- A new mosquito net treated with piperonyl butoxide (PBO) insecticide can protect children against malaria
- Long-lasting insecticidal net spraying (LLINS) and indoor residual spraying (IRS) are the cornerstones of malaria control in sub-Sahara Africa
- The World Health Organization (WHO) recommends PBO LLINs to be used extensively for malaria prevention
The evolving nature of malaria-carrying mosquitoes to resist insecticides is spreading across Africa. These deadly mosquitoes can put many lives at risk.
Types of Malaria Nets
More than 15,000 Tanzanian children were included in the two-year community randomized trial. The study was led by the London School of Hygiene & Tropical Medicine (LSHTM).
‘Mosquito nets treated with piperonyl butoxide (PBO) can improve personal and community protection from malaria in areas where there is high pyrethroid resistance.’
The results showed that a long-lasting insecticidal net, when treated with piperonyl butoxide (PBO LLIN), reduced the prevalence of malaria by 44 percent in the first year and 33 percent in the second year than the standard long-lasting insecticidal net (LLIN) that was treated with a pyrethroid.
Also, through indoor residual spraying (IRS) with the pirimiphos-methyl insecticide, the prevalence of malaria after just a single spray was reduced by 48 percent for an entire year.
The long-lasting insecticidal net spraying (LLINS) and indoor residual spraying (IRS) are now the cornerstones of malaria control in sub-Sahara Africa. Between 2000 and 2015, malaria disease was reduced by 41 percent and malaria deaths by 62 percent globally.
Despite the reduction in the prevalence of malaria, still, half-a-million people die annually because of the disease. For the first time, an increase in malaria cases and mortality rates remained unchanged in 2017, were reported by the World Health Organization (WHO).
There is concurrent evidence, which shows that resistance to pyrethroid insecticide is growing in the Anopheline mosquitoes.
Effect of Long-lasting Insecticidal Net Spraying (LLIN)
Currently, only a limited range of alternative insecticides are available, especially for LLINs, and WHO highly recommends pyrethroids for LLINs.
For almost 20 years, the WHO and LSHTM have been collaborating with the chemical industry to develop new types of LLIN and new insecticides for IRS.
A novel LLIN discovered incorporates piperonyl butoxide (PBO), a chemical that blocks the natural defense mechanisms of insects, i.e., the pyrethroid insecticide on the LLIN remains potent against mosquitoes despite resistance. The chemical PBO stops insects from breaking down the pyrethroid insecticide within their bodies so that the insecticide could stay toxic to the insect.
Dr. Natacha Protopopoff from the London School of Hygiene & Tropical Medicine who led the field research operations in Muleba, Tanzania, 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.”
Malaria in Tanzania
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 this study, children are six months till 14 years were selected randomly from villages in Muleba district of North West Tanzania, as there were high levels of resistance to pyrethroids insecticide in this area.
In 2015, about 48 villages were divided into four groups randomly with different preventative measures, where 45,000 standard LLINs and 45,000 PBO LLINs were distributed to them. Later, the children were tested for malaria at the end of each rainy season.
After nine months, the research team analyzed and found that malaria infection was much lower in the group that received the long-lasting insecticidal net treated with PBO LLIN (31.1%, 275/883).
There was also a reduction seen in the group that received indoor residual spraying and standard LLIN (28.7%, 252/877) when compared to the group that received standard LLIN alone (55.3%, 515/932).
The team analyzed again after twelve months and found that the PBO LLIN effect was almost similar to the standard LLIN.
Mosquito traps were placed by the research team in each study arm to strengthen the evidence for the interventions.
About 87 percent and 67 percent reduced the number of malaria-infected mosquitoes captured by the mosquito traps in the PBO LLIN villages during the first and second years respectively than the standard LLIN villages.
Professor Mark Rowland from LSHTM and 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 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.”
Revised recommendations on LLIN: WHO
In September 2017, WHO revised its recommendations on LLIN as a direct consequence of the trial by giving an interim policy recommendation to PBO LLIN as a new class of LLIN1.
Dr. Jan Kolaczinski, Coordinator for Entomology and Vector Control in the WHO Global Malaria Programme said, “WHO recommends PBO LLINs should be deployed for malaria prevention in areas where mosquitoes are pyrethroid resistant, provided that full coverage is maintained. This would include many endemic areas in Africa where standard LLINs are currently used.”
Professor Rowland said that the research team is pleased with the revised policy of WHO, as it firmly ensures that insecticide-treated nets will be an effective intervention for malaria control. He also said there is a need for further research on alternative insecticides for use on nets and justifies the need for investment.
There were limitations in this study, including the short buffer distance between villages; and any spill-over between villages can underestimate the effect of intervention rather than increasing it.
It is important to use a bed net in areas where there is a high malaria transmission. The standard pyrethroid-only nets are more protective than non-use of nets and should continue to be used till PBO LLIN are used more widely in areas of resistance.
Malaria spread by the bite of an infected female Anopheles mosquito enters the body and infects the red blood cells (RBCs) and liver. The parasites mature into other forms and are subsequently taken up by another mosquito and spread further. Thus, the infection continues cyclically, alternating between the mosquito vector and human hosts.
Currently, there are 3,500 species of mosquitoes and 430 Anopheles species, and only 30-40 species have the potential vectors for transmitting Malaria. Here are some tips that help prevent malaria:
- Prevent mosquito bites by covering all exposed body parts
- Always sleep in a mosquito bed net
- Use mosquito repellent creams or patches
- Take malaria preventive drugs before visiting any endemic malaria regions
- Seek medical help, if there are any symptoms of malaria
With required funds and a joint effort from countries in prevention, we can transform our common vision ‘End Malaria for Good’ into a shared reality.
- Malaria – (http://www.who.int/mediacentre/factsheets/fs094/en/)
- Malaria – (https://medlineplus.gov/malaria.html)