Search

Background: Aedes mosquitoes severely affect the health and wellbeing of human populations by transmitting infectious diseases. In French Polynesia, Aedes aegypti is the main vector of dengue, chikungunya and Zika, and Aedes polynesiensis the primary vector of Bancroftian filariasis and a secondary vector of arboviruses. Tools for assessing the risk of disease transmission or for measuring the efficacy of vector control programmes are scarce. A promising approach to quantify the human-vector contact relies on the detection and the quantification of antibodies directed against mosquito salivary proteins., Methodology/principal Findings: An ELISA test was developed to detect and quantify the presence of immunoglobulin G (IgG) directed against proteins from salivary gland extracts (SGE) of Ae. aegypti and Ae. polynesiensis in human populations exposed to either species, through a cross-sectional study. In Tahiti and Moorea islands where Ae. aegypti and Ae. polynesiensis are present, the test revealed that 98% and 68% of individuals have developed IgG directed against Ae. aegypti and Ae. polynesiensis SGE, respectively. By comparison, ELISA tests conducted on a cohort of people from metropolitan France, not exposed to these Aedes mosquitoes, indicated that 97% of individuals had no IgG directed against SGE of either mosquito species. The analysis of additional cohorts representing different entomological Aedes contexts showed no ELISA IgG cross-reactivity between Ae. aegypti and Ae. polynesiensis SGE., Conclusions/significance: The IgG response to salivary gland extracts seems to be a valid and specific biomarker of human exposure to the bites of Ae. aegypti and Ae. polynesiensis. This new immuno-epidemiological tool will enhance our understanding of people exposure to mosquito bites, facilitate the identification of areas where disease transmission risk is high and permit to evaluate the efficacy of novel vector control strategies in Pacific islands and other tropical settings., Competing Interests: The authors have declared that no competing interests exist.

Mosquito saliva is a very complex concoction of >100 proteins, many of which have unknown functions. The effects of mosquito saliva proteins injected into our skin during blood feeding have been studied mainly in mouse models of injection or biting, with many of these systems producing results that may not be relevant to human disease. Here, we describe the numerous effects that mosquito bites have on human immune cells in mice engrafted with human hematopoietic stem cells. We used flow cytometry and multiplex cytokine bead array assays, with detailed statistical analyses, to detect small but significant variations in immune cell functions after 4 mosquitoes fed on humanized mice footpads. After preliminary analyses, at different early times after biting, we focused on assessing innate immune and subsequent cellular responses at 6 hours, 24 hours and 7 days after mosquito bites. We detected both Th1 and Th2 human immune responses, and delayed effects on cytokine levels in the blood, and immune cell compositions in the skin and bone marrow, up to 7 days post-bites. These are the first measurements of this kind, with human immune responses in whole animals, bitten by living mosquitoes, versus previous studies using incomplete mouse models and salivary gland extracts or needle injected saliva. The results have major implications for the study of hematophagous insect saliva, its effects on the human immune system, with or without pathogen transmission, and the possibility of determining which of these proteins to target for vaccination, in attempts to block transmission of numerous tropical diseases., Competing Interests: The authors have declared that no competing interests exist.

Background: Arboviral diseases are an important public health concerns. Vector control remains the sole strategy to fight against these diseases. Because of the important limits of methods currently used to assess human exposure to Aedes mosquito bites, much effort is being devoted to develop new indicators. Recent studies have reported that human antibody (Ab) responses to Aedes aegypti Nterm-34kDa salivary peptide represent a promising biomarker tool to evaluate the human-Aedes contact. The present study aims investigate whether such biomarker could be used for assessing the efficacy of vector control against Aedes., Methodology/principal Findings: Specific human IgG response to the Nterm-34kDa peptide was assessed from 102 individuals living in urban area of Saint-Denis at La Reunion Island, Indian Ocean, before and after the implementation of vector control against Aedes mosquitoes. IgG response decreased after 2 weeks (P < 0.0001), and remained low for 4 weeks post-intervention (P = 0.0002). The specific IgG decrease was associated with the decline of Aedes mosquito density, as estimated by entomological parameters and closely correlated to vector control implementation and was not associated with the use of individual protection, daily commuting outside of the house, sex and age. Our findings indicate a probable short-term decrease of human exposure to Aedes bites just after vector control implementation., Conclusion/significance: Results provided in the present study indicate that IgG Ab response to Aedes aegypti Nterm-34kDa salivary peptide could be a relevant short-time indicator for evaluating the efficacy of vector control interventions against Aedes species., Competing Interests: The authors have declared that no competing interests exist.

