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LSHTM: WHO Recommends New Malaria Nets Based On Research By LSHTM And Partners

The World Health Organization (WHO) has updated their policy regarding the type of insecticide used on bed nets to prevent malaria.

Against the backdrop of growing resistance of disease-carrying Anopheles mosquitoes to pyrethroid, the insecticide currently used in insecticide-treated nets (ITNs), the WHO now recommends that areas with pyrethroid-resistance should instead use pyrethroid-chlorfenapyr ITNs.

The recommendations are based on over 15 years of research conducted by the London School of Hygiene & Tropical Medicine (LSHTM) and partners, notably results from two large randomised trials.

Findings from Tanzania and Benin, two countries where mosquito resistance to pyrethroids is high,  supported the life-saving potential of chlorfenapyr-treated ITNs – the first time a safe and effective new insecticide for use on nets has been demonstrated for 40 years.

Dr Manfred Accrombessi, Assistant Professor of Epidemiology at LSHTM and trial manager in Benin said: "The Tanzania and Benin trials provide sufficient evidence for the roll out of chlorfenapyr-pyrethroid insecticide treated nets. However, these new generation bed nets should be deployed under a comprehensive, long-term resistance management plan to avoid repeating the mistakes of the past."

Dr Corine Ngufor, Associate Professor of Medical Entomology at LSHTM added: "This WHO recommendation is a major milestone in the fight against malaria, with almost two decades of innovation and research allowing us to reach this point. A massive rollout of these nets across malaria endemic countries would be expected in the next few years, which would help boost progress against malaria.

"Every effort should be made to preserve their efficacy and to remove obstacles to continuous vector control innovation."

ITNs are one of the main control strategies for malaria prevention. These nets are treated with insecticides as they are manufactured, acting as a physical barrier that can also repel and kill disease-carrying mosquitoes.

Until now, ITNs containing only pyrethroid, an insecticide that kills mosquitoes by interfering with their nervous system, were the recommended intervention by the WHO in all areas where malaria is endemic, notably in sub-Saharan Africa.

However, as mosquitoes become resistant to pyrethroids, the efficacy of these nets wanes. Subsequently, cases of malaria are rising, with 627,000 deaths recorded in 2020, mainly in Africa, and predominantly in children.

With the urgent need for solutions, LSHTM scientists helped develop a new type of net, Interceptor® G2 (IG2) (manufactured by BASF), which combines pyrethroid with another insecticide known as chlorfenapyr. Unlike pyrethroids, chlorfenapyr induces muscle cramps in mosquitoes, stopping them moving or flying. This new, unique approach means pyrethroid-resistant mosquitoes are killed after they come into contact with the insecticide.

Evidence from a two-year trial of more than 39,000 households which followed over 4,500 children aged six months to 14 years in Tanzania provided the first large-scale demonstration of the efficacy of IG2 nets. Published in The Lancet in March 2022 and led by researchers from LSHTM, the trial found that IG2 nets nearly halved cases of malaria compared to pyrethroid-only ITNs.

In a sister epidemiological trial of almost 54,000 households in Benin, a similar story to Tanzania was seen. IG2 nets reduced malaria infections in children between six months and 10 years by 46% over two years compared to pyrethroid-only nets. Published in The Lancet in January this year, the findings provided the final piece in the puzzle leading the WHO to update their policy guidance.

Following the announcement, it is hoped that a broad rollout of IG2 nets in malaria-endemic countries will ensue, with the potential to save many young lives worldwide. Researchers who worked on the trials, however, emphasise the need for proper resistance management strategies and a combination of tools beyond nets to prevent a repeat of the resistance seen with pyrethroid.

Dr Natacha Protopopoff, Associate Professor of Entomology at LSHTM said: "The IG2 recommendation is great news for all working on malaria control and is another tool to help fight malaria.

"This is the achievement of over a decade of development and evaluation and has been made possible by a strong collaboration between industries, research institutions and funding agencies. However, programs should consider appropriate replacement strategies and insecticide resistance management plans to maximise the long term impact of these new tools."

Dr Jackie Mosha, National Institute for Medical Research, Tanzania said: "I am extremely proud to have contributed to generating the evidence necessary for IG2 recommendation by the WHO. The roll out of this effective new tool will help to get malaria control efforts back on track and protect communities from this deadly disease in Tanzania and other sub-Saharan African countries."

