Effective population size of Anopheles funestus chromosomal forms in Burkina Faso

BACKGROUND: As Anopheles funestus is one of the principal Afro-tropical malaria vectors, a more complete understanding of its population structure is desirable. In West and Central Africa, An. funestus population structure is complicated by the coexistence of two assortatively mating chromosomal forms. Effective population size (N(e)) is a key parameter in understanding patterns and levels of intraspecific variation, as it reflects the role of genetic drift. Here, N(e )was estimated from both chromosomal forms, Kiribina and Folonzo, in Burkina Faso. METHODS: Short-term N(e )was estimated by evaluating variation at 16 microsatellite loci across temporal samples collected annually from 2000–2002. Estimates were based on standardized variance in allele frequencies or a maximum likelihood method. Long-term N(e )was estimated from genetic diversity estimates using mtDNA sequences and microsatellites. RESULTS: For both forms, short-term and long-term N(e )estimates were on the order of 10(3 )and 10(5), respectively. Long-term N(e )estimates were larger when based on loci from chromosome 3R (both inside and outside of inversions) than loci outside of this arm. CONCLUSION: N(e )values indicate that An. funestus is not subject to seasonal bottlenecks. Though not statistically different because of large and overlapping confidence intervals, short-term N(e )estimates were consistently smaller for Kiribina than Folonzo, possibly due to exploitation of different breeding sites: permanent for Folonzo and intermittent for Kiribina. The higher long-term N(e )estimates on 3R, the arm carrying the two inversions mainly responsible for defining the chromosomal forms, give natural selection broader scope and merit further study

The sticky resting box, a new tool for studying resting behaviour of Afrotropical malaria vectors

Background: Monitoring densities of adult mosquito populations is a major challenge in efforts to evaluate the epidemiology of mosquito-borne diseases, and their response to vector control interventions. In the case of malaria, collection of outdoor-resting Anophelines is rarely incorporated into surveillance and control, partially due to the lack of standardized collection tools. Such an approach, however, is increasingly important to investigate possible changes in mosquito behaviour in response to the scale up of Insecticide Treated Nets and Indoor Residual Spraying. In this study we evaluated the Sticky Resting Box (SRB) - i.e. a sticky variant of previously investigated mosquito Resting Box, which allows passive collection of mosquitoes entering the box – and compared its performance against traditional methods for indoor and outdoor resting mosquito sampling.<p></p> Methods: Daily collections were carried out in two neighbouring villages of Burkina Faso during rainy season 2011 and dry season 2012 by SRB located indoors and outdoors, and by Back-Pack aspiration inside houses (BP) and in ad hoc built outdoor pit-shelters (PIT).<p></p> Results: Overall, almost 20,000 Culicidae specimens belonging to 16 species were collected and morphologically identified. Malaria vectors included Anopheles coluzzii (53%), An. arabiensis (12%), An. gambiae s.s. (2.0%) and An. funestus (4.5%). The diversity of species collected in the two villages was similar for SRB and PIT collections outdoors, and significantly higher for SRB than for BP indoors. The population dynamics of An. gambiae s.l. mosquitoes, as obtained by SRB-collections was significantly correlated with those obtained by the traditional methods. The predicted mean estimates of An. gambiae s.l. specimens/sampling-unit/night-of-collections was 6- and 5-times lower for SRB than for BP indoors and PIT outdoors, respectively.<p></p> Conclusions: Overall, the daily performance of SRB in terms of number of malaria vectors/trap was lower than that of traditionally used approaches for in- and outdoor collections. However, unlike these methods, SRB could be set up to collect mosquitoes passively over at least a week. This makes SRB a promising tool for passively monitoring anopheline resting populations, with data presented here providing guidance for how to set up SRB-based collections to acquire information comparable to those obtained with other methods.<p></p&gt

Aging partially restores the efficacy of malaria vector control in insecticide-resistant populations of Anopheles gambiae s.l. from Burkina Faso

