Primary Vector Of Dengue Research Articles

Dengue vector management using insecticide treated materials and targeted interventions on productive breeding-sites in Guatemala

BackgroundIn view of the epidemiological expansion of dengue worldwide and the availability of new tools and strategies particularly for controlling the primary dengue vector Aedes aegypti, an intervention study was set up to test the efficacy, cost and feasibility of a combined approach of insecticide treated materials (ITMs) alone and in combination with appropriate targeted interventions of the most productive vector breeding-sites.MethodsThe study was conducted as a cluster randomized community trial using “reduction of the vector population” as the main outcome variable. The trial had two arms: 10 intervention clusters (neighborhoods) and 10 control clusters in the town of Poptun Guatemala. Activities included entomological assessments (characteristics of breeding-sites, pupal productivity, Stegomyia indices) at baseline, 6 weeks after the first intervention (coverage of window and exterior doorways made of PermaNet 2.0 netting, factory treated with deltamethrin at 55 mg/m2, and of 200 L drums with similar treated material) and 6 weeks after the second intervention (combination of treated materials and other suitable interventions targeting productive breeding-sites i.e larviciding with Temephos, elimination etc.). The second intervention took place 17 months after the first intervention. The insecticide residual activity and the insecticidal content were also studied at different intervals. Additionally, information about demographic characteristics, cost of the intervention, coverage of houses protected and satisfaction in the population with the interventions was collected.ResultsAt baseline (during the dry season) a variety of productive container types for Aedes pupae were identified: various container types holding >20 L, 200 L drums, washbasins and buckets (producing 83.7% of all pupae). After covering 100% of windows and exterior doorways and a small number of drums (where the commercial cover could be fixed) in 970 study households, tropical rains occurred in the area and lead to an increase of the vector population, more pronounced (but statistically not significant) in the control arm than in the intervention arm. In the second intervention (17 months later and six weeks after implementing the second intervention) the combined approach of ITMs and a combination of appropriate interventions against productive containers (Temephos in >200 L water drums, elimination of small discarded tins and bottles) lead to significant differences on reductions of the total number of pupae (P = 0.04) and the House index (P = 0.01) between intervention and control clusters, and to borderline differences on reductions of the Pupae per Person and Breteau indices (P = 0.05). The insecticide residual activity on treated curtains was high until month 18 but the chemical concentration showed a high variability. The cost per house protected with treated curtains and drum covers and targeting productive breeding-sites of the dengue vector was $ 5.31 USD. The acceptance of the measure was generally high, particularly in families who had experienced dengue.ConclusionEven under difficult environmental conditions (open houses, tropical rainfall, challenging container types mainly in the peridomestic environment) the combination of insecticide treated curtains and to a less extent drum covers and interventions targeting the productive container types can reduce the dengue vector population significantly.

Rhythms and synchronization patterns in gene expression in the Aedes aegypti mosquito

BackgroundAedes aegypti is arguably the most studied of all mosquito species in the laboratory and is the primary vector of both Dengue and Yellow Fever flaviviruses in the field. A large number of transcriptional studies have been made in the species and these usually report transcript quantities observed at a certain age or stage of development. However, circadian oscillation is an important characteristic of gene expression in many animals and plants, modulating both their physiology and behavior. Circadian gene expression in mosquito species has been previously reported but for only a few genes directly involved in the function of the molecular clock.ResultsHerein we analyze the transcription profiles of 21,494 messenger RNAs using an Ae. aegypti Agilent® microarray. Transcripts were quantified in adult female heads at 24 hours and then again at 72 hours and eight subsequent time points spaced four hours apart. We document circadian rhythms in multiple molecular pathways essential for growth, development, immune response, detoxification/pesticide resistance. Circadian rhythms were also noted in ribosomal protein genes used for normalization in reverse transcribed PCR (RT-PCR) to determine transcript abundance. We report pervasive oscillations and intricate synchronization patterns relevant to all known biological pathways.ConclusionThese results argue strongly that transcriptional analyses either need to be made over time periods rather than confining analyses to a single time point or development stage or exceptional care needs to be made to synchronize all mosquitoes to be analyzed and compared among treatment groups.

