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Search Results: 1 - 10 of 193375 matches for " Frédéric Simard "
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Efficacy of bifenthrin-impregnated bednets against Anopheles funestus and pyrethroid-resistant Anopheles gambiae in North Cameroon
Mouhamadou Chouaibou, Frédéric Simard, Fabrice Chandre, Josiane Etang, Frédéric Darriet, Jean-Marc Hougard
Malaria Journal , 2006, DOI: 10.1186/1475-2875-5-77
Abstract: Bifenthrin was used in this experiment because it is considered a promising candidate for bednets impregnation. Nets were treated at 50 mg/m2, a dose that has high insecticidal activity on kdr mosquitoes and at 5 mg/m2, a dose that kills 95% of susceptible mosquitoes under laboratory conditions with 3 minutes exposure. Bednets were holed to mimic physical damage. The trial was conducted in three experimental huts from Pitoa, North-Cameroon where Anopheles gambiae displays metabolic resistance and cohabits with An. funestus.Bifenthrin at 50 mg/m2 significantly reduced anophelines' entry rate (>80%). This was not observed at 5 mg/m2. Both treatments increased exophily in An. gambiae, and to a lesser extent in An. funestus. With bifenthrin at high dosage, over 60% reduction in blood feeding and 75–90% mortality rates were observed in both vectors. Despite presence of holes, only a single An. gambiae and two An. funestus females were collected inside the treated net, and all were found dead. The same trends were observed with low dosage bifenthrin though in most cases, no significant difference was found with the untreated control net.Bifenthrin-impregnated bednets at 50 mg/m2 were efficient in the reduction of human-vector contact in Pitoa. Considerable personal protection was gained against An. funestus and metabolic pyrethroid resistant An. gambiae populations.Insecticide-treated bednets (ITNs) are being strongly promoted as a malaria control tool in Africa by the World Health Organization and other international agencies [1]. Their efficacy in reducing man-vector contact, malaria morbidity and mortality has been demonstrated in various epidemiological situations [2-5]. With current use of pyrethroids in agriculture and increasing scale of ITNs coverage, selective pressure for pyrethroid resistance in mosquitoes is expected to increase [6,7]. Resistance to pyrethroids has been reported in both Anopheles gambiae and Anopheles funestus in many malaria endemic countries
Genetic Structure of the Tiger Mosquito, Aedes albopictus, in Cameroon (Central Africa)
Basile Kamgang,Cécile Brengues,Didier Fontenille,Flobert Njiokou,Frédéric Simard,Christophe Paupy
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0020257
Abstract: Aedes albopictus (Skuse, 1884) (Diptera: Culicidae), a mosquito native to Asia, has recently invaded all five continents. In Central Africa it was first reported in the early 2000s, and has since been implicated in the emergence of arboviruses such as dengue and chikungunya in this region. Recent genetic studies of invasive species have shown that multiple introductions are a key factor for successful expansion in new areas. As a result, phenotypic characters such as vector competence and insecticide susceptibility may vary within invasive pest species, potentially affecting vector efficiency and pest management. Here we assessed the genetic variability and population genetics of Ae. albopictus isolates in Cameroon (Central Africa), thereby deducing their likely geographic origin.
