The entomopathogenic fungus Metarhizium anisopliae shows great promise for the control of adult malaria vectors. A promising strategy for infection of mosquitoes is supplying the fungus at plant feeding sites.
We evaluated the survival of fungus-exposed Anopheles gambiae mosquitoes (males and females) fed on 6% glucose and on sugars of Ricinus communis (Castor oil plant) and Parthenium hysterophorus (Santa Maria feverfew weed). Further, we determined the feeding propensity, quantity of sugar ingested and its digestion rate in the mosquitoes when fed on R. communis for 12 hours, one and three days post-exposure to fungus. The anthrone test was employed to detect the presence of sugar in each mosquito from which the quantity consumed and the digestion rates were estimated.
Fungus-exposed mosquitoes lived for significantly shorter periods than uninfected mosquitoes when both were fed on 6% glucose (7 versus 37 days), R. communis (7 versus 18 days) and P. hysterophorus (5 versus 7 days). Significantly fewer male and female mosquitoes, one and three days post-exposure to fungus, fed on R. communis compared to uninfected controls. Although the quantity of sugar ingested was similar between the treatment groups, fewer fungus-exposed than control mosquitoes ingested small, medium and large meals. Digestion rate was significantly slower in females one day after exposure to M. anisopliae compared to controls but remained the same in males. No change in digestion rate between treatments was observed three days after exposure.
These results demonstrate that (a) entomopathogenic fungi strongly impact survival and sugar-feeding propensity of both sexes of the malaria vector An. gambiae but do not affect their potential to feed and digest meals, and (b) that plant sugar sources can be targeted as fungal delivery substrates. In addition, targeting males for population reduction using entomopathogenic fungi opens up a new strategy for mosquito vector control.
Metarhizium anisopliae; Anopheles gambiae s.s; Host plants; Sugar feeding; Malaria vector
As global efforts to eliminate malaria intensify, accurate information on vector populations and transmission dynamics is critical for directing control efforts, developing new control tools, and predicting the effects of these interventions under various conditions. Currently available sampling tools for mosquito population monitoring suffer from well-recognized limitations. As reported in this workshop summary, a recent gathering of medical entomologists, modelers, and malaria experts reviewed these issues and agreed that efforts are needed to improve methods to monitor key transmission parameters. Identified needs include standardized methods for sampling of both mosquito adults and larvae, improved tools for mosquito species identification and age-grading, and a better means for determining the entomological inoculation rate.
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.
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.
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.
Aedes albopictus; Mosquito; Adult collections; BG-sentinel trap; Attraction; Odour bait; CO2; Synergism
The malaria mosquito Anopheles gambiae has a high preference for human hosts, a characteristic that contributes greatly to its capacity for transmitting human malaria. A sibling species, An. quadriannulatus, has a quite different host preference and feeds mostly on bovids. For this reason it does not contribute to human malaria transmission. Host seeking in mosquitoes is modulated by the olfactory system, which is primarily housed in the antennae and maxillary palps. Therefore, the detection of differing host odors by sibling species may be reflected in the expression level of the olfactory genes involved. Accordingly, we compared the transcriptomes of the antennae and maxillary palps of An. gambiae and An. quadriannulatus.
We identified seven relatively abundant olfactory receptors, nine ionotropic receptors and three odorant binding proteins that are substantially up-regulated in An. gambiae antennae. Interestingly, we find that the maxillary palps of An. gambiae contain a species-specific olfactory receptor, Or52, and five An. gambiae-specific gustatory receptors (AgGr48-52) that are relatively abundant. These five gustatory receptors are also expressed in An. gambiae antennae, although at lower level, indicating a likely role in olfaction, rather than gustation. We also document an approximately three-fold higher overall expression of olfaction genes in the maxillary palps of An. quadriannulatus, indicating an important role of this organ in the olfaction system of this species. Finally, the expression of the CO2 receptor genes is five to six-fold higher in the zoophilic An. quadriannulatus, implying a much higher sensitivity for detecting CO2.
These results identify potential human host preference genes in the malaria vector An. gambiae. Interestingly, species-specific expression of several gustatory receptors in the olfactory organs indicate a role in olfaction rather than gustation. Additionally, a more expansive role for maxillary palps in olfaction is implicated than previously thought, albeit more so in the zoophilic An. quadriannulatus.
