Bendiocarb, a potential alternative against pyrethroid resistant Anopheles gambiae in Benin, West Africa

<p>Abstract</p> <p>Background</p> <p><it>Anopheles gambiae</it>, the main malaria vector in Benin has developed high level of resistance to pyrethroid insecticides, which is a serious concern to the future use of long-lasting insecticidal nets (LLIN) and indoor residual spraying (IRS). In this context, one of the pathways available for malaria vector control would be to investigate alternative classes of insecticides with different mode of action than that of pyrethroids. The goal of this study was to evaluate under field conditions the efficacy of a carbamate (bendiocarb) and an organophosphate (fenitrothion) against pyrethroid-resistant <it>An. gambiae s.s</it>.</p> <p>Methods</p> <p>Wild populations and females from laboratory colonies of five days old <it>An. gambiae </it>were bio-assayed during this study. Two pyrethroids (deltamethrin and alphacypermethrin), an organophosphate (fenitrothion), a carbamate (bendiocarb) and a mixture of an organophosphate (chlorpyriphos + a pyrethroid deltamethrin) were compared in experimental huts as IRS treatments. Insecticides were applied in the huts using a hand-operated compression sprayer. The deterrency, exophily, blood feeding rate and mortality induced by these insecticides against <it>An. gambiae </it>were compared to the untreated control huts.</p> <p>Results</p> <p>Deltamethrin, alphacypermethrin and bendiocarb treatment significantly reduced mosquito entry into the huts (p < 0.05) compared to untreated huts. Blood feeding rates in huts treated with fenitrothion and the mixture chlorpyriphos/deltamethrin were reduced from 10.95% respectively to 3.7% and 4.47% three months after treatment and from 10.20% to 4.4% and 2.04% four months after treatment. Exophily rates in huts with deltamethrin, alphacypermethrin and the mixture chlorpyriphos/deltamethrin were significantly higher than in the huts with fenitrothion. Deltamethrin and alphacypermethrin had the lowest mortality rate while fenitrothion killed 100% of <it>An. gambiae </it>(in the first month) and 77.8% (in the fourth month). Bendiocarb and the mixture chlorpyriphos/deltamethrin mortality rates ranged from 97.9 to 100% the first month and 77.7-88% the third month respectively.</p> <p>Conclusion</p> <p>After four months, fenitrothion, bendiocarb and the mixture chlorpyriphos/deltamethrin performed effectively against pyrethroid-resistant <it>Anopheles</it>. These results showed that bendiocarb could be recommended as an effective insecticide for use in IRS operations in Benin, particularly as the mixture chlorpyriphos/deltamethrin does not have WHOPES authorization and complaints were mentioned by the sleepers about the safety and smell of fenitrothion.</p

Molecular identification of Anopheles gambiae sensu stricto Giles (formerly Anopheles gambiae Savannah Form) in Kamuli District, Uganda

Anopheles gambiae sensu stricto Giles (formerly A. gambiae S molecular form), the largely anthropophilic species, is reportedly the most important malaria vector in Uganda among the A. gambiae complex species. Indoor and outdoor human-biting mosquitoes were caught for four consecutive nights in each of 48 households in Kamuli district using human-baited bed net traps for subsequent identification of the principal Anopheles sibling species responsible for transmitting malaria. Sibling species under the A. gambiae complex were characterized by polymerase chain reaction using species specific single nucleotide polymorphism (SNPs) in the intergenic spacer region (IGS) with primers specific for A. gambiae s.s., Anopheles arabiensis, Anopheles melas, Anopheles merus and Anopheles quadriannulatus. Molecular forms of the A. gambiae s.s. were further discriminated using primers specific for Mopti and Savannah forms. Out of 300 A. gambiae s.l. amplified, 98% (n= 294) were A. gambiae s.s. Out of 142 A. gambiae s.s. samples analyzed for molecular forms, 78.9% (n=112) were identified as A. gambiae s.s. Giles (A. gambiae Savannah (S) form, while the other 21.1% were not identifiable. the presence of A. gambiae s.s. Giles in Kamuli was also reported. Considering the anthropophilic, endophagic and endophilic behavior of A. gambiae s.s. (and of the molecularly similar A. gambiae s.s. Giles), the combined use of insecticide-treated nets (ITNs), indoor residual spraying, larval source management and improved house design in the context of integrated vector management, may be the appropriate vector control strategies in the area. There is also need for regular monitoring of the vector species composition, distribution and behavior for proper planning of appropriate vector control interventions in the future.Key words: Sibling species, molecular forms, Anopheles gambiae complex, anthropophily, IPM