Kdr-based insecticide resistance in Anopheles gambiae s.s populations in Cameroon: spread of the L1014F and L1014S mutations
Philippe Nwane, Josiane Etang, Mouhamadou Choua?bou, Jean Toto, Rémy Mimpfoundi, Frédéric Simard
BMC Research Notes , 2011, DOI: 10.1186/1756-0500-4-463
Abstract: A total of 1,405 anopheline mosquitoes were collected from 21 localities throughout Cameroon and identified as An. gambiae (N = 1,248; 88.8%), An. arabiensis (N = 120; 8.5%) and An. melas (N = 37; 2.6%). Both kdr alleles 1014F and 1014S were identified in the M and S molecular forms of An. gambiae s.s. The frequency of the 1014F allele ranged from 1.7 to 18% in the M-form, and from 2 to 90% in the S-form. The 1014S allele ranged from 3-15% in the S-form and in the M-form its value was below 3%. Some specimens were found to carry both resistant kdr alleles.This study provides an updated distribution map of the kdr alleles in wild An. gambiae populations in Cameroon. The co-occurrence of both alleles in malaria mosquito vectors in diverse ecological zones of the country may be critical for the planning and implementation of malaria vector control interventions based on IRS and ITNs, as currently ongoing in Cameroon.Insecticide resistance is a major concern in all insect groups that are involved in crop destruction or in disease transmission. Four different types of mechanisms including behavioural avoidance, reduction of cuticle penetration, metabolic detoxification and reduced target-site sensitivity lead to insecticide resistance in many arthropod groups [1]. So far, metabolic detoxification and target site insensitivity have been demonstrated to play major roles in conferring resistance to insecticides in some arthropods [2]. While metabolic resistance is due to changes in the arthropod enzyme activity resulting in the detoxification or sequestration of the insecticide, target site insensitivity is due to mutations preventing the binding of the insecticide to its target [3].The target site of DDT and pyrethroid insecticides is the voltage-gated sodium channel. Different point mutations identified in the S6 transmembrane segment of domain II of this para-type sodium channel gene cause a change in affinity between insecticide and its binding site. This induces a phen
Design of a Two-level Adaptive Multi-Agent System for Malaria Vectors driven by an ontology
Guillaume Koum, Augustin Yekel, Bengyella Ndifon, Josiane Etang, Frédéric Simard
BMC Medical Informatics and Decision Making , 2007, DOI: 10.1186/1472-6947-7-19
Abstract: To solve the problem we define an Adaptive Multi-Agent System (AMAS) which has the property to be elastic and is a two-level system as well. This AMAS is a dynamic system where the two levels are linked by an Ontology which allows it to function as a reduced system and as an extended system. In a primary level, the AMAS comprises organization agents and in a secondary level, it is constituted of analysis agents. Its entry point, a User Interface Agent, can reproduce itself because it is given a minimum of background knowledge and it learns appropriate "behavior" from the user in the presence of ambiguous queries and from other agents of the AMAS in other situations.Some of the outputs of our system present a series of tables, diagrams showing some factors like Entomological parameters of malaria transmission, Percentages of malaria transmission per malaria vectors, Entomological inoculation rate. Many others parameters can be produced by the system depending on the inputted data.Our approach is an intelligent one which differs from statistical approaches that are sometimes used in the field. This intelligent approach aligns itself with the distributed artificial intelligence. In terms of fight against malaria disease our system offers opportunities of reducing efforts of human resources who are not obliged to cover the entire territory while conducting surveys. Secondly the AMAS can determine the presence or the absence of malaria vectors even when specific data have not been collected in the geographical area. In the difference of a statistical technique, in our case the projection of the results in the field can sometimes appeared to be more general.Malaria affects hundred of millions of people in the world, particularly in under developed countries. Recent studies carried out show that, malaria is the leading cause of morbidity and mortality. Death rate remains particularly high among children and pregnant women, especially from poor backgrounds. In Cameroon, sta
Insertion polymorphisms of SINE200 retrotransposons within speciation islands of Anopheles gambiae molecular forms
Federica Santolamazza, Emiliano Mancini, Frédéric Simard, Yumin Qi, Zhijian Tu, Alessandra della Torre
Malaria Journal , 2008, DOI: 10.1186/1475-2875-7-163
