Update: Piperonyl butoxide (PBO) combined with pyrethroids in insecticide‐treated nets to prevent malaria in Africa

24 May 2021

Pyrethroid‐PBO nets to prevent malaria


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 it blocks the substance (an enzyme) inside the mosquito that stops pyrethroids from working.

What is the aim of this review?

The aim of this Cochrane Review was to find out if pyrethroid‐PBO nets provide additional protection against malaria when compared to standard pyrethroid‐only nets.

Key messages

Pyrethroid‐PBO nets were more effective than standard pyrethroid‐only nets in killing mosquitoes and preventing blood feeding in areas where mosquito populations are very resistant to pyrethroid insecticides (high‐certainty evidence). Pyrethroid‐PBO nets reduced the number of malaria infections in areas of high pyrethroid resistance (moderate‐certainty evidence), although further studies are needed to measure clinical outcomes for the full lifetime of the net.

What was studied in the review?

We included 16 trials conducted between 2010 and 2020 that compared standard pyrethroid nets to pyrethroid‐PBO nets. These consisted of 10 experimental hut trials that measured the impact of pyrethroid‐PBO nets on a wild population of mosquitoes, four village trials, and two cRCTs. The two cRCTs measured the impact of pyrethroid‐PBO nets on malaria infection in humans; all other studies recorded their impact on mosquito populations. We analysed hut and village studies to determine whether pyrethroid‐PBO nets were better for killing mosquitoes and preventing them from blood feeding. For both cRCT trials, we examined whether pyrethroid‐PBO nets reduced the number of malaria infections. As the benefit of adding PBO to 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?

When mosquitoes show high levels of resistance to pyrethroids, pyrethroid‐PBO nets perform better than standard pyrethroid‐only nets for killing mosquitoes and preventing them from blood feeding. As expected, this effect is not seen in areas where mosquitoes show low or no resistance to pyrethroid‐only insecticides. Two trials looked at the impact of using pyrethroid‐PBO nets on the number of people infected with the malaria parasite. These trials, involving 10,603 participants in total 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 than when standard pyrethroid‐only nets were used.

How up‐to‐date is this review?

We searched for all studies and trials that had been published up to 25 September 2020.