Use of anti-Aedes aegypti salivary extract antibody concentration to correlate risk of vector exposure and dengue transmission risk in Colombia

Prevalence of culicine salivary antibodies in non-human primates living in national parks in Thailand

Macaques are widely distributed in Thailand with remarkable adaptation to living close to humans in residential, religious sites, markets and tourist areas. They play an essential role in the persistence of pathogens in the environment. As reservoir hosts, they are exposed to hematophagous vectors that secrete saliva, a cocktail of bioactive molecules including antigenic components stimulating host antibody production. Subsequent to the detection of mosquito-borne pathogens in macaques living in national parks, we aimed to determine the seroprevalence of antibodies to crude salivary gland extracts (SGEs) from culicine mosquitoes (Aedes aegypti [Linnaeus, 1762], Ae. albopictus [Skuse, 1895] and Culex quinquefasciatus [Say, 1823]) and compare individual titres between macaque species/national parks (33, Macaca arctoides [I. Geoffroy Saint-Hilaire, 1831] [Primates: Cercopithecidae] from Kaeng Krachan, 23 M. leonina leonina [Blyth, 1863] [Primates: Cercopithecidae] from Khao Yai and four M. fascicularis [Raffles, 1821] [Primates: Cercopithecidae] from Mu Ko Ranong). The anti-mosquito SGE antibodies found in 60 macaques from three national parks indicate varying levels of host-vector exposure. Macaque antibody titres were high against culicine mosquitoes. However, the significant difference among national parks (or macaque species) was only observed against Cx. quinquefasciatus. Correlation analysis of titres between Aedes SGE and arboviruses revealed a significantly more intense immune response against Ae. albopictus in DENV3-positive M. arctoides. Current findings support the concept of salivary biomarkers using accessible SGE, available from mosquito colonies of interest. However, we observed cross-reactivity between Aedes species because of crude SGE containing species-shared proteins. Nevertheless, a potential risk of pathogen transmission is emphasised between national park visitors and macaques via mosquitoes as bridge vectors. This information contributes to preventive measures against mosquito bites, including those implemented in tourist areas.

Human IgG responses to Anopheles gambiae immunogenic salivary proteins in urban and rural populations of Burkina Faso: biomarkers of exposure to malaria vector bites

BACKGROUND

Malaria control would be greatly facilitated by the development of new tools for rapidly assessing malaria transmission intensity. In malaria-endemic areas such as Burkina Faso, human populations are frequently exposed to immunomodulatory salivary components injected during mosquito blood feeding. Numerous studies have examined parasite immunity; however, there are few data available on vector immunity as a means of assessing malaria transmission in sub-Saharan Africa. The present study aims to compare IgG-specific response to salivary gland extracts (SGE) of Anopheles gambiae (An. gambiae) in populations living in urban and rural areas in Burkina Faso.

METHODS

A cross-sectional descriptive study was carried out in two sites, Ouagadougou city and Sapouy village, where blood samples (n = 676) from children (0-15 years) and adults were collected. After An. gambiae salivary protein isolation, the antibody (IgG) response to those SGE was evaluated by enzyme-linked immunosorbent assay (ELISA), representing a proxy of Anopheles exposure. The difference in antibody concentrations between groups was tested using parametric tests (Student's t-test and analysis of variance [ANOVA]) and the nonparametric Mann-Whitney U (Wilcoxon rank-sum) test. All differences were considered significant at P < 0.05.

RESULTS

The study population consisted of 63.0% males and 37.0% females (average age = 31.2 ± 17.8 years). IgG antibodies against An. gambiae salivary protein were detected in all study participants. Urban participants demonstrated a greater mean IgG level to An. gambiae bites than rural (P < 0.0001). The mean IgG level was higher in secondary school children compared with primary school children (P < 0.0001). Organic cotton farmers held higher IgG to An. gambiae bites than conventional cotton farmers (P = 0.0027).

CONCLUSIONS

The evaluation of IgG specific to mosquito salivary gland extracts as immunological biomarkers in populations in Burkina Faso allowed us to show that the human anti-SGE IgG level to An. gambiae bites is strongly influenced by the living environment and the use of insecticides in agriculture.

From Bites to Bytes: Evaluating User Engagement and Mosquito Bite Exposure Patterns with the Bite Diary Smartphone Application

Mosquito-borne diseases, including malaria, dengue, chikungunya, and Zika, significantly impact global health. Traditional methods for monitoring human-mosquito contact, such as human landing catch (HLC) and DNA profiling, have limitations, including biases and a lack of detailed temporal and spatial data. HLC may also raise ethical concerns in some settings. To address these challenges, we developed Bite Diary, a smartphone app for systematically recording mosquito bite exposure. Research participants in eastern Florida attended workshops to learn about the project and mosquito identification. They then used a pilot version of Bite Diary over predefined 7-day periods to log mosquito bites, providing data on bite frequency, timing, and context. Finally, they completed an online questionnaire post-monitoring. The study found high levels of participant engagement, and the technical usability of the app was well-received. The estimated bite exposure rate was 0.62 mosquito bites per person per day (SD = 1.63), with 94% of bite records occurring outdoors. A significant correlation was observed between repellent use and self-reported bite reactions. Several design and interface elements requiring improvement were identified for future studies to reduce survey biases. These findings highlight the utility of bite surveys in evaluating human factors that affect mosquito bite exposure and enhancing our understanding of human-mosquito interactions. Our use of a no-code app builder for Bite Diary may enable other research groups to easily create similar surveys, broadening the potential for bite data collection in diverse settings. This tool could significantly aid in developing targeted strategies for mosquito-borne disease prevention and control.

Little disease but lots of bites: social, urbanistic, and entomological risk factors of human exposure to Aedes aegypti in South Texas, U.S

BACKGROUND

Aedes aegypti presence, human-vector contact rates, and Aedes-borne virus transmission are highly variable through time and space. The Lower Rio Grande Valley (LRGV), Texas, is one of the few regions in the U.S. where local transmission of Aedes-borne viruses occurs, presenting an opportunity to evaluate social, urbanistic, entomological, and mobility-based factors that modulate human exposure to Ae. aegypti.

METHODOLOGY & PRINCIPAL FINDINGS

Mosquitoes were collected using BG-Sentinel 2 traps during November 2021 as part of an intervention trial, with knowledge, attitudes, and practices (KAP) and housing quality surveys to gather environmental and demographic data. Human blood samples were taken from individuals and a Bitemark Assay (ELISA) was conducted to quantify human antibodies to the Ae. aegypti Nterm-34kDa salivary peptide as a measure of human exposure to bites. In total, 64 houses were surveyed with 142 blood samples collected. More than 80% of participants had knowledge of mosquito-borne diseases and believed mosquitoes to be a health risk in their community. Our best fit generalized linear mixed effects model found four fixed effects contributed significantly to explaining the variation in exposure to Ae. aegypti bites: higher annual household income, younger age, larger lot area, and higher female Ae. aegypti abundance per trap night averaged over 5 weeks prior to human blood sampling.

CONCLUSIONS

Most surveyed residents recognized mosquitoes and the threat they pose to individual and public health. Urbanistic (i.e., lot size), social (i.e., income within a low-income community and age), and entomological (i.e., adult female Ae. aegypti abundance) factors modulate the risk of human exposure to Ae. aegypti bites. The use of serological biomarker assays, such as the Bitemark Assay, are valuable tools for surveillance and risk assessment of mosquito-borne disease, especially in areas like the LRGV where the transmission of target pathogens is low or intermittent.