Ecological Modeling of Aedes aegypti (L.) Pupal Production in Rural Kamphaeng Phet, Thailand

Background Aedes aegypti (L.) is the primary vector of dengue, the most important arboviral infection globally. Until an effective vaccine is licensed and rigorously administered, Ae. aegypti control remains the principal tool in preventing and curtailing dengue transmission. Accurate predictions of vector populations are required to assess control methods and develop effective population reduction strategies. Ae. aegypti develops primarily in artificial water holding containers. Release recapture studies indicate that most adult Ae. aegypti do not disperse over long distances. We expect, therefore, that containers in an area of high development site density are more likely to be oviposition sites and to be more frequently used as oviposition sites than containers that are relatively isolated from other development sites. After accounting for individual container characteristics, containers more frequently used as oviposition sites are likely to produce adult mosquitoes consistently and at a higher rate. To this point, most studies of Ae. aegypti populations ignore the spatial density of larval development sites.MethodologyPupal surveys were carried out from 2004 to 2007 in rural Kamphaeng Phet, Thailand. In total, 84,840 samples of water holding containers were used to estimate model parameters. Regression modeling was used to assess the effect of larval development site density, access to piped water, and seasonal variation on container productivity. A varying-coefficients model was employed to account for the large differences in productivity between container types. A two-part modeling structure, called a hurdle model, accounts for the large number of zeroes and overdispersion present in pupal population counts.FindingsThe number of suitable larval development sites and their density in the environment were the primary determinants of the distribution and abundance of Ae. aegypti pupae. The productivity of most container types increased significantly as habitat density increased. An ecological approach, accounting for development site density, is appropriate for predicting Ae. aegypti population levels and developing efficient vector control programs.

Biochemical evidence of efficacy of potash alum for the control of dengue vector Aedes aegypti (Linnaeus)

Aedes aegypti is the primary vector of dengue, yellow fever and chikungunya in India and other South East Asian countries, and novel insecticides for vector control are urgently needed. In the present investigation, efficacy of potash alum, a traditionally known double salt in Indian and Chinese medicine system, was tested against the larvae of dengue vector, A. aegypti. LC(50,) LC(90) and LC(99) values were recorded for various instar larvae where I instar larvae were found to be the most susceptible and IV instar larvae as the least susceptible one. The LC(50) values of crude and standard potash alum of various instar larvae ranged between 15.29 and 48.53 ppm and 20.50-65.10 ppm, respectively. Biochemical changes were also evidenced in IV instar A. aegypti larvae following a sublethal exposure for 24 h in the levels of various nutrient reserves and primary metabolites such as sugar, glycogen, lipids and proteins suggesting possible mode of action responsible for larval mortality. Sugar and glycogen concentrations were measured as 24.6 and 10.67 μg per five larvae in controls which were significantly (p<0.05) reduced by 32.11-93.98% and 39.26-94.47%, respectively, in larvae treated with crude alum. In controls, protein and lipid content were recorded as 210.74 and 94.71 μg per five larvae which dropped up to 26.53% and 25.5%, respectively, in larvae following treatment with crude alum. Moreover, drastic changes were also recorded for DNA content with 25.39-44.17% decrease in crude alum-treated larvae. It is evident from these results that potash alum, a fairly cheaper and readily available ecofriendly compound could be recommended as a potential chemical larvicide against dengue vector at mosquito breeding sites in the vicinity of human dwellings.

Structure-Activity Relationships of 33 Carboxamides as Toxicants Against Female &lt;I&gt;Aedes aegypti&lt;/I&gt; (Diptera: Culicidae)

Aedes aegypti L. is the primary vector of dengue and yellow fever viruses, and use of aerosolized insecticides is one of the primary ways to control this medically important mosquito. However, few new insecticides have been developed for mosquito control in recent years. As a part of our effort to search for new insecticides to control mosquitoes, toxicities of 33 carboxamides were evaluated against female A. aegypti by topical application. This group included nine different categories of compounds, namely benzamides, phenyl-propenamides, propanamides, butanamides, butenamides, pentanamides, pentenamides, hexanamides, and hexenamides, that exhibited varying levels of toxicity against this mosquito species. The most toxic compound tested was hexahydro-1-(1-oxohexyl)-1H-azepine, with a 24-h LD50 value of 0.4 microg per mosquito, whereas the most toxic compound at the LD95 level was N-ethyl-2-methyl-N-phenyl-benzamide (1.82 microg per mosquito). The least toxic compound was N,N-bis (2-methylpropyl)-3-phenyl-2-propenamide, with LD50 and LD95 values of 15.66 and 72.07 microg per mosquito, respectively. Results from this initial study may prove useful in guiding further carboxamide modifications for the development of potential new insecticides.

