Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

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    Understanding the long-lasting attraction of malaria mosquitoes to odor baits
    Mweresa, C.K. ; Otieno, B. ; Omusula, P. ; Weldegergis, B.T. ; Verhulst, N.O. ; Dicke, M. ; Loon, J.J.A. van; Takken, W. ; Mukabana, W.R. - \ 2015
    PLoS ONE 10 (2015)3. - ISSN 1932-6203 - 16 p.
    gambiae-sensu-stricto - human skin emanations - anopheles-gambiae - human pathogen - aedes-aegypti - human sweat - identification - culicidae - volatiles - behavior
    The use of odor baits for surveillance and control of malaria mosquitoes requires robust dispensing tools. In this study, the residual activity of a synthetic mosquito attractant blend dispensed from nylon or low density polyethylene (LDPE) sachets was evaluated at weekly intervals for one year without re-impregnation. The potential role of bacteria in modulating the attraction of mosquitoes to odor-treated nylon that had been used repeatedly over the one year study period, without re-impregnation, was also investigated. Significantly higher proportions of female Anopheles gambiae sensu stricto mosquitoes were consistently attracted to treated nylon strips than the other treatments, up to one year post-treatment. Additional volatile organic compounds and various bacterial populations were found on the treated nylon strips after one year of repeated use. The most abundant bacteria were Bacillus thuringiensis and Acinetobacter baumannii. Autoclaving of treated nylon strips prior to exposure had no effect on trap collections of laboratory-reared female An. Gambiae (P = 0.17) or wild female An. Gambiae sensu lato (P = 0.26) and Mansonia spp. (P = 0.17) mosquitoes. Trap catches of wild female An. Funestus (P <0.001) and other anophelines (P <0.007) were higher when treated strips had been autoclaved prior to deployment as opposed to when the treated nylon strips were not autoclaved. By contrast, wild female Culex mosquitoes were more strongly attracted to non-autoclaved compared to autoclaved treated nylon strips (P <0.042). This study demonstrates the feasibility of using odor baits for sampling and surveillance of malaria as well as other mosquito vectors over prolonged periods of time. Preliminary evidence points towards the potential role of bacteria in sustaining prolonged use of nylon material for dispensing synthetic attractant odorants for host-seeking malaria and other mosquito vectors but further investigations are required.
    We can't all be supermodels: the value of comparative transcriptomics to the study of non-model insects
    Oppenheim, S.J. ; Baker, R.H. ; Simon, S. ; DeSalle, R. - \ 2015
    Insect Molecular Biology 24 (2015)2. - ISSN 0962-1075 - p. 139 - 154.
    biased gene-expression - chromosome dosage compensation - seminal fluid proteins - asian tiger mosquito - division-of-labor - rna-seq - anopheles-gambiae - x-chromosome - honey-bees - drosophila-melanogaster
    Insects are the most diverse group of organisms on the planet. Variation in gene expression lies at the heart of this biodiversity and recent advances in sequencing technology have spawned a revolution in researchers' ability to survey tissue-specific transcriptional complexity across a wide range of insect taxa. Increasingly, studies are using a comparative approach (across species, sexes and life stages) that examines the transcriptional basis of phenotypic diversity within an evolutionary context. In the present review, we summarize much of this research, focusing in particular on three critical aspects of insect biology: morphological development and plasticity; physiological response to the environment; and sexual dimorphism. A common feature that is emerging from these investigations concerns the dynamic nature of transcriptome evolution as indicated by rapid changes in the overall pattern of gene expression, the differential expression of numerous genes with unknown function, and the incorporation of novel, lineage-specific genes into the transcriptional profile.
    Field evaluation of a novel synthetic odour blend and of the synergistic role of carbon dioxide for sampling host-seeking Aedes albopictus adults in Rome, Italy
    Pombi, M. ; Jacobs, F.H.H. ; Verhulst, N.O. ; Caputo, B. ; Torre, A. della; Takken, W. - \ 2014
    Parasites & Vectors 7 (2014). - ISSN 1756-3305 - 5 p.