Antibodies to Aedes aegypti D7L salivary proteins as a new serological tool to estimate human exposure to Aedes mosquitoes

Introduction

Aedes spp. are the most prolific mosquito vectors in the world. Found on every continent, they can effectively transmit various arboviruses, including the dengue virus which continues to cause outbreaks worldwide and is spreading into previously non-endemic areas. The lack of widely available dengue vaccines accentuates the importance of targeted vector control strategies to reduce the dengue burden. High-throughput tools to estimate human-mosquito contact and evaluate vector control interventions are lacking. We propose a novel serological tool that allows rapid screening of human cohorts for exposure to potentially infectious mosquitoes.

Methods

We tested 563 serum samples from a longitudinal pediatric cohort study previously conducted in Cambodia. Children enrolled in the study were dengue-naive at baseline and were followed biannually for dengue incidence for two years. We used Western blotting and enzyme-linked immunosorbent assays to identify immunogenic Aedes aegypti salivary proteins and measure total anti-Ae. aegypti IgG.

Results

We found a correlation (rs=0.86) between IgG responses against AeD7L1 and AeD7L2 recombinant proteins and those to whole salivary gland homogenate. We observed seasonal fluctuations of AeD7L1+2 IgG responses and no cross-reactivity with Culex quinquefasciatus and Anopheles dirus mosquitoes. The baseline median AeD7L1+2 IgG responses for young children were higher in those who developed asymptomatic versus symptomatic dengue.

Discussion

The IgG response against AeD7L1+2 recombinant proteins is a highly sensitive and Aedes specific marker of human exposure to Aedes bites that can facilitate standardization of future serosurveys and epidemiological studies by its ability to provide a robust estimation of human-mosquito contact in a high-throughput fashion.

Mosquito Salivary Antigens and Their Relationship to Dengue and P. vivax Malaria

In tropical areas, the simultaneous transmission of multiple vector-borne diseases is common due to ecological factors shared by arthropod vectors. Malaria and dengue virus, transmitted by Anopheles and Aedes mosquitoes, respectively, are among the top vector-borne diseases that cause significant morbidity and mortality in endemic areas. Notably, tropical areas often have suitable conditions for the co-existence of these mosquito species, highlighting the importance of identifying markers that accurately indicate the risk of acquiring each specific disease entity. Aedes are daytime-biting mosquitoes, while Anopheles preferentially bite during the night. These biting patterns raise the possibility of concurrent exposure to bites from both species. This is important because mosquito saliva, deposited in the skin during blood feeding, induces immune responses that modulate pathogen establishment and infection. Previous studies have focused on characterizing such effects on the vector-pathogen interface for an individual pathogen and its mosquito vector. In this study, we evaluated associations between immune responses to salivary proteins from non-dengue and non-malaria vector mosquito species with clinical characteristics of malaria and dengue, respectively. Surprisingly, antibody responses against Anopheles antigens in dengue patients correlated with red blood cell count and hematocrit, while antibody responses against Aedes proteins were associated with platelet count in malaria patients. Our data indicate that concurrent exposure to multiple disease-carrying mosquito vectors and their salivary proteins with differing immunomodulatory properties could influence the transmission, pathogenesis, and clinical presentation of malaria, dengue fever, and other vector-borne illnesses.

Antibodies to Aedes aegypti D7L salivary proteins as a new serological tool to estimate human exposure to Aedes mosquitoes

Introduction

Aedes spp. are the most prolific mosquito vectors in the world. Found on every continent, they can effectively transmit various arboviruses, including the dengue virus which continues to cause outbreaks worldwide and is spreading into previously non-endemic areas. The lack of widely available dengue vaccines accentuates the importance of targeted vector control strategies to reduce the dengue burden. High-throughput sensitive tools to estimate human-mosquito contact and evaluate vector control interventions are lacking. We propose a novel serological tool that allows rapid screening of large human cohorts for exposure to potentially infectious mosquitoes and effective targeting of vector control.

Methods

We tested 563 serum samples from a longitudinal pediatric cohort study previously conducted in Cambodia. Children enrolled in the study were dengue-naïve at baseline and were followed biannually for dengue incidence for two years. We used Western blotting and enzyme-linked immunosorbent assays to identify the most immunogenic Aedes aegypti salivary proteins and measure total anti- Ae. Aegypti IgG.

Results

We found a strong correlation (r s =0.86) between the combined IgG responses against AeD7L1 and AeD7L2 recombinant proteins and those to whole salivary gland homogenate. We observed seasonal fluctuations of AeD7L1+2 IgG responses, corresponding to Aedes spp. abundance in the region, and no cross-reactivity with Culex quinquefasciatus and Anopheles dirus mosquitoes. The baseline median AeD7L1+2 IgG responses for young children were higher in those who developed asymptomatic dengue versus those who developed symptomatic dengue.

Conclusion

The IgG response against AeD7L1+2 recombinant proteins is a highly sensitive and Aedes specific marker of human exposure to Aedes bites that can facilitate standardization of future serosurveys and epidemiological studies by its ability to provide a robust estimation of human-mosquito contact in a high-throughput fashion.

Flying under the radar - impact and factors influencing asymptomatic DENV infections

The clinical outcome of DENV and other Flaviviruses infections represents a spectrum of severity that ranges from mild manifestations to severe disease, which can ultimately lead to death. Nonetheless, most of these infections result in an asymptomatic outcome that may play an important role in the persistent circulation of these viruses. Also, although little is known about the mechanisms that lead to these asymptomatic infections, they are likely the result of a complex interplay between viral and host factors. Specific characteristics of the infecting viral strain, such as its replicating efficiency, coupled with host factors, like gene expression of key molecules involved in the immune response or in the protection against disease, are among crucial factors to study. This review revisits recent data on factors that may contribute to the asymptomatic outcome of the world's widespread DENV, highlighting the importance of silent infections in the transmission of this pathogen and the immune status of the host.

34-kDa salivary protein enhances duck Tembusu virus infectivity in the salivary glands of Aedes albopictus by modulating the innate immune response

Duck Tembusu virus (DTMUV) is an important flavivirus that can be transmitted to poultry via Aedes albopictus bites. Furthermore, humans residing in the DTMUV epidemic area display activated antiviral immune responses to local DTMUV isolates during the pathogenic invasion, thereby raising the primary concern that this flavivirus may be transmitted to humans via mosquito bites. Therefore, we identified the gene AALF004421, which is a homolog of the 34-kDa salivary protein (34 kDa) of Ae. albopictus and studied the salivary protein-mediated enhancement of DTMUV infection in Ae. albopictus salivary glands. We observed that double-stranded RNA-mediated silencing of the 34 kDa in mosquito salivary glands demonstrated that the silenced 34 kDa impaired DTMUV infectivity, similar to inhibition through serine protease. This impairment occurred as a consequence of triggering the innate immune response function of a macroglobulin complement-related factor (MCR). 34-kDa in the salivary gland which had similar activity as a serine protease, results in the abrogation of antimicrobial peptides production and strong enhance DTMUV replication and transmission. Although the function of the 34 kDa in Ae. albopictus is currently unknown; in the present study, we showed that it may have a major role in DTMUV infection in mosquito salivary glands through the suppression of the antiviral immune response in the earliest stages of infection. This finding provides the first identification of a prominently expressed 34 kDa protein in Ae. albopictus saliva that could serve as a target for controlling DTMUV replication in mosquito vectors.

