Wellness & Fitness

New chemicals to tackle resistant malaria mosquitoes

NET

A child sleeps under a mosquito net. FILE PHOTO | NMG

Most households in Kenya own insecticide treated bed nets which are meant to keep malaria spreading mosquitoes at bay.

The nets play a key role in protecting high-risk populations such as pregnant women and children from the adverse effects of the disease.

But over the years the efficacy of these nets in keeping mosquitoes away and the resultant malaria prevention has been waning as the insects develop resistance to insecticides lacing the nets (known as pyrethroids) that are meant to kill them.

As a result, more children have been dying from the disease in high risk areas than was the case years back when the bed nets were rolled out in Kenya.

Even though the problem has not yet reached critical levels, malaria experts have been racking their brains with the aim of finding a sustainable solution to the problem before the nets become completely ineffective in malaria control.

After many years of research, there seems to be light at the end of the tunnel.

A new study published in The Lancet journal shows that bed nets treated with a new chemical known as piperonyl butoxide (PBO) are more effective in malaria control compared to nets treated with pyrethroids only.

The two-year research conducted in Tanzania revealed that the new nets reduced the prevalence of the disease by 44 per cent and 33 per cent in the first and second year respectively compared to standard nets.

The study, which involved more than 15,000 children, is the first to offer clear evidence that nets treated with PBO can significantly improve personal and community protection from malaria compared to standard pyrethroid treated nets in areas where there is high pyrethroid resistance.

Findings of the study also showed unprecedented malaria control through indoor residual spraying (IRS) with a novel insecticide known as pirimiphos methyl, which after a single spraying round reduced malaria infection by 48 per cent for an entire year.

Aside from mosquitoes developing resistance towards them, current insecticides for indoor residual spraying are short-acting and hence need to be re-applied between two and four times a year depending on the type of chemical used.

Indoor residual spraying refers to the application of certain insecticides inside houses, on walls and other surfaces that serve as a resting place for malaria infected mosquitoes.

READ: Children with Malaria attract more mosquitoes

The insecticide kills mosquitoes when they come in contact with treated surfaces, thus, preventing malaria transmission.

The development of these new chemicals is a result of a collaborative initiative between the World Health Organisation (WHO) and the London School of Hygiene and Tropical Medicine (LSHTM).

The two have been working with the chemical industry for over a decade to develop new types of insecticides for use in bed nets and indoor residual sprays.

The project was initiated as a safeguard measure to ensure alternative chemicals for malaria control are available, should the existing ones begin to lose their efficacy, as is currently the case.

“It’s imperative that we try and remain one step ahead of insecticide resistance which threatens to reverse the great gains made in combating malaria,” said Natacha Protopopof, lead author of the study from the LSHTM.

“We must develop an improved strategy based on new classes of long lasting insecticide treated nets to control malaria transmitted by pyrethroid resistant mosquitoes,” said Dr Protopopof.

The counties most affected by the resistance problem include Migori, Kisumu, Homa Bay, Busia and Siaya.

Simon Kariuki, head of the malaria programme at the Kenya Medical Research Institute (Centre for Global Health Research) noted that the study offers hope for malaria control in Kenya which has over the years grappled with mosquitoes’ resistance to insecticides used in bed nets and IRS.

“It’s good that we now have something that is working well. This will give scientists time to come up with new interventions to fight the disease,” said Dr Kariuki.

“We were worried as we seemed to be dealing with the resistance problem everywhere. Aside from bed nets and IRS, malaria treatment drugs were also affected.”
Dr Kariuki said that to delay mosquitoes from developing resistance to insecticides used in malaria control and prevention, scientists were using a combination of two chemicals to develop new insecticides.

“If the mosquitoes develop resistance to one, the other will still work.”

For indoor residual spraying, experts are also recommending the application of two different types of insecticides - on different sides of the wall - so as to minimise resistance.

As a direct consequence of the research trial done in Tanzania, the WHO introduced an interim policy recommendation allowing the use of the new PBO bed nets in affected areas.

Jan Kolaczinski, Coordinator for Entomology and Vector Control in the WHO Global Malaria Programme, noted that the nets should be deployed for malaria prevention in areas where mosquitoes are resistant to pyrethroids, provided that full coverage (of affected populations) is maintained.

Long-lasting insecticidal nets and indoor residual spraying are the cornerstones of malaria control in sub-Saharan Africa.

Together with effective treatment, these interventions are estimated to have globally reduced malaria and arising deaths by 41 per cent and 62 per cent respectively between 2000 and 2015.