    bg-sentinel - diptera-culicidae - anopheles-gambiae - mosquitos - traps - malaria - urban - surveillance - europe
    Background Despite the expanding worldwide distribution of Aedes albopictus and its increasing relevance as arboviral vector, current methods to collect adult specimens are not optimal. Improved approaches are thus needed to monitor their density and pathogen infections, and to establish baseline data for control interventions. A widely used device is the BG-Sentinel (BG-trap) which mostly targets host-seeking females attracted by release of CO2 and/or a synthetic odour blend (the BG lure). We compared the attractiveness of this blend to that of the Mbita (MB5) lure, a new synthetic blend of proven efficiency in attracting Afrotropical malaria vectors, and evaluated the additional effect of CO2 to the two odour baits. Findings We carried out 6x6 Latin square experiments in two Ae. albopictus-infested areas in Rome, baiting the BG-traps as follows: CO2, BG lure, MB5 lure, BG lure¿+¿CO2, MB5 lure¿+¿CO2, no bait. CO2 was derived from yeast-fermented sugar. Overall, 949 females and 816 males were collected. Baited traps collected significantly more females than unbaited ones. Traps baited with either lures in combination with CO2 were more effective than those baited with CO2 alone. No significant differences were observed in female captures between traps baited with any of the two lures, nor between the two lures, independently from the addition of CO2. The use of BG lure¿+¿CO2 significantly increased males catches compared to unbaited traps. Conclusions The results suggest a broad significance of the MB5 lure for sampling medically important mosquito species and highlight the high efficacy of the combination of lures¿+¿CO2 for female Ae. albopictus and of BG lure¿+¿CO2 for males, leading to consider CO2 as an essential additional cue for the sampling of this species.
    Natural variation in virulence of the entomopathogenic fungus Beauveria bassiana against malaria mosquitoes
    Valero Jimenez, C.A. ; Debets, A.J.M. ; Kan, J.A. van; Schoustra, S.E. ; Takken, W. ; Zwaan, B.J. ; Koenraadt, C.J.M. - \ 2014
    Malaria Journal 13 (2014). - ISSN 1475-2875 - 8 p.
    metarhizium-anisopliae - anopheles-gambiae - infection - agents - susceptibility - degradation - persistence - expression - resistance - behavior
    Background Insecticide resistance is greatly hampering current efforts to control malaria and therefore alternative methods are needed. Entomopathogenic fungi have been proposed as an alternative with a special focus on the cosmopolitan species Beauveria bassiana. However, few studies have analysed the effects of natural variation within fungal isolates on mosquito survival, and the implications and possible exploitation for malaria control. Methods Laboratory bioassays were performed on adult female mosquitoes (Anopheles coluzzii) with spores from 29 isolates of B. bassiana, originating from different parts of the world. In addition, phenotypic characteristics of the fungal isolates such as sporulation, spore size and growth rate were studied to explore their relationship with virulence. Results All tested isolates of B. bassiana killed An. coluzzii mosquitoes, and the rate at which this happened differed significantly among the isolates. The risk of mosquitoes dying was around ten times higher when they were exposed to the most virulent as compared to the least virulent isolate. There was significant variation among isolates in spore size, growth rate and sporulation, but none of these morphological characteristics were correlated, and thus predictive, for the ability of the fungal isolate to kill malaria mosquitoes. Conclusions This study shows that there is a wide natural variation in virulence of isolates of B. bassiana, and that selecting an appropriate fungal isolate is highly relevant in killing and thus controlling malaria mosquitoes, particularly if used as part of an integrated vector management strategy. Also, the wide variation observed in virulence offers the opportunity to better understand the molecular and genetic mechanisms that drive this variation and thus to address the potential development of resistance against entomopathogenic fungi
    Modeling larval malaria vector habitat locations using landscape features and cumulative precipitation measures
    Mc Cann, R.S. ; Messina, J.P. ; MacFarlane, D.W. ; Bayoh, M.N. ; Vulule, J.M. ; Gimnig, J.E. ; Walker, E.D. - \ 2014
    International Journal of Health Geographics 13 (2014). - ISSN 1476-072X - 12 p.
    gambiae complex diptera - western kenya highlands - high-spatial-resolution - anopheles-gambiae - land-cover - child-mortality - breeding habitats - culicidae - africa - risk
    BACKGROUND: Predictive models of malaria vector larval habitat locations may provide a basis for understanding the spatial determinants of malaria transmission. METHODS: We used four landscape variables (topographic wetness index [TWI], soil type, land use-land cover, and distance to stream) and accumulated precipitation to model larval habitat locations in a region of western Kenya through two methods: logistic regression and random forest. Additionally, we used two separate data sets to account for variation in habitat locations across space and over time. RESULTS: Larval habitats were more likely to be present in locations with a lower slope to contributing area ratio (i.e. TWI), closer to streams, with agricultural land use relative to nonagricultural land use, and in friable clay/sandy clay loam soil and firm, silty clay/clay soil relative to friable clay soil. The probability of larval habitat presence increased with increasing accumulated precipitation. The random forest models were more accurate than the logistic regression models, especially when accumulated precipitation was included to account for seasonal differences in precipitation. The most accurate models for the two data sets had area under the curve (AUC) values of 0.864 and 0.871, respectively. TWI, distance to the nearest stream, and precipitation had the greatest mean decrease in Gini impurity criteria in these models. CONCLUSIONS: This study demonstrates the usefulness of random forest models for larval malaria vector habitat modeling. TWI and distance to the nearest stream were the two most important landscape variables in these models. Including accumulated precipitation in our models improved the accuracy of larval habitat location predictions by accounting for seasonal variation in the precipitation. Finally, the sampling strategy employed here for model parameterization could serve as a framework for creating predictive larval habitat models to assist in larval control efforts.