Determinants of exposure to Aedes mosquitoes: A comprehensive geospatial analysis in peri-urban Cambodia

Aedes mosquitoes are some of the most important and globally expansive vectors of disease. Public health efforts are largely focused on prevention of human-vector contact. A range of entomological indices are used to measure risk of disease, though with conflicting results (i.e. larval or adult abundance does not always predict risk of disease). There is a growing interest in the development and use of biomarkers for exposure to mosquito saliva, including for Aedes spp, as a proxy for disease risk. In this study, we conduct a comprehensive geostatistical analysis of exposure to Aedes mosquito bites among a pediatric cohort in a peri‑urban setting endemic to dengue, Zika, and chikungunya viruses. We use demographic, household, and environmental variables (the flooding index (NFI), land type, and proximity to a river) in a Bayesian geostatistical model to predict areas of exposure to Aedes aegypti bites. We found that hotspots of exposure to Ae. aegypti salivary gland extract (SGE) were relatively small (< 500 m and sometimes < 250 m) and stable across the two-year study period. Age was negatively associated with antibody responses to Ae. aegypti SGE. Those living in agricultural settings had lower antibody responses than those living in urban settings, whereas those living near recent surface water accumulation were more likely to have higher antibody responses. Finally, we incorporated measures of larval and adult density in our geostatistical models and found that they did not show associations with antibody responses to Ae. aegypti SGE after controlling for other covariates in the model. Our results indicate that targeted house- or neighborhood-focused interventions may be appropriate for vector control in this setting. Further, demographic and environmental factors more capably predicted exposure to Ae. aegypti mosquitoes than commonly used entomological indices.

Aedes aegypti anti-salivary proteins IgG levels in a cohort of DENV-like symptoms subjects from a dengue-endemic region in Colombia

Dengue fever, caused by the dengue virus (DENV), is currently a threat to about half of the world's population. DENV is mainly transmitted to the vertebrate host through the bite of a female Aedes mosquito while taking a blood meal. During this process, salivary proteins are introduced into the host skin and blood to facilitate blood acquisition. These salivary proteins modulate both local (skin) and systemic immune responses. Several salivary proteins have been identified as immunogenic inducing the production of antibodies with some of those proteins also displaying immunomodulatory properties enhancing arboviral infections. IgG antibody responses against salivary gland extracts of a diverse number of mosquitoes, as well as antibody responses against the Ae. aegypti peptide, Nterm-34 kDa, have been suggested as biomarkers of human exposure to mosquito bites while antibodies against AgBR1 and NeSt1 proteins have been investigated for their potential protective effect against Zika virus (ZIKV) and West Nile virus infections. Thus, we were interested in evaluating whether IgG antibodies against AgBR1, NeSt1, Nterm-34 kDa peptide, and SGE were associated with DENV infections and clinical characteristics. For this, we tested samples from volunteers living in a dengue fever endemic area in Colombia in 2019 for the presence of IgG antibodies against those salivary proteins and peptides using an ELISA test. Results from this pilot study suggest an involvement of antibody responses against salivary proteins in dengue disease progression.

Multiple Salivary Proteins from Aedes aegypti Mosquito Bind to the Zika Virus Envelope Protein

Aedes aegypti mosquitoes are important vectors of several debilitating and deadly arthropod-borne (arbo) viruses, including Yellow Fever virus, Dengue virus, West Nile virus and Zika virus (ZIKV). Arbovirus transmission occurs when an infected mosquito probes the host’s skin in search of a blood meal. Salivary proteins from mosquitoes help to acquire blood and have also been shown to enhance pathogen transmission in vivo and in vitro. Here, we evaluated the interaction of mosquito salivary proteins with ZIKV by surface plasmon resonance and enzyme-linked immunosorbent assay. We found that three salivary proteins AAEL000793, AAEL007420, and AAEL006347 bind to the envelope protein of ZIKV with nanomolar affinities. Similar results were obtained using virus-like particles in binding assays. These interactions have no effect on viral replication in cultured endothelial cells and keratinocytes. Additionally, we found detectable antibody levels in ZIKV and DENV serum samples against the recombinant proteins that interact with ZIKV. These results highlight complex interactions between viruses, salivary proteins and antibodies that could be present during viral transmissions.

Development of inapparent dengue associated with increased antibody levels to Aedes aegypti salivary proteins: a longitudinal dengue cohort in Cambodia

BACKGROUND

We established the first prospective cohort to understand how infection with dengue virus is influenced by vector-specific determinants like humoral immunity to Aedes aegypti salivary proteins.

METHODS

Children aged two to nine years old enrolled in the PAGODAS (Pediatric Assessment Group of Dengue and Aedes Saliva) cohort with informed consent by their guardians. Children were followed semi-annually for antibodies to dengue and to proteins in Ae. aegypti salivary gland homogenate using enzyme-linked immunosorbent assays and dengue-specific neutralization titers. Children presented with fever at any time for dengue testing.

RESULTS

From July 13 to August 30, 2018, we enrolled 771 children. At baseline, 22% (173/770) had evidence of neutralizing antibodies to one or more dengue serotypes. By April 2020, 51 children had symptomatic dengue while 148 dengue-naïve children had inapparent dengue defined by neutralization assays. In a multivariate model, individuals with higher antibodies to Ae. aegypti salivary proteins were 1.5x more likely to have dengue infection (HR 1.47 95% CI 1.05-2.06; p=0.02), particularly individuals with inapparent dengue (HR 1.64 95% CI 1.12-2.41; p=0.01).

CONCLUSIONS

High levels of seropositivity to Ae. aegypti salivary proteins are associated with future development of dengue infection, primarily inapparent, in dengue-naïve Cambodian children.

Human-Mosquito Contact: A Missing Link in Our Understanding of Mosquito-Borne Disease Transmission Dynamics

Despite the critical role that contact between hosts and vectors, through vector bites, plays in driving vector-borne disease (VBD) transmission, transmission risk is primarily studied through the lens of vector density and overlooks host-vector contact dynamics. This review article synthesizes current knowledge of host-vector contact with an emphasis on mosquito bites. It provides a framework including biological and mathematical definitions of host-mosquito contact rate, blood-feeding rate, and per capita biting rates. We describe how contact rates vary and how this variation is influenced by mosquito and vertebrate factors. Our framework challenges a classic assumption that mosquitoes bite at a fixed rate determined by the duration of their gonotrophic cycle. We explore alternative ecological assumptions based on the functional response, blood index, forage ratio, and ideal free distribution within a mechanistic host-vector contact model. We highlight that host-vector contact is a critical parameter that integrates many factors driving disease transmission. A renewed focus on contact dynamics between hosts and vectors will contribute new insights into the mechanisms behind VBD spread and emergence that are sorely lacking. Given the framework for including contact rates as an explicit component of mathematical models of VBD, as well as different methods to study contact rates empirically to move the field forward, researchers should explicitly test contact rate models with empirical studies. Such integrative studies promise to enhance understanding of extrinsic and intrinsic factors affecting host-vector contact rates and thus are critical to understand both the mechanisms driving VBD emergence and guiding their prevention and control.

Serological biomarker for assessing human exposure to Aedes mosquito bites during a randomized vector control intervention trial in northeastern Thailand

Background

Aedes mosquitoes are vectors for several major arboviruses of public health concern including dengue viruses. The relationships between Aedes infestation and disease transmission are complex wherein the epidemiological dynamics can be difficult to discern because of a lack of robust and sensitive indicators for predicting transmission risk. This study investigates the use of anti-Aedes saliva antibodies as a serological biomarker for Aedes mosquito bites to assess small scale variations in adult Aedes density and dengue virus (DENV) transmission risk in northeastern Thailand. Individual characteristics, behaviors/occupation and socio-demographics, climatic and epidemiological risk factors associated with human-mosquito exposure are also addressed.

