Evidence for a useful life of more than three years for a polyester-based long-lasting insecticidal mosquito net in Western Uganda

<p>Abstract</p> <p>Background</p> <p>Long-lasting insecticidal nets (LLIN) are now standard for the prevention of malaria. However, only products with recommendation for public use from the World Health Organization should be used and this evaluation includes the assessment of net effectiveness after three years of field use. Results for one of the polyester-based products, Interceptor^®is presented.</p> <p>Methods</p> <p>In five villages, 190 LLIN and 90 nets conventionally treated with the insecticide alpha-cypermethrin at 25 mg/m²were distributed randomly and used by the families. Following a baseline household survey a net survey was carried out every six months to capture use, washing habits and physical condition of the nets. Randomly selected nets were collected after 6, 12, 24, 36 and 42 months and tested for remaining insecticide content and ability to knock-down and kill malaria transmitting mosquitoes.</p> <p>Results</p> <p>During the three and a half years of observation only 16 nets were lost to follow-up resulting in an estimated attrition rate of 12% after three and 20/% after 3.5 years. Nets were used regularly and washed on average 1.5 times per year. After three and a half years 29% of the nets were still in good condition while 13% were seriously torn with no difference between the LLIN and control nets. The conventionally treated nets quickly lost insecticide and after 24 months only 7% of the original dose remained (1.6 mg/m²). Baseline median concentration of alpha-cypermethrin for LLIN was 194.5 mg/m²or 97% of the target dose with between and within net variation of 11% and 4% respectively (relative standard deviation). On the LLIN 73.8 mg/m²alpha-cypermethrin remained after three years of use and 56.2 mg/m²after three and a half and 94% and 81% of the LLIN still had > 15 mg/m²left respectively. Optimal effectiveness in bio-assays (≥95% 60 minute knock-down or ≥ 80% 24 hour mortality) was found in 83% of the sampled LLIN after three and 71% after three and a half years.</p> <p>Conclusions</p> <p>Under conditions in Western Uganda the tested long-lasting insecticidal net Interceptor^®fulfilled the criteria for phase III of WHO evaluations and, based on preliminary criteria of the useful life, this product is estimated to last on average between three and four years.</p

Genome variation and population structure among 1142 mosquitoes of the African malaria vector species Anopheles gambiae and Anopheles coluzzii

Mosquito control remains a central pillar of efforts to reduce malaria burden in sub-Saharan Africa. However, insecticide resistance is entrenched in malaria vector populations, and countries with a high malaria burden face a daunting challenge to sustain malaria control with a limited set of surveillance and intervention tools. Here we report on the second phase of a project to build an open resource of high-quality data on genome variation among natural populations of the major African malaria vector species Anopheles gambiae and Anopheles coluzzii. We analyzed whole genomes of 1142 individual mosquitoes sampled from the wild in 13 African countries, as well as a further 234 individuals comprising parents and progeny of 11 laboratory crosses. The data resource includes high-confidence single-nucleotide polymorphism (SNP) calls at 57 million variable sites, genome-wide copy number variation (CNV) calls, and haplotypes phased at biallelic SNPs. We use these data to analyze genetic population structure and characterize genetic diversity within and between populations. We illustrate the utility of these data by investigating species differences in isolation by distance, genetic variation within proposed gene drive target sequences, and patterns of resistance to pyrethroid insecticides. This data resource provides a foundation for developing new operational systems for molecular surveillance and for accelerating research and development of new vector control tools. It also provides a unique resource for the study of population genomics and evolutionary biology in eukaryotic species with high levels of genetic diversity under strong anthropogenic evolutionary pressures

Detecting Foci of Malaria Transmission with School Surveys: A Pilot Study in the Gambia.

