47 research outputs found
Pyrethroid and etofenprox resistance in Anopheles gambiae and Anopheles coluzzii from vegetable farms in Yaounde, Cameroon: dynamics, intensity and molecular basis
Get PDFPrevious studies have indicated widespread insecticide resistance in malaria vector populations from Cameroon. However, the intensity of this resistance and underlying mechanisms are poorly known. Therefore, we conducted three cross-sectional resistance surveys between April 2018 and October 2019, using the revised World Health Organization protocol, which includes resistance incidences and intensity assessments. Field-collected Anopheles gambiae s.l. populations from Nkolondom, Nkolbisson and Ekie vegetable farms in the city of Yaounde were tested with deltamethrin, permethrin, alpha-cypermethrin and etofenprox, using 1x insecticide diagnostic concentrations for resistance incidence, then 5x and 10x concentrations for resistance intensity. Subsamples were analyzed for species identification and the detection of resistance-associated molecular markers using TaqMan(R) qPCR assays. In Nkolbisson, both An. coluzzii (96%) and An. gambiae s.s. (4%) were found together, whereas only An. gambiae s.s. was present in Nkolondom, and only An. coluzzii was present in Ekie. All three populations were resistant to the four insecticides (<75% mortality rates-MR1x), with intensity generally fluctuating over the time between mod-erate ( /=98%-MR10x) and high (76-97%-MR10x). The kdr L995F, L995S, and N1570Y, and the Ace-1 G280S-resistant alleles were found in An. gambiae from Nkolondom, at 73%, 1%, 16% and 13% frequencies, respectively, whereas only the kdr L995F was found in An. gambiae s.s. from Nkolbisson at a 50% frequency. In An. coluzzii from Nkolbisson and Ekie, we detected only the kdr L995F allele at 65% and 60% frequencies, respectively. Furthermore, expression levels of Cyp6m2, Cyp9k1, and Gste2 metabolic genes were highly upregulated (over fivefold) in Nkolondom and Nkolbisson. Pyrethroid and etofenprox-based vector control interventions may be jeopardized in the prospected areas, due to high resistance intensity, with multiple mechanisms in An. gambiae s.s. and An. coluzzii
Efficacy of PermaNet® 2.0 and PermaNet® 3.0 against insecticide-resistant Anopheles gambiae in experimental huts in Côte d'Ivoire
Get PDF<p>Abstract</p> <p>Background</p> <p>Pyrethroid resistance in vectors could limit the efficacy of long-lasting insecticidal nets (LLINs) because all LLINs are currently treated with pyrethroids. The goal of this study was to evaluate the efficacy and wash resistance of PermaNet<sup>® </sup>3.0 compared to PermaNet<sup>® </sup>2.0 in an area of high pyrethroid in Côte d'Ivoire. PermaNet<sup>® </sup>3.0 is impregnated with deltamethrin at 85 mg/m<sup>2 </sup>on the sides of the net and with deltamethrin and piperonyl butoxide on the roof. PermaNet<sup>® </sup>2.0 is impregnated with deltamethrin at 55 mg/m<sup>2 </sup>across the entire net.</p> <p>Methods</p> <p>The study was conducted in the station of Yaokoffikro, in central Côte d'Ivoire. The efficacy of intact unwashed and washed LLINs was compared over a 12-week period with a conventionally-treated net (CTN) washed to just before exhaustion. WHO cone bioassays were performed on sub-sections of the nets, using wild-resistant <it>An. gambiae </it>and Kisumu strains. Mosquitoes were collected five days per week and were identified to genus and species level and classified as dead or alive, then unfed or blood-fed.</p> <p>Results</p> <p>Mortality rates of over 80% from cone bioassays with wild-caught pyrethroid-resistant <it>An. gambiae </it>s.s were recorded only with unwashed PermaNet<sup>® </sup>3.0. Over 12 weeks, a total of 7,291 mosquitoes were collected. There were significantly more <it>An. gambiae </it>s.s. and <it>Culex </it>spp. caught in control huts than with other treatments (P < 0.001). The proportion of mosquitoes exiting the huts was significantly lower with the control than for the treatment arms (P < 0.001). Mortality rates with resistant <it>An. gambiae </it>s.s and <it>Culex </it>spp, were lower for the control than for other treatments (P < 0.001), which did not differ (P > 0.05) except for unwashed PermaNet<sup>® </sup>3.0 (P < 0.001), which gave significantly higher mortality (P < 0.001).</p> <p>Conclusions</p> <p>This study showed that unwashed PermaNet<sup>® </sup>3.0 caused significantly higher mortality against pyrethroid resistant <it>An. gambiae s.s </it>and <it>Culex </it>spp than PermaNet<sup>® </sup>2.0 and the CTN. The increased efficacy with unwashed PermaNet<sup>® </sup>3.0 over PermaNet<sup>® </sup>2.0 and the CTN was also demonstrated by higher KD and mortality rates (KD > 95% and mortality rate > 80%) in cone bioassays performed with wild pyrethroid-resistant <it>An. gambiae s.s </it>from Yaokoffikro.</p
