An annotated catalogue of salivary gland transcripts in the adult female mosquito, Aedes aegypti

Peptides with Antimicrobial Activity in the Saliva of the Malaria Vector Anopheles coluzzii

Mosquito saliva plays a crucial physiological role in both sugar and blood feeding by helping sugar digestion and exerting antihemostatic functions. During meal acquisition, mosquitoes are exposed to the internalization of external microbes. Since mosquitoes reingest significant amounts of saliva during feeding, we hypothesized that salivary antimicrobial components may participate in the protection of mouthparts, the crop, and the gut by inhibiting bacterial growth. To identify novel potential antimicrobials from mosquito saliva, we selected 11 candidates from Anopheles coluzzii salivary transcriptomic datasets and obtained them either using a cell-free transcription/translation expression system or, when feasible, via chemical synthesis. Hyp6.2 and hyp13, which were predicted to be produced as propeptides and cleaved in shorter mature forms, showed the most interesting results in bacterial growth inhibition assays. Hyp6.2 (putative mature form, 35 amino acid residues) significantly inhibited the growth of Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli and Serratia marcescens) bacteria. Hyp13 (short form, 19 amino acid residues) dose-dependently inhibited E. coli and S. marcescens growth, inducing membrane disruption in both Gram-positive and Gram-negative bacteria as indicated with scanning electron microscopy. In conclusion, we identified two A. coluzzii salivary peptides inhibiting Gram-positive and Gram-negative bacteria growth and possibly contributing to the protection of mosquito mouthparts and digestive tracts from microbial infection during and/or after feeding.

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.

Evaluation of vector susceptibility in Aedes aegypti and Culex pipiens pallens to Tibet orbivirus

Mosquito-borne viruses cause various infectious diseases in humans and animals. Tibet orbivirus (TIBOV), a newly identified arbovirus, efficiently replicates in different types of vertebrate and mosquito cells, with its neutralizing antibodies detected in cattle and goats. However, despite being isolated from Culicoides midges, Anopheles, and Culex mosquitoes, there has been a notable absence of systematic studies on its vector competence. Thus, in this study, Aedes aegypti and Culex pipiens pallens were reared in the laboratory to measure vector susceptibility through blood-feeding infection. Furthermore, RNA sequencing was used to examine the overall alterations in the Ae. aegypti transcriptome following TIBOV infection. The results revealed that Ae. aegypti exhibited a high susceptibility to TIBOV compared to Cx. p. pallens. Effective replication of the virus in Ae. aegypti midguts occurred when the blood-feeding titer of TIBOV exceeded 105 plaque-forming units mL-1. Nevertheless, only a few TIBOV RNA-positive samples were detected in the saliva of Ae. aegypti and Cx. p. pallens, suggesting that these mosquito species may not be the primary vectors for TIBOV. Moreover, at 2 dpi of TIBOV, numerous antimicrobial peptides downstream of the Toll and Imd signaling pathways were significantly downregulated in Ae. aegypti, indicating that TIBOV suppressed mosquitos' defense to survive in the vector at an early stage. Subsequently, the stress-activated protein kinase JNK, a crucial component of the MAPK signaling pathway, exhibited significant upregulation. Certain genes were also enriched in the MAPK signaling pathway in TIBOV-infected Ae. aegypti at 7 dpi.IMPORTANCETibet orbivirus (TIBOV) is an understudied arbovirus of the genus Orbivirus. Our study is the first-ever attempt to assess the vector susceptibility of this virus in two important mosquito vectors, Aedes aegypti and Culex pipiens pallens. Additionally, we present transcriptome data detailing the interaction between TIBOV and the immune system of Ae. aegypti, which expands the knowledge about orbivirus infection and its interaction with mosquitoes.

Niemann-Pick Type C2 Proteins in Aedes aegypti: Molecular Modelling and Prediction of Their Structure-Function Relationships

Aedes aegypti is a major vector that transmits arboviruses through the saliva injected into the host. Salivary proteins help in uninterrupted blood intake and enhance the transmission of pathogens. We studied Niemann-Pick Type C2 (NPC2) proteins, a superfamily of saliva proteins that play an important role in arbovirus infections. In vertebrates, a single conserved gene encodes for the NPC2 protein that functions in cholesterol trafficking. Arthropods, in contrast, have several genes that encode divergent NPC2 proteins. We compared the sequences of 20 A. aegypti NPC2 proteins to the cholesterol-binding residues of human and bovine, and fatty-acid-binding residues of ant NPC2 protein. We identified four mosquito NPC2 proteins as potential sterol-binding proteins. Two of these proteins (AAEL006854 and/or AAEL020314) may play a key role in ecdysteroid biosynthesis and moulting. We also identified one mosquito NPC2 protein as a potential fatty-acid-binding protein. Through molecular modelling, we predicted the structures of the potential sterol- and fatty-acid-binding proteins and compared them to the reference proteins.