Evaluation du comportement trophique de Aedes aegypti dans la ville de cotonou au sud du Bénin

In order to evaluate the trophic behavior of Aedes aegypti in the city of Cotonou, southern Benin, a cross-sectional study was conducted in urban and periurban neighborhoods from April 2016 to August 2017 to collect Ae. Aegypti populations. To achieve this goal, day and night collections, twice a month for one year were done where Ae. Aegypti populations were caught by Human Landing Catch and BG-Sentinel traps. 3,892 Aedes caught by different methods showed that Ae. Aegypti and Ae. circumluteolus are more abundant in urban than peri-urban areas (p&lt;0.05). The aggressive density of Ae. aegypti populations was significantly higher in urban areas (157.43 bites per man per hour) than in peri-urban areas (32.43 bites per man per hour) (p&lt;0.05). Also, out of 250 females blood-fed Ae. Aegypti tested by ELISA (Enzyme Linked Immunosorbent Assay) technique for blood meal identification, 86.80% took their blood meal on humans compared to 4.4% which took their blood meal on sheeps. These findings showed that the city of Cotonou in southern Benin, offered good condition for the development of Ae. aegypti population. The anthropology and endophagy behavior of this mosquito observed through the results of this study is a very favorable clue to vector control strategies based on the use of long-lasting impregnated mosquito nets and insecticide residual sprays adopted in Benin

Sensibilité des populations d’ Aedes Aegypti vis-à-vis des organochlorés, pyréthrinoïdes et des carbamates dans la commune de Natitingou au Nord-Est du Bénin

Insecticide treatments for crop protection have often be cited as the main factor of the resistance selection of Aedes aegypti. This is however the main vector dengue fever. To verify this hypothesis, bioassay tests was performed on adults collected from the field (2 urban and 2 rural areas) at Natitingou to assess the susceptibility of dengue vectors to insecticideimpregnated papers (permethrin 0.75%, delthamethrin 0.05%, lambdacyalothrin 0.05%, DDT 4%, and bendiocarb 0.1%) following WHO Pesticide Evaluation Scheme. Results from this study showed that Ae. Aegypti populations were resistant to DDT and pyrethroids with 12% and 38% respectively as mean of mortality despite the areas of mosquitoes collection. However, they were fully susceptible to bendiocarb. Our study showed that Aedes aegypti populations had developed resistance to organochlorine and pyrethroids, but are susceptible to carbamate. The low mortality rate recorded in all populations of Ae. Aegypti with bendiocarb is encouraging in regards to the use of this insecticide as an alternative in case of outbreak of dengue fever in this district of Benin

The impact of the expansion of urban vegetable farming on malaria transmission in major cities of Benin