Background: Three laboratory studies were conducted to assess the repellent and insecticidal efficacy of a combination of fipronil and permethrin (Frontline Tri- Act/Frontect) against three mosquito species (Aedes albopictus, Aedes aegypti and Culex pipiens) on dogs., Methods: In each study, 16 healthy adult dogs were allocated to two groups. Eight dogs were treated with the new topical spot-on combination of fipronil and permethrin on Day 0 and the other eight dogs served as untreated controls. Each dog was exposed to mosquitoes on Days 1, 7, 14, 21 and 28 (and also on Day 35 in the A. aegypti study). After a 1-h exposure period, all mosquitoes were counted and categorized as live or dead and fed or non-fed. Live mosquitoes were kept in an insectary and observed for mortality counts 4, 24 and 48 h post-exposure (PE) for Aedes spp. and 24 and 48 h PE for C. pipiens. Repellency and insecticidal efficacies were defined as the percent reduction in the number of fed and live mosquitoes, respectively, in the treated group as compared to the untreated control group., Results: Repellency against A. albopictus was ≥93.4% through Day 21 and 86.9% on Day 28. It was ≥91.0% through Day 35 against A. aegypti and ≥90.4% through Day 28 against C. pipiens. Insecticidal efficacy against A. albopictus was ≥97.1% at 24 h PE from Day 7 to Day 28. It was ≥98.0% for the first 3 weeks and still 75.7% on Day 35 against A. aegypti at 24 h PE. For C. pipiens, insecticidal efficacy ranged from 93.8% (Day 7) to 30.9% (Day 28) at 48 h PE., Conclusions: A single topical administration of the combination of fipronil and permethrin provides repellency against mosquitoes on dogs for at least 4 weeks. The product may therefore significantly reduce the potential for the transmission of vector-borne pathogens through the inhibition of mosquito feeding, as well as the discomfort associated with mosquito bites. Moreover, mosquito mortality was induced by contact with the treated dogs, which could aid in the control of mosquitoes, and hence the control of mosquito-borne diseases, in the local vicinity of treated dogs.

Classic vector control strategies target mosquitoes indoors as the main transmitters of malaria are indoor-biting and -resting mosquitoes. However, the intensive use of insecticide-treated bed-nets (ITNs) and indoor residual spraying have put selective pressure on mosquitoes to adapt in order to obtain human blood meals. Thus, early-evening and outdoor vector activity is becoming an increasing concern. This study assessed the effect of a deltamethrin-treated net (100 mg/m(2)) attached to a one-meter high fence around outdoor cattle enclosures on the number of mosquitoes landing on humans. Mosquitoes were collected from four cattle enclosures: Pen A - with cattle and no net; B - with cattle and protected by an untreated net; C - with cattle and protected by a deltamethrin-treated net; D - no cattle and no net. A total of 3217 culicines and 1017 anophelines were collected, of which 388 were Anopheles gambiae and 629 An. ziemanni. In the absence of cattle nearly 3 times more An. gambiae (p<0.0001) landed on humans. The deltamethrin-treated net significantly reduced (nearly three-fold, p<0.0001) culicine landings inside enclosures. The sporozoite rate of the zoophilic An. ziemanni, known to be a secondary malaria vector, was as high as that of the most competent vector An. gambiae; raising the potential of zoophilic species as secondary malaria vectors. After deployment of the ITNs a deltamethrin persistence of 9 months was observed despite exposure to African weather conditions. The outdoor use of ITNs resulted in a significant reduction of host-seeking culicines inside enclosures. Further studies investigating the effectiveness and spatial repellence of ITNs around other outdoor sites, such as bars and cooking areas, as well as their direct effect on vector-borne disease transmission are needed to evaluate its potential as an appropriate outdoor vector control tool for rural Africa.

To assess the role of Aedes albopictus in transmission of filarial nematodes of veterinary importance, researches were carried out in different geographical areas. In Italy a first research was performed to study the susceptibility of Ae. albopictus to Dirofilaria repens, D. immitis and Setaria labiatopapillosa. The development of L3 larvae was longer than in other species of mosquitoes but Ae. albopictus could be a suitable vector of filariae. To understand the role of Ae. albopictus in the natural transmission of Dirofilaria and to assess the risk for animal and human health, in 2000, 2001 and 2002 another study was carried out in the town of Padua. A total of 2,534 Ae. albopictus were caught on human-attracted mosquitoes. Specific primers and sequencing identified filarial DNA as D. immitis; Ae. albopictus was proved a natural vector of D. immitis. Similar results were confirmed in Central Italy also for D. repens. The presence of Ae. albopictus increased the probability of transmission of canine and human dirofilariosis in urban environment and it could change the epidemiology of dirofilariosis, in particular for what concern the time of biting and the risk season. These aspects must be considered to outline a correct prophylaxis.

