Publications (20)62.21 Total impact
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Article: First Attempt To Validate Human IgG Antibody Response to Nterm-34kDa Salivary Peptide as Biomarker for Evaluating Exposure to Aedes aegypti Bites.
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ABSTRACT: Much effort is being devoted for developing new indicators to evaluate the human exposure to Aedes mosquito bites and the risk of arbovirus transmission. Human antibody (Ab) responses to mosquito salivary components could represent a promising tool for evaluating the human-vector contact. To develop a specific biomarker of human exposure to Aedes aegypti bites, we measured IgG Ab response to Ae. aegypti Nterm-34 kDa salivary peptide in exposed children in 7 villages of Southern Benin (West Africa). Results showed that specific IgG response presented high inter-individual heterogeneity between villages. IgG response was associated with rainfall and IgG level increased from dry (low exposure) to rainy (high exposure) seasons. These findings indicate that IgG Ab to Nterm-34 kDa salivary peptide may represent a reliable biomarker to detect variation in human exposure to Ae. aegypti bites. This preliminary study highlights the potential use of Ab response to this salivary peptide for evaluating human exposure to Ae. aegypti. This biomarker could represent a new promising tool for assessing the risk of arbovirus transmission and for evaluating the efficacy of vector control interventions.PLoS Neglected Tropical Diseases 11/2012; 6(11):e1905. · 4.69 Impact Factor -
Article: Loss of household protection from use of insecticide-treated nets against pyrethroid-resistant mosquitoes, benin.
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ABSTRACT: Pyrethroid resistance is becoming widespread in Anopheles gambiae mosquitoes, coinciding with expanded use of insecticide-treated nets (ITNs) throughout Africa. To investigate whether nets in use are still protective, we conducted household trials in northern and southern Benin, where An. gambiae mosquitoes are susceptible and resistant, respectively, to pyrethroids. Rooms were fitted with window traps and monitored for mosquito biting and survival rates before and after the nets were treated with pyrethroid. Sleeping under an ITN in the location with resistant mosquitoes was no more protective than sleeping under an untreated net, regardless of its physical condition. By contrast, sleeping under an ITN in the location with susceptible mosquitoes decreased the odds of biting by 66%. ITNs provide little or no protection once the mosquitoes become resistant and the netting acquires holes. Resistance seriously threatens malaria control strategies based on ITN.Emerging Infectious Diseases 07/2012; 18(7):1101-6. · 6.79 Impact Factor -
Article: Combination of malaria vector control interventions in pyrethroid resistance area in Benin: a cluster randomised controlled trial.
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ABSTRACT: Malaria control efforts and elimination in Africa are being challenged by the development of resistance of parasites to antimalarial drugs and vectors to insecticides. We investigated whether the combination of long-lasting insecticidal mosquito nets (LLINs) with indoor residual spraying (IRS) or carbamate-treated plastic sheeting (CTPS) conferred enhanced protection against malaria and better management of pyrethroid-resistance in vectors than did LLINs alone. We did a cluster randomised controlled trial in 28 villages in southern Benin, west Africa. Inclusion criteria of the villages were moderate level of pyrethroid resistance in malaria vectors and minimum distance between villages of 2 km. We assessed four malaria vector control interventions: LLIN targeted coverage to pregnant women and children younger than 6 years (TLLIN, reference group), LLIN universal coverage of all sleeping units (ULLIN), TLLIN plus full coverage of carbamate-IRS applied every 8 months (TLLIN+IRS), and ULLIN plus full coverage of CTPS lined up to the upper part of the household walls (ULLIN+CTPS). The interventions were allocated to villages by a block randomisation on the basis of preliminary surveys and children of each village were randomly selected to participate with computer-generated numbers. The primary endpoint was the incidence density rate of Plasmodium falciparum clinical malaria in children younger than 6 years as was analysed by Poisson regression taking into account the effect of age and the sampling design with a generalised estimating equation approach. Clinical and parasitological information were obtained by active case detection of malaria episodes during 12 periods of 6 consecutive days scheduled at six weekly intervals and by cross-sectional surveys of asymptomatic plasmodial infections. Children or study investigators were not masked to study group. This study is registered with Current Controlled Trials, number ISRCTN07404145. Of 58 villages assessed, 28 were randomly assigned to intervention groups. 413-429 children were followed up in each intervention group for 18 months. The clinical incidence density of malaria was not reduced in the children from the ULLIN group (incidence density rate 0·95, 95% CI 0·67-1·36, p=0·79), nor in those from the TLLIN+IRS group (1·32, 0·90-1·93, p=0·15) or from the ULLIN+CTPS group (1·05, 0·75-1·48, p=0·77) compared with the reference group (TLLIN). The same trend was observed with the prevalence and parasite density of asymptomatic infections (non significant regression coefficients). No significant benefit for reducing malaria morbidity, infection, and transmission was reported when combining LLIN+IRS or LLIN+CTPS compared with a background of LLIN coverage. These findings are important for national malaria control programmes and should help the design of more cost-effective strategies for malaria control and elimination. Ministère Français des Affaires Etrangères et Européennes (FSP project 2006-22), Institut de Recherche pour le Développement, President's Malaria Initiative (PMI) of US Governement.The Lancet Infectious Diseases 06/2012; 12(8):617-26. · 17.39 Impact Factor -
Article: Combining indoor residual spraying with chlorfenapyr and long-lasting insecticidal bed nets for improved control of pyrethroid-resistant Anopheles gambiae: an experimental hut trial in Benin.