BACKGROUND: Urban agricultural practices are expanding in several cities of the Republic of Benin. This study aims to assess the impact of such practices on transmission of the malaria parasite in major cities of Benin. METHOD: A cross sectional entomological study was carried out from January to December 2009 in two vegetable farming sites in southern Benin (Houeyiho and Acron) and one in the northern area (Azèrèkè). The study was based on sampling of mosquitoes by Human Landing Catches (HLC) in households close to the vegetable farms and in others located far from the farms. RESULTS: During the year of study, 71,678 female mosquitoes were caught by HLC of which 25% (17,920/71,678) were Anopheles species. In the areas surveyed, the main malaria parasite, Plasmodium falciparum was transmitted in the south by Anopheles gambiae s.s. Transmission was high during the two rainy seasons (April to July and October to November) but declined in the two dry seasons (December to March and August to September). In the north, transmission occurred from June to October during the rainy season and was vehicled by two members of the An. gambiae complex: Anopheles gambiae s.s. (98%) and Anopheles arabiensis (2%).At Houeyiho, Acron and Azèrèkè, the Entomological Inoculation Rates (EIRs) and the Human Biting Rates (HBRs) were significantly higher during the dry season in Households Close to Vegetable Farms (HCVF) than in those located far from the vegetable areas (HFVF) (p 0.05).The knock-down resistance (kdr) mutation was the main resistance mechanism detected at high frequency (0.86 to 0.91) in An. gambiae s.l. at all sites. The ace-1R mutation was also found but at a very low frequency (< 0.1). CONCLUSION: These findings showed that communities living close to vegetable farms are permanently exposed to malaria throughout the year, whereas the risk in those living far from such agricultural practices is limited and only critical during the rainy seasons. Measures must be taken by African governments to create awareness among farmers and ultimately decentralize farming activities from urban to rural areas where human-vector contact is limited

Cotton pest management practices and the selection of pyrethroid resistance in Anopheles gambiae population in Northern Benin

<p>Abstract</p> <p>Background</p> <p>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 <it>Anopheles gambiae </it>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 <it>An. gambiae </it>in surrounding breeding sites.</p> <p>Methods</p> <p>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 <it>An. gambiae</it>. 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.</p> <p>Results</p> <p>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.</p> <p>Susceptibility test results confirmed a high resistance to DDT. Mean mortality of <it>An. gambiae </it>collected from the farms practicing CCP, TICP and BP methods were 33%, 42% and 65% respectively. <it>An. gambiae </it>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 <it>An. gambiae </it>from BP areas gave a high level of susceptibility to permethrin with an average mortality of 94%.</p> <p>Molecular analysis identified <it>An. gambiae </it>s.s, and <it>An. arabiensis </it>with a high predominance of <it>An. gambiae s.s </it>(90%). The two molecular forms, M and S, were also determined with a high frequency of the S form (96%).</p> <p>The <it>Kdr </it>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 <it>ace-1R </it>gene was very low (< 0.1).</p> <p>The presence of inhibiting factors in soil samples under insecticide treatments were found and affected negatively in delaying the development of <it>An. gambiae </it>larval populations.</p> <p>Conclusions</p> <p>This research shows that <it>Kdr </it>has spread widely in <it>An. gambiae</it>, 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 <it>An. gambiae </it>populations.</p

Insecticide resistance status in Anopheles gambiae in southern Benin

BACKGROUND: The emergence of pyrethroid resistance in Anopheles gambiae has become a serious concern to the future success of malaria control. In Benin, the National Malaria Control Programme has recently planned to scaling up long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) for malaria prevention. It is, therefore, crucial to monitor the level and type of insecticide resistance in An. gambiae, particularly in southern Benin where reduced efficacy of insecticide-treated nets (ITNs) and IRS has previously been reported. METHODS: The protocol was based on mosquito collection during both dry and rainy seasons across forty districts selected in southern Benin. Bioassay were performed on adults collected from the field to assess the susceptibility of malaria vectors to insecticide-impregnated papers (permethrin 0.75%, delthamethrin 0.05%, DDT 4%, and bendiocarb 0.1%) following WHOPES guidelines. The species within An. gambiae complex, molecular form and presence of kdr and ace-1 mutations were determined by PCR. RESULTS: Strong resistance to permethrin and DDT was found in An. gambiae populations from southern Benin, except in Aglangandan where mosquitoes were fully susceptible (mortality 100%) to all insecticides tested. PCR showed the presence of two sub-species of An. gambiae, namely An. gambiae s.s, and Anopheles melas, with a predominance for An. gambiae s.s (98%). The molecular M form of An. gambiae was predominant in southern Benin (97%). The kdr mutation was detected in all districts at various frequency (1% to 95%) whereas the Ace-1 mutation was found at a very low frequency (<or= 5%). CONCLUSION: This study showed a widespread resistance to permethrin in An. gambiae populations from southern Benin, with a significant increase of kdr frequency compared to what was observed previously in Benin. The low frequency of Ace-1 recorded in all populations is encouraging for the use of bendiocarb as an alternative insecticide to pyrethroids for IRS in Benin