    Development and optimization of the Suna trap as a tool for mosquito monitoring and control
    Hiscox, A.F. ; Otieno, B. ; Kibet, A. ; Mweresa, C.K. ; Omusula, P. ; Geier, M. ; Rose, A. ; Mukabana, W.R. ; Takken, W. - \ 2014
    Malaria Journal 13 (2014). - ISSN 1475-2875 - 14 p.
    human-landing catches - cdc light-trap - anopheles-gambiae - carbon-dioxide - malaria transmission - field-evaluation - diptera-culicidae - equatorial-guinea - vector control - western kenya
    Background Monitoring of malaria vector populations provides information about disease transmission risk, as well as measures of the effectiveness of vector control. The Suna trap is introduced and evaluated with regard to its potential as a new, standardized, odour-baited tool for mosquito monitoring and control. Methods Dual-choice experiments with female Anopheles gambiae sensu lato in a laboratory room and semi-field enclosure, were used to compare catch rates of odour-baited Suna traps and MM-X traps. The relative performance of the Suna trap, CDC light trap and MM-X trap as monitoring tools was assessed inside a human-occupied experimental hut in a semi-field enclosure. Use of the Suna trap as a tool to prevent mosquito house entry was also evaluated in the semi-field enclosure. The optimal hanging height of Suna traps was determined by placing traps at heights ranging from 15 to 105 cm above ground outside houses in western Kenya. Results In the laboratory the mean proportion of An. gambiae s.l. caught in the Suna trap was 3.2 times greater than the MM-X trap (P <0.001), but the traps performed equally in semi-field conditions (P = 0.615). As a monitoring tool , the Suna trap outperformed an unlit CDC light trap (P <0.001), but trap performance was equal when the CDC light trap was illuminated (P = 0.127). Suspending a Suna trap outside an experimental hut reduced entry rates by 32.8% (P <0.001). Under field conditions, suspending the trap at 30 cm above ground resulted in the greatest catch sizes (mean 25.8 An. gambiae s.l. per trap night). Conclusions The performance of the Suna trap equals that of the CDC light trap and MM-X trap when used to sample An. gambiae inside a human-occupied house under semi-field conditions. The trap is effective in sampling mosquitoes outside houses in the field, and the use of a synthetic blend of attractants negates the requirement of a human bait. Hanging a Suna trap outside a house can reduce An. gambiae house entry and its use as a novel tool for reducing malaria transmission risk will be evaluated in peri-domestic settings in sub-Saharan Africa.
    Assessing the efficacy of candidate mosquito repellents against the background of an attractive source that mimics a human host
    Menger, D.J. ; Loon, J.J.A. van; Takken, W. - \ 2014
    Medical and Veterinary Entomology 28 (2014)4. - ISSN 0269-283X - p. 407 - 413.
    anopheles-gambiae - malaria mosquito - behavioral-response - carbon-dioxide - human skin - culicidae - diptera - aedes - identification - odor
    Mosquito repellents are used around the globe to protect against nuisance biting and disease-transmitting mosquitoes. Recently, there has been renewed interest in the development of repellents as tools to control the transmission of mosquito-borne diseases. We present a new bioassay for the accurate assessment of candidate repellent compounds, using a synthetic odour that mimics the odour blend released by human skin. Using DEET (N,N-diethyl-meta-toluamide) and PMD (p-menthane-3,8-diol) as reference compounds, nine candidate repellents were tested, of which five showed significant repellency to the malaria mosquito Anopheles gambiae sensu stricto (Diptera: Culicidae). These included: 2-nonanone; 6-methyl-5-hepten-2-one; linalool; d-decalactone, and d-undecalactone. The lactones were also tested on the yellow fever mosquito Aedes aegypti (Stegomyia aegypti) (Diptera: Culicidae), against which they showed similar degrees of repellency. We conclude that the lactones are highly promising repellents, particularly because these compounds are pleasant-smelling, natural products that are also present in human food sources.
