Due to the rapid extension of pyrethroid resistance in malaria vectors worldwide, manufacturers are developing new vector control tools including insecticide mixtures containing at least two active ingredients with different mode of action as part of insecticide resistance management. Olyset® Plus is a new long-lasting insecticidal net (LLIN) incorporating permethrin and a synergist, piperonyl butoxide (PBO), into its fibres in order to counteract metabolic-based pyrethroid resistance of mosquitoes. In this study, we evaluated the efficacy of Olyset® Plus both in laboratory and field against susceptible and multi-resistant malaria vectors and compared with Olyset Net, which is a permethrin incorporated into polyethylene net. In laboratory, Olyset® Plus performed better than Olyset® Net against susceptible Anopheles gambiae strain with a 2-day regeneration time owing to an improved permethrin bleeding rate with the new incorporation technology. It also performed better than Olyset® Net against multiple resistant populations of An. gambiae in experimental hut trials in West Africa. Moreover, the present study showed evidence for a benefit of incorporating a synergist, PBO, with a pyrethroid insecticide into mosquito netting. These results need to be further validated in a large-scale field trial to assess the durability and acceptability of this new tool for malaria vector control.

BackgroundDetermination of residual activity of insecticides is essential information for the selection of appropriate indoor spraying operation. The present study was undertaken to evaluate the residual effect of three candidate insecticide formulations on different indoor surfaces in order to guide future interventions, in the context of Cameroon and other African countries.MethodsThe study was conducted in the Ntougou neighbourhood in Yaoundé (capital city of Cameroon). Bendiocarb WP, lambda-cyhalothrin CS and deltamethrin WG were sprayed on the indoor wall surfaces of local cement, wood and mud houses. Their effects on the knockdown and mortality of the Kisumu susceptible strain of Anopheles gambiae s.s were assessed each month from March to September 2009, using the WHO plastic cones test. Knockdown and mortality rates were compared between different surfaces using Chi-square test. A Kaplan-Meir model was used to estimate the time of treatment failure.ResultsWith bendiocarb WP, the knockdown rates were frequently above 98% during 13 weeks after spraying, except on mud walls where it significantly decreased at the 13th week (P < 0.05). With lambda cyhalothrin CS, the knockdown rates remained 100% on wood surfaces during the 26 weeks trial. However, it significantly decreased on concrete and mud surfaces from the 11th (83%) and the 20th (88%) weeks respectively (P < 0.05). With deltamethrin WG, it remained high on concrete surfaces during 26 weeks (> 98%); while it varied between 60 and 100% on wood or mud surfaces. The survival estimates of bendiocarb WP treatments remaining effective in killing An. gambiae s.s. (mortality rate ≥ 80%) was > 13 weeks on cement and wood surfaces and 13 weeks on mud surfaces. Those of lambda-cyhalothrin CS were > 26 weeks on wood surfaces, and 20 weeks on concrete and mud surfaces. By contrast, those of deltamethrin WG were 26 weeks on concrete, 20 weeks on mud surfaces and 15 weeks on wood surfaces.ConclusionCurrent data suggest variable durations of spray cycles for each product, according to the type of wall surfaces, highlighting the importance of testing candidate products in local context before using them in large scale.

Background Effective malaria control relies on evidence-based interventions. Anopheline behaviour and Plasmodium infections were investigated in North Cameroon, following long-lasting insecticidal net (LLIN) distribution in 2010. Methods During four consecutive years from 2011 to 2014, adult mosquitoes were collected indoors, outdoors and in exit traps across 38 locations in the Garoua, Pitoa and Mayo-Oulo health districts. Anophelines were morphologically and molecularly identified, then analysed for blood meal origins and Plasmodium falciparum circumsporozoite protein ( Pf -CSP). Blood from children under 5 years-old using LLINs was examined for Plasmodium infections. Results Overall, 9376 anophelines belonging to 14 species/sibling species were recorded. Anopheles gambiae ( s.l. ) [ An. arabiensis (73.3%), An. coluzzii (17.6%) and An. gambiae ( s.s. ) (9.1%)] was predominant (72%), followed by An. funestus ( s.l. ) (20.5%) and An. rufipes (6.5%). The recorded blood meals were mainly from humans (28%), cattle (15.6%) and sheep (11.6%) or mixed (45%). Pf -CSP rates were higher indoors (3.2–5.4%) versus outdoors (0.8–2.0%), and increased yearly ( χ 2 < 18, df = 10, P < 0.03). Malaria prevalence in children under 5 years-old, in households using LLINs was 30% (924/3088). Conclusions The present study revealed the variability of malaria vector resting and feeding behaviour, and the persistence of Plasmodium infections regardless the use of LLINs. Supplementary interventions to LLINs are therefore needed to sustain malaria prevention in North Cameroon.