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Insects Apr 2024Epidemics of arboviruses in general, and dengue fever in particular, are an increasing threat in areas where is present. The effectiveness of chemical control of is...
Epidemics of arboviruses in general, and dengue fever in particular, are an increasing threat in areas where is present. The effectiveness of chemical control of is jeopardized by the increasing frequency of insecticide resistance. The aim of this study was to determine the susceptibility status of to public health insecticides and assess the underlying mechanisms driving insecticide resistance. eggs were collected in two study sites in the vicinity of houses for two weeks using gravid traps (GATs). After rearing the mosquitoes to adulthood, female were exposed to diagnostic doses of permethrin, deltamethrin and bendiocarb, using Centers for Disease Control and Prevention (CDC) bottle bioassays. Unexposed, un-engorged female were tested individually for mixed-function oxidase (MFO), glutathione--transferase (GST) and α and β esterase activities. Finally, allele-specific PCR (AS-PCR) was used to detect possible mutations (F1534C, S989P, and V1016G) in the voltage-gated sodium channel gene in insecticide-exposed Most traps were oviposition positive; 93.2% and 97% of traps contained eggs in the 10 arrondissement of Cotonou and in Godomey-Togoudo, respectively. Insecticide bioassays detected resistance to permethrin and deltamethrin in both study sites and complete susceptibility to bendiocarb. By comparison to the insecticide-susceptible Rockefeller strain, field populations had significantly higher levels of GSTs and significantly lower levels of α and β esterases; there was no significant difference between levels of MFOs. AS-PCR genotyping revealed the possible presence of 3 mutations (F1534C, S989P, and V1016G) at high frequencies; 80.9% (228/282) of the tested had at least 1 mutation, while the simultaneous presence of all 3 mutations was identified in 13 resistant individuals. Study findings demonstrated phenotypic pyrethroid resistance, the over-expression of key detoxification enzymes, and the possible presence of several mutations in populations, emphasizing the urgent need to implement vector control strategies targeting arbovirus vector species in Benin.
PubMed: 38667425
DOI: 10.3390/insects15040295 -
MedRxiv : the Preprint Server For... Mar 2024Tororo District, Uganda experienced a dramatic decrease in malaria burden from 2015-19 following 5 years of indoor residual spraying (IRS) with carbamate (Bendiocarb)...
BACKGROUND
Tororo District, Uganda experienced a dramatic decrease in malaria burden from 2015-19 following 5 years of indoor residual spraying (IRS) with carbamate (Bendiocarb) and then organophosphate (Actellic) insecticides. However, a marked resurgence occurred in 2020, which coincided with a change to a clothianidin-based IRS formulations (Fludora Fusion/SumiShield). To quantify the magnitude of the resurgence, investigate causes, and evaluate the impact of a shift back to IRS with Actellic in 2023, we assessed changes in malaria metrics in regions within and near Tororo District.
METHODS
Malaria surveillance data from Nagongera Health Center, Tororo District was included from 2011-2023. In addition, a cohort of 667 residents from 84 houses was followed from August 2020 through September 2023 from an area bordering Tororo and neighboring Busia District, where IRS has never been implemented. Cohort participants underwent passive surveillance for clinical malaria and active surveillance for parasitemia every 28 days. Mosquitoes were collected in cohort households every 2 weeks using CDC light traps. Female were speciated and tested for sporozoites and phenotypic insecticide resistance. Temporal comparisons of malaria metrics were stratified by geographic regions.
