Efficacy of PermaNet® 2.0 and PermaNet® 3.0 against insecticide-resistant Anopheles gambiae in experimental huts in Cote d'Ivoire

Background: Pyrethroid resistance in vectors could limit the efficacy of long-lasting insecticidal nets (LLINs) because all LLINs are currently treated with pyrethroids. The goal of this study was to evaluate the efficacy and wash resistance of PermaNet (R) 3.0 compared to PermaNet (R) 2.0 in an area of high pyrethroid in Cote d'Ivoire. PermaNet (R) 3.0 is impregnated with deltamethrin at 85 mg/m(2) on the sides of the net and with deltamethrin and piperonyl butoxide on the roof. PermaNet (R) 2.0 is impregnated with deltamethrin at 55 mg/m(2) across the entire net. Methods: The study was conducted in the station of Yaokoffikro, in central Cote d'Ivoire. The efficacy of intact unwashed and washed LLINs was compared over a 12-week period with a conventionally-treated net (CTN) washed to just before exhaustion. WHO cone bioassays were performed on sub-sections of the nets, using wild-resistant An. gambiae and Kisumu strains. Mosquitoes were collected five days per week and were identified to genus and species level and classified as dead or alive, then unfed or blood-fed. Results: Mortality rates of over 80% from cone bioassays with wild-caught pyrethroid-resistant An. gambiae s.s were recorded only with unwashed PermaNet (R) 3.0. Over 12 weeks, a total of 7,291 mosquitoes were collected. There were significantly more An. gambiae s.s and Culex spp. caught in control huts than with other treatments (P < 0.001). The proportion of mosquitoes exiting the huts was significantly lower with the control than for the treatment arms (P < 0.001). Mortality rates with resistant An. gambiae s.s and Culex spp, were lower for the control than for other treatments (P < 0.001), which did not differ (P > 0.05) except for unwashed PermaNet (R) 3.0 (P < 0.001), which gave significantly higher mortality (P < 0.001). Conclusions: This study showed that unwashed PermaNet (R) 3.0 caused significantly higher mortality against pyrethroid resistant An. gambiae s.s and Culex spp than PermaNet (R) 2.0 and the CTN. The increased efficacy with unwashed PermaNet (R) 3.0 over PermaNet (R) 2.0 and the CTN was also demonstrated by higher KD and mortality rates (KD > 95% and mortality rate > 80%) in cone bioassays performed with wild pyrethroid-resistant An. gambiae s.s from Yaokoffikro.