Electronic supplementary material
The online version of this article (doi:10.1186/1471-2164-15-1089) contains supplementary material, which is available to authorized users.
There has been increasing effort in recent years to incorporate user needs in technology design and re-design. This project employed a bottom-up approach that engaged end users from the outset. Bottom-up approaches have the potential to bolster novel interventions and move them towards adaptive and evidence-based strategies. The present study concerns an innovative use of solar-powered mosquito trapping systems (SMoTS) to control malaria in western Kenya. Our paper highlights the co-dependence of research associated with the development of the SMoTS technology on one hand and research for enhancing the sustainable uptake of that very same intervention within the community on the other.
During the pre-intervention year, we examined the design, re-design and piloting of a novel technology to generate lessons for malaria elimination on Rusinga Island. Initial ideas about many technological necessities were evaluated and re-designed following feedback from various sources, including technical and social research as well as broader interactions with the social environment. We documented the interlocking of the multiple processes and activities that took place through process observation and document reviews. We analysed the data within the conceptual framework of system innovation by identifying mutual shaping between technical and social factors.
Our findings illustrate how various project stakeholders including project staff, collaborators, donor, and community members simultaneously pursued interdependent technological transformations and social interests. In the ongoing process, we observed how partial outcomes in the technological domain influenced social events at a later phase and vice versa.
Looking at malaria intervention projects employing novel technologies as niches that may evolve towards system innovation, helps to reveal interrelations between the various technical and social aspects. Revealing these interrelations requires a different role for research and different perspective on innovation where innovation is more than the technical aspects. This approach therefore requires that research is designed in a way that enables obtaining feedback from both aspects.
Malaria; Co-evolution; Socio-technical; System innovation; Solar; Mosquito trap; Feedback; Community; Kenya
The full-scale impact of odour-baited technology on the surveillance, sampling and control of vectors of infectious diseases is partly limited by the lack of methods for the efficient and sustainable dispensing of attractants. In this study we investigated whether locally-available and commonly used textiles are efficient substrates for the release of synthetic odorant blends attracting malaria mosquitoes.
The relative efficacy of (a) polyester, (b) cotton, (c) cellulose + polyacrylate, and (d) nylon textiles as substrates for dispensing a synthetic odour blend (Ifakara blend 1(IB1)) that attracts malaria mosquitoes was evaluated in western Kenya. The study was conducted through completely randomized Latin square experimental designs under semi-field and field conditions.
Traps charged with IB1-impregnated polyester, cotton and cellulose + polyacrylate materials caught significantly more female Anopheles gambiae sensu stricto (semi-field conditions) and An. gambiae sensu lato (field conditions) mosquitoes than IB1-treated nylon (P = 0.001). The IB1-impregnated cellulose + polyacrylate material was the most attractive to female An. funestus mosquitoes compared to all other dispensing textile substrates (P < 0.001). The responses of female An. funestus mosquitoes to IB1-treated cotton and polyester were equal (P = 0.45). Significantly more female Culex mosquitoes were attracted to IB1-treated cotton than to the other treatments (P < 0.001). Whereas IB1-impregnated cotton and cellulose + polyacrylate material attracted equal numbers of female Mansonia mosquitoes (P = 0.44), the catches due to these two substrates were significantly higher than those associated with the other substrates (P < 0.001).
The number and species of mosquitoes attracted to a synthetic odour blend is influenced by the type of odour-dispensing material used. Thus, surveillance and intervention programmes for malaria and other mosquito vectors using attractive odour baits should select an odour-release material that optimizes the odour blend.
Anopheles gambiae; Anopheles funestus; IB1-impregnated nylon; Polyester; Cotton; Cellulose; Sodium polyacrylate; Attraction; Trapping; Kenya
Anaplasma phagocytophilum is the etiological agent of granulocytic anaplasmosis in humans and animals. Wild animals and ticks play key roles in the enzootic cycles of the pathogen. Potential ecotypes of A. phagocytophilum have been characterized genetically, but their host range, zoonotic potential and transmission dynamics has only incompletely been resolved.
The presence of A. phagocytophilum DNA was determined in more than 6000 ixodid ticks collected from the vegetation and wildlife, in 289 tissue samples from wild and domestic animals, and 69 keds collected from deer, originating from various geographic locations in The Netherlands and Belgium. From the qPCR-positive lysates, a fragment of the groEL-gene was amplified and sequenced. Additional groEL sequences from ticks and animals from Europe were obtained from GenBank, and sequences from human cases were obtained through literature searches. Statistical analyses were performed to identify A. phagocytophilum ecotypes, to assess their host range and their zoonotic potential. The population dynamics of A. phagocytophilum ecotypes was investigated using population genetic analyses.
