47 research outputs found
Biology and Behaviour of Aedes aegypti in the Human Environment: Opportunities for Vector Control of Arbovirus Transmission
Get PDFAedes aegypti is a ubiquitous vector of arboviruses mostly in urbanised areas throughout the tropics and subtropics and a growing threat beyond. Control of Ae. aegypti is difficult and costly, and no vaccines are available for most of the viruses it transmits. With practical control solutions our goal, ideally suitable for delivery by householders in affected communities, we reviewed the literature on adult Ae. aegypti biology and behaviour, within and close to the human home, the arena where such interventions must impact.
We found that knowledge was vague or important details were missing for multiple events or activities in the mosquito life cycle, such as the duration or location of the many periods when females rest between blood feeding and oviposition. The existing body of literature, though substantial, is not wholly reliable, and evidence for commonly held âfactsâ range from untraceable to extensive. Source references of some basic information are poor or date back more than 60 years, while other information that today is accepted widely as âfactâ is not supported by evidence in the literature.
Many topics, e.g., sugar feeding, resting preferences (location and duration), and blood feeding, merit being revisited in new geographical regions and ecological contexts to identify vulnerabilities for exploitation in contro
Insecticide resistance in Anopheles gambiae: data from the first year of a multi-country study highlight the extent of the problem
Get PDF<p>Abstract</p> <p>Background</p> <p>Insecticide resistance in malaria vectors is a growing concern in many countries which requires immediate attention because of the limited chemical arsenal available for vector control. The current extent and distribution of this resistance in many parts of the continent is unknown and yet such information is essential for the planning of effective malaria control interventions.</p> <p>Methods</p> <p>In 2008, a network was established, with financial support from WHO/TDR, to investigate the extent of insecticide resistance in malaria vectors in five African countries. Here, the results of bioassays on <it>Anopheles gambiae sensu lato </it>from two rounds of monitoring from 12 sentinel sites in three of the partner countries are reported.</p> <p>Results</p> <p>Resistance is very heterogeneous even over relatively small distances. Furthermore, in some sites, large differences in mortality rates were observed during the course of the malaria transmission season. Using WHO diagnostic doses, all populations from Burkina Faso and Chad and two of the four populations from Sudan were classified as resistant to permethrin and/or deltamethrin. Very high frequencies of DDT resistance were found in urban areas in Burkina Faso and Sudan and in a cotton-growing district in Chad. In areas where both <it>An. gambiae s.s</it>. and <it>Anopheles arabiensis </it>were present, resistance was found in both species, although generally at a higher frequency in <it>An gambiae s.s</it>. <it>Anopheles gambiae s.l</it>. remains largely susceptible to the organophosphate fenitrothion and the carbamate bendiocarb in the majority of the sentinel sites with the exception of two sites in Burkina Faso. In the cotton-growing region of Soumousso in Burkina Faso, the vector population is resistant to all four classes of insecticide available for malaria control.</p> <p>Conclusions</p> <p>Possible factors influencing the frequency of resistant individuals observed in the sentinel sites are discussed. The results of this study highlight the importance of standardized longitudinal insecticide resistance monitoring and the urgent need for studies to monitor the impact of this resistance on malaria vector control activities.</p
Detection of G119S ace-1 R mutation in field-collected Anopheles gambiae mosquitoes using allele-specific loop-mediated isothermal amplification (AS-LAMP) method
Get PDFAdhesion and virulence properties of native Metarhizium fungal strains from Burkina Faso for the control of malaria vectors
Get PDFBackground: Local strains of the entomopathogenic fungus Metarhizium pingshaense in Burkina Faso have demonstrated remarkable virulence against malaria vectors, positioning them as promising candidates for inclusion in the future arsenal of malaria control strategies. However, the underlying mechanisms responsible for this virulence remain
unknown. To comprehend the fungal infection process, it is crucial to investigate the attachment mechanisms of fungal spores to the mosquito cuticle and explore the relationship between virulence and attachment kinetics. This study aims to assess the adhesion and virulence properties of native Metarhizium fungal strains from Burkina Faso for controlling malaria vectors.
Methods: Fungal strains were isolated from 201 insects and 1399 rhizosphere samples, and four strains of Metarhizium fungi were selected. Fungal suspensions were used to infect 3-day-old female Anopheles coluzzii mosquitoes at three different concentrations (106, 107, 108 conidia/ml). The survival of the mosquitoes was measured over 14 days, and fungal growth was quantified after 1 and 24 h to assess adhesion of the fungal strains onto the mosquito cuticle.
Results: All four fungi strains increased mosquito mortality compared to control (P<2.2â16). Adhesion of the fungal strains was observed on the mosquito cuticle after 24 h at high concentrations (1Ă 108 conidia/ml), with one strain, having the highest virulent, showing adhesion after just 1 h.