Current resistance status to temephos in Aedes aegypti from different regions of Argentina

In Argentina, more than 25,000 cases of dengue were reported in the summer of 2009, even in provinces where the disease was formerly absent. We analysed the susceptibility levels to the larvicide temephos in seven populations of Aedes aegypti, the primary vector of dengue, collected during summer 2007/2008, using the susceptible Rockefeller strain as a control. Although no control failures were observed during the experiment, a majority of the lethal concentration and resistance ratio values indicate an incipient resistance. An integrative program to monitor the resistance of Ae. aegypti to insecticides is needed in the country.

The impact of transgenic mosquitoes on dengue virulence to humans and mosquitoes.

Dengue is a major public health concern in the tropics and subtropics. Innovative transgenic strategies to render Aedes aegypti mosquitoes, the primary vector of dengue, incompetent for dengue transmission are under development. We modeled the evolutionary impact of different transgenic mosquito strategies on dengue-induced mortality, that is, dengue virulence, to both humans and mosquitoes. This model incorporates various evolutionary trade-offs in dengue virus epidemiological traits, for example, a trade-off between dengue transmission rate and its virulence to humans. Our results indicate that strategies that block transmission or reduce mosquito biting impose selection on dengue virulence in humans. This selection can be for either higher or lower virulence, depending on the interaction between the effect of the transgene and the trade-offs in epidemiological traits, highlighting the need for detailed quantitative data to understand more fully the impact of mosquito transgenesis on dengue virulence. Dengue virulence in mosquitoes can be selected on by transgenic strategies of blocking transmission, decreased mosquito biting, increased mosquito background mortality, and increased mosquito infection-induced mortality. Our results suggest that dengue control strategies that raise mosquito background mortality or mosquito infection-induced mortality pose less risk of causing increased virulence to humans than strategies that block transmission or reduce mosquito biting.

Topically Applied AaeIAP1 Double-Stranded RNA Kills Female Adults of Aedes aegypti

Aedes aegypti (L.) (Diptera: Culicidae) is the primary vector of both dengue and yellow fever. Use of insecticides is one of the primary ways to control this medically important insect pest. However, few new insecticides have been developed for mosquito control in recent years. As a part of our effort to develop new insecticides to control mosquitoes, an inhibitor of apoptosis protein 1 gene in Aedes aegypti (AaeIAP1) was targeted for the development of molecular pesticides. Herein, for the first time, we report that topically applied AaeIAP1 double-stranded RNA products are able to kill female adults of Ae. aegypti. Our results indicate that critical pathways or genes could be targeted to develop molecular pesticides for the control of medically important diseases vectors.

Topically Applied &lt;I&gt;AaeIAP1&lt;/I&gt; Double-Stranded RNA Kills Female Adults of &lt;I&gt;Aedes aegypti&lt;/I&gt;

Aedes aegypti (L.) (Diptera: Culicidae) is the primary vector of both dengue and yellow fever. Use of insecticides is one of the primary ways to control this medically important insect pest. However, few new insecticides have been developed for mosquito control in recent years. As a part of our effort to develop new insecticides to control mosquitoes, an inhibitor of apoptosis protein 1 gene in Aedes aegypti (AaeIAP1) was targeted for the development of molecular pesticides. Herein, for the first time, we report that topically applied AaeIAP1 double-stranded RNA products are able to kill female adults of Ae. aegypti. Our results indicate that critical pathways or genes could be targeted to develop molecular pesticides for the control of medically important diseases vectors.

Identity and transfer of male reproductive gland proteins of the dengue vector mosquito, Aedes aegypti: Potential tools for control of female feeding and reproduction

Male reproductive gland proteins (mRGPs) impact the physiology and/or behavior of mated females in a broad range of organisms. We sought to identify mRGPs of the yellow fever mosquito, Aedes aegypti, the primary vector of dengue and yellow fever viruses. Earlier studies with Ae. aegypti demonstrated that “matrone” (a partially purified male reproductive accessory gland substance) or male accessory gland fluid injected into virgin female Ae. aegypti affect female sexual refractoriness, blood feeding and digestion, flight, ovarian development, and oviposition. Using bioinformatic comparisons to Drosophila melanogaster accessory gland proteins and mass spectrometry of proteins from Ae. aegypti male accessory glands and ejaculatory ducts (AG/ED) and female reproductive tracts, we identified 63 new putative Ae. aegypti mRGPs. Twenty-one of these proteins were found in the reproductive tract of mated females but not of virgin females suggesting that they are transferred from males to females during mating. Most of the putative mRGPs fall into the same protein classes as mRGPs in other organisms, although some appear to be evolving rapidly and lack identifiable homologs in Culex pipiens, Anopheles gambiae, and D. melanogaster. Our results identify candidate male-derived molecules that may have an important influence on behavior, survival, and reproduction of female mosquitoes.

