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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)