Efficacy of bifenthrin-impregnated bednets against Anopheles funestus and pyrethroid-resistant Anopheles gambiae in North Cameroon
Get PDFBACKGROUND: Recent field studies indicated that insecticide-treated bednets (ITNs) maintain their efficacy despite a high frequency of the knock-down resistance (kdr) gene in Anopheles gambiae populations. It was essential to evaluate ITNs efficacy in areas with metabolic-based resistance. METHODS: Bifenthrin was used in this experiment because it is considered a promising candidate for bednets impregnation. Nets were treated at 50 mg/m(2), a dose that has high insecticidal activity on kdr mosquitoes and at 5 mg/m(2), 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. RESULTS: Bifenthrin at 50 mg/m(2 )significantly reduced anophelines' entry rate (>80%). This was not observed at 5 mg/m(2). 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. CONCLUSION: Bifenthrin-impregnated bednets at 50 mg/m(2 )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
Impact of three years of large scale Indoor Residual Spraying (IRS) and Insecticide Treated Nets (ITNs) interventions on insecticide resistance in Anopheles gambiae s.l. in Benin
Get PDF<p>Abstract</p> <p>Background</p> <p>In Benin, Indoor Residual Spraying (IRS) and long-lasting insecticidal nets (LLINs) are the cornerstones of malaria prevention. In the context of high resistance of <it>Anopheles gambiae </it>to pyrethroids, The National Malaria Control Program (NMCP) has undertaken a full coverage of IRS in a no-flood zone in the Oueme region, coupled with the distribution of LLINs in a flood zone. We assessed the impact of this campaign on phenotypic resistance, <it>kdr </it>(knock-down resistance) and <it>ace-1<sup>R </sup></it>(insensitive acetylcholinesterase) mutations.</p> <p>Methods</p> <p>Insecticides used for malaria vector control interventions were bendiocarb WP (0.4 g/m<sup>2</sup>) and deltamethrin (55 mg/m<sup>2</sup>), respectively for IRS and LLINs. Susceptibility status of <it>An. gambiae </it>was assessed using World Health Organization bioassay tests to DDT, permethrin, deltamethrin and bendiocarb in the Oueme region before intervention (2007) and after interventions in 2008 and 2010. <it>An. gambiae </it>specimens were screened for identification of species, molecular M and S forms and for the detection of the West African <it>kdr </it>(L1014F) as well as <it>ace-1<sup>R </sup></it>mutations using PCR techniques.</p> <p>Results</p> <p>The univariate logistic regression performed showed that <it>kdr </it>frequency has increased significantly during the three years in the intervention area and in the control area. Several factors (LLINs, IRS, mosquito coils, aerosols, use of pesticides for crop protection) could explain the selection of individual resistant <it>An. gambiae</it>. The <it>Kdr </it>resistance gene could not be the only mechanism of resistance observed in the Oueme region. The high susceptibility to bendiocarb is in agreement with a previous study conducted in Benin. However, the occurrence of <it>ace-1<sup>R </sup></it>heterozygous individuals even on sites far from IRS areas, suggests other factors may contribute to the selection of resistance other than those exerted by the vector control program.</p> <p>Conclusion</p> <p>The results of this study have confirmed that <it>An.gambiae </it>have maintained and developed the resistance to pyrethroids, but are still susceptible to bendiocarb. Our data clearly shows that selection of resistant individuals was caused by other insecticides than those used by the IRS and LLINs.</p
Trends in DDT and pyrethroid resistance in Anopheles gambiae s.s. populations from urban and agro-industrial settings in southern Cameroon