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ABSTRACT: Neither indoor residual spraying (IRS) nor long-lasting insecticidal nets (LLINs) are able to fully interrupt transmission in holoendemic Africa as single interventions. The combining of IRS and LLINs presents an opportunity for improved control and management of pyrethroid resistance through the simultaneous presentation of unrelated insecticides. Chlorfenapyr IRS and a pyrethroid-impregnated polyester LLIN (WHO approved) were tested separately and together in experimental huts in southern Benin against pyrethroid resistant Anopheles gambiae and Culex quinquefasciatus. The bed nets were deliberately holed with either six or 80 holes to examine the effect of increasing wear and tear on protectiveness. Anopheles gambiae were genotyped for the kdr gene to assess the combination's potential to prevent the selection of pyrethroid resistance. The frequency of kdr was 84%. The overall mortality rates of An. gambiae were 37% and 49% with the six-hole and 80-hole LLINs, respectively, and reached 57% with chlorfenapyr IRS. Overall mortality rates were significantly higher with the combination treatments (82-83%) than with the LLIN or IRS individual treatments. Blood feeding (mosquito biting) rates were lowest with the 6-hole LLIN (12%), intermediate with the 80-hole LLIN (32%) and highest with untreated nets (56% with the 6-hole and 54% with the 80-hole nets). Blood feeding (biting) rates and repellency of mosquitoes with the combination of LLIN and chlorfenapyr IRS showed significant improvement compared to the IRS treatment but did not differ from the LLIN treatments indicating that the LLINs were the primary agents of personal protection. The combination killed significantly higher proportions of Cx. quinquefasciatus (51%, 41%) than the LLIN (15%, 13%) or IRS (32%) treatments. The chlorfenapyr IRS component was largely responsible for controlling pyrethroid-resistant mosquitoes and the LLIN component was largely responsible for blood feeding inhibition and personal protection. Together, the combination shows potential to provide additional levels of transmission control and personal protection against pyrethroid-resistant mosquitoes, thereby justifying the additional resources required. Chlorfenapyr has potential to manage pyrethroid resistance in the context of an expanding LLIN/IRS strategy.Malaria Journal 11/2011; 10:343. · 3.19 Impact Factor -
Article: Cotton pest management practices and the selection of pyrethroid resistance in Anopheles gambiae population in northern Benin.
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ABSTRACT: Pyrethroid insecticides, carbamate and organophosphate are the classes of insecticides commonly used in agriculture for crop protection in Benin. Pyrethroids remain the only class of insecticides recommended by the WHO for impregnation of bed nets. Unfortunately, the high level of pyrethroid resistance in Anopheles gambiae s.l., threatens to undermine the success of pyrethroid treated nets. This study focuses on the investigation of agricultural practices in cotton growing areas, and their direct impact on larval populations of An. gambiae in surrounding breeding sites. The protocol was based on the collection of agro-sociological data where farmers were subjected to semi-structured questionnaires based on the strategies used for crop protection. This was complemented by bioassay tests to assess the susceptibility of malaria vectors to various insecticides. Molecular analysis was performed to characterize the resistance genes and the molecular forms of An. gambiae. Insecticide residues in soil samples from breeding sites were investigated to determine major factors that can inhibit the normal growth of mosquito larvae by exposing susceptible and resistant laboratory strains. There is a common use by local farmers of mineral fertilizer NPK at 200 kg/ha and urea at 50 kg/hectare following insecticide treatments in both the Calendar Control Program (CCP) and the Targeted Intermittent Control Program (TICP). By contrast, no chemicals are involved in Biological Program (BP) where farmers use organic and natural fertilizers which include animal excreta.Susceptibility test results confirmed a high resistance to DDT. Mean mortality of An. gambiae collected from the farms practicing CCP, TICP and BP methods were 33%, 42% and 65% respectively. An. gambiae populations from areas using the CCP and TICP programs showed resistance to permethrin with mortality of 50% and 58% respectively. By contrast, bioassay test results of An. gambiae from BP areas gave a high level of susceptibility to permethrin with an average mortality of 94%.Molecular analysis identified An. gambiae s.s, and An. arabiensis with a high predominance of An. gambiae s.s (90%). The two molecular forms, M and S, were also determined with a high frequency of the S form (96%).The Kdr gene seemed the main target- site resistance mechanism detected in CCP, TICP, and BP areas at the rates ranging from 32 to 78%. The frequency of ace-1R gene was very low (< 0.1).The presence of inhibiting factors in soil samples under insecticide treatments were found and affected negatively in delaying the development of An. gambiae larval populations. This research shows that Kdr has spread widely in An. gambiae, mainly in CCP and TICP areas where pyrethroids are extensively used. To reduce the negative impact of pesticides use in cotton crop protection, the application of BP-like programs, which do not appear to select for vector resistance would be useful. These results could serve as scientific evidence of the spread of resistance due to a massive agricultural use of insecticides and contribute to the management of pesticides usage on cotton crops hence reducing the selection pressure of insecticides on An. gambiae populations.Parasites & Vectors 01/2011; 4:60. · 2.94 Impact Factor -
Article: An experimental hut evaluation of PermaNet(®) 3.0, a deltamethrin-piperonyl butoxide combination net, against pyrethroid-resistant Anopheles gambiae and Culex quinquefasciatus mosquitoes in southern Benin.