<br>Background: The operational impact of insecticide resistance on the effectiveness of long-lasting insecticide nets (LLINs) and indoor residual spraying (IRS) is poorly understood. One factor which may prolong the effectiveness of these tools in the field is the increase in insecticide susceptibility with mosquito age. In this study, LLINs and IRS were tested against young (three to five days) and old (17-19 days) pyrethroid resistant Anopheles gambiae s.l. from Burkina Faso.</br> <br>Methods: Blood-fed adult Anopheles gambiae s.l. were collected from south-west Burkina Faso and identified to species/form level. Cohorts of the F1 progeny of An. gambiae s.s. S-forms were exposed to deltamethrin (0.05%) at three to five or 17-19 days post-emergence and tested for the frequency of the resistance allele 1014F. Isofemale lines of the M, S- form of An. gambiae s.s. and Anopheles arabiensis were exposed in WHO cone tests to either a) LLINs deployed in households for two years or (b) bendiocarb sprayed walls.</br> <br>Results: Mortality rates in response to deltamethrin (0.05%) increased from levels indicative of strong resistance in three to five day old F1 mosquitoes, to near full susceptibility in the 17-19 day old cohort. On exposure to LLINs sampled from the field, the mortality rate in isofemale lines was higher in older mosquitoes than young (OR = 5.28, CI 95% = 2.81-9.92), although the mortality estimates were affected by the LLIN tested. In general, the LLINs sampled from the field performed poorly in WHO cone bioassays using either laboratory susceptible or field caught mosquito populations. Finally, there was a clear relationship between mortality and age on exposure to bendiocarb-sprayed walls, with older mosquitoes again proving more susceptible (OR = 3.39, CI 95% = 2.35-4.90).</br> <br>Conclusions: Age is a key factor determining the susceptibility of mosquitoes to insecticides, not only in laboratory studies, but in response to field-based vector control interventions. This has important implications for understanding the epidemiological impact of resistance. If mosquitoes old enough to transmit malaria are still being suppressed with available insecticides, is resistance potentially having less of an impact than often assumed? However, the poor performance of LLINs used in this study in Burkina Faso, is a cause for concern and requires urgent investigation.</br&gt

De Novo Transcriptome Sequencing in Anopheles funestus Using Illumina RNA-Seq Technology

BACKGROUND: Anopheles funestus is one of the primary vectors of human malaria, which causes a million deaths each year in sub-Saharan Africa. Few scientific resources are available to facilitate studies of this mosquito species and relatively little is known about its basic biology and evolution, making development and implementation of novel disease control efforts more difficult. The An. funestus genome has not been sequenced, so in order to facilitate genome-scale experimental biology, we have sequenced the adult female transcriptome of An. funestus from a newly founded colony in Burkina Faso, West Africa, using the Illumina GAIIx next generation sequencing platform. METHODOLOGY/PRINCIPAL FINDINGS: We assembled short Illumina reads de novo using a novel approach involving iterative de novo assemblies and "target-based" contig clustering. We then selected a conservative set of 15,527 contigs through comparisons to four Dipteran transcriptomes as well as multiple functional and conserved protein domain databases. Comparison to the Anopheles gambiae immune system identified 339 contigs as putative immune genes, thus identifying a large portion of the immune system that can form the basis for subsequent studies of this important malaria vector. We identified 5,434 1:1 orthologues between An. funestus and An. gambiae and found that among these 1:1 orthologues, the protein sequence of those with putative immune function were significantly more diverged than the transcriptome as a whole. Short read alignments to the contig set revealed almost 367,000 genetic polymorphisms segregating in the An. funestus colony and demonstrated the utility of the assembled transcriptome for use in RNA-seq based measurements of gene expression. CONCLUSIONS/SIGNIFICANCE: We developed a pipeline that makes de novo transcriptome sequencing possible in virtually any organism at a very reasonable cost ($6,300 in sequencing costs in our case). We anticipate that our approach could be used to develop genomic resources in a diversity of systems for which full genome sequence is currently unavailable. Our An. funestus contig set and analytical results provide a valuable resource for future studies in this non-model, but epidemiologically critical, vector insect

Design and methods for a quasi-experimental pilot study to evaluate the impact of dual active ingredient insecticide-treated nets on malaria burden in five regions in sub-Saharan Africa