    Alternative treatments for indoor residual spraying for malaria control in a village with pyrethroid- and DDT-resistant vectors in The Gambia
    Tangena, J.A.A. ; Adiamoh, M. ; Alessandro, U. D'; Jarju, L. ; Jawara, M. ; Jeffries, D. ; Malik, N. ; Nwakanma, D. ; Kaur, H. ; Takken, W. ; Lindsay, S.W. ; Pinder, M. - \ 2013
    PLoS ONE 8 (2013)9. - ISSN 1932-6203
    insecticide-treated nets - anopheles-gambiae - pirimiphos-methyl - molecular-forms - area - complex - susceptibility - identification - protection - mozambique
    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.
    Malaria Infected Mosquitoes Express Enhanced Attraction to Human Odor
    Smallegange, R.C. ; Gemert, G.J. van; Vegte-Bolmer, M. van de; Gezan, S. ; Takken, W. ; Sauerwein, R.W. ; Logan, J.G. - \ 2013
    PLoS ONE 8 (2013)5. - ISSN 1932-6203
    anopheles-gambiae - plasmodium-falciparum - vector
    There is much evidence that some pathogens manipulate the behaviour of their mosquito hosts to enhance pathogen transmission. However, it is unknown whether this phenomenon exists in the interaction of Anopheles gambiae sensu stricto with the malaria parasite, Plasmodium falciparum - one of the most important interactions in the context of humanity, with malaria causing over 200 million human cases and over 770 thousand deaths each year. Here we demonstrate, for the first time, that infection with P. falciparum causes alterations in behavioural responses to host-derived olfactory stimuli in host-seeking female An. gambiae s.s. mosquitoes. In behavioural experiments we showed that P. falciparum-infected An. gambiae mosquitoes were significantly more attracted to human odors than uninfected mosquitoes. Both P. falciparum-infected and uninfected mosquitoes landed significantly more on a substrate emanating human skin odor compared to a clean substrate. However, significantly more infected mosquitoes landed and probed on a substrate emanating human skin odor than uninfected mosquitoes. This is the first demonstration of a change of An. gambiae behaviour in response to olfactory stimuli caused by infection with P. falciparum. The results of our study provide vital information that could be used to provide better predictions of how malaria is transmitted from human being to human being by An. gambiae s.s. females. Additionally, it highlights the urgent need to investigate this interaction further to determine the olfactory mechanisms that underlie the differential behavioural responses. In doing so, new attractive compounds could be identified which could be used to develop improved mosquito traps for surveillance or trapping programmes that may even specifically target P. falciparum-infected An. gambiae s.s. females.
    Advances in methods for colour marking of mosquitoes
    Verhulst, N.O. ; Loonen, J.A.C.M. ; Takken, W. - \ 2013
    Parasites & Vectors 6 (2013). - ISSN 1756-3305 - 7 p.
    sensu-stricto diptera - anopheles-gambiae - release-recapture - aedes-aegypti - fluorescent powder - dispersal - culicidae - population - queensland - arabiensis
    Background: Different techniques are available for colour marking insects and each technique may be suitable for different insect species. Mosquitoes can be marked to determine population size, distribution and flight distance or distinguish closely related species. In this study, two methods of colour marking mosquitoes were described in detail and the impact of both methods on the survival and host-seeking behaviour of the malaria mosquito Anopheles gambiae sensu stricto was investigated. Methods: Mosquitoes were marked in groups with fluorescent powder or fluorescent dye. The powder was applied by creating a cloud of powder in a paper cup and the dye was applied with an airbrush. The effect of marking on the survival of mosquitoes of different age groups was tested under controlled conditions. The effect of marking on the host seeking response of the mosquitoes was tested in an olfactometer with human and cow odour as baits. Results: No effect of either of the marking methods was found on the survival of mosquitoes that were treated 1 or 3 days after emergence, however, the survival of mosquitoes treated 5 or 9 days after emergence was significantly reduced. The host-seeking response of mosquitoes to human or cow odour was tested in a dual-port olfactometer and was not found to be affected by treatment with fluorescent powder or dye. Conclusions: Both methods are suitable for colour marking large groups of mosquitoes. Marking with fluorescent powder, however, is preferred because the method is simpler, visible without a UV light and no specific materials are required.