Dr Astrid Benfield, CEO of Malaria No More UK, added: "Today's news is an exciting and significant milestone in the race against insecticide resistance, with UK-based organisations LSHTM and Innovative Vector Control Consortium (IVCC) leading the addition of an effective new tool to our malaria arsenal.

"This is a remarkable achievement in British-backed science innovation, but without strengthened funding for programmes like the IVCC-led New Nets Project to test and deliver the latest technologies, these and other life-saving innovations will not reach the vulnerable populations who need them most."

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WHO Asks Countries To Issue New Malaria Bed Nets

The World Health Organisation (WHO) has advised malaria-endemic countries to roll out new malaria bed nets to fight resistance. The international health body now recommends the use of malaria bed nets that have been treated with new insecticides in areas with parasite resistance.For years, countries including Kenya have been using insecticides known as pyrethroids in treating mosquito nets.But WHO now says the insects in many countries have become resistant to routine use of pyrethroids.After a successful trial of new insecticides, Pyrethroid-chlorfenapyr nets combine a pyrethroid and a pyrrole insecticide to enhance the killing effect of the net and Pyrethroid-pyriproxyfen nets combine a pyrethroid with an insect growth regulator (IGR).The IGR disrupts mosquito growth and reproduction. The WHO is now asking countries to adopt the new nets in the trial conducted in Tanzania and Benin. Insecticide-treated bed nets are key tools for malaria prevention.Both trials have shown a significant reduction in malaria infections compared to the standard pyrethroid bed nets.Read: Kemri scientists shed light on how malaria parasite adapts to host environmentIn Tanzania, malaria prevalence was reduced in children that received the pyrethroid-chlorfenapyr-treated bed nets at 26 per cent, compared to 49 per cent in those that received pyrethroid-only bed nets, after 24 months.In Benin, after 18 months, malaria prevalence stood at 28 per cent in the group that received pyrethroid-chlorfenapyr-treated bed nets compared to 39 per cent in the group that received pyrethroid-only bed nets.The new recommendations published in the WHO Guidelines for malaria are asking countries to roll out new nets."These new types of nets were designed to have a greater impact against pyrethroid-resistant mosquitoes. By including two active ingredients in an insecticides- treated net, the likelihood of mosquitoes being resistant to both is greatly reduced," Dr Jan Kolaczinski, who leads the Vector Control and Insecticide Resistance Unit within the WHO Global Malaria Programme said.He said that compared to pyrethroid-only nets, pyrethroid-chlorfenapyr-treated nets should have an increased killing effect against pyrethroid-resistant malaria vectors and, thus, a greater impact against malaria.According to WHO's latest World Malaria Report, the emergence and wide geographic spread of pyrethroid resistance among malaria-transmitting mosquitoes is a threat to the effectiveness of nets.Since 2005, over two billion insecticide-treated nets (ITNs) have been distributed worldwide to prevent malaria. All of these nets were treated with only one insecticide class pyrethroids. However, as mosquitoes in many areas are now resistant to pyrethroids, nets treated with other active ingredients are needed to control malaria.Over the last two decades, treated nets have contributed significantly to reduction of malaria cases worldwide. In Kenya, millions of insecticide-treated bed nets have been distributed.In 2000, Supanet, a treated mosquito net, was launched in Kilifi. It was a new form of intervention as existing nets were not treated.In April 2001, there was a rebrand as Supanet introduced a retreatment kit dubbed Power Tab. The tablet would be dissolved in water before the net was dipped in. Soon after that, long-lasting insecticide-treated nets were developed.Kenya began distributing treated nets in malaria-endemic regions in partnership with the WHO to test their effectiveness. In 2007, based on the promising results from Kenya, the WHO issued global guidance on the use of treated mosquito nets.Read: Red flag over control as malaria cases, deaths riseIn July 2021, 15.7 million insecticide-treated mosquito nets were distributed in 27 high malaria burden counties. However, the threat still persists.Malaria remains the second biggest cause of reported deaths after respiratory infections, with nearly 70 per cent of the country's 46 million people at grave risk. Every year, the country reports nearly 3.5 million new clinical cases and 10,700 deaths.With the introduction of the vaccine called RTS developed by the pharmaceutical giant GSK and proven effective six years ago, malaria cases fell nationally from a prevalence of eight per cent in 2015 to 5.6 per cent in 2020.In the lake regions, the prevalence has since dropped from 27 per cent in 2015 to 19 per cent in 2020 and from eight per cent to 4.5 per cent currently at the Coast — almost 50 per cent reduction, according to the Malaria Indicator Survey 2020.Aoketch@ke.Nationmedia.Com Provided by SyndiGate Media Inc. (Syndigate.Info).