DNA of A. phagocytophilum was present in all stages of questing and feeding Ixodes ricinus, feeding I. hexagonus, I. frontalis, I. trianguliceps, and deer keds, but was absent in questing I. arboricola and Dermacentor reticulatus. DNA of A. phagocytophilum was present in feeding ticks and tissues from many vertebrates, including roe deer, mouflon, red foxes, wild boar, sheep and hedgehogs but was rarely found in rodents and birds and was absent in badgers and lizards. Four geographically dispersed A. phagocytophilum ecotypes were identified, that had significantly different host ranges. All sequences from human cases belonged to only one of these ecotypes. Based on population genetic parameters, the potentially zoonotic ecotype showed significant expansion.
Four ecotypes of A. phagocytophilum with differential enzootic cycles were identified. So far, all human cases clustered in only one of these ecotypes. The zoonotic ecotype has the broadest range of wildlife hosts. The expansion of the zoonotic A. phagocytophilum ecotype indicates a recent increase of the acarological risk of exposure of humans and animals.
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The online version of this article (doi:10.1186/1756-3305-7-365) contains supplementary material, which is available to authorized users.
Anaplasma phagocytophilum; Zoonoses; Ixodes ricinus; Wildlife; Epidemiology
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.
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.
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).
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.
Anopheles mosquito; Malaria vector; Suna trap; CDC light trap; MM-X trap; Attractant; Odour bait; Surveillance
Pathogen transmission by mosquitos is known to be highly sensitive to mosquito bionomic parameters. Mosquito mark-release-recapture (MMRR) experiments are a standard method for estimating such parameters including dispersal, population size and density, survival, blood feeding frequency and blood meal host preferences.
We assembled a comprehensive database describing adult female MMRR experiments. Bibliographic searches were used to build a digital library of MMRR studies and selected data describing the reported outcomes were extracted.
The resulting database contained 774 unique adult female MMRR experiments involving 58 vector mosquito species from the three main genera of importance to human health: Aedes, Anopheles and Culex. Crude examination of these data revealed patterns associated with geography as well as mosquito genus, consistent with bionomics varying by species-specific life history and ecological context. Recapture success varied considerably and was significantly different amongst genera, with 8, 4 and 1% of adult females recaptured for Aedes, Anopheles and Culex species, respectively. A large proportion of experiments (59%) investigated dispersal and survival and many allowed disaggregation of the release and recapture data. Geographic coverage was limited to just 143 localities around the world.
This MMRR database is a substantial contribution to the compilation of global data that can be used to better inform basic research and public health interventions, to identify and fill knowledge gaps and to enrich theory and evidence-based ecological and epidemiological studies of mosquito vectors, pathogen transmission and disease prevention. The database revealed limited geographic coverage and a relative scarcity of information for vector species of substantial public health relevance. It represents, however, a wealth of entomological information not previously compiled and of particular interest for mosquito-borne pathogen transmission models.
Mosquito; Vector; Mark-release-recapture; Database; Pathogen transmission models
Most odour baits for haematophagous arthropods contain carbon dioxide (CO2). The CO2 is sourced artificially from the fermentation of refined sugar (sucrose), dry ice, pressurized gas cylinders or propane. These sources of CO2 are neither cost-effective nor sustainable for use in remote areas of sub-Saharan Africa. In this study, molasses was evaluated as a potential substrate for producing CO2 used as bait for malaria mosquitoes.
The attraction of laboratory-reared and wild Anopheles gambiae complex mosquitoes to CO2 generated from yeast-fermentation of molasses was assessed under semi-field and field conditions in western Kenya. In the field, responses of wild Anopheles funestus were also assessed. Attraction of the mosquitoes to a synthetic mosquito attractant, Mbita blend (comprising ammonia, L-lactic acid, tetradecanoic acid and 3-methyl-1-butanol) when augmented with CO2 generated from yeast fermentation of either molasses or sucrose was also investigated.