FINDINGS
At Nagongera Health Center average monthly malaria cases varied from 419 prior to implementation of IRS; to 56 after 5 years of IRS with Bendiocarb and Actellic; to 1591 after the change in IRS to Fludora Fusion/SumiShield; to 155 after a change back to Actellic. Among cohort participants living away from the border in Tororo, malaria incidence increased over 8-fold (0.36 vs. 2.97 episodes per person year, p<0.0001) and parasite prevalence increased over 4-fold (17% vs. 70%, p<0.0001) from 2021 to 2022 when Fludora Fusion/SumiShield was used. Incidence decreased almost 5-fold (2.97 vs. 0.70, p<0.0001) and prevalence decreased by 39% (70% vs. 43%, p<0.0001) after shifting back to Actellic. There was a similar pattern among those living near the border in Tororo, with increased incidence between 2021 and 2022 (0.93 vs. 2.40, p<0.0001) followed by a decrease after the change to Actellic (2.40 vs. 1.33, p<0.001). Among residents of Busia, malaria incidence did not change significantly over the 3 years of observation. Malaria resurgence in Tororo was temporally correlated with the replacement of by as the primary vector, with a marked decrease in the density of following the shift back to IRS with Actellic. In Busia, remained the primary vector throughout the observation period. Sporozoite rates were approximately 50% higher among compared to the other common malaria vectors. Insecticide resistance phenotyping of revealed high tolerance to clothianidin, but full susceptibility to Actellic.
CONCLUSIONS
A dramatic resurgence of malaria in Tororo was temporally associated with a change to clothianidin-based IRS formulations and emergence of as the predominant vector. Malaria decreased after a shift back to IRS with Actellic. This study highlights the ability of malaria vectors to rapidly circumvent control efforts and the importance of high-quality surveillance systems to assess the impact of malaria control interventions and generate timely, actionable data.
PubMed: 38559091
DOI: 10.1101/2024.03.15.24304352 -
Parasites & Vectors Mar 2024Indoor residual spraying (IRS) was first implemented in the Atacora department, Benin from 2011 to 2012 using bendiocarb (carbamate) followed by annual spraying with...
The frequency of kdr and ace-1 alleles in Anopheles gambiae s.l. before and during indoor residual spraying (IRS) implementation and four years after IRS withdrawal in three districts in Atacora, Benin.
BACKGROUND
Indoor residual spraying (IRS) was first implemented in the Atacora department, Benin from 2011 to 2012 using bendiocarb (carbamate) followed by annual spraying with pirimiphos-methyl (organophosphate) from 2013 to 2018. Before and after IRS implementation in Atacora, standard pyrethroid insecticide-treated bed nets were the main method of vector control in the area. This study investigated the knockdown resistance (kdr) gene (L1014F) and the acetylcholinesterase (ace-1) gene (G119S), before and during IRS implementation, and 4-years after IRS withdrawal from Atacora. This was done to assess how changes in insecticide pressure from indoor residual spraying may have altered the genotypic resistance profile of Anopheles gambiae s.l.
METHOD
Identification of sibling species of An. gambiae s.l. and detection of the L1014F mutation in the kdr gene and G119S mutation in ace-1 genes was done using molecular analysis. Allelic and genotypic frequencies were calculated and compared with each other before and during IRS implementation and 4 years after IRS withdrawal. The Hardy-Weinberg equilibrium and genetic differentiation within and between populations were assessed.
RESULTS
Prevalence of the L1014F mutation in all geographic An. gambiae s.l. (An. gambiae s.s., Anopheles. coluzzii, Anopheles. arabiensis, and hybrids of "An. gambiae s.s. and An. coluzzii") populations increased from 69% before IRS to 87% and 90% during and after IRS. The G119S allele frequency during IRS (20%) was significantly higher than before IRS implementation (2%). Four years after IRS withdrawal, allele frequencies returned to similar levels as before IRS (3%). Four years after IRS withdrawal, the populations showed excess heterozygosity at the ace-1 gene and deficit heterozygosity at the kdr gene, whereas both genes had excess heterozygosity before and during IRS (F < 0). No genetic differentiation was observed within the populations.