Background:Vector control tools have contributed significantly to a reduction in malaria burden since 2000, primar‑ily through insecticidal‑treated bed nets (ITNs) and indoor residual spraying. In the face of increasing insecticide resist‑ance in key malaria vector species, global progress in malaria control has stalled. Innovative tools, such as dual active ingredient (dual‑AI) ITNs that are effective at killing insecticide‑resistant mosquitoes have recently been introduced. However, large‑scale uptake has been slow for several reasons, including higher costs and limited evidence on their incremental effectiveness and cost‑effectiveness. The present report describes the design of several observational studies aimed to determine the effectiveness and cost‑effectiveness of dual‑AI ITNs, compared to standard pyre‑throid‑only ITNs, at reducing malaria transmission across a variety of transmission settings.Methods:Observational pilot studies are ongoing in Burkina Faso, Mozambique, Nigeria, and Rwanda, leveraging dual‑AI ITN rollouts nested within the 2019 and 2020 mass distribution campaigns in each country. Enhanced surveil‑lance occurring in select study districts include annual cross‑sectional surveys during peak transmission seasons, monthly entomological surveillance, passive case detection using routine health facility surveillance systems, and studies on human behaviour and ITN use patterns. Data will compare changes in malaria transmission and disease burden in districts receiving dual‑AI ITNs to similar districts receiving standard pyrethroid‑only ITNs over three years. The costs of net distribution will be calculated using the provider perspective including financial and economic costs, and a cost‑effectiveness analysis will assess incremental cost‑effectiveness ratios for Interceptor® G2, Royal Guard®, and piperonyl butoxide ITNs in comparison to standard pyrethroid‑only ITNs, based on incidence rate ratios calcu‑lated from routine data.Conclusions:Evidence of the effectiveness and cost‑effectiveness of the dual‑AI ITNs from these pilot studies will complement evidence from two contemporary cluster randomized control trials, one in Benin and one in Tanzania, to provide key information to malaria control programmes, policymakers, and donors to help guide decision‑making and planning for local malaria control and elimination strategies. Understanding the breadth of contexts where these dual‑AI ITNs are most effective and collecting robust information on factors influencing comparative effectiveness could improve uptake and availability and help maximize their impact

Effective population size of Anopheles funestus chromosomal forms in Burkina Faso

Abstract Background As Anopheles funestus is one of the principal Afro-tropical malaria vectors, a more complete understanding of its population structure is desirable. In West and Central Africa, An. funestus population structure is complicated by the coexistence of two assortatively mating chromosomal forms. Effective population size (N e) is a key parameter in understanding patterns and levels of intraspecific variation, as it reflects the role of genetic drift. Here, N ewas estimated from both chromosomal forms, Kiribina and Folonzo, in Burkina Faso. Methods Short-term N ewas estimated by evaluating variation at 16 microsatellite loci across temporal samples collected annually from 2000–2002. Estimates were based on standardized variance in allele frequencies or a maximum likelihood method. Long-term N ewas estimated from genetic diversity estimates using mtDNA sequences and microsatellites. Results For both forms, short-term and long-term N eestimates were on the order of 103 and 105, respectively. Long-term N eestimates were larger when based on loci from chromosome 3R (both inside and outside of inversions) than loci outside of this arm. Conclusion Nevalues indicate that An. funestus is not subject to seasonal bottlenecks. Though not statistically different because of large and overlapping confidence intervals, short-term Neestimates were consistently smaller for Kiribina than Folonzo, possibly due to exploitation of different breeding sites: permanent for Folonzo and intermittent for Kiribina. The higher long-term Neestimates on 3R, the arm carrying the two inversions mainly responsible for defining the chromosomal forms, give natural selection broader scope and merit further study.http://deepblue.lib.umich.edu/bitstream/2027.42/112376/1/12936_2006_Article_293.pd

Unexpectedly low Human Blood Index associated to high Plasmodium sporozoite rates in Anopheles gambiae complex species from a LINN-protected village in Burkina Faso

The global effectiveness of long-lasting insecticidal nets (LLINs) in reducing malaria transmission is indisputable. However, in areas where malaria transmission levels are extremely high, substantial reductions in transmission intensity only led to a modest reduction in human parasitaemia. A paradigmatic case is represented by Burkina Faso where, after a few years of mass distribution of LLINs, the burden of malaria has not significantly changed as highlighted by WHO Country statistics and statistical bureau of Burkina Faso. We here report the results of a longitudinal survey on host choice and Plasmodium sporozoite rate (SR) in malaria vectors belonging to Anopheles gambiae complex in a rural village of Burkina Faso where LLINs were broadly distributed the year before the sampling (August - November 2011). The human blood index (HBI) was 18.8% (N=112) and 8% (N=75), in An. coluzzii and An. arabiensis, the two most abundant malaria vectors in the area. These values are much lower than usually reported particularly for An. coluzzii, which is known as a highly anthropophilic species, but consistent with the hypothesis that LLINs reduced the availability of human hosts to mosquitoes. Unexpectedly, Plasmodium sporozoite rates (An. coluzzii: 7.6%, N=449; An. arabiensis: 5.2%, N=229) were found to be in the range of those reported in the region before LLIN implementation when much higher HBIs were observed. This suggests that, despite LLINs have significantly reduced human/vector contact, this has not apparently yielded to a substantial reduction of mosquito infection rates. Further investigations are needed to confirm these results; however, they are fully consisten