Methods

The study was conducted within a randomized clustered control trial in Roi Et and Khon Kaen provinces over a consecutive 19 months period. Thirty-six (36) clusters were selected, each of ten houses. Serological and entomological surveys were conducted in all houses every four months and monthly in three sentinel households per cluster between September 2017 and April 2019 for blood spot collections and recording concurrent immature and adult Aedes indices. Additionally, the human exposure to Aedes mosquito bites (i.e., Mosquito Exposure Index or MEI) was estimated by ELISA measuring levels of human antibody response to the specific Nterm-34 kDa salivary antigen. The relationships between the MEI, vector infestation indices (adult and immature stages) and vector DENV infection were evaluated using a two-level (house and individual levels) mixed model analysis with one-month lag autoregressive correlation.

Results

There was a strong positive relationship between the MEI and adult Aedes (indoor and outdoor) density. Individuals from households with a medium mosquito density (mean difference: 0.091, p<0.001) and households with a high mosquito density (mean difference: 0.131, p<0.001) had higher MEI’s compared to individuals from households without Aedes. On a similar trend, individuals from households with a low, medium or high indoor Aedes densities (mean difference: 0.021, p<0.007, 0.053, p<0.0001 and 0.037, p<0.0001 for low, medium and high levels of infestation, respectively) had higher MEI than individuals from houses without indoor Aedes. The MEI was driven by individual characteristics, such as gender, age and occupation/behaviors, and varied according to climatic, seasonal factors and vector control intervention (p<0.05). Nevertheless, the study did not demonstrate a clear correlation between MEI and the presence of DENV-infected Aedes.

Conclusion

This study represents an important step toward the validation of the specific IgG response to the Aedes salivary peptide Nterm-34kDa as a proxy measure for Aedes infestation levels and human-mosquito exposure risk in a dengue endemic setting. The use of the IgG response to the Nterm-34 kDa peptide as a viable diagnostic tool for estimating dengue transmission requires further investigations and validation in other geographical and transmission settings.

Aedes mosquitoes and the viruses they transmit are major public health concerns for over half of the global human population. However, the quantitative relationships between virus transmission and vector mosquito infestation remain unclear despite numerous indicators used to estimate transmission risk and predict dengue outbreaks. The aim of this study is to investigate the use of a salivary biomarker to assess the small-scale variation in human exposure to Aedes bites and the risk of dengue infection in the context of a vector control intervention in northeastern Thailand. A cohort of 539 persons visited every four months, including 161 individuals visited monthly, were recruited for routine serological and concurrent household entomological surveys during 19 consecutive months follow-up. Antibody response to Aedes bites was measured by enzyme-linked immunosorbent assays to assess the mosquito exposure index (MEI) and association with the Aedes adult and immature abundance as well as the presence of dengue virus (DENV) in adult mosquitoes (transmission risk). Additionally, the individual (cohort), climatic, and vector control intervention risk factors associated with MEI are explored. This study demonstrates that the MEI was strongly related to household adult Aedes density, particularly indoors resting mosquitoes. Additionally, the MEI was influenced by individual characteristics (i.e., person age, gender, staying indoors), and varied according to seasons and intervention. Nonetheless, no clear relationship between MEI and dengue transmission risk (i.e., vector infection) was detected. This study demonstrated the potential usefulness of the MEI to assess heterogeneity in adult Aedes infestation indices that could assist public health authorities to rapidly identify mosquito “hot spots” and the timeliness of effective vector control interventions.

Vector saliva controlled inflammatory response of the host may represent the Achilles heel during pathogen transmission

Infection with vector-borne pathogens starts with the inoculation of these pathogens during blood feeding. In endemic regions, the population is regularly bitten by naive vectors, implicating a permanent stimulation of the immune system by the vector saliva itself (pre-immune context). Comparatively, the number of bites received by exposed individuals from non-infected vectors is much higher than the bites from infected ones. Therefore, vector saliva and the immunological response in the skin may play an important role, so far underestimated, in the establishment of anti-pathogen immunity in endemic areas. Hence, the parasite biology and the disease pathogenesis in “saliva-primed” and “saliva-unprimed” individuals must be different. This integrated view on how the pathogen evolves within the host together with vector salivary components, which are known to be endowed with a variety of pharmacological and immunological properties, must remain the focus of any investigational study dealing with vector-borne diseases.

Considering this three-way partnership, the host skin (immune system), the pathogen, and the vector saliva, the approach that consists in the validation of vector saliva as a source of molecular entities with anti-disease vaccine potential has been recently a subject of active and fruitful investigation. As an example, the vaccination with maxadilan, a potent vasodilator peptide extracted from the saliva of the sand fly Lutzomyia longipalpis, was able to protect against infection with various leishmanial parasites. More interestingly, a universal mosquito saliva vaccine that may potentially protect against a range of mosquito-borne infections including malaria, dengue, Zika, chikungunya and yellow fever. In this review, we highlight the key role played by the immunobiology of vector saliva in shaping the outcome of vector-borne diseases and discuss the value of studying diseases in the light of intimate cross talk among the pathogen, the vector saliva, and the host immune mechanisms.

Vertebrate Responses against Arthropod Salivary Proteins and Their Therapeutic Potential

The saliva of hematophagous arthropods contains a group of active proteins to counteract host responses against injury and to facilitate the success of a bloodmeal. These salivary proteins have significant impacts on modulating pathogen transmission, immunogenicity expression, the establishment of infection, and even disease severity. Recent studies have shown that several salivary proteins are immunogenic and antibodies against them may block infection, thereby suggesting potential vaccine candidates. Here, we discuss the most relevant salivary proteins currently studied for their therapeutic potential as vaccine candidates or to control the transmission of human vector-borne pathogens and immune responses against different arthropod salivary proteins.

Molecular characterization, gas chromatography mass spectrometry analysis, phytochemical screening and insecticidal activities of ethanol extract of Lentinus squarrosulus against Aedes aegypti (Linnaeus)

Mosquito-transmitted diseases like zika, dengue, chikungunya, and yellow fever are known to affect human health worldwide. Numerous synthetic insecticides have been used as vector control for these diseases, but there is the challenge of environmental toxicity and vector resistance. This study investigated the medicinal and insecticidal potential of Lentinus squarrosulus against Aedes aegypti. The fruiting bodies were identified morphologically as well as using internal transcribed spacer (ITS) sequences for its molecular characterization. Genomic deoxyribonucleic acid (DNA) yield was confirmed with NanoDrop Spectrophotometer ND-1000 and amplified with ITSl and ITS4 primers. The amplicons were sequenced and the National Center for Biotechnology Information (NCBI) database identified the nucleotides. Its ethanol extract was subjected to phytochemical screening and gas chromatography mass spectrometry (GC-MS) analysis and tested against the pupa and fourth instar larva of Aedes aegypti with percentage mortality monitored. The Macrofungus was identified morphologically and confirmed with molecular characterization as Lentinus squarrosulus (LS). The gene sequence was deposited in GenBank (Accession number MK629662.1). GC-MS analysis showed that its ethanol extract has 25 bioactive compounds with 9,12-Octadecadienoic acid, ethyl ester having the highest percentage of 43.32% as well as methyl-2-oxo-1-pyrrolidine acetate and 17-octadecynoic acid having the lowest percentage (0.09%). The macrofungus contained varied concentrations of phytochemicals including phenols (159 mg/g GAE), tannins (1.6 mg/g TAE), and flavonoids (31.4 mg/g QE). The ethanol extract had significant potent effects on Aedes aegypti larva and pupa which could be due to the occurrence and abundance of 9,12-octadecadienoic acid in LS. The LC₅₀ of the extract for larvicidal and pupicidal activities were 2.95 mg/mL and 3.55 mg/mL, respectively, while its LC₉₀ were 6.31 mg/mL and 5.75 mg/mL respectively. Lentinus squarrosulus had insecticidal effects against the Aedes aegypti larva and pupa and possessed great potential as a source of alternative medicine and eco-friendly insecticides.