    Relation between HLA genes, human skin volatiles and attractiveness of humans to malaria mosquitoes
    Verhulst, N.O. ; Beijleveld, H. ; Qiu, Y.T. ; Maliepaard, C.A. ; Verduyn, W. ; Haasnoot, G.W. ; Claas, F.H.J. ; Mumm, R. ; Bouwmeester, H.J. ; Takken, W. ; Loon, J.J.A. van; Smallegange, R.C. - \ 2013
    Infection, Genetics and Evolution 18 (2013). - ISSN 1567-1348 - p. 87 - 93.
    major histocompatibility complex - gambiae-sensu-stricto - human axillary odor - anopheles-gambiae - aedes-aegypti - mating preferences - carbon dioxide - essential oils - host-seeking - body odors
    Chemical cues are considered to be the most important cues for mosquitoes to find their hosts and humans can be ranked for attractiveness to mosquitoes based on the chemical cues they emit. Human leukocyte antigen (HLA) genes are considered to be involved in the regulation of human body odor and may therefore affect human attractiveness to mosquitoes, and hence, affect the force of malaria transmission. In the present study the correlations between HLA profiles, human skin volatiles and human attractiveness to the malaria mosquito Anopheles gambiae Giles sensu stricto were examined. Skin emanations of 48 volunteers were collected by rubbing a foot over glass beads. Previously the attractiveness of these emanations to An. gambiae was determined. In this study, the chemical composition of these emanations was determined by gas chromatography–mass spectroscopy (GC–MS) and blood samples of all volunteers were taken for HLA analysis. Hierarchical cluster analysis (HCA), partial least squares discriminant analysis (PLS-DA), Fisher’s exact test and random forest regression were used to test for correlations between individuals classified as either highly or poorly attractive to mosquitoes and their HLA profile and volatile composition. HLA profiling suggests that people carrying HLA gene Cw*07 are more attractive to mosquitoes. GC–MS revealed that limonene, 2-phenylethanol and 2-ethyl-1-hexanol were associated with individuals that were poorly attractive to An.gambiae and lactic acid, 2-methylbutanoic acid, tetradecanoic acid and octanal with individuals that were highly attractive. Such compounds offer potential for disruption of mosquito behavior in malaria intervention programs.
    Geographic coincidence of increased malaria transmission hazard and vulnerability occurring at the periphery of two Tanzanian villages.
    Russell, T.L. ; Lwetoijera, D.W. ; Knols, B.G.J. ; Takken, W. ; Killeen, G.F. ; Kelly-Hope, L.A. - \ 2013
    Malaria Journal 12 (2013). - ISSN 1475-2875 - 11 p.
    treated bed nets - entomological inoculation rate - western kenya highlands - gambiae s.l. diptera - anopheles-gambiae - risk-factors - environmental-factors - rural tanzania - house-entry - light-traps
    Background - The goal of malaria elimination necessitates an improved understanding of any fine-scale geographic variations in transmission risk so that complementary vector control tools can be integrated into current vector control programmes as supplementary measures that are spatially targeted to maximize impact upon residual transmission. This study examines the distribution of host-seeking malaria vectors at households within two villages in rural Tanzania. Methods - Host-seeking mosquitoes were sampled from 72 randomly selected households in two villages on a monthly basis throughout 2008 using CDC light-traps placed beside occupied nets. Spatial autocorrelation in the dataset was examined using the Moran’s I statistic and the location of any clusters was identified using the Getis-Ord Gi* statistic. Statistical associations between the household characteristics and clusters of mosquitoes were assessed using a generalized linear model for each species. Results - For both Anopheles gambiae sensu lato and Anopheles funestus, the density of host-seeking females was spatially autocorrelated, or clustered. For both species, houses with low densities were clustered in the semi-urban village centre while houses with high densities were clustered in the periphery of the villages. Clusters of houses with low or high densities of An. gambiae s.l. were influenced by the number of residents in nearby houses. The occurrence of high-density clusters of An. gambiae s.l. was associated with lower elevations while An. funestus was also associated with higher elevations. Distance from the village centre was also positively correlated with the number of household occupants and having houses constructed with open eaves. Conclusion - The results of the current study highlight that complementary vector control tools could be most effectively targeted to the periphery of villages where the households potentially have a higher hazard (mosquito densities) and vulnerability (open eaves and larger households) to malaria infection.