Abstract: A SINE-PCR approach was carried out on thirteen SINE200 insertions in M and S females collected along the whole range of distribution of A. gambiae s.s. in sub-Saharan Africa. Ten specimens each for Anopheles arabiensis, Anopheles melas, Anopheles quadriannulatus A and 15 M/S hybrids from laboratory crosses were also analysed.Eight loci were successfully amplified and were found to be specific for A. gambiae s.s.: 5 on 2L chromosome and one on X chromosome resulted monomorphic, while two loci positioned respectively on 2R (i.e. S200 2R12D) and X (i.e. S200 X6.1) chromosomes were found to be polymorphic. S200 2R12D was homozygote for the insertion in most S-form samples, while intermediate levels of polymorphism were shown in M-form, resulting in an overall high degree of genetic differentiation between molecular forms (Fst = 0.46 p < 0.001) and within M-form (Fst = 0.46 p < 0.001). The insertion of S200 X6.1 was found to be fixed in all M- and absent in all S-specimens. This led to develop a novel easy-to-use PCR approach to straightforwardly identify A. gambiae molecular forms. This novel approach allows to overcome the constraints associated with markers on the rDNA region commonly used for M and S identification. In fact, it is based on a single copy and irreversible SINE200 insertion and, thus, is not subjected to peculiar evolutionary patterns affecting rDNA markers, e.g. incomplete homogenization of the arrays through concerted evolution and/or mixtures of M and S IGS-sequences among the arrays of single chromatids.The approach utilized allowed to develop new easy-to-use co-dominant markers for the analysis of genetic differentiation between M and S-forms and opens new perspectives in the study of the speciation process ongoing within A. gambiae.Anopheles gambiae sensu stricto (s.s.) is the most important vector of human malaria in Africa, causing 90% of the fatalcases worldwide [1]. It is believed that the differentiation of this very synanthropic and anthrop
Behavioural responses of Anopheles gambiae sensu stricto M and S molecular form larvae to an aquatic predator in Burkina Faso
Geoffrey Gimonneau, Marco Pombi, Roch K Dabiré, Abdoulaye Diabaté, Serge Morand, Frédéric Simard
Parasites & Vectors , 2012, DOI: 10.1186/1756-3305-5-65
Abstract: Larvae used in these experiments were obtained from eggs laid by wild female An. gambiae collected from two localities in south-western Burkina Faso during the 2008 rainy season. Single larvae were observed in an experimental arena, and behavioural traits were recorded and quantified a) in the absence of a predator and b) in the presence of a widespread mosquito predator, the backswimmer Anisops jaczewskii. Differences in the proportion of time allocated to each behaviour were assessed using Principal Component Analysis and Multivariate Analysis of Variance.The behaviour of M and S form larvae was found to differ significantly; although both forms mainly foraged at the water surface, spending 60-90% of their time filtering water at the surface or along the wall of the container, M form larvae spent on average significantly more time browsing at the bottom of the container than S form larvae (4.5 vs. 1.3% of their overall time, respectively; P < 0.05). In the presence of a predator, larvae of both forms modified their behaviour, spending significantly more time resting along the container wall (P < 0.001). This change in behaviour was at least twice as great in the M form (from 38.6 to 66.6% of the time at the wall in the absence and presence of the predator, respectively) than in the S form (from 48.3 to 64.1%). Thrashing at the water surface exposed larvae to a significantly greater risk of predation by the notonectid (P < 0.01), whereas predation occurred significantly less often when larvae were at the container wall (P < 0.05) and might reflect predator vigilance.Behavioural differences between larvae of the M and S form of An. gambiae in response to an acute predation risk is likely to be a reflection of different trade-offs between foraging and predator vigilance that might be of adaptive value in contrasting aquatic ecosystems. Future studies should explore the relevance of these findings under the wide range of natural settings where both forms co-exist in A
Notes on the blood-feeding behavior of Aedes albopictus (Diptera: Culicidae) in Cameroon
Basile Kamgang, Elysée Nchoutpouen, Frédéric Simard, Christophe Paupy
Parasites & Vectors , 2012, DOI: 10.1186/1756-3305-5-57
Abstract: Analysis of ingested blood in outdoor-resting females showed that Ae. albopictus preferentially fed on humans rather than on available domestic animals (95% of the blood meals contained human blood). Our results further showed that Ae. albopictus is a day-biting species in Yaoundé, with a main peak of activity in the late afternoon.This is the first report on the feeding behavior of Ae. albopictus in Central Africa. The species is highly aggressive to humans and might therefore be involved in human-human virus transmission in this setting.Aedes albopictus (Skuse, 1894) is an invasive mosquito species that originated in Asian forests [1] and expanded to temperate and tropical regions of America, Africa and Europe, mainly during the last three decades [2]. Aedes albopictus is widely considered as a secondary vector of human arboviruses such as dengue virus (DENV), because it is thought to preferentially feed on animals rather than humans, contrary to the highly anthropophilic Aedes aegypti (L., 1762) [3]. Yet, Ae. albopictus has been incriminated as a primary vector in recent chikungunya virus (CHIKV) epidemics