A new type of bed net that can neutralise mosquitoes resistant to traditional insecticides has significantly reduced malaria infections in Tanzania, scientists say.

The net demonstrated a significant reduction in malaria prevalence compared to the standard pyrethroid-only net, nearly halving infections in children over the two years it has been on trial and reducing clinical episodes of the disease by 44 percent.

According to research published in The Lancet in March, unlike insecticides that kill mosquitoes, the new bed net renders the insect unable to fend for itself by making it unable to move or bite, starving it to death.

In the study involving more than 39,000 households and over 4,500 children in Tanzania, it was found that a long-lasting insecticidal net treated with two insecticides — chlorfenapyr and pyrethroid (chlorfenapyr LLIN) — reduced the prevalence of malaria by 43 percent in the first year and by 37 percent in the second, compared to the standard pyrethroid-only net.

Grounding mosquitoes

The research found that the chlorfenapyr net also reduced the number of malaria-infected mosquitoes captured by 85 percent.

According to the scientists, chlorfenapyr works differently from pyrethroid, causing wing muscle cramps that stop flight muscles from functioning. This prevents mosquitoes from making host contact or biting, ultimately leading to their death.

“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, associate professor at University of Ottawa’s School of Epidemiology and Public Health.

Comparison

In comparison, a bed net treated with piperonyl butoxide (PBO) to enhance the potency of pyrethroid reduced malaria infections by 27 percent over the first 12 months of the trial, but after two years malaria infection in this group was similar to those who used the standard net.

A third type of bed net, treated with pyrethroid and pyriproxyfen (which sterilises female mosquitoes) had little additional effect compared to the standard pyrethroid net. The reason is not fully understood but likely due to insufficient pyriproxyfen remaining on the net over time.

“Though more expensive, the higher costs of the chlorfenapyr LLIN were offset by the savings from reducing the number of malaria cases requiring treatment. Distributing chlorfenapyr nets is, therefore, expected to cost households and society less overall than standard, PBO or pyriproxyfen nets,” said the team of scientists who hope the World Health Organisation and malaria control programmes will adopt the new net in areas with insecticide resistant mosquitoes.

The findings from the study by the National Institute for Medical Research, the Kilimanjaro Christian Medical University College, the London School of Hygiene & Tropical Medicine (LSHTM), and the University of Ottawa are welcome news on a continent where standard mosquito nets have failed to protect people from the parasite.

Long-lasting insecticidal nets are the cornerstone of malaria control in sub-Saharan Africa.

Insecticide-treated nets helped prevent 68 percent of malaria cases in sub-Saharan Africa between 2000-2015. However, in the past few years the decline in malaria incidence has stalled and even reversed in some countries.

In 2020, there were 627,000 deaths from malaria, compared to 409,000 deaths in 2019, mainly in Africa and in children.

Resistance fears

The study’s lead author, Dr Jacklin Mosha from the National Institute for Medical Research, Tanzania, said, “These exciting results highlight that we have another effective tool to help control malaria.”

The research team says the “no flight, no bite mosquito grounding bed net” that goes by the trade name ‘Interceptor® G2 could lead to significant malaria control gains in sub-Saharan Africa.

However, they say more research is needed to examine feasibility of a scale-up and to come up with resistance management strategies needed to preserve the effectiveness in the long term.

“Caution is needed,” warned co-author Natacha Protopopoff. “The massive scale-up of standard pyrethroid LLINs 10-20 years ago led to the rapid spread of pyrethroid resistance. The challenge now is to preserve chlorfenapyr’s effectiveness by developing rational resistance management strategies.”

This is the first of several trials of chlorfenapyr nets. The others are in Benin, Ghana, Burkina Faso and Côte d'Ivoire.