More About Insecticide Treated Bed Nets

Malaria is a vector-borne human disease transmitted by mosquitoes that has high rates of morbidity and mortality globally. While preventive medication holds great promise for reducing malaria incidence in the future, mosquito-vector control remains the most efficacious strategy for reducing disease incidence.
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For years, bed nets were used as a protective physical barrier for people while sleeping under the netting, but netting treated with an insecticide was found to be significantly more protective than untreated nets. Insecticide-treated bed nets (ITNs) have been shown to be highly effective mosquito-control agents that reduce malaria incidence and deaths as well as the predisposition to other childhood diseases.

Community-wide efficacy trials in sub-Saharan Africa have demonstrated that ITNs reduced mortality rates in children < 5 years from all causes by about 20%. The World Health Organization (WHO) now recommends that ITNs be used not just by the most vulnerable groups, i.e., pregnant women and children under 5 years of age, but all community members where malaria is endemic.
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The insecticides used for treating bed nets work by both killing and repelling mosquitoes, and if ITN usage in a community is high, mosquito populations are reduced in the entire area. Consequently, community members will be protected from mosquitoes regardless of whether they use an ITN.

Previously, ITNs had to be retreated every 6 to 12 months by dipping them into an insecticidal solution and allowing them to dry. The need for frequent insecticide retreatment was a barrier to acceptance of ITNs. To overcome this barrier, ITNs were developed with a pyrethroid embedded in the netting enabling nets to be laundered and used for multiple years without retreatment, and the chemical properties of pyrethroids are well suited for this type of manufacturing.

The adoption of long-lasting insecticidal nets (LLIN) has led to marked decreases in global malaria cases from 2005 to 2015. The rise of pyrethroid resistance, however, has impacted the efficacy of pyrethroid-treated ITNs. As a resistance management strategy, newer pyrethroid ITNs are being manufactured with a synergist, such as piperonyl butoxide-PBO, or mixed with an insecticide of a different mode of action, primarily chlorfenapyr and pyriproxyfen. Although resistance to pyrethroids has increased in Anopheles mosquitoes, end users still prefer this class of chemistry due to its rapid knockdown of adult mosquitoes and cost-effectiveness.

Photo Source: WHO/S. TorfinnWomen demonstrating the use of insecticide-treated nets in Kisumu, Kenya

“Pyrethroid-treated bed netting has been shown to be the most efficacious and cost-effective means to reduce the mosquito-vector population and the incidence and impact of malaria world-wide.”

Over the last 2 decades, ITNs have contributed significantly to the progress seen in reducing malaria cases worldwide. A 2015 modelling analysis published in Nature showed that ITNs and LLINs drove much of the declines in malaria seen from 2005 to 2015, particularly in moderate-to-high malaria-transmission areas. According to the WHO, manufacturer data from 2004 to 2022 show that more than 2.9 billion bed nets have been distributed globally with 2.5 billion (86%) being provided to sub-Saharan Africa alone. In 2021 alone, approximately 220 million ITNs were provided to malaria-endemic countries. Of these, 46% were pyrethroid–piperonyl butoxide (PBO) nets and 9% were dual active-ingredient ITNs. Globally, the percentage of the population sleeping under an ITN also increased from 2000 to 2021 from 3 to 53% for children under 5 years of age, 3 to 53% for pregnant women, and 2 to 47% for the entire population.
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Overall, pyrethroid-treated bed netting has been shown to be the most efficacious and cost-effective means to reduce the mosquito-vector population and the incidence and impact of malaria world-wide.