Antibody Responses Against Anopheles darlingi Immunogenic Peptides in Plasmodium Infected Humans

Introduction: Malaria is still an important vector-borne disease in the New World tropics. Despite the recent decline in malaria due to Plasmodium falciparum infection in Africa, a rise in Plasmodium infections has been detected in several low malaria transmission areas in Latin America. One of the main obstacles in the battle against malaria is the lack of innovative tools to assess malaria transmission risk, and the behavioral plasticity of one of the main malaria vectors in Latin America, Anopheles darlingi.

Methods: We used human IgG antibodies against mosquito salivary gland proteins as a measure of disease risk. Whole salivary gland antigen (SGA) from Anopheles darlingi mosquitoes was used as antigen in Western blot experiments, in which a ~65 kDa protein was visualized as the main immunogenic band and sent for sequencing by mass spectrometry. Apyrase and peroxidase peptides were designed and used as antigens in an ELISA-based test to measure human IgG antibody responses in people with different clinical presentations of malaria.

Results: Liquid chromatography–mass spectrometry revealed 17 proteins contained in the ~65 kDa band, with an apyrase and a peroxidase as the two most abundant proteins. Detection of IgG antibodies against salivary antigens by ELISA revealed a significant higher antibody levels in people with malaria infection when compared to uninfected volunteers using the AnDar_Apy1 and AnDar_Apy2 peptides. We also detected a significant positive correlation between the anti-peptides IgG levels and antibodies against the Plasmodium vivax and P. falciparum antigens PvMSP1 and PfMSP1. Odd ratios suggest that people with higher IgG antibodies against the apyrase peptides were up to five times more likely to have a malaria infection.

Conclusion: Antibodies against salivary peptides from An. darlingi salivary gland proteins may be used as biomarkers for malaria risk.

Safety and immunogenicity of a mosquito saliva peptide-based vaccine: a randomised, placebo-controlled, double-blind, phase 1 trial

BACKGROUND

In animal models, immunity to mosquito salivary proteins protects animals against mosquito-borne disease. These findings provide a rationale to vaccinate against mosquito saliva instead of the pathogen itself. To our knowledge, no vector salivary protein-based vaccine has been tested for safety and immunogenicity in humans. We aimed to assess the safety and immunogenicity of Anopheles gambiae saliva vaccine (AGS-v), a peptide-based vaccine derived from four A gambiae salivary proteins, in humans.

METHODS

In this randomised, placebo-controlled, double-blind, phase 1 trial, participants were enrolled at the National Institutes of Health Clinical Center in Bethesda, MD, USA. Participants were eligible if they were healthy adults, aged 18-50 years with no history of severe allergic reactions to mosquito bites. Participants were randomly assigned (1:1:1), using block randomisation and a computer-generated randomisation sequence, to treatment with either 200 nmol of AGS-v vaccine alone, 200 nmol of AGS-v with adjuvant (Montanide ISA 51), or sterile water as placebo. Participants and clinicians were masked to treatment assignment. Participants were given a subcutaneous injection of their allocated treatment at day 0 and day 21, followed by exposure to feeding by an uninfected Aedes aegypti mosquito at day 42 to assess subsequent risk to mosquito bites in a controlled setting. The primary endpoints were safety and immunogenicity at day 42 after the first immunisation. Participants who were given at least one dose of assigned treatment were assessed for the primary endpoints and analysis was by intention to treat. The trial was registered with ClinicalTrials.gov, NCT03055000, and is closed for accrual.

FINDINGS

Between Feb 15 and Sept 10, 2017, we enrolled and randomly assigned 49 healthy adult participants to the adjuvanted vaccine (n=17), vaccine alone (n=16), or placebo group (n=16). Five participants did not complete the two-injection regimen with mosquito feeding at day 42, but were included in the safety analyses. No systemic safety concerns were identified; however, one participant in the adjuvanted vaccine group developed a grade 3 erythematous rash at the injection site. Pain, swelling, erythema, and itching were the most commonly reported local symptoms and were significantly increased in the adjuvanted vaccine group compared with both other treatment groups (nine [53%] of 17 participants in the adjuvanted vaccine group, two [13%] of 16 in the vaccine only group, and one [6%] of 16 in the placebo group; p=0·004). By day 42, participants who were given the adjuvanted vaccine had a significant increase in vaccine-specific total IgG antibodies compared with at baseline than did participants who were give vaccine only (absolute difference of log10-fold change of 0·64 [95% CI 0·39 to 0·89]; p=0·0002) and who were given placebo (0·62 [0·34 to 0·91]; p=0·0001). We saw a significant increase in IFN-γ production by peripheral blood mononuclear cells at day 42 in the adjuvanted vaccine group compared with in the placebo group (absolute difference of log10 ratio of vaccine peptide-stimulated vs negative control 0·17 [95% CI 0·061 to 0·27]; p=0·009) but we saw no difference between the IFN-γ production in the vaccine only group compared with the placebo group (0·022 [-0·072 to 0·116]; p=0·63).

INTERPRETATION

AGS-v was well tolerated, and, when adjuvanted, immunogenic. These findings suggest that vector-targeted vaccine administration in humans is safe and could be a viable option for the increasing burden of vector-borne disease.

FUNDING

Office of the Director and the Division of Intramural Research at the National Institute of Allergy and Infectious Diseases, and National Institutes of Health.

Route of inoculation and mosquito vector exposure modulate dengue virus replication kinetics and immune responses in rhesus macaques

Dengue virus (DENV) is transmitted by infectious mosquitoes during blood-feeding via saliva containing biologically-active proteins. Here, we examined the effect of varying DENV infection modality in rhesus macaques in order to improve the DENV nonhuman primate (NHP) challenge model. NHPs were exposed to DENV-1 via subcutaneous or intradermal inoculation of virus only, intradermal inoculation of virus and salivary gland extract, or infectious mosquito feeding. The infectious mosquito feeding group exhibited delayed onset of viremia, greater viral loads, and altered clinical and immune responses compared to other groups. After 15 months, NHPs in the subcutaneous and infectious mosquito feeding groups were re-exposed to either DENV-1 or DENV-2. Viral replication and neutralizing antibody following homologous challenge were suggestive of sterilizing immunity, whereas heterologous challenge resulted in productive, yet reduced, DENV-2 replication and boosted neutralizing antibody. These results show that a more transmission-relevant exposure modality resulted in viral replication closer to that observed in humans.

Dengue virus is transmitted into the skin of humans by mosquitoes as they take a blood meal. In contrast, many animal models are infected in the laboratory using a syringe to inject below the skin. Here, we looked at how different routes and methods of infection altered dengue infection in rhesus macaques. We found that infection via mosquito feeding resulted in a number of changes compared to other routes and methods, including a delay in the time to detection of dengue virus and overall greater quantities of dengue virus in the blood, and changes in the amounts of various components of blood that have been associated with dengue disease in humans. After 15 months, we exposed the macaques again to either the same or a different type of dengue virus. We found that animals exposed to the same type of dengue virus were protected from infection, whereas those animals exposed to a different type were only partially protected. Overall, our results show that dengue virus delivery using the natural transmission vector, mosquitoes, results in infection that is closer to what is observed in humans and may influence the interpretation of future studies of candidate vaccines.