    Insecticide-treated plastic sheeting for emergency malaria prevention and shelter among displaced populations: an observational cohort study in a refugee setting in Sierra Leone
    Burns, M.R. ; Rowland, M. ; N'Guessan, R. ; Carneiro, I. ; Beeche, A. ; Sesler Ruiz, S. ; Kamara, S. ; Takken, W. ; Carnevale, P. ; Allan, R. - \ 2012
    American Journal of Tropical Medicine and Hygiene 87 (2012)2. - ISSN 0002-9637 - p. 242 - 250.
    anopheles-gambiae - rural area - children - vectors - camps - transmission - nets - resistance - exposure - infants
    A double-blind phase III malaria prevention trial was conducted in two refugee camps using pre-manufactured insecticide-treated plastic sheeting (ITPS) or untreated polyethylene sheeting (UPS) randomly deployed to defined sectors of each camp. In Largo camp the ITPS or UPS was attached to inner walls and ceilings of shelters, whereas in Tobanda the ITPS or UPS was used to line only the ceiling and roof. In Largo the Plasmodium falciparum incidence rate in children up to 3 years of age who were cleared of parasites and monitored for 8 months was 163/100 person-years under UPS and 63 under ITPS (adjusted odds ratio [AOR] = 0.40, 95% confidence interval [CI] = 0.33–0.47). In Tobanda incidence was 157/100 person-years under UPS and 134 under ITPS (AOR = 0.85, 95% CI = 0.75–0.95). Protective efficacy was 61% under fully lined ITPS and 15% under roof lined ITPS. Anemia rates improved under ITPS in both camps. This novel tool proved to be a convenient, safe, and long-lasting method of malaria control when used as a full shelter lining in an emergency setting.
    Lessons from Agriculture for the Sustainable Management of Malaria Vectors
    Thomas, M.B. ; Godfray, H.C.J. ; Read, A.F. ; Berg, H. van den; Tabashnik, B.E. ; Lenteren, J.C. van; Waage, J.K. ; Takken, W. - \ 2012
    PLOS Medicine 9 (2012)7. - ISSN 1549-1676
    anopheles-gambiae - pest-management - insecticide resistance - borne diseases - field trial - mosquito - strategies - impacts - africa - system
    The effectiveness of insecticide-treated bed nets and indoor insecticide sprays to control adult mosquito vectors is being threatened by the spread of insecticide resistance. We argue for expanding beyond “insecticide monotherapy” to more sustainable integrated vector management strategies that use optimal suites of control tactics. Experience in agriculture suggests that such integrated approaches can provide more effective and durable pest management. This shift will require increased investment in research and translational science. Failure to act risks a resurgence of malaria and erosion of community support and donor commitment.
    A Novel Synthetic Odorant Blend for Trapping of Malaria and Other African Mosquito Species
    Mukabana, W.R. ; Mweresa, C.K. ; Otieno, B. ; Omusula, P. ; Smallegange, R.C. ; Loon, J.J.A. van; Takken, W. - \ 2012
    Journal of Chemical Ecology 38 (2012)3. - ISSN 0098-0331 - p. 235 - 244.
    gambiae-sensu-stricto - human skin microbiota - tsetse-flies diptera - anopheles-gambiae - carbon-dioxide - host-seeking - identification - culicidae - tanzania - glossinidae
    Estimating the biting fraction of mosquitoes is of critical importance for risk assessment of malaria transmission. Here, we present a novel odor-based tool that has been rigorously assessed in semi-field assays and traditional African villages for estimating the number of mosquitoes that enter houses in search of a blood meal. A standard synthetic blend (SB) consisting of ammonia, (S)-lactic acid, tetradecanoic acid, and carbon dioxide was complemented with isovaleric acid, 4,5 dimethylthiazole, 2-methyl-1-butanol, and 3-methyl-1-butanol in various combinations and concentrations, and tested for attractiveness to the malaria mosquito Anopheles gambiae. Compounds were released through low density polyethylene (LDPE) material or from nylon strips (nylon). Studies were done in a semi-field facility and two traditional villages in western Kenya. The alcohol 3-methyl-1-butanol significantly increased the attraction of SB. The other compounds proved less effective or inhibitory. Tested in a village, 3-methyl-1-butanol, released from LDPE, increased the attraction of SB. Further studies showed a significantly enhanced attraction of adding 3-methyl-1-butanol to SB compared to previously-published attractive blends both under semi-field and village conditions. Other mosquito species with relevance for public health were collected with this blend in significantly higher numbers as well. These results demonstrate the advent of a novel, reliable odor-based sampling tool for the collection of malaria and other mosquitoes. The advantage of this odor-based tool over existing mosquito sampling tools is its reproducibility, objectiveness, and relatively low cost compared to current standards of CDC light traps or the human landing catch.