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ABSTRACT: PermaNet 3.0 is a long-lasting combination net with deltamethrin present on the sides and a mixture of deltamethrin and piperonyl butoxide (PBO), an oxidase synergist, on the top panel. An experimental hut trial comparing unwashed and 20 times washed PermaNet 3.0 and PermaNet 2.0, Olyset Net and a conventional deltamethrin-treated net washed three times was conducted in southern Benin. Anopheles gambiae and Culex quinquefasciatus from this area are highly resistant to pyrethroids through kdr and cytochrome P450 mechanisms. The unwashed PermaNet 3.0 killed slightly more A. gambiae (52%) than the unwashed PermaNet 2.0 (44%) (P=0.036), indicating only partial synergism of resistance. After washing there was significant loss of activity to a similar level, with PermaNet 3.0 killing 31%, PermaNet 2.0 killing 29% and the conventional net killing 26%. Blood-feeding rates were partially inhibited for unwashed PermaNet 3.0 and Olyset Net (27% inhibition). Personal protection against A. gambiae derived from PermaNet 3.0 was similar to that from PermaNet 2.0 before washing (50% vs. 47%), and after 20 washes it decreased to 30%. Against C. quinquefasciatus, no treatment killed >24% entering the huts. The synergism from unwashed PermaNet 3.0 was lower than expected, probably due to an unidentified resistance mechanism unaffected by PBO.Transactions of the Royal Society of Tropical Medicine and Hygiene 10/2010; 104(12):758-65. · 2.16 Impact Factor -
Article: Malaria vectors in the Republic of Benin: distribution of species and molecular forms of the Anopheles gambiae complex.
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ABSTRACT: Members of the Anopheles gambiae complex are among the best malaria vectors in the world, but their vectorial capacities vary between species and populations. A large-scale sampling of An. gambiae sensu lato was carried out in 2006 and 2007 in various bioclimatic areas of Benin (West Africa). The objective of this study was to collate data on the relative frequencies of species and forms within the An. gambiae complex and to produce a map of their spatial distribution. Sampling took place at 30 sites and 2122 females were analyzed. Two species were identified through molecular methods. The overall collection showed a preponderance of An. gambiae s.s., but unexpectedly, An. arabiensis was reported in the coastal-Guinean bioclimatic area characterized by a mean annual rainfall of >1500 mm where only An. gambiae s.s. was reported previously. Our study of Benin indicates that An. arabiensis would be adapted not only to the urban areas but also to the rural humid regions. Among 1717 An. gambiae s.s., 26.5% were of the M form and 73.3% were S form. Few hybrid specimens between the M and S forms were observed (0.2%). Only the spatial distribution of the M form appears to be mainly a function of bioclimatic area. Factors that influence the distribution of these malaria vectors are discussed. This study underlines the need of further investigations of biological, ecological, and behavioral traits of these species and forms to better appreciate their vectorial capacities. Acquisition of entomological field data appears essential to better estimate the stratification of malaria risk and help improve malaria vector control interventions.Acta tropica 02/2010; 114(2):116-22. · 2.22 Impact Factor -
Article: Control of pyrethroid and DDT-resistant Anopheles gambiae by application of indoor residual spraying or mosquito nets treated with a long-lasting organophosphate insecticide, chlorpyrifos-methyl.
