Evaluation of efficacy of Interceptor® G2, a long-lasting insecticide net coated with a mixture of chlorfenapyr and alpha-cypermethrin, against pyrethroid resistant Anopheles gambiae s.l. in Burkina Faso

Koama Bayili, Severin N'do, Moussa Namountougou, Roger Sanou, Abdoulaye Ouattara, Roch K Dabiré, Anicet G Ouédraogo, David Malone, Abdoulaye Diabaté, Koama Bayili, Severin N'do, Moussa Namountougou, Roger Sanou, Abdoulaye Ouattara, Roch K Dabiré, Anicet G Ouédraogo, David Malone, Abdoulaye Diabaté

Abstract

Background: Malaria vectors have acquired widespread resistance throughout sub-Saharan Africa to many of the currently used insecticides. Hence, there is an urgent need to develop alternative strategies including the development of new insecticides for effective management of insecticide resistance. To maintain progress against malaria, it is necessary to identify other residual insecticides for mosquito nets. In the present WHOPES phase II analogue study, the utility of chlorfenapyr, a pyrrole class insecticide mixed with alpha-cypermethrin on a long-lasting mosquito bed net was evaluated against Anopheles gambiae s.l.

Methods: Bed nets treated with chlorfenapyr and alpha-cypermethrin and mixture of both compounds were tested for their efficacy on mosquitoes. Washed (20 times) and unwashed of each type of treated nets and were tested according to WHOPES guidelines. Efficacy of nets were expressed in terms of blood-feeding inhibition rate, deterrence, induced exophily and mortality rate. The evaluation was conducted in experimental huts of Vallée du Kou seven (VK7) in Burkina Faso (West Africa) following WHOPES phase II guidelines. In addition, a WHOPES phase I evaluation was also performed.

Results: Mixture treated nets killed significantly (P < 0.05) more mosquitoes than solo alpha-cypermethrin nets, unwashed and washed. Proportionally, this equated to mortalities of 78 and 76% (for mixture nets) compared to only 17 and 10% (for solo alpha-cypermethrin) to An. gambiae, respectively. In contrast mixture net proportions were not significantly (P > 0.05) different from nets treated with chlorfenapyr 200 mg/m2 unwashed (86%). The washed and unwashed nets treated with the mixtures resulted in personal protection against An. gambiae s.l. biting 34 and 44%. In contrast the personal protection observed for washed and unwashed alpha-cypermethrin treated nets generated (14 and 24%), and chlorfenapyr solo treated net was rather low (22%).

Conclusion: Among all nets trialled, the combination of chlorfenapyr and alpha-cypermethrin on bed nets provided better mortality in phase II after 20 washes. Results suggest that this combination could be a potential insecticide resistance management tool for preventing malaria transmission in areas compromised by the spread of pyrethroid resistance.

Keywords: Anopheles gambiae; Bed net; Chlorfenapyr; Insecticide; Malaria; Pyrethroid resistance.

Figures

Fig. 1
Fig. 1
Blood feeding inhibition rates of Anopheles gambiae s.l. collected in experimental huts with treatments relative to control. Means comparison values for histograms sharing the same letter label are not significantly different (P > 0.05). Error bars represent 95% confidence intervals
Fig. 2
Fig. 2
Mortality rates of An. gambiae s.l. collected in experimental huts with treatments versus untreated control. Means separation values for histograms sharing the same letter label are not significantly different (P > 0.05). Error bars represent 95% confidence intervals. Asterisk denoted highly significant
Fig. 3
Fig. 3
Mortality of An. gambiae adult females that were field collected as larvae from Vallée du Kou. Cone test bioassays were conducted in situ
Fig. 4
Fig. 4
Insecticide concentration in a.i. mg/m2 of Interceptor G2 on initial and used nets

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