CONCLUSIONS
This study shows that the withdrawal of IRS with bendiocarb and pirimiphos-methyl may have slowed down the selection of individual mosquitoes with ace-1 resistance alleles in contrast to populations of An. gambiae s.l. with the L1014F resistance allele of the kdr gene. This may suggest that withdrawing the use of carbamates or organophosphates from IRS or rotating alternative insecticides with different modes of action may slow the development of ace-1 insecticide-resistance mutations. The increase in the prevalence of the L1014F mutation of the kdr gene in the population, despite the cessation of IRS, could be explained by the growing use of pyrethroids and DDT in agriculture and for other domestic use. More observational studies in countries where carbamates or organophosphates are still being used as public health insecticides may provide additional insights into these associations.
Topics: Animals; Insecticides; Anopheles; Benin; Alleles; Acetylcholinesterase; Mosquito Vectors; Pyrethrins; Insecticide Resistance; Carbamates; Organophosphates; Mosquito Control; Phenylcarbamates
PubMed: 38454494
DOI: 10.1186/s13071-024-06206-8 -
Malaria Journal Mar 2024There are several indications that pesticides used in agriculture contribute to the emergence and spread of resistance of mosquitoes to vector control insecticides....
The impact of agrochemical pollutant mixtures on the selection of insecticide resistance in the malaria vector Anopheles gambiae: insights from experimental evolution and transcriptomics.
BACKGROUND
There are several indications that pesticides used in agriculture contribute to the emergence and spread of resistance of mosquitoes to vector control insecticides. However, the impact of such an indirect selection pressure has rarely been quantified and the molecular mechanisms involved are still poorly characterized. In this context, experimental selection with different agrochemical mixtures was conducted in Anopheles gambiae. The multi-generational impact of agrochemicals on insecticide resistance was evaluated by phenotypic and molecular approaches.
METHODS
Mosquito larvae were selected for 30 generations with three different agrochemical mixtures containing (i) insecticides, (ii) non-insecticides compounds, and (iii) both insecticide and non-insecticide compounds. Every five generations, the resistance of adults to deltamethrin and bendiocarb was monitored using bioassays. The frequencies of the kdr (L995F) and ace1 (G119S) target-site mutations were monitored every 10 generations. RNAseq was performed on all lines at generation 30 in order to identify gene transcription level variations and polymorphisms associated with each selection regime.
RESULTS
Larval selection with agrochemical mixtures did not affect bendiocarb resistance and did not select for ace1 mutation. Contrastingly, an increased deltamethrin resistance was observed in the three selected lines. Such increased resistance was not majorly associated with the presence of kdr L995F mutation in selected lines. RNA-seq identified 63 candidate resistance genes over-transcribed in at least one selected line. These include genes coding for detoxification enzymes or cuticular proteins previously associated with insecticide resistance, and other genes potentially associated with chemical stress response. Combining an allele frequency filtering with a Bayesian FST-based genome scan allowed to identify genes under selection across multiple genomic loci, supporting a multigenic adaptive response to agrochemical mixtures.
CONCLUSION
This study supports the role of agrochemical contaminants as a significant larval selection pressure favouring insecticide resistance in malaria vectors. Such selection pressures likely impact kdr mutations and detoxification enzymes, but also more generalist mechanisms such as cuticle resistance, which could potentially lead to cross-tolerance to unrelated insecticide compounds. Such indirect effect of global landscape pollution on mosquito resistance to public health insecticides deserves further attention since it can affect the nature and dynamics of resistance alleles circulating in malaria vectors and impact the efficacy of control vector strategies.
Topics: Animals; Anopheles; Agrochemicals; Environmental Pollutants; Insecticides; Bayes Theorem; Insecticide Resistance; Malaria; Mosquito Vectors; Gene Expression Profiling; Nitriles; Pyrethrins; Phenylcarbamates
PubMed: 38443984
DOI: 10.1186/s12936-023-04791-0 -
Evolutionary Applications Feb 2024Molecular mechanisms driving the escalation of pyrethroid resistance in the major malaria mosquitoes of Central Africa remain largely uncharacterized, hindering...
