Culicidae diversity, malaria transmission and insecticide resistance alleles in malaria vectors in Ouidah-Kpomasse-Tori district from Benin (West Africa): A pre-intervention study

Parasites & Vectors, Sep 2010

Background To implement an Insecticide Resistance Management (IRM) strategy through a randomized controlled trial (phase III), 28 villages were selected in southern Benin. No recent entomological data being available in these villages, entomological surveys were performed between October 2007 and May 2008, before vector control strategies implementation, to establish baseline data. Methods Mosquitoes were sampled by human landing collection (16 person-nights per village per survey per village) during 5 surveys. Mosquitoes were identified morphologically and by molecular methods. The Plasmodium falciparum circumsporozoïte indexes were measured by ELISA, and the entomological inoculation rates (EIRs) were calculated. Molecular detection of pyrethroid knock down resistance (Kdr) and of insensitive acetylcholinesterase were performed. Results 44,693 mosquitoes belonging to 28 different species were caught from October 2007 to May 2008. Among mosquitoes caught, 318 were An. gambiae s.s., 2 were An. nili, 568 were An. funestus s.s., and one individual was An. leesoni. EIR was 2.05 ± 1.28 infective bites per human per 100 nights on average, of which 0.67 ± 0.60 were from An. funestus and 1.38 ± 0.94 infective bites were from An. gambiae. Important variations were noted between villages considering mosquito density and malaria transmission indicating a spatial heterogeneity in the study area. The kdr allelic frequency was 28.86% in An. gambiae s.s. on average and significantly increases from October 2007 (10.26%) to May 2008 (33.87%) in M molecular form of An. gambiae s.s. Ace 1 mutation was found in S molecular of An. gambiae s.s at a low frequency (< 1%). Conclusion This study updates information on mosquito diversity and malaria risk in rural villages from south Benin. It showed a high spatial heterogeneity in mosquito distribution and malaria transmission and underlines the need of further investigations of biological, ecological, and behavioral traits of malaria vectors species and forms. This study is a necessary prerequisite to cartography malaria risk and to improve vector control operations in southern Benin.

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Culicidae diversity, malaria transmission and insecticide resistance alleles in malaria vectors in Ouidah-Kpomasse-Tori district from Benin (West Africa): A pre-intervention study

Parasites & Vectors Culicidae diversity, malaria transmission and insecticide resistance alleles in malaria vectors in Ouidah-Kpomasse-Tori district from Benin (West Africa): A pre-intervention study Armel Djènontin 0 Sahabi Bio-Bangana 0 Nicolas Moiroux Marie-Claire Henry Olayidé Bousari Joseph Chabi Razaki Ossè 0 Sébastien Koudénoukpo 0 Vincent Corbel Martin Akogbéto 0 Fabrice Chandre 0 Centre de Recherche Entomologique de Cotonou (CREC) , 06 BP 2604 Cotonou , Bénin Background: To implement an Insecticide Resistance Management (IRM) strategy through a randomized controlled trial (phase III), 28 villages were selected in southern Benin. No recent entomological data being available in these villages, entomological surveys were performed between October 2007 and May 2008, before vector control strategies implementation, to establish baseline data. Methods: Mosquitoes were sampled by human landing collection (16 person-nights per village per survey per village) during 5 surveys. Mosquitoes were identified morphologically and by molecular methods. The Plasmodium falciparum circumsporozoïte indexes were measured by ELISA, and the entomological inoculation rates (EIRs) were calculated. Molecular detection of pyrethroid knock down resistance (Kdr) and of insensitive acetylcholinesterase were performed. Results: 44,693 mosquitoes belonging to 28 different species were caught from October 2007 to May 2008. Among mosquitoes caught, 318 were An. gambiae s.s., 2 were An. nili, 568 were An. funestus s.s., and one individual was An. leesoni. EIR was 2.05 ± 1.28 infective bites per human per 100 nights on average, of which 0.67 ± 0.60 were from An. funestus and 1.38 ± 0.94 infective bites were from An. gambiae. Important variations were noted between villages considering mosquito density and malaria transmission indicating a spatial heterogeneity in the study area. The kdr allelic frequency was 28.86% in An. gambiae s.s. on average and significantly increases from October 2007 (10.26%) to May 2008 (33.87%) in M molecular form of An. gambiae s.s. Ace 1 mutation was found in S molecular of An. gambiae s.s at a low frequency (< 1%). Conclusion: This study updates information on mosquito diversity and malaria risk in rural villages from south Benin. It showed a high spatial heterogeneity in mosquito distribution and malaria transmission and underlines the need of further investigations of biological, ecological, and behavioral traits of malaria vectors species and forms. This study is a necessary prerequisite to cartography malaria risk and to improve vector control operations in southern Benin. Background Malaria remains a major cause of morbidity and mortality in sub-Saharan Africa and represents one of the most critical public health challenges for Africa. In 2008, 243 million cases of malaria was estimated worldwide leading to 863 000 deaths of which 89% were in the African Region [ 1 ]. Treatment with Artemisinin Combination Therapy (ACT), the use of Indoor Residual Spraying (IRS) and Insecticide Treated Nets (ITNs) represent the main approaches of malaria control [ 1 ]. Household ITNs ownership reached more than 50% in several high burden African countries [ 1 ]. Pyrethroids are the only insecticides used for net impregnation because of their strong efficacy, their fast acting effect at low doses and their low toxicity for mammals [ 2 ]. Unfortunately, pyrethroids resistance in malaria vectors has spread across Africa and is now present in most of countries where national malaria control programmes (NMCP) are implementing large scale distribution of Long Lasting Nets to populations at risk, i.e. children under five and pregnant women [ 3 ]. Up to now, there is no evidence that pyrethroids resistance reduce the effectiveness of ITNs for malaria control at operational scale [ 4 ]. However, a small scale field trial carried out in an area of resistance in southern Benin (Ladji) and Burkina Faso (Kou Valley) showed a reduction of personal protection and overall insecticidal effect of ITNs in experimental huts [ 5-7 ]. It is then urgent to find ways to manage this resistance in malaria vectors. In this context, malaria vectors control and insecticide resistance management tools based on the use (alone or in combination with pyrethroid-treated mosquito nets) of alternative classes of insecticides with different mode of action than pyrethroids were developed and have already been evaluated in experimental huts, with good results against wild populations of strongly resistant An. gambiae [ 6,7 ]. To validate these strategies, their impact on malaria transmission and insecticide resistance dynamic in malaria vectors must be accessed through randomized controlled trials under phase III. For that purpose, 28 villages were selected in Ouidah-Kpomasse-Tori (OKT) health district in southern Benin. No entomological data from OKT health district was available. Recent data relative to Culicidae fauna of Benin go (...truncated)


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Armel Djènontin, Sahabi Bio-Bangana, Nicolas Moiroux, Marie-Claire Henry, Olayidé Bousari, Joseph Chabi, Razaki Ossè, Sébastien Koudénoukpo, Vincent Corbel, Martin Akogbéto, Fabrice Chandre. Culicidae diversity, malaria transmission and insecticide resistance alleles in malaria vectors in Ouidah-Kpomasse-Tori district from Benin (West Africa): A pre-intervention study, Parasites & Vectors, 2010, pp. 83, 3, DOI: 10.1186/1756-3305-3-83