Investigations were carried out in Padova town (Veneto region, NE Italy) to define the actual role of Aedes albopictus in the natural transmission of Dirofilaria nematodes, and to assess the risk that its presence might represent for veterinary and medical health. During summer 2000-2002 daytime captures of human-attracted mosquitoes were carried out in three areas of the town. The presence of filarial parasites in mosquitoes was evaluated by PCR, and sequencing confirmed species assessment. DNA extraction was performed separately on pools of the insect abdomen and thorax-head, to discriminate between Dirofilaria infected/infective specimens. A total of 2721 mosquitoes were caught and A. albopictus was the most abundant species (2534). Filarial DNA was found in 27.5% (19/69) of the abdomen pools formed with mosquitoes collected in summer 2000, and in 11.1% (16/144) and 4.9% (6/123) thorax-head pools coming from samplings 2001 and 2002, respectively. Filarial DNA was belonging to D. immitis and all studied areas harboured infective specimens. These results prove A. albopictus as natural vector of D. immitis in Italy. Moreover, they support the hypothesis that the presence of the mosquito could affect the transmission pattern of canine heartworm disease in urban environment and, considering the aggressive anthropophylic behaviour of the species (30-48 bites/h) proven in Padova town, could enhance the circulation of filarial nematodes from animals to humans.

We evaluated a histologic technique for its usefulness in detecting multiple blood feeding by Aedes aegypti (L.) in a single gonotrophic cycle. To standardize the procedure, we carried out a laboratory study in which 166 mosquitoes imbibed two blood meals at known intervals. Eighty percent (78/98) of the multiple meals were detected when the interval between meals was from 1 to < to = 24 h and the time from the second meal to fixation ranged from 0 to 12 hr. At intervals outside this range, only 34% (23/68) of the multiple meals were detected. Overall, 61% (101/166) of the double meals were detected. Examination of 96 engorged Ae. aegypti collected by aspiration from inside houses in San Juan, Puerto Rico, indicated that 50% had imbibed multiple meals. Most wild-caught mosquitoes took their last meal the day before capture, and most multiple feeders fed twice on consecutive days. A dark line of digested blood, or heme, around the first meal and a physical separation between meals were the most useful histologic parameters for detecting multiple feeding in wild Ae. aegypti. An association of multiple feeding with advanced stages of oocyte development suggests that, at the time of collection, most Ae. aegypti from the study site had fed twice in each gonotrophic cycle. We conclude that, although it is labor intensive, histologic examination is an appropriate technique for a longitudinal, community-wide survey of multiple feeding by Ae. aegypti.

We tested a theoretical model based on the physics of capillary flow and confirmed that anaemia accelerates blood intake in the yellow-fever mosquito, Aedes aegypti (L.). We also investigated the influence of anaemic blood on egg production of mosquitoes and found that it has a negative influence on fecundity. Based strictly on egg production and the physics of fluid intake, we propose that although anaemia associated with blood-borne parasites may be detrimental to mosquitoes that can engorge to repletion in one session, it may be beneficial to those interrupted before repletion because the greater quantity of the bloodmeal may compensate for its lower quality. Epidemiological consequences are discussed but require further inquiry.

Nectar- and blood-feeding time distributions of Aedes vexans (Meigen) and Aedes trivittatus (Coquillett) were determined from collections of mosquitoes attempting to feed on flowers and human bait during six nights in an Ohio field. Distributions of nectar and blood feeding were different in Ae. vexans on three of five nights when analyses were possible, and they were different in pooled Ae. trivittatus data. Higher proportions of blood feeders appeared in earlier time intervals, but both nectar and blood feeding had broadly overlapping peaks and distributions. These results suggest that the nectar- and blood-feeding rhythms are probably in phase in Ae. vexans females, and that possibly the earlier onset of blood feeding reflects a strategy taking advantage of blood when it is available. Male Ae. vexans had later peak nectar-feeding times than females. Nectar feeding in males may be delayed by mating activity early in the activity period.