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ABSTRACT: Scaling up of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) with support from the Global Fund and President's Malaria Initiative is providing increased opportunities for malaria control in Africa. The most cost-effective and longest-lasting residual insecticide DDT is also the most environmentally persistent. Alternative residual insecticides exist, but are too short-lived or too expensive to sustain. Dow Agrosciences have developed a microencapsulated formulation (CS) of the organophosphate chlorpyrifos methyl as a cost-effective, long-lasting alternative to DDT. Chlorpyrifos methyl CS was tested as an IRS or ITN treatment in experimental huts in an area of Benin where Anopheles gambiae and Culex quinquefasiactus are resistant to pyrethroids, but susceptible to organophosphates. Efficacy and residual activity was compared to that of DDT and the pyrethroid lambdacyalothrin. IRS with chlorpyrifos methyl killed 95% of An. gambiae that entered the hut as compared to 31% with lambdacyhalothrin and 50% with DDT. Control of Cx. quinquefasciatus showed a similar trend; although the level of mortality with chlorpyrifos methyl was lower (66%) it was still much higher than for DDT (14%) or pyrethroid (15%) treatments. Nets impregnated with lambdacyhalothrin were compromised by resistance, killing only 30% of An. gambiae and 8% of Cx. quinquefasciatus. Nets impregnated with chlorpyrifos methyl killed more (45% of An gambiae and 15% of Cx. quinquefasciatus), but its activity on netting was of short duration. Contact bioassays on the sprayed cement-sand walls over the nine months of monitoring showed no loss of activity of chlorpyrifos methyl, whereas lambdacyhalothrin and DDT lost activity within a few months of spraying. As an IRS treatment against pyrethroid resistant mosquitoes chlorpyrifos methyl CS outperformed DDT and lambdacyhalothrin. In IRS campaigns, chlorpyrifos methyl CS should show higher, more-sustained levels of malaria transmission control than conventional formulations of DDT or pyrethroids. The remarkable residual activity indicates that cost-effective alternatives to DDT are feasible through modern formulation technology.Malaria Journal 02/2010; 9:44. · 3.19 Impact Factor -
Article: Field efficacy of a new mosaic long-lasting mosquito net (PermaNet 3.0) against pyrethroid-resistant malaria vectors: a multi centre study in Western and Central Africa.
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ABSTRACT: Due to the spread of pyrethroid-resistance in malaria vectors in Africa, new strategies and tools are urgently needed to better control malaria transmission. The aim of this study was to evaluate the performances of a new mosaic long-lasting insecticidal net (LLIN), i.e. PermaNet 3.0, against wild pyrethroid-resistant Anopheles gambiae s.l. in West and Central Africa. A multi centre experimental hut trial was conducted in Malanville (Benin), Vallée du Kou (Burkina Faso) and Pitoa (Cameroon) to investigate the exophily, blood feeding inhibition and mortality induced by PermaNet 3.0 (i.e. a mosaic net containing piperonyl butoxide and deltamethrin on the roof) comparatively to the WHO recommended PermaNet 2.0 (unwashed and washed 20-times) and a conventionally deltamethrin-treated net (CTN). The personal protection and insecticidal activity of PermaNet 3.0 and PermaNet 2.0 were excellent (>80%) in the "pyrethroid-tolerant" area of Malanville. In the pyrethroid-resistance areas of Pitoa (metabolic resistance) and Vallée du Kou (presence of the L1014F kdr mutation), PermaNet 3.0 showed equal or better performances than PermaNet 2.0. It should be noted however that the deltamethrin content on PermaNet 3.0 was up to twice higher than that of PermaNet 2.0. Significant reduction of efficacy of both LLIN was noted after 20 washes although PermaNet 3.0 still fulfilled the WHO requirement for LLIN. The use of combination nets for malaria control offers promising prospects. However, further investigations are needed to demonstrate the benefits of using PermaNet 3.0 for the control of pyrethroid resistant mosquito populations in Africa.Malaria Journal 01/2010; 9:113. · 3.19 Impact Factor -
Article: Field efficacy of a new mosaic long-lasting mosquito net (PermaNet<sup>® </sup>3.0) against pyrethroid-resistant malaria vectors: a multi centre study in Western and Central Africa
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ABSTRACT: Abstract Background Due to the spread of pyrethroid-resistance in malaria vectors in Africa, new strategies and tools are urgently needed to better control malaria transmission. The aim of this study was to evaluate the performances of a new mosaic long-lasting insecticidal net (LLIN), i.e. PermaNet<sup>® </sup>3.0, against wild pyrethroid-resistant Anopheles gambiae s.l . in West and Central Africa. Methods A multi centre experimental hut trial was conducted in Malanville (Benin), Vallée du Kou (Burkina Faso) and Pitoa (Cameroon) to investigate the exophily, blood feeding inhibition and mortality induced by PermaNet<sup>® </sup>3.0 (i.e. a mosaic net containing piperonyl butoxide and deltamethrin on the roof) comparatively to the WHO recommended PermaNet<sup>® </sup>2.0 (unwashed and washed 20-times) and a conventionally deltamethrin-treated net (CTN). Results The personal protection and insecticidal activity of PermaNet 3.0 and PermaNet<sup>® </sup>2.0 were excellent (>80%) in the "pyrethroid-tolerant" area of Malanville. In the pyrethroid-resistance areas of Pitoa (metabolic resistance) and Vallée du Kou (presence of the L1014F kdr mutation), PermaNet<sup>® </sup>3.0 showed equal or better performances than PermaNet<sup>® </sup>2.0. It should be noted however that the deltamethrin content on PermaNet<sup>® </sup>3.0 was up to twice higher than that of PermaNet<sup>® </sup>2.0. Significant reduction of efficacy of both LLIN was noted after 20 washes although PermaNet<sup>® </sup>3.0 still fulfilled the WHO requirement for LLIN. Conclusion The use of combination nets for malaria control offers promising prospects. However, further investigations are needed to demonstrate the benefits of using PermaNet<sup>® </sup>3.0 for the control of pyrethroid resistant mosquito populations in Africa.Malaria Journal. 01/2010; -
Article: Efficacy of an insecticide paint against malaria vectors and nuisance in West Africa--part 2: field evaluation.
