Community evaluation of the physical and insecticidal durability of DuraNet® Plus, an alpha-cypermethrin and piperonyl butoxide incorporated mosquito net: protocol for a multi-country study in West, Central and East Africa

Abstract

Background Pyrethroid-PBO nets have demonstrated improved impact against clinical malaria transmitted by pyrethroid resistant mosquito vectors and are being scaled up across Africa. However very little is known about their physical and insecticidal durability under operational conditions. This study will investigate the attrition, fabric integrity, insecticide content and bioefficacy of DuraNet® Plus, a new WHO prequalified alphacypermethrin and PBO incorporated net developed by Shobikaa Impex Private Limited over 3 years of field use in communities in Benin, Cameroon and Tanzania. Methods The study will be conducted in parallel in selected villages in Zakpota District in Benin, Mbalmayo, District in Cameroon and Muheza District in Tanzania. In each country, ~ 1800 households will be recruited and randomised to receive DuraNet® Plus or DuraNet® (a WHO prequalified alphacypermethrin-only ITN). Follow up surveys will be performed at 1 month post distribution to investigate adverse events and subsequently every 6–12 months to assess ITN attrition and fabric integrity following standard WHO procedures. A second cohort of nets will be withdrawn every 6–12 months and assessed for alpha-cypermethrin and PBO content and for entomological activity in laboratory bioassays (cone bioassays and tunnel tests). Alpha-cypermethrin bioefficacy will be monitored using the susceptible Anopheles gambiae Kisumu strain in cone bioassays while PBO bioefficacy will be monitored using pyrethroid resistant strains with overexpressed P450 enzymes in tunnel tests to determine the proportion of efficacious nets (≥ 95% knockdown, ≥ 80% mortality or ≥ 90% blood feeding inhibition in tunnels) at each time point. Nets withdrawn at 12, 24 and 36 months from each country will also be tested in experimental hut trials against wild free-flying pyrethroid resistant Anopheles gambiae sl in Côvè Benin to investigate the superiority of DuraNet® Plus over DuraNet® at each time point under semi field conditions. Conclusion This large-scale multi country trial will provide useful information on the durability of a pyrethroid-PBO net (DuraNet® Plus) in 3 different regions in sub-Saharan Africa. The methods proposed for bioefficacy testing could also contribute towards the development of new standardised guidelines for monitoring the insecticidal efficacy of pyrethroid-PBO nets under operational conditions.

Evaluating the attrition, fabric integrity and insecticidal durability of two dual active ingredient nets (Interceptor® G2 and Royal® Guard): methodology for a prospective study embedded in a cluster randomized controlled trial in Benin

“…Despite the methodological modifications we propose for laboratory bioassays in this study, it is unclear whether typical ITN laboratory bioassay techniques (cone bioassays and tunnel tests) would be sufficiently informative of the insecticidal durability of dual AI ITNs as these methods were developed for pyrethroid-only ITNs [ 22 , 23 ]. Other bioassay methods under consideration for dual AI ITNs are the WHO wire ball assay [ 13 , 40 ] and the net-in-tube test [ 22 ] that provide a more forced contact between the mosquito and the net potentially resulting in greater levels of AI pick up from the net than in cone bioassays.…”

“…Laboratory bioassay methods and strains used for assessing their bioefficacy on ITNs must, therefore, be aligned with the mode of action of these insecticides. In addition to bioassays (cone bioassays and tunnel tests), experimental hut trials have also been proposed as a suitable method for investigating the insecticidal durability of ITNs under operational conditions [ 22 , 23 ]. Using hut trials, ITNs can be assessed against wild free-flying mosquito vectors providing more realistic estimates of their capacity to provide personal and community protection to householders as they age.…”