge, fighting insecticide resistance and accelerating the fight to end malaria for good,” said Gareth Jenkins, director of advocacy at Malaria No More UK, who was not involved in the latest research. 

Called chlorfenapyr, the new insecticide causes wing muscle cramps which leave mosquitoes unable to move, fly – or bite humans. 

This contrasts from the traditionally used insecticides, called pyrethroids, which kill insects by attacking the nervous system. 

According to a two-year trial in Tanzania, lacing bed nets with a combination of chlorfenapyr and pyrethroid significantly reduces malaria incidence, including in regions where insecticide resistance is widespread. 

The study, published in the Lancet on Thursday, found prevalence among 4,500 children dropped by 43 per cent and 37 per cent in the first and second year respectively, compared to traditional long-lasting bed nets. Clinical cases fell by 44 per cent overall. 

“By essentially ‘grounding’ the mosquito, our work on adding chlorfenapyr to standard pyrethroid bed nets has great potential to maintain control of malaria transmitted by resistant mosquitoes in Africa,” said Dr Manisha Kulkarni, a scientist at the University of Ottawa’s Faculty of Medicine.

The university conducted the research – part funded by the UK government – alongside the London School of Hygiene & Tropical Medicine (LSHTM), National Institute for Medical Research and Kilimanjaro Christian Medical University College in Tanzania. 

“We urgently need new interventions to get control efforts back on track and protect young people from this deadly disease,” added Dr Jacklin F. Mosha from the National Institute for Medical Research, Tanzania. “These exciting results highlight that we have another effective tool to help control malaria.”

The study also trialled two other insecticide combinations, but the results were disappointing. 

A combination of pyrethroid and pyriproxyfen, which sterilises female mosquitoes, made little difference.

Meanwhile a bed net that included piperonyl butoxide – which blocks the enzymes allowing mosquitoes to develop resistance – reduced infections by 27 per cent in the first year, but made little difference thereafter. Researchers think it could be because the nets were more prone to holes, so discarded more quickly. 

But the finding that chlorfenapyr is safe and effective is significant and – if a second study confirms the new insecticide reduces malaria transmission – may trigger the World Health Organization to recommend the rollout of chlorfenapyr-coated bed nets. 

The data needed for this decision could arrive this summer. A study in Benin, conducted by Centre de Recherche Entomologique de Cotonou in collaboration with the LSHTM, is “ongoing and results should be available mid of 2022”, Dr Natacha Protopopoff, principal investigator of the Tanzania trial, told The Telegraph.

She added that, although the “mosquito grounding” bed nets are almost $1 more expensive than those currently used, the higher costs are offset by the savings generated by reducing the number of malaria patients seeking medical care. 

But Dr Protopopoff warned that “caution is needed” in the rollout of the bednets to avoid history repeating itself.

“The massive scale-up of standard pyrethroid [long-lasting insecticidal nets] 10-20 years ago led to the rapid spread of pyrethroid resistance,” she said. “The challenge now is to preserve chlorfenapyr’s effectiveness by developing rational resistance management strategies.”

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