Since 2005, more than 2 billion insecticide-treated nets (ITNs) have been distributed globally to prevent malaria, but they have all been treated with pyrethroids. However, as many mosquitoes have developed resistance to pyrethroids, nets treated with other active ingredients are now necessary for malaria control.
In 2017, the World Health Organization (WHO) began recommending a new type of ITN that combines pyrethroids with piperonyl-butoxide (PBO), which enhances the potency of pyrethroids against resistant mosquitoes.
Today, the WHO Guidelines for malaria have published new recommendations covering two new classes of dual-ingredient ITNs with different modes of action:
- Pyrethroid-chlorfenapyr nets, which combine a pyrethroid and a pyrrole insecticide to increase the net’s killing effect.
- Pyrethroid-pyriproxyfen nets, which combine a pyrethroid with an insect growth regulator (IGR) that disrupts mosquito growth and reproduction.
Dr Jan Kolaczinski, who heads the Vector Control and Insecticide Resistance unit within the WHO Global Malaria Programme, explains that these new types of nets have been designed to have a greater impact against pyrethroid-resistant mosquitoes. By incorporating two active ingredients in an ITN, the probability of mosquitoes developing resistance to both is significantly reduced.