In semi-field, the release rate of CO2 and proportion of An. gambiae mosquitoes attracted increased in tandem with an increase in the quantity of yeast-fermented molasses up to an optimal ratio of molasses and dry yeast. More An. gambiae mosquitoes were attracted to a combination of the Mbita blend plus CO2 produced from fermenting molasses than the Mbita blend plus CO2 from yeast-fermented sucrose. In the field, significantly more female An. gambiae sensu lato mosquitoes were attracted to the Mbita blend augmented with CO2 produced by fermenting 500 g of molasses compared to 250 g of sucrose or 250 g of molasses. Similarly, significantly more An. funestus, Culex and other anopheline mosquito species were attracted to the Mbita blend augmented with CO2 produced from fermenting molasses than the Mbita blend with CO2 produced from sucrose. Augmenting the Mbita blend with CO2 produced from molasses was associated with high catches of blood-fed An. gambiae s.l. and An. funestus mosquitoes.
Molasses is a suitable ingredient for the replacement of sucrose as a substrate for the production of CO2 for sampling of African malaria vectors and other mosquito species. The finding of blood-fed malaria vectors in traps baited with the Mbita blend and CO2 derived from molasses provides a unique opportunity for the study of host-vector interactions.
Carbon dioxide; Sugar; Sucrose; Molasses; Anopheles gambiae; Anopheles funestus; Malaria; Mosquitoes; Attraction; Behaviour
In the past decade, two pathogens transmitted by Culicoides biting midges (Diptera: Ceratopogonidae), bluetongue virus and Schmallenberg virus, have caused serious economic losses to the European livestock industry, most notably affecting sheep and cattle. These outbreaks of arboviral disease have highlighted large knowledge gaps on the biology and ecology of indigenous Culicoides species. With these research gaps in mind, and as a means of assessing what potential disease outbreaks to expect in the future, an international workshop was held in May 2013 at Wageningen University, The Netherlands. It brought together research groups from Belgium, France, Germany, Spain, Switzerland, United Kingdom and The Netherlands, with diverse backgrounds in vector ecology, epidemiology, entomology, virology, animal health, modelling, and genetics. Here, we report on the key findings of this workshop.
Culicoides; Midge; Schmallenberg virus; Bluetongue virus; Emerging disease; Ecology
Mosquitoes are the dominant vectors of pathogens that cause infectious diseases such as malaria, dengue, yellow fever and filariasis. Current vector control strategies often rely on the use of pyrethroids against which mosquitoes are increasingly developing resistance. Here, a push-pull system is presented, that operates by the simultaneous use of repellent and attractive volatile odorants.
Experiments were carried out in a semi-field set-up: a traditional house which was constructed inside a screenhouse. The release of different repellent compounds, para-menthane-3,8-diol (PMD), catnip oil e.o. and delta-undecalactone, from the four corners of the house resulted in significant reductions of 45% to 81.5% in house entry of host-seeking malaria mosquitoes. The highest reductions in house entry (up to 95.5%), were achieved by simultaneously repelling mosquitoes from the house (push) and removing them from the experimental set-up using attractant-baited traps (pull).
The outcome of this study suggests that a push-pull system based on attractive and repellent volatiles may successfully be employed to target mosquito vectors of human disease. Reductions in house entry of malaria vectors, of the magnitude that was achieved in these experiments, would likely affect malaria transmission. The repellents used are non-toxic and can be used safely in a human environment. Delta-undecalactone is a novel repellent that showed higher effectiveness than the established repellent PMD. These results encourage further development of the system for practical implementation in the field.
Mosquitoes; Malaria; Vector control; Repellent; Push-pull
Essential oils of eight plants, selected after an ethnobotanical survey conducted in Bukusu community in Bungoma County, western Kenya (Tagetes minuta, Tithonia diversifolia, Juniperus procera, Solanecio mannii, Senna didymobotrya, Lantana camara, Securidaca longepedunculata, and Hoslundia opposita), were initially screened (at two doses) for their repellence against brown ear tick, Rhipicephalus appendiculatus, using a dual-choice climbing assay. The oils of T. minuta and T. diversifolia were then selected for more detailed study. Dose-response evaluations of these oils showed that T. minuta oil was more repellent (RD50 = 0.0021 mg) than that of T. diversifolia (RD50 = 0.263 mg). Gas chromatography-linked mass spectrometric (GC-MS) analyses showed different compositions of the two oils. T. minuta oil is comprised mainly of cis-ocimene (43.78%), dihydrotagetone (16.71%), piperitenone (10.15%), trans-tagetone (8.67%), 3,9-epoxy-p-mentha-1,8(10)diene (6.47%), β-ocimene (3.25%), and cis-tagetone (1.95%), whereas T. diversifolia oil is comprised mainly of α-pinene (63.64%), β-pinene (15.00%), isocaryophyllene (7.62%), nerolidol (3.70%), 1-tridecanol (1.75%), limonene (1.52%), and sabinene (1.00%). The results provide scientific rationale for traditional use of raw products of these plants in controlling livestock ticks by the Bukusu community and lay down some groundwork for exploiting partially refined products such as essential oils of these plants in protecting cattle against infestations with R. appendiculatus.