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ABSTRACT: Widespread resistance of the main malaria vector Anopheles gambiae to pyrethroids reported in many African countries and operational drawbacks to current IRS methods suggest the convenience of exploring new products and approaches for vector control. Insecticide paint Inesfly 5A IGR™, containing two organophosphates (OPs), chlorpyrifos and diazinon, and one insect growth regulator (IGR), pyriproxyfen, was tested in Benin, West Africa, for 12 months. Field trials were conducted in six experimental huts that were randomly allocated to one or two layers of insecticide at 1 Kg/6 m2 or control. Evaluations included: (i) early mosquito collection, (ii) mosquito release experiments, (iii) residual efficacy tests and (iv) distance tests. Early mosquito collections were performed on local populations of pyrethroid-resistant An. gambiae and Culex quinquefasciatus. As per WHOPES phase II procedures, four entomological criteria were evaluated: deterrence, excito-repellence, blood-feeding inhibition and mortality. Mosquito release experiments were done using local malaria-free An. gambiae females reared at the CREC insectarium. Residual efficacy tests and distance tests were performed using reference susceptible strains of An. gambiae and Cx. quinquefasciatus. Six months after treatment, mortality rates were still 90-100% against pyrethroid-resistant mosquito populations in experimental huts. At nine months, mortality rates in huts treated with two layers was still about 90-93% against An. gambiae and 55% against Cx. quinquefasciatus. Malaria-free local mosquito release experiments yielded a 90% blood-feeding inhibition in the absence of a physical barrier. A long-term residual efficacy of 12 months was observed by WHO-bioassays in huts treated with two layers (60-80%). Mortality after an overnight exposition at distances of 1 meter was 96-100% for up to 12 months. The encouraging results obtained on the insecticide paint Inesfly 5A IGR™ in terms of mortality, be it in direct contact or at a distance, and its new operational approach could constitute an additional option in malaria control efforts in areas of pyrethroid resistance. Phase III studies will be performed to assess the product's epidemiological impact and sociological acceptance.Malaria Journal 01/2010; 9:341. · 3.19 Impact Factor -
Article: Decreased motivation in the use of insecticide-treated nets in a malaria endemic area in Burkina Faso.
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ABSTRACT: The use of insecticide-treated nets (ITN) is an important tool in the Roll Back Malaria (RBM) strategy. For ITNs to be effective they need to be used correctly. Previous studies have shown that many factors, such as wealth, access to health care, education, ethnicity and gender, determine the ownership and use of ITNs. Some studies showed that free distribution and public awareness campaigns increased the rate of use. However, there have been no evaluations of the short- and long-term impact of such motivation campaigns. A study carried out in a malaria endemic area in south-western Burkina Faso indicated that this increased use declined after several months. The reasons were a combination of the community representation of malaria, the perception of the effectiveness and usefulness of ITNs and also the manner in which households are organized by day and by night. PermaNet 2.0 and Olyset were distributed in 455 compounds at the beginning of the rainy season. The community was educated on the effectiveness of nets in reducing malaria and on how to use them. To assess motivation, qualitative tools were used: one hundred people were interviewed, two hundred houses were observed directly and two houses were monitored monthly throughout one year. The motivation for the use of bednets decreased after less than a year. Inhabitants' conception of malaria and the inconvenience of using bednets in small houses were the major reasons. Acceptance that ITNs were useful in reducing malaria was moderated by the fact that mosquitoes were considered to be only one of several factors which caused malaria. The appropriate and routine use of ITNs was adversely affected by the functional organization of the houses, which changed as between day and night. Bednets were not used when the perceived benefits of reduction in mosquito nuisance and of malaria were considered not to be worth the inconvenience of daily use. In order to bridge the gap between possession and use of bednets, concerted efforts are required to change behaviour by providing accurate information, most particularly by convincing people that mosquitoes are the only source of malaria, whilst recognising that there are other diseases with similar symptoms, caused in other ways. The medical message must underline the seriousness of malaria and the presence of the malaria vector in the dry season as well as the wet, in order to encourage the use of bednets whenever transmission can occur. Communities would benefit from impregnated bednets and other vector control measures being better adapted to their homes, thus reducing the inconvenience of their use.Malaria Journal 08/2009; 8:175. · 3.19 Impact Factor -
Article: Development of vegetable farming: a cause of the emergence of insecticide resistance in populations of Anopheles gambiae in urban areas of Benin.