Get PDFBackground: Pyrethroid insecticides are widely used for insect pest control in Cameroon. In certain insect species, particularly the malaria vector Anopheles gambiae, resistance to this class of insecticides is a source of great concern and needs to be monitored in order to sustain the efficacy of vector control operations in the fields. This study highlights trends in DDT and pyrethroid resistance in wild An. gambiae populations from South Cameroon. Methods: Mosquitoes were collected between 2001 and 2007 in four sites in South Cameroon, where insecticides are used for agricultural or personal protection purposes. Insecticide use was documented in each site by interviewing residents. Batches of 2-4 days old adult female mosquitoes reared from larval collections were tested for susceptibility to DDT, permethrin and deltamethrin using standard WHO procedures. Control, dead and survivors mosquitoes from bioassays were identified by PCR-RFLP and characterized for the kdr mutations using either the AS-PCR or the HOLA method. Results: Four chemical insecticide groups were cited in the study sites: organochlorines, organophosphates, carbamates and pyrethroids. These chemicals were used for personal, crop or wood protection. In the four An. gambiae populations tested, significant variation in resistance levels, molecular forms composition and kdr frequencies were recorded in the time span of the study. Increases in DDT and pyrethroid resistance, as observed in most areas, were generally associated with an increase in the relative frequency of the S molecular form carrying the kdr mutations at higher frequencies. In Mangoum, however, where only the S form was present, a significant increase in the frequency of kdr alleles between 2003 to 2007 diverged with a decrease of the level of resistance to DDT and pyrethroids. Analyses of the kdr frequencies in dead and surviving mosquitoes showed partial correlation between the kdr genotypes and resistance phenotypes, suggesting that the kdr mechanism may act with certain cofactors to be identified. Conclusion: These results demonstrate the ongoing spread of kdr alleles in An. gambiae in Central Africa. The rapid evolution of insecticide resistance in this highly dynamic and genetically polymorphic species remains a challenge for its control
Dynamics of insecticide resistance in malaria vectors in Benin: first evidence of the presence of L1014S kdr mutation in Anopheles gambiae from West Africa
Get PDF<p>Abstract</p> <p>Background</p> <p>Insecticide resistance monitoring is essential to help national programmers to implement more effective and sustainable malaria control strategies in endemic countries. This study reported the spatial and seasonal variations of insecticide resistance in malaria vectors in Benin, West Africa.</p> <p>Methods</p> <p><it>Anopheles gambiae s.l </it>populations were collected from October 2008 to June 2010 in four sites selected on the basis of different use of insecticides and environment. WHO susceptibility tests were carried out to detect resistance to DDT, fenitrothion, bendiocarb, permethrin and deltamethrin. The synergist piperonyl butoxide was used to assess the role of non-target site mechanisms in pyrethroid resistance. <it>Anopheles gambiae </it>mosquitoes were identified to species and to molecular M and S forms using PCR techniques. Molecular and biochemical assays were carried out to determine <it>kdr </it>and <it>Ace.1<sup>R </sup></it>allelic frequencies and activity of the detoxification enzymes.</p> <p>Results</p> <p>Throughout the surveys very high levels of mortality to bendiocarb and fenitrothion were observed in <it>An. gambiae s.l</it>. populations. However, high frequencies of resistance to DDT and pyrethroids were seen in both M and S form of <it>An. gambiae s.s</it>. and <it>Anopheles arabiensis</it>. PBO increased the toxicity of permethrin and restored almost full susceptibility to deltamethrin. <it>Anopheles gambiae s.l</it>. mosquitoes from Cotonou and Malanville showed higher oxidase activity compared to the Kisumu susceptible strain in 2009, whereas the esterase activity was higher in the mosquitoes from Bohicon in both 2008 and 2009. A high frequency of <it>1014F kdr </it>allele was initially showed in <it>An. gambiae </it>from Cotonou and Tori-Bossito whereas it increased in mosquitoes from Bohicon and Malanville during the second year. For the first time the <it>L1014S kdr </it>mutation was found in <it>An. arabiensis </it>in Benin. The <it>ace.1<sup>R </sup></it>mutation was almost absent <it>in An. gambiae s.l</it>.</p> <p>Conclusion</p> <p>Pyrethroid and DDT resistance is widespread in malaria vector in Benin and both metabolic and target site resistance are implicated. Resistance was not correlated with a change of malaria species and/or molecular forms. The <it>1014S kdr </it>allele was first identified in wild population of <it>An. arabiensis </it>hence confirming the expansion of pyrethroid resistance alleles in Africa.</p