    Hitting Hotspots: Spatial Targeting of Malaria for Control and Elimination
    Bousema, T. ; Griffin, J.T. ; Sauerwein, R.W. ; Smith, D.L. ; Churcher, T.S. ; Takken, W. ; Ghani, A. ; Drakeley, C. ; Gosling, R. - \ 2012
    PLOS Medicine 9 (2012)1. - ISSN 1549-1676
    plasmodium-falciparum - anopheles-gambiae - rural area - vector populations - control programs - young-children - urban malaria - west-africa - transmission - infection
    Current malaria elimination guidelines are based on the concept that malaria transmission becomes heterogeneous in the later phases of malaria elimination [1]. In the pre-elimination and elimination phases, interventions have to be targeted to entire villages or towns with higher malaria incidence until only individual episodes of malaria remain and become the centre of attention [1]. With increasing evidence of clustering of malaria episodes within villages, we argue that there is an intermediate step. Heterogeneity in malaria transmission within villages is present long before areas enter the pre-elimination phase, and identifying and targeting hotspots of malaria transmission should form the cornerstone of both successful malaria control and malaria elimination.
    Composition of Human Skin Microbiota Affects Attractiveness to Malaria Mosquitoes
    Verhulst, N.O. ; Qiu, Y.T. ; Beijleveld, H. ; Maliepaard, C.A. ; Knights, D. ; Schulz, S. ; Berg-Lyons, D. ; Lauber, C.L. ; Verduijn, W. ; Haasnoot, G.W. ; Mumm, R. ; Bouwmeester, H.J. ; Claas, F.H.J. ; Dicke, M. ; Loon, J.J.A. van; Takken, W. ; Knight, R. ; Smallegange, R.C. - \ 2011
    PLoS ONE 6 (2011)12. - ISSN 1932-6203 - 7 p.
    major histocompatibility complex - human axillary odor - anopheles-gambiae - mating preferences - aedes-aegypti - microflora - spectrometry - diversity - responses - selection
    The African malaria mosquito Anopheles gambiae sensu stricto continues to play an important role in malaria transmission, which is aggravated by its high degree of anthropophily, making it among the foremost vectors of this disease. In the current study we set out to unravel the strong association between this mosquito species and human beings, as it is determined by odorant cues derived from the human skin. Microbial communities on the skin play key roles in the production of human body odour. We demonstrate that the composition of the skin microbiota affects the degree of attractiveness of human beings to this mosquito species. Bacterial plate counts and 16S rRNA sequencing revealed that individuals that are highly attractive to An. gambiae s.s. have a significantly higher abundance, but lower diversity of bacteria on their skin than individuals that are poorly attractive. Bacterial genera that are correlated with the relative degree of attractiveness to mosquitoes were identified. The discovery of the connection between skin microbial populations and attractiveness to mosquitoes may lead to the development of new mosquito attractants and personalized methods for protection against vectors of malaria and other infectious diseases
    Dominant negative phenotype of Bacillus thuringiensis Cry1Ab, Cry11Aa and Cry4Ba mutants suggest hetero-oligomer formation among different Cry toxins.
    Carmona, D. ; Rodriguez-Almazan, C. ; Munoz-Garay, C. ; Portugal, L. ; Perez, C. ; Maagd, R.A. de; Bakker, P. ; Soberon, M. ; Bravo, A. - \ 2011
    PLoS ONE 6 (2011)5. - ISSN 1932-6203 - 6 p.
    subsp israelensis - delta-endotoxin - manduca-sexta - alkaline-phosphatase - protective antigen - anopheles-gambiae - toxicity - crystal - anthrax - mutagenesis
    Background - Bacillus thuringiensis Cry toxins are used worldwide in the control of different insect pests important in agriculture or in human health. The Cry proteins are pore-forming toxins that affect the midgut cell of target insects. It was shown that non-toxic Cry1Ab helix a-4 mutants had a dominant negative (DN) phenotype inhibiting the toxicity of wildtype Cry1Ab when used in equimolar or sub-stoichiometric ratios (1:1, 0.5:1, mutant:wt) indicating that oligomer formation is a key step in toxicity of Cry toxins. Methodology/Principal Findings - The DN Cry1Ab-D136N/T143D mutant that is able to block toxicity of Cry1Ab toxin, was used to analyze its capacity to block the activity against Manduca sexta larvae of other Cry1 toxins, such as Cry1Aa, Cry1Ac, Cry1Ca, Cry1Da, Cry1Ea and Cry1Fa. Cry1Ab-DN mutant inhibited toxicity of Cry1Aa, Cry1Ac and Cry1Fa. In addition, we isolated mutants in helix a-4 of Cry4Ba and Cry11Aa, and demonstrate that Cry4Ba-E159K and Cry11Aa-V142D are inactive and completely block the toxicity against Aedes aegypti of both wildtype toxins, when used at sub-stoichiometric ratios, confirming a DN phenotype. As controls we analyzed Cry1Ab-R99A or Cry11Aa-E97A mutants that are located in helix a-3 and are affected in toxin oligomerization. These mutants do not show a DN phenotype but were able to block toxicity when used in 10:1 or 100:1 ratios (mutant:wt) probably by competition of binding with toxin receptors. Conclusions/Significance - We show that DN phenotype can be observed among different Cry toxins suggesting that may interact in vivo forming hetero-oligomers. The DN phenotype cannot be observed in mutants affected in oligomerization, suggesting that this step is important to inhibit toxicity of other toxins
    Linking individual phenotype to density-dependent population growth: the influence of body size on the population dynamics of malaria vectors
    Russell, T.L. ; Lwetoijera, D.W. ; Knols, B.G.J. ; Takken, W. ; Killeen, G.F. ; Ferguson, H.M. - \ 2011
    Proceedings of the Royal Society. B: Biological Sciences 278 (2011)1721. - ISSN 0962-8452 - p. 3142 - 3151.