Mosquito fitness is determined largely by body size and nutritional reserves. Plasmodium infections in the mosquito and resultant transmission of malaria parasites might be compromised by the vector’s nutritional status. We studied the effects of nutritional stress and malaria parasite infections on transmission fitness of Anopheles mosquitoes.
Larvae of Anopheles gambiae sensu stricto and An. stephensi were reared at constant density but with nutritionally low and high diets. Fitness of adult mosquitoes resulting from each dietary class was assessed by measuring body size and lipid, protein and glycogen content. The size of the first blood meal was estimated by protein analysis. Mosquitoes of each dietary class were fed upon a Plasmodium yoelii nigeriensis-infected mouse, and parasite infections were determined 5 d after the infectious blood meal by dissection of the midguts and by counting oocysts. The impact of Plasmodium infections on gonotrophic development was established by dissection.
Mosquitoes raised under low and high diets emerged as adults of different size classes comparable between An. gambiae and An. stephensi. In both species low-diet females contained less protein, lipid and glycogen upon emergence than high-diet mosquitoes. The quantity of larval diet impacted strongly upon adult blood feeding and reproductive success. The prevalence and intensity of P. yoelii nigeriensis infections were reduced in low-diet mosquitoes of both species, but P. yoelii nigeriensis impacted negatively only on low-diet, small-sized An. gambiae considering survival and egg maturation. There was no measurable fitness effect of P. yoelii nigeriensis on An. stephensi.
Under the experimental conditions, small-sized An. gambiae expressed high mortality, possibly caused by Plasmodium infections, the species showing distinct physiological concessions when nutrionally challenged in contrast to well-fed, larger siblings. Conversely, An. stephensi was a robust, successful vector regardless of its nutrional status upon emergence. The data suggest that small-sized An. gambiae, therefore, would contribute little to malaria transmission, whereas this size effect would not affect An. stephensi.
Anopheles gambiae sensu stricto; Anopheles stephensi; Mosquito; Plasmodium yoelii nigeriensis; Blood-feeding; Body size; Fitness
Chemical cues play an important role in the host-seeking behavior of blood-feeding mosquitoes (Diptera: Culicidae). A field study was carried out in The Gambia to investigate the effects of human odor or synthetic odor blends on the attraction of mosquitoes. MM-X traps baited with 16 odor blends to which carbon dioxide (CO2) was added were tested in four sets of experiments. In a second series of experiments, MM-X traps with 14 odor blends without CO2 were tested. A blend of ammonia and l-lactic acid with or without CO2 was used as control odor in series 1 and 2, respectively. Centers for Disease Control and Prevention (CDC) traps were placed in a traditional house and an experimental house to monitor mosquito densities during the experiments. The MM-X traps caught a total number of 196,756 mosquitoes, with the most abundant species belonging to the genera Mansonia (70.6%), Anopheles (17.5%), and Culex (11.5%). The most abundant mosquito species caught by the CDC traps (56,290 in total) belonged to the genera Mansonia (59.4%), Anopheles (16.0% An. gambiae s.l. Giles, and 11.3% An. ziemanni Grünberg), and Culex (11.6%). MM-X traps baited with synthetic blends were in many cases more attractive than MM-X traps baited with human odors. Addition of CO2 to synthetic odors substantially increased the catch of all mosquito species in the MM-X traps. A blend of ammonia + L-lactic acid + CO2 + 3-methylbutanoic acid was the most attractive odor for most mosquito species. The candidate odor blend shows the potential to enhance trap collections so that traps will provide better surveillance and possible control.
mosquito sampling; odor baits; carbon dioxide; human odor
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.
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
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.
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.
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.
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.
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.
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.
Anopheles gambiae; Marking; Survival; Host-seeking; Olfactometer; Fluorescent paint
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.