Molecular mechanisms driving the escalation of pyrethroid resistance in the major malaria mosquitoes of Central Africa remain largely uncharacterized, hindering effective management strategies. Here, resistance intensity and the molecular mechanisms driving it were investigated in a population of from northern Cameroon. High levels of pyrethroid and organochloride resistance were observed in population, with no mortality for 1× permethrin; only 11% and 33% mortalities for 5× and 10× permethrin diagnostic concentrations, and <2% mortalities for deltamethrin and DDT, respectively. Moderate bendiocarb resistance (88% mortality) and full susceptibility to malathion were observed. Synergist bioassays with piperonyl butoxide recovered permethrin susceptibility, with mortalities increasing to 53.39%, and 87.30% for 5× and 10× permethrin, respectively, implicating P450 monooxygenases. Synergist bioassays with diethyl maleate (DEM) recovered permethrin and DDT susceptibilities (mortalities increasing to 34.75% and 14.88%, respectively), implicating glutathione -transferases. RNA-seq-based genome-wide transcriptional analyses supported by quantitative PCR identified glutathione -transferase, (RNA-seqFC = 2.93 and qRT-PCRFC = 8.4, < 0.0043) and CYP450, (RNA-seqFC = 2.39 and qRT-PCRFC = 11.7, < 0.0177) as the most overexpressed detoxification genes in the pyrethroid-resistant mosquitoes, compared to mosquitoes of the susceptible Ngousso colony. Other overexpressed genes include P450s, (FC = 1.68, < 0.0114), (FC = 2.02, < 0.0005), and (FC = 1.86, < 0.0276). While high frequency of the 1014F mutation (50%) and low frequencies of 1014S (6.61%) and 1575Y (10.29%) were observed, no -1 mutation was detected in bendiocarb-resistant populations, suggesting the preeminent role of metabolic mechanism. Overexpression of metabolic resistance genes (including and known to confer resistance to multiple insecticides) in from the Sudan Savannah of Cameroon highlights the need for alternative management strategies to reduce malaria burden in northern Cameroon.
PubMed: 38410533
DOI: 10.1111/eva.13641 -
PLoS Neglected Tropical Diseases Feb 2024Insecticide resistance is a serious threat to our ability to control mosquito vectors which transmit pathogens including malaria parasites and arboviruses. Understanding...
Insecticide resistance is a serious threat to our ability to control mosquito vectors which transmit pathogens including malaria parasites and arboviruses. Understanding the underlying mechanisms is an essential first step in tackling the challenges presented by resistance. This study aimed to functionally characterise the carboxylesterase, CCEae3A, the elevated expression of which has been implicated in temephos resistance in Aedes aegypti and Aedes albopictus larvae. Using our GAL4/UAS expression system, already established in insecticide-sensitive Anopheles gambiae mosquitoes, we produced transgenic An. gambiae mosquitoes that express an Ae. aegypti CCEae3A ubiquitously. This new transgenic line permits examination of CCEae3A expression in a background in which there is not a clear orthologue in Vectorbase and allows comparison with existing An. gambiae GAL4-UAS lines. Insecticide resistance profiling of these transgenic An. gambiae larvae indicated significant increases in resistance ratio for three organophosphate insecticides, temephos (6), chloropyriphos (6.6) and fenthion (3.2) when compared to the parental strain. Cross resistance to adulticides from three major insecticide classes: organophosphates (malathion, fenitrothion and pirimiphos methyl), carbamates (bendiocarb and propoxur) and pyrethroid (alpha-cypermethrin) was also detected. Resistance to certain organophosphates and carbamates validates conclusions drawn from previous expression and phenotypic data. However, detection of resistance to pirimiphos methyl and alphacypermethrin has not previously been formally associated with CCEae3A, despite occurring in Ae. aegypti strains where this gene was upregulated. Our findings highlight the importance of characterising individual resistance mechanisms, thereby ensuring accurate information is used to guide future vector control strategies.
