In a two-year community randomized trial involving more than 15,000 children in Tanzania, a long lasting insecticidal net treated with piperonyl butoxide (PBO LLIN) reduced the prevalence of malaria by 44% and 33% in the first and second year respectively, compared to a standard long lasting insecticidal net (LLIN) treated with pyrethroid only.
The study also showed unprecedented malaria control through indoor residual spraying (IRS) with the insecticide pirimiphos methyl, which after a single spray round reduced malaria infection by 48% for an entire year.
LLINS and IRS are the cornerstones of malaria control in sub-Sahara Africa, and have been estimated to reduce malaria disease by 41% and malaria deaths by 62% between 2000 and 2015 globally. Despite this public health success, malaria still kills nearly half a million people annually, and for the first time in many years the World Health Organization (WHO) reported an increase in malaria cases and no change in the number of malaria deaths in 2017.
There is concurrent evidence that resistance to pyrethroid insecticide is growing in the Anopheline mosquitoes which transmit the disease. Only a limited range of alternative insecticides are available, particularly for LLINs for which pyrethroids are the only class of insecticide fully recommended by the WHO.
Anticipating the possible failure of current control tools due to resistance, WHO and LSHTM have been collaborating with the chemical industry for almost 20 years to develop new types of LLIN and new insecticides for IRS. One of these is a novel LLIN which incorporates piperonyl butoxide (PBO), a chemical which blocks the natural defence mechanisms of insects - the oxidase enzymes that would otherwise metabolise insecticide - which means the pyrethroid on the LLIN remains potent against mosquitoes despite resistance. This chemical synergist stops insects from breaking down the pyrethroid within their bodies, so the insecticide stays toxic to the insect.
The research lead said: "It's imperative we try and remain one step ahead of insecticide resistance which threatens to reverse the great gains made in combating malaria. We must develop an improved strategy based on new classes of LLIN to control malaria transmitted by pyrethroid resistant mosquitoes."
This new study involved randomly selected children aged six months to 14 years from villages in Muleba district of North West Tanzania, where high levels of resistance to pyrethroids have been reported. In 2015, 48 villages were randomised into four groups with different preventative measures. Altogether 45,000 standard LLINs and 45,000 PBO LLINs were distributed. Children were then tested for malaria at the end of each rainy season.
After nine months, malaria infection was considerably lower in the group that received just the net treated with piperonyl butoxide - PBO LLIN - (31.1%, 275/883) and the group that received indoor residual spraying and standard LLIN (28.7%, 252/877), compared to the group that received standard LLIN alone (55.3%, 515/932). Twelve months later, the PBO LLIN effect was still persisting relative to the standard LLIN.
To strengthen the evidence for the interventions, mosquito traps were placed in each study arm. The number of malaria infected mosquitoes captured in the PBO LLIN villages was reduced by 87% and 67% during the first and second years respectively compared to the standard LLIN villages.
The Principal Investigator, said: "This project is a game-changer. The trial is the first clear evidence that nets treated with piperonyl butoxide can significantly improve personal and community protection from malaria compared to standard pyrethroid-only nets in areas where there is high pyrethroid resistance. It also demonstrated that pyrethroid resistance is now a significant problem in some areas and standard LLIN are less effective than before, and that the new IRS controlled malaria for an entire year before needing to be re-sprayed."
As a direct consequence of the trial, WHO revised its reccomendations on LLIN in September 2017, giving an interim policy recommendation to PBO LLIN as a new class of LLIN1.
The authors acknowledge the study does have limitations, including the short buffer distance between villages; however, any spill-over between villages would tend to underestimate the intervention effect rather than increase it.
The authors also stress that it is important to always sleep under a bed net in areas of malaria transmission, and until PBO LLIN are deployed more widely in areas of resistance, standard pyrethroid-only nets will be more protective than non-use of nets and should continue to be used.
https://www.lshtm.ac.uk/newsevents/news/2018/resistance-breaking-mosquito-net-provides-children-greater-protection-against
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(18)30427-6/fulltext
Latest News
Protein that helps COVID-19…
By newseditor
Posted 26 Jul
Spinal Muscular Atrophy (SM…
By newseditor
Posted 26 Jul
Link between bowel movement…
By newseditor
Posted 26 Jul
Inhibition of IL-11 signall…
By newseditor
Posted 25 Jul
Brain changes linked to obe…
By newseditor
Posted 25 Jul
Other Top Stories
Targeting fat-tissue hormone may lead to type 2 diabetes treatment
Read more
Liver signals to brain to control sugar intake
Read more
Protein Phosphorylation: A Major Switch Mechanism for Metabolic Reg…
Read more
The Genetics of Pediatric Obesity
Read more
The miRNA Interactome in Metabolic Homeostasis
Read more
Protocols
A systems biology approach…
By newseditor
Posted 24 Jul
quantms: a cloud-based pipe…
By newseditor
Posted 22 Jul
Emerging tools and best pra…
By newseditor
Posted 19 Jul
Directly selecting cell-typ…
By newseditor
Posted 17 Jul
PUFFFIN: an ultra-bright, c…
By newseditor
Posted 16 Jul
Publications
Hepatocyte-intrinsic SMN de…
By newseditor
Posted 26 Jul
Aberrant bowel movement fre…
By newseditor
Posted 26 Jul
A pseudoautosomal glycosyla…
By newseditor
Posted 26 Jul
Microglia protect against a…
By newseditor
Posted 26 Jul
Rigor and reproducibility i…
By newseditor
Posted 26 Jul
Presentations
Myelin plasticity in the ve…
By newseditor
Posted 10 Jun
Hydrogels in Drug Delivery
By newseditor
Posted 12 Apr
Lipids
By newseditor
Posted 31 Dec
Cell biology of carbohydrat…
By newseditor
Posted 29 Nov
RNA interference (RNAi)
By newseditor
Posted 23 Oct
Posters
A chemical biology/modular…
By newseditor
Posted 22 Aug
Single-molecule covalent ma…
By newseditor
Posted 04 Jul
ASCO-2020-HEALTH SERVICES R…
By newseditor
Posted 23 Mar
ASCO-2020-HEAD AND NECK CANCER
By newseditor
Posted 23 Mar
ASCO-2020-GENITOURINARY CAN…
By newseditor
Posted 23 Mar