Body size‐associated survival and dispersal rates of Aedes aegypti in Rio de Janeiro

The daily survival rate of Aedes aegypti (L) (Diptera: Culicidae) is one of the most important parameters in mathematical models of dengue transmission. In this report, we evaluate the effect of adult body size on the survival and dispersal rates of male and female Ae. aegypti, the primary dengue vector in Brazil. Independent of larval diet (i.e. size), the daily survival rate of females recaptured in the field was greater than that of males (smaller: t = 5.617; d.f. = 15; P < 0.05; larger: t = 4.241; d.f. = 16; P < 0.05). Larger males lived longer than smaller males (t = 2.2893; d.f. = 7; P < 0.05), but no size effect was observed for females (t =- 0.086; d.f. = 19; P= 0.932). The daily survival rate of smaller females was similar to that of larger females (0.712 and 0.730, respectively, as calculated by an exponential model, and 0.743 and 0.779, respectively, calculated by a non-linear model), and they dispersed further than larger females (mean distances travelled were 78.8 m and 40.9 m, respectively; t =- 10.22; d.f. = 323; P < 0.05). Adult body size did not influence male dispersal distances (t = 0.904; d.f. = 206; P= 0.367). Given our evidence that smaller females appear to have similar lifespans and evidence from other studies that they bite more frequently during a single gonotrophic cycle than larger females, our results suggest that smaller females have a higher vectorial capacity.

Structure–Activity Relationships of 33 Piperidines as Toxicants Against Female Adults of &lt;I&gt;Aedes aegypti&lt;/I&gt; (Diptera: Culicidae)

Aedes aegypti (L.) (Diptera: Culicidae) is the primary vector of both dengue and yellow fever. Use of insecticides is one of the primary ways to control this medically important insect pest. However, few new insecticides have been developed for mosquito control in recent years. As a part of our collaborative effort to search for new insecticides to control mosquitoes, piperidine was used as base compound for further optimization. Herein, we report the structure-activity relationships of 33 piperidines against adult female Ae. aegypti. On the basis of 24-h LD50 values after topical application, the most toxic compound was 2-ethyl-piperidine, with an LD50 as low as 0.8 microg per mosquito. The toxicities of piperidine derivatives were significantly decreased when a benzyl moiety was attached to the carbon of the piperidine ring, with an LD50 value as high as 29.2 microg per mosquito. The toxicity order of three moieties attached to the carbon of the piperidine ring was ethyl- > methyl- > benzyl-derivatives. When the same moiety was attached to the piperidine ring, the carbon position to which the moiety was attached conferred different toxicity and the toxicity order was second carbon > third carbon > fourth carbon. Together, these preliminary results may be useful in guiding further piperidine ring modifications in the development of potential new insecticides.

DENGUE-2 VIRUS ARTIFICIAL INFECTION OF BRAZILIAN COLONIZED AEDES AEGYPTI

Dengue is a viral disease transmitted by mosquitoes and caused by four viral serotypes (DENV 1-4). This mosquito-borne disease is a major public health problem and a threat to more than 2.5 billion people, who live in endemic areas. Aedes aegypti is the primary vector of dengue in the Americas. The present study shows the susceptibility of a colony strain of A. aegypti to Dengue 2 virus (DENV-2). A. aegypti females from a laboratory colony were infected with DENV-2 using a membrane feeding technique. The engorged females were dissected on different days (3, 6, 9, 12 and 15). The midguts, ovaries, carcasses and heads were separated. The samples were fixed and immunolabeled with anti-DENV-2 antibody to be analyzed by laser confocal microscopy (LCM). Infected mosquitoes from the 15th day had their heads and bodies dissected, separated and analyzed by RT-PCR with specific primers. Immunolabeling of the midguts and ovaries showed the presence of DENV-2 in the mosquitoes dissected from the third day until the last day of the experiment. The RT-PCR reactions of the heads and the bodies confirmed the mosquito infection with DENV-2. These results showed that the methodology used for the artificial infection with dengue virus was successful and demonstrated that our colonized A. aegypti mosquitoes were susceptible to artificial dengue infection. Future studies are in progress to better understand the process of invasion by dengue virus in Aedes mosquito. DOI: http://dx.doi.org/10.17525/vrr.v11i1-2.5