    plasmodium-falciparum malaria - anopheles-gambiae - multimodel inference - culicidae - diptera - transmission - arabiensis - mosquitos - fecundity - abundance
    Understanding the endogenous factors that drive the population dynamics of malaria mosquitoes will facilitate more accurate predictions about vector control effectiveness and our ability to destabilize the growth of either low- or high-density insect populations. We assessed whether variation in phenotypic traits predict the dynamics of Anopheles gambiae sensu lato mosquitoes, the most important vectors of human malaria. Anopheles gambiae dynamics were monitored over a six-month period of seasonal growth and decline. The population exhibited density-dependent feedback, with the carrying capacity being modified by rainfall (97% wAICc support). The individual phenotypic expression of the maternal (p = 0.0001) and current (p = 0.040) body size positively influenced population growth. Our field-based evidence uniquely demonstrates that individual fitness can have population-level impacts and, furthermore, can mitigate the impact of exogenous drivers (e.g. rainfall) in species whose reproduction depends upon it. Once frontline interventions have suppressed mosquito densities, attempts to eliminate malaria with supplementary vector control tools may be attenuated by increased population growth and individual fitness
    First report of the infection of insecticide-resistant malaria vector mosquitoes with an entomopathogenic fungus under field conditions
    Howard, A.F.V. ; N'Guessan, R. ; Koenraadt, C.J.M. ; Asidi, A. ; Farenhorst, M. ; Akogbeto, M. ; Knols, B.G.J. ; Takken, W. - \ 2011
    Malaria Journal 10 (2011). - ISSN 1475-2875 - 8 p.
    anopheles-gambiae - culex-quinquefasciatus - metarhizium-anisopliae - beauveria-bassiana - conidial thermotolerance - west-africa - efficacy - benin - nets - pathogenicity
    Background - Insecticide-resistant mosquitoes are compromising the ability of current mosquito control tools to control malaria vectors. A proposed new approach for mosquito control is to use entomopathogenic fungi. These fungi have been shown to be lethal to both insecticide-susceptible and insecticide-resistant mosquitoes under laboratory conditions. The goal of this study was to see whether entomopathogenic fungi could be used to infect insecticide-resistant malaria vectors under field conditions, and to see whether the virulence and viability of the fungal conidia decreased after exposure to ambient African field conditions. Methods - This study used the fungus Beauveria bassiana to infect the insecticide-resistant malaria vector Anopheles gambiae s.s (Diptera: Culicidae) VKPER laboratory colony strain. Fungal conidia were applied to polyester netting and kept under West African field conditions for varying periods of time. The virulence of the fungal-treated netting was tested 1, 3 and 5 days after net application by exposing An. gambiae s.s. VKPER mosquitoes in WHO cone bioassays carried out under field conditions. In addition, the viability of B. bassiana conidia was measured after up to 20 days exposure to field conditions. Results - The results show that B. bassiana infection caused significantly increased mortality with the daily risk of dying being increased by 2.5× for the fungus-exposed mosquitoes compared to the control mosquitoes. However, the virulence of the B. bassiana conidia decreased with increasing time spent exposed to the field conditions, the older the treatment on the net, the lower the fungus-induced mortality rate. This is likely to be due to the climate because laboratory trials found no such decline within the same trial time period. Conidial viability also decreased with increasing exposure to the net and natural abiotic environmental conditions. After 20 days field exposure the conidial viability was 30%, but the viability of control conidia not exposed to the net or field conditions was 79%. Conclusions - This work shows promise for the use of B. bassiana fungal conidia against insecticide-resistant mosquitoes in the field, but further work is required to examine the role of environmental conditions on fungal virulence and viability with a view to eventually making the fungal conidia delivery system more able to withstand the ambient African climate.
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