WHO Clears Malaria Nets Treated With Combination Of Insecticides To Dodge Resistance

The World Health Organization (WHO) has updated its malaria policy guidelines to recommend the use of nets treated with a combination of insecticides, in what researchers say could be a game-changer in the global fight against the disease if managed effectively.

Malaria is a leading cause of illness and death in many of the world's poorest countries, with young children and pregnant women most affected. In 2021, malaria killed 619,000 worldwide—with 96% of those deaths occurring in Africa, according to WHO estimates.

There has been a growing resistance of malaria-transmitting anopheles mosquitoes to pyrethroid, the insecticide currently used in insecticide-treated nets.

The WHO now recommends that malaria-endemic regions experiencing pyrethroid resistance switch to the more effective pyrethroid-chlorfenapyr nets.

Years of research

The recommendations follow years of research conducted by the London School of Hygiene and Tropical Medicine (LSHTM) and partners into the efficacy of pyrethroid-chlorfenapyr nets.

Corine Ngufor, associate professor of medical entomology at the disease control department of LSHTM, said the development was a "major milestone" towards achieving malaria elimination targets, but warned that work to combat resistance must continue.

"This is the first time WHO is approving a new non-pyrethroid insecticide on mosquito nets," she told SciDev.Net.

"We just need to learn from the past and ensure we preserve the efficacy of products and also continue to innovate."

She challenged procurement agencies like the Global Fund to Fight AIDS, Tuberculosis and Malaria, to support countries to increase uptake of the nets, which are treated as they are manufactured.

"There is also need to sensitize countries on the improved public health value the nets can provide, in order for governments to prioritize them for high transmission areas," Ngufor said.

Until now, WHO recommended only nets treated with pyrethroid for malaria control in endemic regions, especially Sub-Saharan Africa. The organic compound kills mosquitoes by interfering with their nervous system.

However, resistance to this chemical has grown over time, leading to an uptick of malaria cases, according to the WHO.

The LSHTM's Interceptor G2 nets, which combine pyrethroid with chlorfenapyr, induce muscle cramps in mosquitoes, stopping them from moving or flying and curtailing their ability to spread malaria.

Trials among over 4,500 children aged six months to 14 years from 39,000 households in Tanzania showed that the nets reduced malaria cases by almost half compared to pyrethroid-only treated nets. The results were published in The Lancet in March last year.

Another trial study in Benin, which sampled nearly 54,000 households, found that the nets reduced malaria infection in children aged between six months and ten years old by 46%.

'Massive impact'

Natacha Protopopoff, associate professor of entomology at LSHTM, said the WHO recommendation based on the evidence from the two community trials was a great outcome.

"We expect that chlorfenapyr-pyrethroid [nets] will perform and reduce malaria as did standard pyrethroid nets before pyrethroid resistance emerged," she told SciDev.Net.

"With the scale-up we can expect massive impact on malaria burden, provided that high coverage is sustained and resistance to chlorfenapyr does not develop too fast."

She noted that mechanisms for scaling up pyrethroid-chlorfenapyr nets were already in place through initiatives such as a new project led by the Innovative Vector Control Consortium and funded by UNITAID and the Global Fund, or the Global Fund's Net Transition Initiative.

"While the production might not be able to meet the demand now, two brands including the one evaluated in our trials are available for scale-up and, with this WHO recommendation, other manufactures may also develop pyrethroid-chlorfenapyr nets," Protopopoff added.

Peter Ofware, Kenya country director for the global health and human rights organization HealthRight International, said while the recommended new nets were promising, there was still need for a combination of various malaria control strategies such as early detection and treatment in order to defeat malaria, especially among children under five in Sub-Saharan Africa.

"The roll out of the nets must also be well funded and managed to ensure wider coverage and WHO and donor organizations must take the lead," he told SciDev.Net.

Journal information: The Lancet

Provided by SciDev.Net

Citation: WHO clears malaria nets treated with combination of insecticides to dodge resistance (2023, March 24) retrieved 20 April 2023 from https://medicalxpress.Com/news/2023-03-malaria-nets-combination-insecticides-dodge.Html

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