Risk factors of exposure to Aedes albopictus bites in mainland France using an immunological biomarker

In recent decades, the invasive Aedes albopictus vector has spread across Europe and is responsible for numerous outbreaks of autochthonous arboviral disease. The aim of this study was to identify epidemiological and sociological risk factors related to individual levels of exposure to Aedes albopictus bites. A multidisciplinary survey was conducted with volunteer blood donors living in areas either colonised or not by Aedes albopictus in mainland France. Individual levels of exposure were evaluated by measuring the IgG level specific to Aedes albopictus saliva. The most striking risk factors concerned the localisation and characteristics of the dwelling. Individuals living in areas colonised prior to 2009 or recently colonised (between 2010 and 2012) had higher anti-salivary gland extract IgG levels compared with those who were living in areas not yet colonised by Ae. albopictus. The type of dwelling did not seem to impact the level of exposure to Aedes bites. People living in apartments had a higher anti-salivary gland extract IgG level than those living in individual houses but the difference was not statistically significant. Interestingly, the presence of air conditioning or window nets was associated with a noticeable reduction in bite intensity.

The Pharmacopea within Triatomine Salivary Glands

Triatomines are blood-feeding insects that prey on vertebrate hosts. Their saliva is largely responsible for their feeding success. The triatomine salivary content has been studied over the past decades, revealing multifunctional bioactive proteins targeting the host´s hemostasis and immune system. Recently, sequencing of salivary-gland mRNA libraries revealed increasingly complex and complete transcript databases that have been used to validate the expression of deduced proteins through proteomics. This review provides an insight into the journey of discovery and characterization of novel molecules in triatomine saliva.

Ecology of Francisella tularensis

Tularemia is a Holarctic zoonosis caused by the gamma proteobacterium Francisella tularensis and is considered to be a vector-borne disease. In many regions, human risk is associated with the bites of flies, mosquitoes, or ticks. But the biology of the agent is such that risk may be fomite related, and large outbreaks can occur due to inhalation or ingestion of contaminated materials. Such well-documented human risk factors suggest a role for these risk factors in the enzootic cycle as well. Many arthropods support the growth or survival of the agent, but whether arthropods (ticks in particular) are obligately required for the perpetuation of F. tularensis remains to be demonstrated. As with most zoonoses, our knowledge of the ecology of F. tularensis has been driven with the objective of understanding human risk. In this review, we focus on the role of the arthropod in maintaining F. tularensis, particularly with respect to long-term enzootic persistence.

Analysis in a murine model points to IgG responses against the 34k2 salivary proteins from Aedes albopictus and Aedes aegypti as novel promising candidate markers of host exposure to Aedes mosquitoes

Background

Aedes mosquitoes are vectors of arboviral diseases of great relevance for public health. The recent outbreaks of dengue, Zika, chikungunya and the rapid worldwide spreading of Aedes albopictus emphasize the need for improvement of vector surveillance and control. Host antibody response to mosquito salivary antigens is emerging as a relevant additional tool to directly assess vector-host contact, monitor efficacy of control interventions and evaluate risk of arboviral transmission.

Methodology/principal findings

Groups of four BALB/c mice were immunized by exposure to bites of either Aedes albopictus or Aedes aegypti. The 34k2 salivary proteins from Ae. albopictus (al34k2) and Ae. aegypti (ae34k2) were expressed in recombinant form and Ae. albopictus salivary peptides were designed through B-cell epitopes prediction software. IgG responses to salivary gland extracts, peptides, al34k2 and ae34k2 were measured in exposed mice. Both al34k2 and ae34k2, with some individual and antigen-specific variation, elicited a clearly detectable antibody response in immunized mice. Remarkably, the two orthologous proteins showed very low level of immune cross-reactivity, suggesting they may eventually be developed as species-specific markers of host exposure. The al34k2 immunogenicity and the limited immune cross-reactivity to ae34k2 were confirmed in a single human donor hyperimmune to Ae. albopictus saliva.

Conclusions/significance

Our study shows that exposure to bites of Ae. albopictus or Ae. aegypti evokes in mice species-specific IgG responses to al34k2 or ae34k2, respectively. Deeper understanding of duration of antibody response and validation in natural conditions of human exposure to Aedes mosquitoes are certainly needed. However, our findings point to the al34k2 salivary protein as a promising potential candidate for the development of immunoassays to evaluate human exposure to Ae. albopictus. This would be a step forward in the establishment of a serological toolbox for the simultaneous assessment of human exposure to Aedes vectors and the pathogens they transmit.

Taking advantage of several factors, as worldwide trading, climatic changes and urbanization, Aedes mosquitoes are impressively expanding their geographic distribution. A paradigm is provided by the rapid global spreading of Aedes albopictus, a species that is a competent vector of several arboviral diseases (e.g. dengue, Zika, chikungunya) and has been responsible of quite a few outbreaks in the last decade. Historically, vector control always played a pivotal role for the containment of arthropod-borne diseases, and this appears especially crucial for arboviral diseases for which no effective vaccines or specific medications are available. Currently, host exposure to mosquitoes is indirectly evaluated by entomological methods; however, exploitation of human immune responses to mosquito salivary proteins is emerging as a relevant additional tool, with important epidemiological implications for the evaluation of mosquito-borne disease risk. This study provides preliminary but solid indications that the 34k2 salivary proteins from Ae. albopictus and Aedes aegypti may be suitable candidates for the development of serological assays to evaluate spatial and/or temporal variation of human exposure to Aedes vectors. Combined to the presently available tools to assess arboviral exposure/infection, this may be of great help for the development of a serological toolbox allowing for the simultaneous determination of human exposure to Aedes vectors and to the pathogens they transmit.

Mosquito Saliva: The Hope for a Universal Arbovirus Vaccine?

Arthropod-borne viruses (arboviruses) are taxonomically diverse causes of significant morbidity and mortality. In recent decades, important mosquito-borne viruses such as West Nile, chikungunya, dengue, and Zika have re-emerged and spread widely, in some cases pandemically, to cause serious public health emergencies. There are no licensed vaccines against most of these viruses, and vaccine development and use has been complicated by the number of different viruses to protect against, by subtype and strain variation, and by the inability to predict when and where outbreaks will occur. A new approach to preventing arboviral diseases is suggested by the observation that arthropod saliva facilitates transmission of pathogens, including leishmania parasites, Borrelia burgdorferi, and some arboviruses. Viruses carried within mosquito saliva may more easily initiate host infection by taking advantage of the host's innate and adaptive immune responses to saliva. This provides a rationale for creating vaccines against mosquito salivary proteins, rather than against only the virus proteins contained within the saliva. As proof of principle, immunization with sand fly salivary antigens to prevent leishmania infection has shown promising results in animal models. A similar approach using salivary proteins of important vector mosquitoes, such as Aedes aegypti, might protect against multiple mosquito-borne viral infections.