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ABSTRACT: A fast development of urban agriculture has recently taken place in many areas in the Republic of Benin. This study aims to assess the rapid expansion of urban agriculture especially, its contribution to the emergence of insecticide resistance in populations of Anopheles gambiae. The protocol was based on the collection of sociological data by interviewing vegetable farmers regarding various agricultural practices and the types of pesticides used. Bioassay tests were performed to assess the susceptibility of malaria vectors to various agricultural insecticides and biochemical analysis were done to characterize molecular status of population of An. gambiae. This research showed that:(1) The rapid development of urban agriculture is related to unemployment observed in cities, rural exodus and the search for a balanced diet by urban populations;(2) Urban agriculture increases the farmers' household income and their living standard;(3) At a molecular level, PCR revealed the presence of three sub-species of An. gambiae (An. gambiae s.s., Anopheles melas and Anopheles arabiensis) and two molecular forms (M and S). The kdr west mutation recorded in samples from the three sites and more specifically on the M forms seems to be one of the major resistance mechanisms found in An. gambiae from agricultural areas. Insecticide susceptibility tests conducted during this research revealed a clear pattern of resistance to permethrin (76% mortality rate at Parakou; 23.5% at Porto-Novo and 17% at Cotonou). This study confirmed an increase activity of the vegetable farming in urban areas of Benin. This has led to the use of insecticide in an improper manner to control vegetable pests, thus exerting a huge selection pressure on mosquito larval population, which resulted to the emergence of insecticide resistance in malaria vectors.Malaria Journal 06/2009; 8:103. · 3.19 Impact Factor -
Article: Control of pyrethroid-resistant Anopheles gambiae and Culex quinquefasciatus mosquitoes with chlorfenapyr in Benin.
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ABSTRACT: To compare the efficacy of chlorfenapyr applied on mosquito nets and as an indoor residual spray against populations of Anopheles gambiae and Culex quinquefasciatus in an area of Benin that shows problematic levels of pyrethroid resistance. Eight-week trial conducted in experimental huts. Indoor residual spraying killed 82.9% of An. gambiae overall (mean mortality: 79.5%) compared to 53.5% overall (mean mortality: 61.7%) in the hut containing the lower dosed ITN. Analysis of data on a fortnightly basis showed high levels of mosquito mortality and blood-feeding inhibition during the first few weeks after treatment. Control of C. quinquefasciatus by the IRS and ITN interventions showed a similar trend to that of An. gambiae and though the average level of mortality was lower it was still much higher than with pyrethroid treatments against this population. Chlorfenapyr's reputation for being rather slow acting was evident particularly at lower dosages. The treatments showed no evidence of excito-repellent activity in this trial. Chlorfenapyr has the potential to control pyrethroid resistant populations of A. gambiae. There is a need to develop long-lasting formulations of chlorfenapyr to prolong its residual life on nets and sprayed surfaces. On nets it could be combined with a contact irritant pyrethroid to give improved protection against mosquito biting while killing pyrethroid-resistant mosquitoes that come into contact with the net.Tropical Medicine & International Health 03/2009; 14(4):389-95. · 2.80 Impact Factor -
Article: Development of vegetable farming: a cause of the emergence of insecticide resistance in populations of Anopheles gambiae in urban areas of Benin
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ABSTRACT: Abstract Background A fast development of urban agriculture has recently taken place in many areas in the Republic of Benin. This study aims to assess the rapid expansion of urban agriculture especially, its contribution to the emergence of insecticide resistance in populations of Anopheles gambiae . Methods The protocol was based on the collection of sociological data by interviewing vegetable farmers regarding various agricultural practices and the types of pesticides used. Bioassay tests were performed to assess the susceptibility of malaria vectors to various agricultural insecticides and biochemical analysis were done to characterize molecular status of population of An. gambiae . Results This research showed that: (1) The rapid development of urban agriculture is related to unemployment observed in cities, rural exodus and the search for a balanced diet by urban populations; (2) Urban agriculture increases the farmers' household income and their living standard; (3) At a molecular level, PCR revealed the presence of three sub-species of An. gambiae ( An. gambiae s.s., Anopheles melas and Anopheles arabiensis ) and two molecular forms (M and S). The kdr west mutation recorded in samples from the three sites and more specifically on the M forms seems to be one of the major resistance mechanisms found in An. gambiae from agricultural areas. Insecticide susceptibility tests conducted during this research revealed a clear pattern of resistance to permethrin (76% mortality rate at Parakou; 23.5% at Porto-Novo and 17% at Cotonou). Conclusion This study confirmed an increase activity of the vegetable farming in urban areas of Benin. This has led to the use of insecticide in an improper manner to control vegetable pests, thus exerting a huge selection pressure on mosquito larval population, which resulted to the emergence of insecticide resistance in malaria vectors.Malaria Journal. 01/2009; -
Article: Decreased motivation in the use of insecticide-treated nets in a malaria endemic area in Burkina Faso
[show abstract] [hide abstract]
