Piperonyl butoxide (PBO) combined with pyrethroids in insecticide‐treated nets to prevent malaria in Africa
Bed nets treated with pyrethroid insecticides are an effective way to reduce malaria transmission and have been deployed across Africa. However, mosquitoes that spread malaria are now developing resistance to this type of insecticide. One way to overcome this resistance is to add another chemical, piperonyl butoxide (PBO), to the net. PBO is not an insecticide but blocks the substance (an enzyme) inside the mosquito that stops pyrethroids working.
What is the aim of this review?
The aim of this Cochrane Review was to find out if pyrethroid‐PBO nets add additional protection against malaria when compared to standard pyrethroid‐only nets.
Pyrethroid‐PBO nets are more effective than standard pyrethroid‐only nets in killing mosquitoes and preventing them from blood feeding in areas where the mosquito populations are very resistant to pyrethroid insecticides (high‐certainty evidence). Pyrethroid‐PBO nets probably reduce the number of malaria infections (moderate‐certainty evidence), although further high‐quality studies measuring clinical outcomes are needed.
What was studied in the review?
We included 15 trials conducted between 2010 to 2018 that compared standard pyrethroid nets to pyrethroid‐PBO nets. These consisted of two laboratory trials, eight experimental hut trials that measured the impact of the pyrethroid‐PBO nets on a wild population of mosquitoes, and five village trials. Only one village trial measured the impact of pyrethroid‐PBO nets on malaria infection in humans; all other studies recorded the impact on mosquito populations. We analysed all studies to determine whether the pyrethroid‐PBO nets were better at killing mosquitoes and preventing them from blood feeding. For the single clinical trial, we examined whether pyrethroid‐PBO nets reduced the number of malaria infections. As the benefit of adding PBOto nets is likely to depend on the level of pyrethroid resistance in the mosquito population, we performed separate analyses for studies conducted in areas of high‐, medium‐, and low‐levels of pyrethroid resistance.
What are the main results of the review?
Where mosquitoes show high levels of resistance to pyrethroids, pyrethroid‐PBO nets perform better than standard pyrethroid‐only nets at killing mosquitoes and preventing them from blood feeding. As expected, this effect is not seen in areas where the mosquitoes show low or no resistance to the pyrethroid‐only insecticides. Only one trial looked at the impact of using pyrethroid‐PBO nets on the number of people infected with the malaria parasite. This trial, involving 3966 participants and conducted in an area where mosquitoes are very resistant to pyrethroids, found that fewer people were infected with malaria when the population used pyrethroid‐PBO nets compared to standard pyrethroid‐only nets.