Insecticide treated nets
WHO recommends the use of insecticide-treated nets (ITNs), which in many settings are long-lasting insecticidal net products, as a core intervention to provide partial protection to populations at risk of malaria. An ITN may repel, kill or sterilize mosquitoes that come into contact with the insecticide or other active ingredients on the netting material. Beyond the personal protection provided, ITNs can have a community effect, whereby even members of the community who do not sleep under a net may still have some protection from malaria if a large proportion of the community uses ITNs. To date, pyrethroid insecticides are used in all the ITNs that have been comprehensively evaluated by WHO. ITNs containing other active ingredients have not yet been evaluated for their epidemiological impact, but some new products have been prequalified. These exceptions were made to support the transition from the former WHO Pesticide Evaluation Programme (WHOPES) to a new WHO evaluation process for vector control products led by PQT-VC.
The following ITNs are under review by VCAG.
1.1 Pyrethroid–piperonyl butoxide net
How the intervention works: These nets contain both a pyrethroid insecticide and the synergist piperonyl butoxide (PBO). PBO increases the potency of certain insecticides by inhibiting metabolic enzymes in the mosquito that otherwise detoxify insecticides. The addition of PBO to an ITN enhances the killing effect of pyrethroids, particularly in mosquito populations that have developed metabolic resistance.
Disease(s) that may be reduced in prevalence or prevented: Malaria
Population(s) intended to be protected: Populations living in areas endemic for malaria in which mosquitoes have become resistant to pyrethroids.
Status of review: Pyrethroid–PBO nets received, exceptionally, a conditional policy recommendation1 by WHO in 2017 on the basis of evidence from only one clinical trial, based on a single pyrethroid–PBO net.2 A second trial is under way, the results of which will be assessed by VCAG in 2020 to determine whether a full recommendation for this intervention class is warranted. Pyrethroid–PBO nets are currently recommended by WHO for deployment instead of pyrethroid-only long-lasting insecticidal nets in areas where the main malaria vector(s) have pyrethroid resistance that is: (i) confirmed, (ii) of intermediate level and (iii) conferred (at least in part) by a monooxygenase-based resistance mechanism, as determined by standard procedures.3
1.2 Pyrethroid – chlorfenapyr net
How the intervention works: An example of a product being evaluated under this intervention class is the Interceptor® G2 insecticide-treated net. This net contains a pyrethroid (alpha-cypermethrin) and chlorfenapyr. Chlorfenapyr is an insecticide repurposed from agriculture that disrupts the insect’s ability to produce energy, thus killing it.
Disease(s) that may be reduced in prevalence or prevented: Malaria
Population(s) intended to be protected: Populations living in areas endemic for malaria, including in settings where mosquitoes have pyrethroid resistance.
Status of review: VCAG has reviewed 2 epidemiological trial protocols. One trial commenced in early 2019, and the other started at the beginning of 2020. A policy recommendation will be developed as soon as data from both trials have been received by WHO and reviewed by VCAG. Interceptor® G2 will also be deployed and monitored in pilot studies conducted in a number of countries through the New Nets Project of the Global Fund and Unitaid.4 Under the former WHOPES evaluation process, Interceptor® G2 was granted an interim recommendation. Following the transition to the new WHO evaluation system for vector control interventions, it is now listed as a WHO-prequalified vector control product.
1.3 Pyrethroid plus insect growth regulator net
How the intervention works: An example of a product being evaluated under this intervention class is the Royal Guard® insecticide-treated net. This net contains a pyrethroid (alpha-cypermethrin) plus an insect growth regulator (pyriproxyfen). Pyriproxyfen was added to sterilize female mosquitoes that might survive exposure to a pyrethroid alone (probably because of resistance), so that they are unable to have offspring. The nets are intended to enhance control of pyrethroid-resistant mosquitoes. The intended benefit of sterilizing female mosquitoes is an overall reduction in the vector population.
Disease(s) that may be reduced in prevalence or prevented: Malaria
Population(s) intended to be protected: Populations living in areas endemic for malaria, including in settings where mosquitoes have pyrethroid resistance.
Status of review: VCAG reviewed 2 epidemiological trial protocols. One trial commenced in early 2019, and the other started at the beginning of 2020. A policy recommendation will be developed as soon as data from both trials have been received by WHO and reviewed by VCAG. Royal Guard® will also be deployed and monitored in pilot studies conducted in a number of countries through the New Nets Project of the Global Fund and Unitaid.4 A policy recommendation will be developed once data from both trials have been received by WHO and reviewed by VCAG. Royal Guard® was under WHOPES review at the time of transition to the new WHO evaluation system for vector control interventions and was subsequently reviewed and prequalified by PQT-VC.
Notes:
1. WHO does not usually issue conditional policy recommendations.
2. See recommendation 4 in Conditions for deployment of mosquito nets treated with a pyrethroid and piperonyl butoxide.
Geneva: World Health Organization; 2017.
3. Test procedures for insecticide resistance monitoring in malaria vector mosquitoes, 2nd edition.
Geneva: World Health Organization; 2016.
4. The New Nets Project in partnership with the Global Fund. In: Unitaid [www.unitaid.org].
Geneva: Unitaid.