Differential Tick Salivary Protein Profiles and Human Immune Responses to Lone Star Ticks (Amblyomma americanum) From the Wild vs. a Laboratory Colony

Ticks are a growing concern to human and animal health worldwide and they are leading vectors of arthropod-borne pathogens in the United States. Ticks are pool blood feeders that can attach to the host skin for days to weeks using their saliva to counteract the host defenses. Tick saliva, as in other hematophagous arthropods, contains pharmacological and immunological active compounds, which modulate local and systemic immune responses and induce antibody production. In the present study, we explore differences in the salivary gland extract (SGE) protein content of Amblyomma americanum ticks raised in a laboratory colony (CT) vs. those collected in the field (FT). First, we measured the IgG antibody levels against SGE in healthy volunteers residing in Kansas. ELISA test showed higher IgG antibody levels when using the SGE from CT as antigen. Interestingly, antibody levels against both, CT-SGE and FT-SGE, were high in the warm months (May-June) and decreased in the cold months (September-November). Immunoblot testing revealed a set of different immunogenic bands for each group of ticks and mass spectrometry data revealed differences in at 19 proteins specifically identified in the CT-SGE group and 20 from the FT-SGE group. Our results suggest that differences in the salivary proteins between CT-SGE and FT-SGE may explain the differential immune responses observed in this study.

Serologic Tools and Strategies to Support Intervention Trials to Combat Zika Virus Infection and Disease

Zika virus is an emerging mosquito-borne flavivirus that recently caused a large epidemic in Latin America characterized by novel disease phenotypes, including Guillain-Barré syndrome, sexual transmission, and congenital anomalies, such as microcephaly. This epidemic, which was declared an international public health emergency by the World Health Organization, has highlighted shortcomings in our current understanding of, and preparation for, emerging infectious diseases in general, as well as challenges that are specific to Zika virus infection. Vaccine development for Zika virus has been a high priority of the public health response, and several candidates have shown promise in pre-clinical and early phase clinical trials. The optimal selection and implementation of imperfect serologic assays are among the crucial issues that must be addressed in order to advance Zika vaccine development. Here, I review key considerations for how best to incorporate into Zika vaccine trials the existing serologic tools, as well as those on the horizon. Beyond that, this discussion is relevant to other intervention strategies to combat Zika and likely other emerging infectious diseases.

IgG1 and IgG4 antibodies against Aedes aegypti salivary proteins and risk for dengue infections

Dengue virus (DENV) is an arbovirus responsible for a significant number of deaths in Latin America. This virus is transmitted through the bite of Aedes aegypti, the main mosquito vector, and Ae. albopictus. During blood uptake, the mosquito injects its saliva into the host to facilitate the feeding process. Mosquito saliva contains potent immunogens capable of inducing antibody production directly related to mosquito bite exposure intensity and disease risk. In this study, we first determined the DENV infection status by two different DENV non-structural protein 1 (NS1) based rapid tests and qRT-PCR, then measured the levels of IgG1 and IgG4 antibodies against salivary proteins of Ae. aegypti female mosquitoes in volunteers living in a dengue endemic area. Our results show that people with a positive DENV diagnosis present higher levels of IgG4 antibodies than people with a negative diagnostic test, and that these antibody levels were higher in people with secondary DENV infections. With this study, we show that detection of IgG4 antibodies against mosquito saliva may be a reliable method to evaluate the risk of dengue infection.

The PAGODAS protocol: pediatric assessment group of dengue and Aedes saliva protocol to investigate vector-borne determinants of Aedes-transmitted arboviral infections in Cambodia

BACKGROUND

Mosquito-borne arboviruses, like dengue virus, continue to cause significant global morbidity and mortality, particularly in Southeast Asia. When the infectious mosquitoes probe into human skin for a blood meal, they deposit saliva containing a myriad of pharmacologically active compounds, some of which alter the immune response and influence host receptivity to infection, and consequently, the establishment of the virus. Previous reports have highlighted the complexity of mosquito vector-derived factors and immunity in the success of infection. Cumulative evidence from animal models and limited data from humans have identified various vector-derived components, including salivary components, that are co-delivered with the pathogen and play an important role in the dissemination of infection. Much about the roles and effects of these vector-derived factors remain to be discovered.

METHODS/DESIGN

We describe a longitudinal, pagoda (community)-based pediatric cohort study to evaluate the burden of dengue virus infection and document the immune responses to salivary proteins of Aedes aegypti, the mosquito vector of dengue, Zika, and chikungunya viruses. The study includes community-based seroprevalence assessments in the peri-urban town of Chbar Mon in Kampong Speu Province, Cambodia. The study aims to recruit 771 children between the ages of 2 and 9 years for a three year period of longitudinal follow-up, including twice per year (rainy and dry season) serosurveillance for dengue seroconversion and Ae. aegypti salivary gland homogenate antibody intensity determinations by ELISA assays. Diagnostic tests for acute dengue, Zika and chikungunya viral infections will be performed by RT-PCR.

DISCUSSION

This study will serve as a foundation for further understanding of mosquito saliva immunity and its impact on Aedes-transmitted arboviral diseases endemic to Cambodia.

TRIAL REGISTRATION

NCT03534245 registered on 23 May 2018.

New Immuno-Epidemiological Biomarker of Human Exposure to Aedes Vector Bites: From Concept to Applications

Arthropod-borne viruses (arboviruses) such as dengue virus (DENV), chikungunya virus (CHIKV), Zika virus (ZIKV), and yellow fever virus (YFV) are the most important 'emerging pathogens' because of their geographic spread and their increasing impact on vulnerable human populations. To fight against these arboviruses, vector control strategies (VCS) remain one of the most valuable means. However, their implementation and monitoring are labour intensive and difficult to sustain on large scales, especially when transmission and Aedes mosquito densities are low. To increase the efficacy of VCS, current entomological methods should be improved by new complementary tools which measure the risk of arthropod-borne diseases' transmission. The study of human⁻Aedes immunological relationships can provide new promising serological tools, namely antibody-based biomarkers, allowing to accurately estimate the human⁻Aedes contact and consequently, the risk of transmission of arboviruses and the effectiveness of VCS. This review focuses on studies highlighting the concept, techniques, and methods used to develop and validate specific candidate biomarkers of human exposure to Aedes bites. Potential applications of such antibody-based biomarkers of exposure to Aedes vector bites in the field of operational research are also discussed.

Specific human antibody responses to Aedes aegypti and Aedes polynesiensis saliva: A new epidemiological tool to assess human exposure to disease vectors in the Pacific

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.

Serosurvey of Human Antibodies Recognizing Aedes aegypti D7 Salivary Proteins in Colombia

Background

Dengue is one of the most geographically significant mosquito-borne viral diseases transmitted by Aedes mosquitoes. During blood feeding, mosquitoes deposit salivary proteins that induce antibody responses. These can be related to the intensity of exposure to bites. Some mosquito salivary proteins, such as D7 proteins, are known as potent allergens. The antibody response to D7 proteins can be used as a marker to evaluate the risk of exposure and disease transmission and provide critical information for understanding the dynamics of vector–host interactions.

Methods

The study was conducted at the Los Patios Hospital, Cucuta, Norte de Santander, Colombia. A total of 63 participants were enrolled in the study. Participants were categorized into three disease status groups, age groups, and socioeconomic strata. The level of IgG antibodies against D7 Aedes proteins was determined by ELISA. We used a statistical approach to determine if there is an association between antibody levels and factors such as age, living conditions, and dengue virus (DENV) infection.

Results

We found that IgG antibodies against D7 proteins were higher in non-DENV infected individuals in comparison to DENV-infected participants. Also, the age factor showed a significant positive correlation with IgG antibodies against D7 proteins, and the living conditions (socioeconomic stratification), in people aged 20 years or older, are a statistically significant factor in the variability of IgG antibodies against D7 proteins.

Conclusion

This pilot study represents the first approximation to elucidate any correlation between the antibody response against mosquito D7 salivary proteins and its correlation with age, living conditions, and DENV infection in a dengue endemic area.

