To combat malaria, more than 2 billion Insecticide-Treated Nets have been supplied globally since 2005. Just the pyrethroid pesticide class was used to treat all of these nets. But in order to combat malaria, nets laced with other active components are required because mosquitoes in many locations are now pyrethroid-resistant. A new type of Insecticide-Treated Nets that combines pyrethroids with piperonyl-butoxide (PBO), a substance that increases the potency of pyrethroids against resistant mosquitoes, began to be recommended by WHO in 2017.
Two new kinds of dual component Insecticide-Treated Nets with various mechanisms of action are covered by new guidelines that were just released in the WHO Guidelines for Malaria. To increase the killing power of the net, pyrethroid-chlorfenapyr nets mix a pyrethroid and a pyrrole insecticide. Insect growth regulators and pyrethroids are combined in pyrethroid-pyriproxyfen nets (IGR). The IGR prevents mosquito reproduction and growth.
Dr. Jan Kolaczinski, who oversees the WHO Global Malaria Programme’s Vector Control and Insecticide Resistance unit, said that these new varieties of nets were created to be more effective against pyrethroid-resistant mosquitoes. “The likelihood of mosquitoes developing resistance to both active components is significantly lowered by using two active compounds in an Insecticide-Treated Nets.”
WHO recommendations for malaria
The updated WHO recommendations for treating malaria are collected in a single web-based document known as the Consolidated WHO Guidelines for Malaria. Recommendations are examined and, as necessary, updated utilizing the rigorous and open guideline development process used by the WHO. The user-friendly MAGICapp platform also offers the recommendations, which are constantly updated and include the date of the most recent change.
Pyrethroid-chlorfenapyr nets have a new recommendation as opposed to pyrethroid-only nets. In places where mosquitoes have developed pyrethroid resistance, WHO strongly advises against using pyrethroid-only nets to combat malaria in adults and children. Instead, use pyrethroid-chlorfenapyr ITNs. The guideline assumes that pyrethroid-chlorfenapyr ITNs should have a better lethal effect against pyrethroid-resistant malaria vectors and, therefore, a greater impact against malaria than pyrethroid-only nets or pyrethroid-PBO nets.
Pyrethroid-chlorfenapyr nets against pyrethroid-PBO nets: new suggestion
In areas with pyrethroid resistance, WHO is making a conditional recommendation to use pyrethroid-chlorfenapyr ITNs rather than pyrethroid-PBO nets to prevent malaria in adults and children. The WHO Guidelines Review Group (GDG) determined that the balance of favorable and unfavorable effects likely favors pyrethroid-chlorfenapyr nets over pyrethroid-PBO nets, which is the basis for the recommendation’s conditionality. The recommendation is supported by data from just one African court case. pyrethroid-pyriproxyfen nets are now advised in preference to pyrethroid-only nets.
In places where pyrethroid resistance is present, WHO is making a conditional recommendation to use pyrethroid-pyriproxyfen nets rather than pyrethroid-only nets to prevent malaria in adults and children. The GDG’s worries about the inferior cost-effectiveness of pyrethroid-pyriproxyfen nets compared to pyrethroid-only nets are the basis for the recommendation’s conditionality; the additional funds now needed to buy these ITNs could have a detrimental effect on coverage and equity.
In place of pyrethroid-PBO nets, WHO has issued a conditional recommendation against using pyrethroid-pyriproxyfen nets. The conditionality of the recommendation is based on the GDG’s assessment that pyrethroid-PBO nets are more cost-effective than pyrethroid-pyriproxyfen nets given the balance of effects in favor of the former.
Novel recommendations for ITN prioritizing in environments with limited resources
In addition to the updated recommendations, WHO is also releasing updated advice to assist national malaria programs in choosing which mosquito nets to prioritize in environments with constrained resources. In order to ensure ITN coverage for vulnerable groups, including children under the age of five and pregnant women, this guidance first concentrates on planning for high-volume net distribution campaigns. Any nations installing ITNs can use the guidance, which is based on best practices developed in Africa recently, as part of their prioritizing procedures.
Risks to ITNs, a vital tool for preventing malaria
ITNs have considerably aided in the worldwide decline in malaria cases during the past 20 years. According to a 2015 modeling research reported in Nature, ITNs, particularly in regions with moderate to high transmission, were mostly responsible for the decreases in malaria cases observed between 2005 and 2015. However, development has stalled since 2015. The most well-known danger to the efficacy of ITNs, according to the most recent World Malaria Report from the WHO, is the emergence and widespread geographic spread of pyrethroid resistance in mosquitoes that transmit malaria.
Additional risks to this important preventive measure include inadequate access and coverage, problems with the physical and chemical durability of nets, and a change in mosquito behavior that appears to be biting early in the evening and resting outside while avoiding insecticide exposure.
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