A longitudinal study of malaria vectors was carried out in three villages in Suriname between 2006 and 2010. During 13,392 man hours of collections, 3,180 mosquitoes were collected, of which 33.7% were anophelines. Of these, Anopheles darlingi accounted for 88.1%, and An. nuneztovari accounted for 11.1%. The highest mean An. darlingi human biting rate (HBR) observed per survey was 1.43 bites/man per hour outdoor and 1.09 bites/man per hour indoor; 2 An. darlingi of the 683 tested were infected with Plasmodium falciparum. The anopheline HBR decreased to zero after the onset of malaria intervention activities, including insecticide-treated net (ITN) distribution, in 2006. Malaria transmission decreased to pre-elimination levels. It is concluded that the combination of ITN and climatic events has led to the collapse of malaria vector populations in the study sites in the interior of the country. The results are discussed in relation to the stability of malaria transmission in areas with low-density human populations.
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.
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.
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.
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.
Ixodes ricinus transmits Borrelia burgdorferi sensu lato, the etiological agent of Lyme disease. Previous studies have also detected Rickettsia helvetica, Anaplasma phagocytophilum, Neoehrlichia mikurensis, and several Babesia species in questing ticks in The Netherlands. In this study, we assessed the acarological risk of exposure to several tick-borne pathogens (TBPs), in The Netherlands. Questing ticks were collected monthly between 2006 and 2010 at 21 sites and between 2000 and 2009 at one other site. Nymphs and adults were analysed individually for the presence of TBPs using an array-approach. Collated data of this and previous studies were used to generate, for each pathogen, a presence/absence map and to further analyse their spatiotemporal variation. R. helvetica (31.1%) and B. burgdorferi sensu lato (11.8%) had the highest overall prevalence and were detected in all areas. N. mikurensis (5.6%), A. phagocytophilum (0.8%), and Babesia spp. (1.7%) were detected in most, but not all areas. The prevalences of pathogens varied among the study areas from 0 to 64%, while the density of questing ticks varied from 1 to 179/100 m2. Overall, 37% of the ticks were infected with at least one pathogen and 6.3% with more than one pathogen. One-third of the Borrelia-positive ticks were infected with at least one other pathogen. Coinfection of B. afzelii with N. mikurensis and with Babesia spp. occurred significantly more often than single infections, indicating the existence of mutual reservoir hosts. Alternatively, coinfection of R. helvetica with either B. afzelii or N. mikurensis occurred significantly less frequent. The diversity of TBPs detected in I. ricinus in this study and the frequency of their coinfections with B. burgdorferi s.l., underline the need to consider them when evaluating the risks of infection and subsequently the risk of disease following a tick bite.
vector-borne disease; Borrelia burgdorferi; Candidatus Neoehrlichia mikurensis; Rickettsia helvetica; Rickettsia conorii; Anaplasma phagocytophilum; Babesia; Ixodes ricinus
Between 1994 and 2009, a threefold increase has been observed in consultations of general practitioners for tick bites and Lyme disease in The Netherlands. The objective of this study was to determine whether an increase in the number of questing ticks infected with B. burgdorferi sensu lato is a potential cause of the rise in Lyme disease incidence.
Historic data on land usage, temperature and wildlife populations were collected and analyzed together with data from two longitudinal field studies on density of questing ticks. Effective population sizes of Borrelia burgdorferi s.l. were calculated.
Long-term trend analyses indicated that the length of the annual tick questing season increased as well as the surface area of tick-suitable habitats in The Netherlands. The overall abundances of feeding and reproductive hosts also increased. Mathematical analysis of the data from the field studies demonstrated an increase in mean densities/activities of questing ticks, particularly of larvae between 2006 and 2009. No increase in infection rate of ticks with Borrelia burgdorferi sensu lato was found. Population genetic analysis of the collected Borrelia species points to an increase in B. afzelii and B. garinii populations.
Together, these findings indicate an increase in the total number of Borrelia-infected ticks, providing circumstantial evidence for an increase in the risk of acquiring a bite of a tick infected with B. burgdorferi s.l. Due to the high spatiotemporal variation of tick densities/activities, long-term longitudinal studies on population dynamics of I. ricinus are necessary to observe significant trends.
Borrelia burgdorferi sensu lato; Ixodes ricinus; Population dynamics; Lyme disease; The Netherlands