A deep insight into the male and female sialotranscriptome of adult Culex tarsalis mosquitoes

Previously, a Sanger-based sialotranscriptome analysis of adult female Culex tarsalis was published based on ∼2000 ESTs. During the elapsed 7.5 years, pyrosequencing has been discontinued and Illumina sequences have increased considerable in size and decreased in price. We here report an Illumina-based sialotranscriptome that allowed finding the missing apyrase from the salivary transcriptome of C. tarsalis, to determine several full-length members of the 34-62 kDa family, when a single EST has been found previously, in addition to identifying many salivary families with lower expression levels that were not detected previously. The use of multiple libraries including salivary glands and carcasses from male and female organisms allowed for an unprecedented insight into the tissue specificity of transcripts, and in this particular case permitting identification of transcripts putatively associated with blood feeding, when exclusive of female salivary glands, or associated with sugar feeding, when transcripts are found upregulated in both male and female glands.

Non-human primate antibody response to mosquito salivary proteins: Implications for dengue virus transmission in Puerto Rico

An important step to incriminate a mosquito as a vector of a disease pathogen is finding evidence of direct contact between the mosquito and humans. Typically, this is accomplished through landing/biting catches, or host blood meal analysis in engorged mosquitoes via immunologic assays. An alternate approach is to identify the presence of specific mosquito anti-saliva protein antibodies in the blood of exposed hosts. Following the discovery of dengue infected, free roaming non-human primates in Puerto Rico, we investigated which mosquito species had bitten these primates using a serologic assay. Serum samples from 20 patas monkeys (Erythrocebus patas) and two rhesus macaques (Macaca mulatta) were used to evaluate mosquito bite exposure to Aedes aegypti, Aedes mediovittatus, Aedes taeniorhynchus, and Culex quinquefasciatus mosquitoes. Of 22 non-human primates examined 20 (90%), 17 (77%), 13 (59%), and 7 (31%) were positive for exposure to Ae. mediovittatus, Cx. quinquefasciatus, Ae. taeniorhynchus, and Ae. aegypti, respectively. Our findings indicated that free-roaming primates in Puerto Rico were exposed to the bites of one proven dengue vector, Ae. aegypti and one potential dengue vector, Ae. mediovittatus.

Natural Mosquito-Pathogen Hybrid IgG4 Antibodies in Vector-Borne Diseases: A Hypothesis

Chronic exposure to antigens may favor the production of IgG4 antibodies over other antibody types. Recent studies have shown that up to a 30% of normal human IgG4 is bi-specific and is able to recognize two antigens of different nature. A requirement for this specificity is the presence of both eliciting antigens in the same time and at the same place where the immune response is induced. During transmission of most vector-borne diseases, the pathogen is delivered to the vertebrate host along with the arthropod saliva during blood feeding and previous studies have shown the existence of IgG4 antibodies against mosquito salivary allergens. However, there is very little ongoing research or information available regarding IgG4 bi-specificity with regard to infectious disease, particularly during immune responses to vector-borne diseases, such as malaria, filariasis, or dengue virus infection. Here, we provide background information and present our hypothesis that IgG4 may not only be a useful tool to measure exposure to infected mosquito bites, but that these bi-specific antibodies may also play an important role in modulation of the immune response against malaria and other vector-borne diseases in endemic settings.

Salivary Biomarkers in the Control of Mosquito-Borne Diseases

Vector control remains the most effective measure to prevent the transmission of mosquito-borne diseases. However, the classical entomo-parasitological methods used to evaluate the human exposure to mosquito bites and the effectiveness of control strategies are indirect, labor intensive, and lack sensitivity in low exposure/transmission areas. Therefore, they are limited in their accuracy and widespread use. Studying the human antibody response against the mosquito salivary proteins has provided new biomarkers for a direct and accurate evaluation of the human exposure to mosquito bites, at community and individual levels. In this review, we discuss the development, applications and limits of these biomarkers applied to Aedes- and Anopheles-borne diseases.

Dengue Virus Infection of Aedes aegypti Requires a Putative Cysteine Rich Venom Protein

Dengue virus (DENV) is a mosquito-borne flavivirus that causes serious human disease and mortality worldwide. There is no specific antiviral therapy or vaccine for DENV infection. Alterations in gene expression during DENV infection of the mosquito and the impact of these changes on virus infection are important events to investigate in hopes of creating new treatments and vaccines. We previously identified 203 genes that were ≥5-fold differentially upregulated during flavivirus infection of the mosquito. Here, we examined the impact of silencing 100 of the most highly upregulated gene targets on DENV infection in its mosquito vector. We identified 20 genes that reduced DENV infection by at least 60% when silenced. We focused on one gene, a putative cysteine rich venom protein (SeqID AAEL000379; CRVP379), whose silencing significantly reduced DENV infection in Aedes aegypti cells. Here, we examine the requirement for CRVP379 during DENV infection of the mosquito and investigate the mechanisms surrounding this phenomenon. We also show that blocking CRVP379 protein with either RNAi or specific antisera inhibits DENV infection in Aedes aegypti. This work identifies a novel mosquito gene target for controlling DENV infection in mosquitoes that may also be used to develop broad preventative and therapeutic measures for multiple flaviviruses.

An. gambiae gSG6-P1 evaluation as a proxy for human-vector contact in the Americas: a pilot study

Background

During blood meal, the female mosquito injects saliva able to elicit an immune response in the vertebrate. This immune response has been proven to reflect the intensity of exposure to mosquito bites and risk of infection for vector transmitted pathogens such as malaria. The peptide gSG6-P1 of An. gambiae saliva has been demonstrated to be antigenic and highly specific to Anopheles as a genus. However, the applicability of gSG6-P1 to measure exposure to different Anopheles species endemic in the Americas has yet to be evaluated. The purpose of this pilot study was to test whether human participants living in American countries present antibodies able to recognize the gSG6-P1, and whether these antibodies are useful as a proxy for mosquito bite exposure and malaria risk.

Methods

We tested human serum samples from Colombia, Chile, and the United States for the presence of IgG antibodies against gSG6-P1 by ELISA. Antibody concentrations were expressed as delta optical density (ΔOD) of each sera tested in duplicates. The difference in the antibody concentrations between groups was tested using the nonparametric Mann Whitney test (independent groups) and the nonparametric Wilcoxon matched-pairs signed rank test (dependent groups). All differences were considered significant with a P < 0.05.

Results

We found that the concentration of gSG6-P1 antibodies was significantly correlated with malaria infection status and mosquito bite exposure history. People with clinical malaria presented significantly higher concentrations of IgG anti-gSG6-P1 antibodies than healthy controls. Additionally, a significant raise in antibody concentrations was observed in subjects returning from malaria endemic areas.

Conclusion

Our data shows that gSG6-P1 is a suitable candidate for the evaluation of exposure to Anopheles mosquito bites, risk of malaria transmission, and effectiveness of protection measures against mosquito bites in the Americas.

Long-Lasting Permethrin-Impregnated Clothing Protects Against Mosquito Bites in Outdoor Workers

Outdoor exposure to mosquitoes is a risk factor for many diseases, including malaria and dengue. We have previously shown that long-lasting permethrin-impregnated clothing protects against tick and chigger bites in a double-blind randomized controlled trial in North Carolina outdoor workers. Here, we evaluated whether this clothing is protective against mosquito bites by measuring changes in antibody titers to mosquito salivary gland extracts. On average, there was a 10-fold increase in titer during the spring and summer when mosquito exposure was likely to be the highest. During the first year of the study, the increase in titer in subjects wearing treated uniforms was 2- to 2.5-fold lower than that of control subjects. This finding suggests that long-lasting permethrin-impregnated clothing provided protection against mosquito bites.