ABSTRACT: Abstract Background The use of insecticide-treated nets (ITN) is an important tool in the Roll Back Malaria (RBM) strategy. For ITNs to be effective they need to be used correctly. Previous studies have shown that many factors, such as wealth, access to health care, education, ethnicity and gender, determine the ownership and use of ITNs. Some studies showed that free distribution and public awareness campaigns increased the rate of use. However, there have been no evaluations of the short- and long-term impact of such motivation campaigns. A study carried out in a malaria endemic area in south-western Burkina Faso indicated that this increased use declined after several months. The reasons were a combination of the community representation of malaria, the perception of the effectiveness and usefulness of ITNs and also the manner in which households are organized by day and by night. Methods PermaNet 2.0<sup>® </sup>and Olyset<sup>® </sup>were distributed in 455 compounds at the beginning of the rainy season. The community was educated on the effectiveness of nets in reducing malaria and on how to use them. To assess motivation, qualitative tools were used: one hundred people were interviewed, two hundred houses were observed directly and two houses were monitored monthly throughout one year. Results The motivation for the use of bednets decreased after less than a year. Inhabitants' conception of malaria and the inconvenience of using bednets in small houses were the major reasons. Acceptance that ITNs were useful in reducing malaria was moderated by the fact that mosquitoes were considered to be only one of several factors which caused malaria. The appropriate and routine use of ITNs was adversely affected by the functional organization of the houses, which changed as between day and night. Bednets were not used when the perceived benefits of reduction in mosquito nuisance and of malaria were considered not to be worth the inconvenience of daily use. Conclusion In order to bridge the gap between possession and use of bednets, concerted efforts are required to change behaviour by providing accurate information, most particularly by convincing people that mosquitoes are the only source of malaria, whilst recognising that there are other diseases with similar symptoms, caused in other ways. The medical message must underline the seriousness of malaria and the presence of the malaria vector in the dry season as well as the wet, in order to encourage the use of bednets whenever transmission can occur. Communities would benefit from impregnated bednets and other vector control measures being better adapted to their homes, thus reducing the inconvenience of their use.Malaria Journal. 01/2009; -
Article: Expression of the cytochrome P450s, CYP6P3 and CYP6M2 are significantly elevated in multiple pyrethroid resistant populations of Anopheles gambiae s.s. from Southern Benin and Nigeria.
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ABSTRACT: Insecticide resistance in Anopheles mosquitoes is threatening the success of malaria control programmes. This is particularly true in Benin where pyrethroid resistance has been linked to the failure of insecticide treated bed nets. The role of mutations in the insecticide target sites in conferring resistance has been clearly established. In this study, the contribution of other potential resistance mechanisms was investigated in Anopheles gambiae s.s. from a number of localities in Southern Benin and Nigeria. The mosquitoes were sampled from a variety of breeding sites in a preliminary attempt to investigate the role of contamination of mosquito breeding sites in selecting for resistance in adult mosquitoes. All mosquitoes sampled belonged to the M form of An. gambiae s.s. There were high levels of permethrin resistance in an agricultural area (Akron) and an urban area (Gbedjromede), low levels of resistance in mosquito samples from an oil contaminated site (Ojoo) and complete susceptibility in the rural Orogun location. The target site mutation kdrW was detected at high levels in two of the populations (Akron f = 0.86 and Gbedjromede f = 0.84) but was not detected in Ojoo or Orogun. Microarray analysis using the Anopheles gambiae detox chip identified two P450s, CYP6P3 and CYP6M2 up regulated in all three populations, the former was expressed at particularly high levels in the Akron (12.4-fold) and Ojoo (7.4-fold) populations compared to the susceptible population. Additional detoxification and redox genes were also over expressed in one or more populations including two cuticular pre-cursor genes which were elevated in two of the three resistant populations. Multiple resistance mechanisms incurred in the different breeding sites contribute to resistance to permethrin in Benin. The cytochrome P450 genes, CYP6P3 and CYP6M2 are upregulated in all three resistant populations analysed. Several additional potential resistance mechanisms were also identified that warrant further investigation. Metabolic genes were over expressed irrespective of the presence of kdr, the latter resistance mechanism being absent in one resistant population. The discovery that mosquitoes collected from different types of breeding sites display differing profiles of metabolic genes at the adult stage may reflect the influence of a range of xenobiotics on selecting for resistance in mosquitoes.BMC Genomics 12/2008; 9:538. · 4.07 Impact Factor -
Article: Expression of the cytochrome P450s, CYP6P3 and CYP6M2 are significantly elevated in multiple pyrethroid resistant populations of Anopheles gambiae s.s . from Southern Benin and Nigeria
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ABSTRACT: Abstract Background Insecticide resistance in Anopheles mosquitoes is threatening the success of malaria control programmes. This is particularly true in Benin where pyrethroid resistance has been linked to the failure of insecticide treated bed nets. The role of mutations in the insecticide target sites in conferring resistance has been clearly established. In this study, the contribution of other potential resistance mechanisms was investigated in Anopheles gambiae s.s. from a number of localities in Southern Benin and Nigeria. The mosquitoes were sampled from a variety of breeding sites in a preliminary attempt to investigate the role of contamination of mosquito breeding sites in selecting for resistance in adult mosquitoes. Results All mosquitoes sampled belonged to the M form of An. gambiae s.s. There were high levels of permethrin resistance in an agricultural area (Akron) and an urban area (Gbedjromede), low levels of resistance in mosquito samples from an oil contaminated site (Ojoo) and complete susceptibility in the rural Orogun location. The target site mutation kdrW was detected at high levels in two of the