in the Indian Ocean, Central Africa and Europe [4-6], suggesting sustained man-vector contact in these settings. In Cameroon (Central Africa), Ae. albopictus was first recorded in the early 2000s [7] and rapidly spread throughout the south of the country [8]. In Cameroonian urban centers such as Yaoundé, the species now pullulates [9] and is gradually replacing autochthonous Ae. aegypti populations. Concomitant with the spread of Ae. albopictus in Central Africa, an increase in DENV and CHIKV outbreaks was reported in a number of countries, including Cameroon [10], Gabon [5,11] and the Republic of Congo [12]. Indeed, Cameroonian Ae. albopictus populations were shown to be orally susceptible to DEN-2 virus and CHIKV infection [5], and the species was recognized as the main vector of both viruses in 2007 in Libreville, Gabon [5,11].Although Ae. albopictus prefere
New Insights into the Population Structure of Anopheles gambiae s.s. in the Gulf of Guinea Islands Revealed by Herves Transposable Elements
Patrícia Salgueiro, Marta Moreno, Frédéric Simard, David O'Brochta, Jo?o Pinto
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0062964
Abstract: Transposable elements (TEs) are mobile portions of DNA that are able to replicate and spread in the genome of many organisms. TEs can be used as a means to insert transgenes in insects, being stably inherited throughout generations. Anopheles gambiae is the main vector of human malaria in Sub-Saharan Africa. Given the extraordinary burden this disease imposes, the mosquito became a choice target for genetic control approaches with the purpose of reducing malaria transmission. In this study, we investigated the abundance and distribution of Herves TE in An. gambiae s.s. from Cameroon and four islands in the Gulf of Guinea, in order to determine their genetic structure. We have detected a population subdivision between Equatorial Guinea islands and the islands of S?o Tomé, Príncipe and mainland. This partitioning associates more with political rather than geographic boundaries, possibly reflecting different mainland source populations colonizing the islands.
Autochthonous Chikungunya Transmission and Extreme Climate Events in Southern France
David Roiz?,Philippe Boussès?,Frédéric Simard,Christophe Paupy?,Didier Fontenille
PLOS Neglected Tropical Diseases , 2015, DOI: 10.1371/journal.pntd.0003854
Abstract: Background Extreme precipitation events are increasing as a result of ongoing global warming, but controversy surrounds the relationship between flooding and mosquito-borne diseases. A common view among the scientific community and public health officers is that heavy rainfalls have a flushing effect on breeding sites, which negatively affects vector populations, thereby diminishing disease transmission. During 2014 in Montpellier, France, there were at least 11 autochthonous cases of chikungunya caused by the invasive tiger mosquito Aedes albopictus in the vicinity of an imported case. We show that an extreme rainfall event increased and extended the abundance of the disease vector Ae. albopictus, hence the period of autochthonous transmission of chikungunya. Methodology/Principal Findings We report results from close monitoring of the adult and egg population of the chikungunya vector Ae. albopictus through weekly sampling over the entire mosquito breeding season, which revealed an unexpected pattern. Statistical analysis of the seasonal dynamics of female abundance in relation to climatic factors showed that these relationships changed after the heavy rainfall event. Before the inundations, accumulated temperatures are the most important variable predicting Ae. albopictus seasonal dynamics. However, after the inundations, accumulated rainfall over the 4 weeks prior to capture predicts the seasonal dynamics of this species and extension of the transmission period. Conclusions/Significance Our empirical data suggests that heavy rainfall events did increase the risk of arbovirus transmission in Southern France in 2014 by favouring a rapid rise in abundance of vector mosquitoes. Further studies should now confirm these results in different ecological contexts, so that the impact of global change and extreme climatic events on mosquito population dynamics and the risk of disease transmission can be adequately understood.
Association Mapping of Insecticide Resistance in Wild Anopheles gambiae Populations: Major Variants Identified in a Low-Linkage Disequilbrium Genome
David Weetman,Craig S. Wilding,Keith Steen,John C. Morgan,Frédéric Simard,Martin J. Donnelly
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0013140
Abstract: Association studies are a promising way to uncover the genetic basis of complex traits in wild populations. Data on population stratification, linkage disequilibrium and distribution of variant effect-sizes for different trait-types are required to predict study success but are lacking for most taxa. We quantified and investigated the impacts of these key variables in a large-scale association study of a strongly selected trait of medical importance: pyrethroid resistance in the African malaria vector Anopheles gambiae.
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