Conclusion: The native strains of Metarhizium spp. fungi found in Burkina Faso have the potential to be effective biocontrol agents against malaria vectors, with some strains showing high levels of both virulence and adhesion to the mosquito cuticle
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Effects of defoliation by the edible caterpillar âchitoumouâ ( Cirina butyrospermi ) on harvests of shea ( Vitellaria paradoxa ) and growth of maize ( Zea mays )
Get PDFAbstract: Edible insects are found in agricultural systems worldwide, and are an important source of food and income. However, many edible insects are also pests of important food crops, which raises the question of how far their presence might be costly to farmers in terms of reduced crop yields. In this study we aimed to understand the impact of defoliation of shea trees by edible caterpillars on yields of shea and maize in a mixed agroforestry system in Burkina Faso, West Africa. We collected field data in two consecutive years. Our results suggest that tree defoliation by caterpillars has no effect on shea fruit yields, and that defoliation may have a positive effect on maize productivity. We conclude that this appears to be an example of an agricultural system in which nutritionally and economically important plants and insects are both harvested by humans without risking yield reductions of harvested plants
Anopheline species composition and the 1014F-genotype in different ecological settings of Burkina Faso in relation to malaria transmission
Get PDFBackground:
A three-year longitudinal study was conducted in four sentinel sites from different ecological settings in Burkina Faso, between 2008 and 2010 to identify longitudinal changes in insecticide resistance within Anopheles gambiae complex species based on larval collection. During this study, adult mosquitoes were also collected indoor and outdoor using several methods of collection. The present study reports the diversity of malaria vectors and the 1014F-genotype from this adult collection and investigates the association between this 1014F-genotype and sporozoite rate.
Methods:
Adult mosquitoes were collected from July to August (corresponding to the start of rainy season) and October to November (corresponding to the end of rainy season) over 3 years (2008â2010) at four sites across the country, using pyrethrum spray catches (PSC), exit traps and pit shelters. Anopheles gambiae complex mosquitoes were identified to species and genotyped for the L1014F kdr mutation by PCR using genomic DNA. The circumsporozoite antigen of Plasmodium falciparum was detected in mosquitoes using sandwich ELISA.
Results:
Overall 9212 anopheline mosquitoes were collected during the study period. Of those, 6767 mosquitoes were identified as Anopheles gambiae sensu lato (s.l.). Anopheles arabiensis, Anopheles coluzzii, Anopheles gambiae and or Anopheles funestus were incriminated as vectors of P. falciparum in the study area with an average sporozoite rate of 5%, (95% CI 4.14â5.99%). The kdr1014F-genotype frequencies were 11.44% (95% CI 2.5â39.85%), 19.2% (95% CI 4.53â53.73%) and 89.9 (95% CI 63.14â97.45%), respectively for An. arabiensis, An. coluzzii and An. gambiae. The proportion of the 1014F-genotype varied between sporozoite-infected and uninfected An. gambiae s.l. group. There was no significant difference in the 1014F-genotype frequency between infected and uninfected mosquitoes.
Conclusion:
The current study shows the diversity of malaria vectors and significant interaction between species composition and kdr1014F-genotype in An. gambiae complex mosquitoes from Burkina Faso. In this study, no associations were found between the 1014F-genotype and P. falciparum infection in the major malaria vector An. gambiae s.l
Three years of insecticide resistance evolution and associated mechanisms in Aedes aegypti populations of Ouagadougou, Burkina Faso
Get PDFBackground
Resistance to insecticides is spreading among populations of Aedes aegypti, the primary vector of important human arboviruses. The escalating insecticide resistance poses a significant threat to dengue vector control, with an expanding number of countries affected by the disease.
To gain a deeper insight into the evolution of insecticide resistance, it is essential to have longitudinal surveillance results, which are currently lacking, particularly from African Ae. aegypti populations.
Here we report on three-years of surveillance of Ae. aegypti susceptibility to insecticide resistance phenotypes and associated kdr mutations in Burkina Faso, a country with regular dengue outbreaks.
Methods
Ae. aegypti susceptibility to insecticides and the V410L, V1016I, and F1534C kdr target site mutations linked to pyrethroid insecticide resistance were monitored in Ouagadougou from 2016 to 2018. Larvae were collected from artificial containers at two sites and reared to adulthood in an insectary. Bioassays were conducted on female adults, along with a laboratory-susceptible strain, following standard WHO protocols. Allele-specific PCR genotyping assays were utilized to identify the V410L, V1016I, and F1534C kdr pyrethroid target site mutations.
Results
Bioassays revealed a high level of resistance to permethrin and deltamethrin that progressively increased over the three-year period in both localities. The 1534C mutation was nearly fixed throughout the three years at each locality, and while the closely-related 410L and 1016I mutations did not vary between localities, their frequency notably increased from 2016 to 2018. Interestingly, Ae. aegypti populations in both areas remained susceptible to bendiocarb, fenitrothion, and malathion. Modelling the mortality data further confirmed the escalating resistance trend over the years and emphasized the significant role played by the three kdr mutations in conferring resistance to pyrethroids.