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
Get PDF<p>Abstract</p> <p>Background</p> <p>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 <it>Anopheles gambiae s.l</it>. in West and Central Africa.</p> <p>Methods</p> <p>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).</p> <p>Results</p> <p>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 <it>kdr </it>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.</p> <p>Conclusion</p> <p>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.</p
Increasing role of Anopheles funestus and Anopheles arabiensis in malaria transmission in the Kilombero Valley, Tanzania
Full text linkThe dominant Anopheles vectors of human malaria in Africa, Europe and the Middle East: occurrence data, distribution maps and bionomic précis
Get PDF<p>Abstract</p> <p>Background</p> <p>This is the second in a series of three articles documenting the geographical distribution of 41 dominant vector species (DVS) of human malaria. The first paper addressed the DVS of the Americas and the third will consider those of the Asian Pacific Region. Here, the DVS of Africa, Europe and the Middle East are discussed. The continent of Africa experiences the bulk of the global malaria burden due in part to the presence of the <it>An. gambiae </it>complex. <it>Anopheles gambiae </it>is one of four DVS within the <it>An. gambiae </it>complex, the others being <it>An. arabiensis </it>and the coastal <it>An. merus </it>and <it>An. melas</it>. There are a further three, highly anthropophilic DVS in Africa, <it>An. funestus</it>, <it>An. moucheti </it>and <it>An. nili</it>. Conversely, across Europe and the Middle East, malaria transmission is low and frequently absent, despite the presence of six DVS. To help control malaria in Africa and the Middle East, or to identify the risk of its re-emergence in Europe, the contemporary distribution and bionomics of the relevant DVS are needed.</p> <p>Results</p> <p>A contemporary database of occurrence data, compiled from the formal literature and other relevant resources, resulted in the collation of information for seven DVS from 44 countries in Africa containing 4234 geo-referenced, independent sites. In Europe and the Middle East, six DVS were identified from 2784 geo-referenced sites across 49 countries. These occurrence data were combined with expert opinion ranges and a suite of environmental and climatic variables of relevance to anopheline ecology to produce predictive distribution maps using the Boosted Regression Tree (BRT) method.</p> <p>Conclusions</p> <p>The predicted geographic extent for the following DVS (or species/suspected species complex*) is provided for Africa: <it>Anopheles </it>(<it>Cellia</it>) <it>arabiensis</it>, <it>An. </it>(<it>Cel.</it>) <it>funestus*</it>, <it>An. </it>(<it>Cel.</it>) <it>gambiae</it>, <it>An. </it>(<it>Cel.</it>) <it>melas</it>, <it>An. </it>(<it>Cel.</it>) <it>merus</it>, <it>An. </it>(<it>Cel.</it>) <it>moucheti </it>and <it>An. </it>(<it>Cel.</it>) <it>nili*</it>, and in the European and Middle Eastern Region: <it>An. </it>(<it>Anopheles</it>) <it>atroparvus</it>, <it>An. </it>(<it>Ano.</it>) <it>labranchiae</it>, <it>An. </it>(<it>Ano.</it>) <it>messeae</it>, <it>An. </it>(<it>Ano.</it>) <it>sacharovi</it>, <it>An. </it>(<it>Cel.</it>) <it>sergentii </it>and <it>An. </it>(<it>Cel.</it>) <it>superpictus*</it>. These maps are presented alongside a bionomics summary for each species relevant to its control.</p
Mixed-function oxidases and esterases associated with permethrin, deltamethrin and bendiocarb resistance in Anopheles gambiae s.l. in the south-north transect Benin, West Africa
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