Topics: Animals; Aedes; Carbamates; Insecticides; Organophosphates; Temefos; Animals, Genetically Modified; Pyrethrins; Organothiophosphorus Compounds
PubMed: 38377131
DOI: 10.1371/journal.pntd.0011595 -
Malawi Medical Journal : the Journal of... Sep 2023The rise in rice production in the district of Malanville, Northen Benin, is a present concern, as it has resulted in the widespread usage of pesticides for crop...
AIM
The rise in rice production in the district of Malanville, Northen Benin, is a present concern, as it has resulted in the widespread usage of pesticides for crop protection. This could impact human health but also life cycle of , the main vector of malaria.
METHODS
Therefore, insecticide susceptibility bioassays were carried out on populations of s.l aged to 3-5 days old (two from areas where insecticide is highly used and other two areas of low insecticide use) and subjected to insecticide-impregnated papers (Permethrin 0.75%; deltamethrin 0.05%; DDT 4% and bendiocarb 0.1%) following WHO protocol. Polymerase Chain Reactions (PCRs) were used for the detection of Acethlylcholinestrase (Ace-1) and the knock down resistance (kdr) L1014F mutations in populations. Finally, indirect bioassays were conducted for the investigating on the factors affecting the life cycle of due to the use of pesticides.
RESULTS
from the four sites were resistant to DDT (6 to 8% and 10 to 14% respectively from areas of high and low dose), pyrethroids (22 to 26% and 30 to 36% for permethrin, from areas of high and low dose respectively and 66 to 70% and 72 to 80% for deltamethrin, from high and low dose) but susceptible to carbamate. The kdr L1014F mutation was detected in populations (0.88 to 0.90 and 0.84 to 0.88 from high and low dose, respectively). The ace-1 was detected at low frequencies (<0.002). Bioassays on the impacts of the use of pesticides in the life cycle of showed that soil substrates with pesticides residues have a negative impact on the life cycle eggs of .
CONCLUSION
These findings confirmed the negative impacts of pesticides use in rice farming and its impacts on the life cycle of .
Topics: Animals; Humans; Aged; Insecticide Resistance; Insecticides; Permethrin; Anopheles; Oryza; Benin; DDT; Mosquito Vectors; Agriculture; Nitriles; Pyrethrins
PubMed: 38362286
DOI: 10.4314/mmj.v35i3.6 -
Malaria Journal Dec 2023The primary reason for the failure of malaria vector control across endemic regions is the widespread insecticide resistance observed in Anopheles vectors. The most... (Review)
Review
The primary reason for the failure of malaria vector control across endemic regions is the widespread insecticide resistance observed in Anopheles vectors. The most dominant African vectors of malaria parasites are Anopheles gambiae and Anopheles funestus mosquitoes. These species often exhibit divergent behaviours and adaptive changes underscoring the importance of deploying active and effective measures in their control. Unlike An. gambiae, An. funestus mosquitoes are poorly studied in Benin Republic. However, recent reports indicated that An. funestus can adapt and colonize various ecological niches owing to its resistance against insecticides and adaptation to changing breeding habitats. Unfortunately, scientific investigations on the contribution of An. funestus to malaria transmission, their susceptibility to insecticide and resistance mechanism developed are currently insufficient for the design of better control strategies. In an attempt to gather valuable information on An. funestus, the present review examines the progress made on this malaria vector species in Benin Republic and highlights future research perspectives on insecticide resistance profiles and related mechanisms, as well as new potential control strategies against An. funestus. Literature analysis revealed that An. funestus is distributed all over the country, although present in low density compared to other dominant malaria vectors. Interestingly, An. funestus is being found in abundance during the dry seasons, suggesting an adaptation to desiccation. Among the An. funestus group, only An. funestus sensu stricto (s.s.) and Anopheles leesoni were found in the country with An. funestus s.s. being the most abundant species. Furthermore, An. funestus s.s. is the only one species in the group contributing to malaria transmission and have adapted biting times that allow them to bite at dawn. In addition, across the country, An. funestus were found resistant to pyrethroid insecticides used for bed nets impregnation and also resistant to bendiocarb which is currently being introduced in indoor residual spraying formulation in malaria endemic regions. All these findings highlight the challenges faced in controlling this malaria vector. Therefore, advancing the knowledge of vectorial competence of An. funestus, understanding the dynamics of insecticide resistance in this malaria vector, and exploring alternative vector control measures, are critical for sustainable malaria control efforts in Benin Republic.