Conclusion
Mortality rates indicate that Ae. aegypti populations from Ouagadougou are becoming increasingly resistant to pyrethroid insecticides, likely due to an increase in the frequencies of the 410L and 1016I kdr mutations. Organophosphate insecticides are likely to be better alternative options for control
The contribution of âchitoumouâ, the edible caterpillar Cirina butyrospermi, to the food security of smallholder farmers in southwestern Burkina Faso
Get PDFAbstract: Edible insects have been advocated as a means to combat food insecurity, which is prevalent in West Africa. In this study we look at the contribution of the shea caterpillar Cirina butyrospermi, colloquially known as âchitoumouâ, to the food security of smallholder households in rural southwestern Burkina Faso. We used a mixed methods approach to understand the relationship between caterpillar collection, consumption, and sale by smallholder households, and their seasonal food security status. We found that caterpillars are an important source of food and income for households, significantly increasing the household consumption of animal protein and, with shea nuts, representing the main income source for the majority of women. We also found that food security is higher during caterpillar season, and that household-level food security during this season can be predicted by the amount of caterpillars collected, consumed and sold. However, this relationship holds only during the caterpillar season, suggesting that the positive impact of caterpillars on food security is temporally limited. We conclude that the shea caterpillar is an example of an edible insect that is crucial for seasonal food security in a widespread agricultural system
Interplay Between Oxytetracycline and the Homozygote kdr (L1014F) Resistance Genotype on Fecundity in Anopheles gambiae (Diptera: Culicidae) Mosquitoes
Get PDFThe insecticide resistance in Anopheles gambiae mosquitoes has remained the major threat for vector control programs but the fitness effects conferred by these mechanisms are poorly understood. To fill this knowledge gap, the present study aimed at testing the hypothesis that antibiotic oxytetracycline could have an interaction with insecticide resistance genotypes and consequently inhibit the fecundity in An. gambiae. Four strains of An. gambiae: Kisumu (susceptible), KisKdr (kdr (L1014F) resistant), AcerKis (ace-1 (G119S) resistant) and AcerKdrKis (both kdr (L1014F) and ace-1 (G119S) resistant) were used in this study. The different strains were allowed to bloodfeed on a rabbit previously treated with antibiotic oxytetracycline at a concentration of 39·10â5 M. Three days later, ovarian follicles were dissected from individual mosquito ovaries into physiological saline solution (0.9% NaCl) under a stereomicroscope and the eggs were counted. Fecundity was substantially lower in oxytetracycline-exposed KisKdr females when compared to that of the untreated individuals and oxytetracycline-exposed Kisumu females. The exposed AcerKis females displayed an increased fecundity compared to their nontreated counterparts whereas they had reduced fecundity compared to that of oxytetracycline-exposed Kisumu females. There was no substantial difference between the fecundity in the treated and untreated AcerKdrKis females. The oxytetracycline-exposed AcerKdrKis mosquitoes had an increased fecundity compared to that of the exposed Kisumu females. Our data indicate an indirect effect of oxytetracycline in reducing fecundity of An. gambiae mosquitoes carrying kdrR (L1014F) genotype. These findings could be useful for designing new integrated approaches for malaria vector control in endemic countries
Phenotypic Insecticide Resistance in Anopheles gambiae (Diptera: Culicidae): Specific Characterization of Underlying Resistance Mechanisms Still Matters
Get PDFAn effective control of malaria vectors requires an extensive knowledge of mechanisms underlying the resistance-phenotypes developed by these vectors against insecticides. We investigated Anopheles gambiae mosquitoes from Benin and Togo for their intensity of insecticide resistance and we discussed the involvement of genotyped mechanisms in the resistance-phenotypes observed. Three- to five-day-old adult mosquitoes emerged from field and laboratory An. gambiae larvae were assayed using WHO tube intensity tests against various doses of deltamethrin: 1Ă (0.05%); 2Ă (0.1%); 5Ă (0.25%); 7.5Ă (0.375%) and those of pirimiphos-methyl: 0.5Ă (0.125%); 1Ă (0.25%). Members of An. gambiae complex were screened in field populations using polymerase chain reaction (PCR) assays. The presence of kdrR(1014F/1014S) and ace-1R(119S) mutations was also investigated using TaqMan and PCR-RFLP techniques, respectively. Anopheles gambiae from field were very resistant to deltamethrin, whereas KisKdr and AcerKdrKis strains displayed 100% mortality rates at 2Ă the diagnostic dose. In contrast, the field mosquitoes displayed a low resistance-intensity against 1Ă the diagnostic dose of pirimiphos-methyl, whereas AcerKis and AcerKdrKis strains showed susceptibility at 0.5Ă the diagnostic dose. Anopheles gambiae s.s., Anopheles coluzzii, and Anopheles arabiensis were identified. Allelic frequencies of kdrR (1014F) and ace-1R (119S) mutations in the field populations varied from 0.65 to 1 and 0 to 0.84, respectively. The field An. gambiae displayed high-resistance levels against deltamethrin and pirimiphos-methyl when compared with those of the laboratory An. gambiae-resistant strains. These results exhibit the complexity of underlying insecticide resistance mechanisms in these field malaria vectors