BACKGROUND: In areas of declining malaria transmission such as in The Gambia, the identification of malaria infected individuals becomes increasingly harder. School surveys may be used to identify foci of malaria transmission in the community. METHODS: The survey was carried out in May-June 2011, before the beginning of the malaria transmission season. Thirty two schools in the Upper River Region of The Gambia were selected with probability proportional to size; in each school approximately 100 children were randomly chosen for inclusion in the study. Each child had a finger prick blood sample collected for the determination of antimalarial antibodies by ELISA, malaria infection by microscopy and PCR, and for haemoglobin measurement. In addition, a simple questionnaire on socio-demographic variables and the use of insecticide-treated bed nets was completed. The cut-off for positivity for antimalarial antibodies was obtained using finite mixture models. The clustered nature of the data was taken into account in the analyses. RESULTS: A total of 3,277 children were included in the survey. The mean age was 10 years (SD = 2.7) [range 4-21], with males and females evenly distributed. The prevalence of malaria infection as determined by PCR was 13.6% (426/3124) [95% CI = 12.2-16.3] with marked variation between schools (range 3-25%, p<0.001), while the seroprevalence was 7.8% (234/2994) [95%CI = 6.4-9.8] for MSP119, 11.6% (364/2997) [95%CI = 9.4-14.5] for MSP2, and 20.0% (593/2973) [95% CI = 16.5-23.2) for AMA1. The prevalence of all the three antimalarial antibodies positive was 2.7% (79/2920). CONCLUSIONS: This survey shows that malaria prevalence and seroprevalence before the transmission season were highly heterogeneous

Resistance to pirimiphos-methyl in West African Anopheles is spreading via duplication and introgression of the Ace1 locus

Vector population control using insecticides is a key element of current strategies to prevent malaria transmission in Africa. The introduction of effective insecticides, such as the organophosphate pirimiphos-methyl, is essential to overcome the recurrent emergence of resistance driven by the highly diverse Anopheles genomes. Here, we use a population genomic approach to investigate the basis of pirimiphos-methyl resistance in the major malaria vectors Anopheles gambiae and A. coluzzii. A combination of copy number variation and a single non-synonymous substitution in the acetylcholinesterase gene, Ace1, provides the key resistance diagnostic in an A. coluzzii population from Coˆte d’Ivoire that we used for sequence-based association mapping, with replication in other West African populations. The Ace1 substitution and duplications occur on a unique resistance haplotype that evolved in A. gambiae and introgressed into A. coluzzii, and is now common in West Africa primarily due to selection imposed by other organophosphate or carbamate insecticides. Our findings highlight the predictive value of this complex resistance haplotype for phenotypic resistance and clarify its evolutionary history, providing tools to for molecular surveillance of the current and future effectiveness of pirimiphos-methyl based interventions

The dominant Anopheles vectors of human malaria in Africa, Europe and the Middle East: occurrence data, distribution maps and bionomic précis

<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

High hybridization rate between Anopheles gambiae molecular forms at the western extreme of their range highlights possible gene-flow in the X-chromosome “speciation island”

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Alternative Treatments for Indoor Residual Spraying for Malaria Control in a Village with Pyrethroid- and DDT-Resistant Vectors in The Gambia

Background: Malaria vector control is threatened by resistance to pyrethroids, the only class of insecticides used for treating bed nets. The second major vector control method is indoor residual spraying with pyrethroids or the organochloride DDT. However, resistance to pyrethroids frequently confers resistance to DDT. Therefore, alternative insecticides are urgently needed. Methodology/Principal Findings: Insecticide resistance and the efficacy of indoor residual spraying with different insecticides was determined in a Gambian village. Resistance of local vectors to pyrethroids and DDT was high (31% and 46% mortality, respectively) while resistance to bendiocarb and pirimiphos methyl was low (88% and 100% mortality, respectively). The vectors were predominantly Anopheles gambiae s.s. with 94% of them having the putative resistant genotype kdr 1014F. Four groups of eight residential compounds were each sprayed with either (1) bendiocarb, a carbamate, (2) DDT, an organochlorine, (3) microencapsulated pirimiphos methyl, an organophosphate, or (4) left unsprayed. All insecticides tested showed high residual activity up to five months after application. Mosquito house entry, estimated by light traps, was similar in all houses with metal roofs, but was significantly less in IRS houses with thatched roofs (p=0.02). Residents participating in focus group discussions indicated that IRS was considered a necessary nuisance and also may decrease the use of long-lasting insecticidal nets. Conclusion/Significance: Bendiocarb and microencapsulated pirimiphos methyl are viable alternatives for indoor residual spraying where resistance to pyrethroids and DDT is high and may assist in the management of pyrethroid resistance