Topics: Animals; Insecticide Resistance; Insecticides; Anopheles; Malaria; Benin; Mosquito Vectors; Mosquito Control
PubMed: 38129880
DOI: 10.1186/s12936-023-04815-9 -
BioRxiv : the Preprint Server For... Dec 2023Malaria control relies on insecticides targeting the mosquito vector, but this is increasingly compromised by insecticide resistance, which can be achieved by elevated...
Malaria control relies on insecticides targeting the mosquito vector, but this is increasingly compromised by insecticide resistance, which can be achieved by elevated expression of detoxifying enzymes that metabolize the insecticide. In diploid organisms, gene expression is regulated both in , by regulatory sequences on the same chromosome, and by acting factors, affecting both alleles equally. Differing levels of transcription can be caused by mutations in -regulatory modules (CRM), but few of these have been identified in mosquitoes. We crossed bendiocarb resistant and susceptible A strains to identify -regulated genes that might be responsible for the resistant phenotype using RNAseq, and -regulatory module sequences controlling gene expression in insecticide resistance relevant tissues were predicted using machine learning. We found 115 genes showing allele specific expression in hybrids of insecticide susceptible and resistant strains, suggesting regulation is an important mechanism of gene expression regulation in The genes showing allele specific expression included a higher proportion of specific genes on average younger than genes those with balanced allelic expression.
PubMed: 38045426
DOI: 10.1101/2023.11.22.568226 -
Heliyon Nov 2023Regular monitoring of insecticide resistance status is an important step in implementing appropriate and adapted insecticide-based strategies for vector control. In...
Regular monitoring of insecticide resistance status is an important step in implementing appropriate and adapted insecticide-based strategies for vector control. In Senegal, Indoor Residual Spraying (IRS) and a national distribution campaign for long-lasting insecticide-treated net (LLIN) have been implemented since 2007 and 2009, respectively to prevent malaria transmission. To expand and ensure the sustainability of these strategies, we conducted a study on the status of insecticide resistance in malaria vectors in the seaside area of Mbour and its suburbs where no data were previously available. larvae were sampled from four study sites (two in both coastal and inland areas) and reared to adulthood in the insectarium. Non-blood-fed females aged 3-5 days were then tested for susceptibility to permethrin, deltamethrin, lambdacyhalothrin, bendiocarb and pirimiphos-methyl. PCR amplification was used to identify sibling species of the complex and genotyping for the presence of resistance knockdown (kdr) , and . was the only species present in the area. At all four sites, mosquitoes were resistant to deltamethrin, permethrin, and lambdacyhalothrin, and exhibited varying degrees of resistance to bendiocarb and pirimiphos-methyl. Overall, high levels of leucine-serine/phenylalanine substitutions at position 1014 (/) were observed, with frequencies ranging from 76.4 to 85.2 % for , and from 43.2 to 66.7 % for , compared to 8.1 to 28.3 for the mutation. These results indicate a high level of phenotypic and genotypic resistance to insecticides, which is alarming, as it could have a significant impact on the operational effectiveness of current vector control tools that rely on pyrethroids. However, in the case of bendiocarb and pirimiphos-methyl, while some level of tolerance was observed, their potential use requires regular monitoring to prevent operational failure, as their deployment could potentially lead to an increase in resistance to them.
PubMed: 38027803
DOI: 10.1016/j.heliyon.2023.e21968