populations (Akron f = 0.86 and Gbedjromede f = 0.84) but was not detected in Ojoo or Orogun. Microarray analysis using the Anopheles gambiae detox chip identified two P450s, CYP6P3 and CYP6M2 up regulated in all three populations, the former was expressed at particularly high levels in the Akron (12.4-fold) and Ojoo (7.4-fold) populations compared to the susceptible population. Additional detoxification and redox genes were also over expressed in one or more populations including two cuticular pre-cursor genes which were elevated in two of the three resistant populations. Conclusion Multiple resistance mechanisms incurred in the different breeding sites contribute to resistance to permethrin in Benin. The cytochrome P450 genes, CYP6P3 and CYP6M2 are upregulated in all three resistant populations analysed. Several additional potential resistance mechanisms were also identified that warrant further investigation. Metabolic genes were over expressed irrespective of the presence of kdr , the latter resistance mechanism being absent in one resistant population. The discovery that mosquitoes collected from different types of breeding sites display differing profiles of metabolic genes at the adult stage may reflect the influence of a range of xenobiotics on selecting for resistance in mosquitoes.BMC Genomics. 01/2008; -
Article: Quantification of the efficiency of treatment of Anopheles gambiae breeding sites with petroleum products by local communities in areas of insecticide resistance in the Republic of Benin
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ABSTRACT: Abstract Background The emergence of Anopheles populations capable of withstanding lethal doses of insecticides has weakened the efficacy of most insecticide based strategies of vector control and, has highlighted the need for developing new insecticidal molecules or, improving the efficacy of existing insecticides or abandoning those to which resistance has emerged. The use of petroleum products (PP) against mosquito larvae had an immense success during early programmes of malaria control, but these compounds were abandoned and replaced in the 1950s by synthetic insecticides probably because of the high performances given by these new products. In the current context of vector resistance, it is important to elucidate the empirical use of PP by quantifying their efficiencies on resistant strains of Anopheles . Methods Larvae of Anopheles Ladji a local resistant strain were exposed to increasing concentrations of various PP (kerosene, petrol and engine oils) for 24 hours and the lethal activities recorded. The highest concentration (HiC) having no lethal activity (also referred as the NOEL or no effect level) and the lowest concentration (LoC<sub>100</sub>) yielding 100% mortality were rated for each PP on the Ladji strain. Prior to laboratory analysis, KAP studies were conducted in three traditional communities were insecticide resistance is clearly established to confirm the use of PP against mosquitoes. Results Laboratory analysis of petrol, kerosene and engine oils, clearly established their lethal activities on resistant strains of Anopheles larvae. Contrary to existing references, this research revealed that exposed larvae of Anopheles were mostly killed by direct contact toxicity and not by suffocation as indicated in some earlier reports. Conclusion This research could serve as scientific basis to backup the empirical utilisation of PP on mosquito larvae and to envisage possibilities of using PP in some traditional settings where Anopheles have developed resistance to currently used insecticides.Malaria Journal. 01/2007; -
Article: Does the spillage of petroleum products in Anopheles breeding sites have an impact on the pyrethroid resistance?
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ABSTRACT: Abstract Background The emergence of Anopheles populations capable of withstanding lethal doses of insecticides has weakened the efficacy of most insecticide based strategies of vector control and, has highlighted the need for further studies on the mechanisms of insecticide resistance and the various factors selecting resistant populations of mosquitoes. This research targeted the analysis of breeding sites and the oviposition behaviour of susceptible and resistant populations of Anopheles in localities of spilled petroleum products. The aim was to establish the possible contribution of oil spillage in the selection of pyrethroid resistance in malaria vectors. Methods Anopheles breeding sites were identified and the insecticide susceptibility of the Anopheles gambiae populations mapped in 15 localities of South Western Nigeria. The presence of oil particles as well as the turbidity, the dissolved oxygen and the pH of each identified breeding site was recorded. Data were cross-analysed to correlate the habitat types and the insecticide susceptibility status of emerging mosquitoes. The second phase of this study was basically a laboratory model to provide more information on the implication of the spillage of petroleum on the selection of pyrethroid resistance in An. gambiae . Results Moderate levels of resistance following exposure to permethrin-impregnated papers were recorded with the majority of An. gambiae samples collected in the South Western Nigeria. Data from this study established a link between the constituency of the breeding sites and the resistance status of the emerging Anopheles . Conclusion This study has revealed the segregational occupation of breeding habitats by pyrethroid resistant and susceptible strains of An. gambiae in south-western Nigeria. Compiled results from field and laboratory research point out clear relationships between oil spillage and pyrethroid resistance in malaria vectors. The identification of this factor of resistance could serve as strong information in the management of insecticide resistance in some West African settings.Malaria Journal. 01/2007;
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2009–2012
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London School of Hygiene and Tropical Medicine
London, ENG, United Kingdom
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2009–2011
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Centre de Recherche Entomologique de Cotonou
Cotonou, Departement du Littoral, Benin
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