Development of vegetable farming: a cause of the emergence of insecticide resistance in populations of Anopheles gambiae in urban areas of Benin

<p>Abstract</p> <p>Background</p> <p>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 <it>Anopheles gambiae</it>.</p> <p>Methods</p> <p>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 <it>An. gambiae</it>.</p> <p>Results</p> <p>This research showed that:</p> <p>(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;</p> <p>(2) Urban agriculture increases the farmers' household income and their living standard;</p> <p>(3) At a molecular level, PCR revealed the presence of three sub-species of <it>An. gambiae </it>(<it>An. gambiae s.s., Anopheles melas and Anopheles arabiensis</it>) and two molecular forms (M and S). The <it>kdr </it>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 <it>An. gambiae </it>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).</p> <p>Conclusion</p> <p>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.</p

Attrition, physical integrity and insecticidal activity of long-lasting insecticidal nets in sub-Saharan Africa and modelling of their impact on vectorial capacity

Long-lasting insecticidal nets (LLINs) are the primary malaria prevention and control intervention in many parts of sub-Saharan Africa. While LLINs are expected to last at least 3 years under normal use conditions, they can lose effectiveness because they fall out of use, are discarded, repurposed, physically damaged, or lose insecticidal activity. The contributions of these different interrelated factors to durability of nets and their protection against malaria have been unclear.; Starting in 2009, LLIN durability studies were conducted in seven countries in Africa over 5 years. WHO-recommended measures of attrition, LLIN use, insecticidal activity, and physical integrity were recorded for eight different net brands. These data were combined with analyses of experimental hut data on feeding inhibition and killing effects of LLINs on both susceptible and pyrethroid resistant malaria vectors to estimate the protection against malaria transmission-in terms of vectorial capacity (VC)-provided by each net cohort over time. Impact on VC was then compared in hypothetical scenarios where one durability outcome measure was set at the best possible level while keeping the others at the observed levels.; There was more variability in decay of protection over time by country than by net brand for three measures of durability (ratios of variance components 4.6, 4.4, and 1.8 times for LLIN survival, use, and integrity, respectively). In some countries, LLIN attrition was slow, but use declined rapidly. Non-use of LLINs generally had more effect on LLIN impact on VC than did attrition, hole formation, or insecticide loss.; There is much more variation in LLIN durability among countries than among net brands. Low levels of use may have a larger impact on effectiveness than does variation in attrition or LLIN degradation. The estimated entomological effects of chemical decay are relatively small, with physical decay probably more important as a driver of attrition and non-use than as a direct cause of loss of effect. Efforts to maximize LLIN impact in operational settings should focus on increasing LLIN usage, including through improvements in LLIN physical integrity. Further research is needed to understand household decisions related to LLIN use, including the influence of net durability and the presence of other nets in the household

The evolving SARS-CoV-2 epidemic in Africa: insights from rapidly expanding genomic surveillance

Investment in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequencing in Africa over the past year has led to a major increase in the number of sequences that have been generated and used to track the pandemic on the continent, a number that now exceeds 100,000 genomes. Our results show an increase in the number of African countries that are able to sequence domestically and highlight that local sequencing enables faster turnaround times and more-regular routine surveillance. Despite limitations of low testing proportions, findings from this genomic surveillance study underscore the heterogeneous nature of the pandemic and illuminate the distinct dispersal dynamics of variants of concern—particularly Alpha, Beta, Delta, and Omicron—on the continent. Sustained investment for diagnostics and genomic surveillance in Africa is needed as the virus continues to evolve while the continent faces many emerging and reemerging infectious disease threats. These investments are crucial for pandemic preparedness and response and will serve the health of the continent well into the 21st century