Comparative transcriptomic analysis of salivary glands between the zoophytophagous Cyrtorhinus lividipennis and the phytozoophagous Apolygus lucorum

BACKGROUND

Saliva plays a crucial role in shaping the feeding behavior of insects, involving processes such as food digestion and the regulation of interactions between insects and their hosts. Cyrtorhinus lividipennis serves as a predominant natural enemy of rice pests, while Apolygus lucorum, exhibiting phytozoophagous feeding behavior, is a destructive agricultural pest. In this study, a comparative transcriptome analysis, incorporating the published genomes of C.lividipennis and A.lucorum, was conducted to reveal the role of salivary secretion in host adaptation.

RESULTS

In contrast to A.lucorum, C.lividipennis is a zoophytophagous insect. A de novo genome analysis of C.lividipennis yielded 19,706 unigenes, including 16,217 annotated ones. On the other hand, A.lucorum had altogether 20,111 annotated genes, as obtained from the published official gene set (20,353 unigenes). Functional analysis of the top 1,000 salivary gland (SG)-abundant genes in both insects revealed that the SG was a dynamically active tissue engaged in protein synthesis and secretion. Predictions of other tissues and signal peptides were compared. As a result, 94 and 157 salivary proteins were identified in C.lividipennis and A.lucorum, respectively, and were categorized into 68 and 81 orthogroups. Among them, 26 orthogroups were shared, potentially playing common roles in digestion and detoxification, including several venom serine proteases. Furthermore, 42 and 55 orthogroups were exclusive in C.lividipennis and A.lucorum, respectively, which were exemplified by a hyaluronidase in C.lividipennis that was associated with predation, while polygalacturonases in A.lucorum were involved in mesophyll-feeding patterns.

CONCLUSIONS

Findings in this study provide a comprehensive insight into saliva secretions in C.lividipennis and A.lucorum via a transcriptome approach, reflecting the intricate connections between saliva secretions and feeding behaviors. It is found that conserved salivary secretions are involved in shaping the overlapping feeding patterns, while a plethora of unique salivary secretions may drive the evolution of specific feeding behaviors crucial for their survival. These results enhance our understanding of the feeding mechanisms in different insects from the perspective of saliva and contribute to future environmentally friendly pest control by utilizing predatory insects.

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.

Protein target highlights in CASP15: Analysis of models by structure providers

We present an in-depth analysis of selected CASP15 targets, focusing on their biological and functional significance. The authors of the structures identify and discuss key protein features and evaluate how effectively these aspects were captured in the submitted predictions. While the overall ability to predict three-dimensional protein structures continues to impress, reproducing uncommon features not previously observed in experimental structures is still a challenge. Furthermore, instances with conformational flexibility and large multimeric complexes highlight the need for novel scoring strategies to better emphasize biologically relevant structural regions. Looking ahead, closer integration of computational and experimental techniques will play a key role in determining the next challenges to be unraveled in the field of structural molecular biology.

A C-type lectin in saliva of Aedes albopictus (Diptera: Culicidae) bind and agglutinate microorganisms with broad spectrum

Via complex salivary mixture, mosquitos can intervene immune response and be helpful to transmit several viruses causing deadly human diseases. Some C-type lectins (CTLs) of mosquito have been reported to be pattern recognition receptor to either resist or promote pathogen invading. Here, we investigated the expression profile and agglutination function of an Aedes albopictus CTL (Aalb_CTL2) carrying a single carbohydrate-recognition domain (CRD) and WND/KPD motifs. The results showed that Aalb_CTL2 was found to be specifically expressed in mosquito saliva gland and its expression was not induced by blood-feeding. The recombinant Aalb_CTL2 (rAalb_CTL2) could agglutinate mouse erythrocytes in the presence of calcium and the agglutinating activity could be inhibited by EDTA. rAalb_CTL2 also displayed the sugar binding ability to D-mannose, D-galactose, D-glucose, and maltose. Furthermore, it was demonstrated that rAalb_CTL2 could bind and agglutinate Gram positive bacteria Staphylococcus aureus and Bacillus subtilis, Gram negative bacteria Escherichia coli and Pseudomonas aeruginosa, as well as fungus Candida albicans in vitro in a calcium dependent manner. However, rAalb_CTL2 could not promote type 2 dengue virus (DENV-2) replication in THP-1 and BHK-21 cell lines. These findings uncover that Aalb_CTL2 might be involved in the innate immunity of mosquito to resist microorganism multiplication in sugar and blood meals to help mosquito survive in the varied natural environment.

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.

Research progress toward the influence of mosquito salivary proteins on the transmission of mosquito-borne viruses

Mosquito-borne viruses (MBVs) are a large class of viruses transmitted mainly through mosquito bites, including dengue virus, Zika virus, Japanese encephalitis virus, West Nile virus, and chikungunya virus, which pose a major threat to the health of people around the world. With global warming and extended human activities, the incidence of many MBVs has increased significantly. Mosquito saliva contains a variety of bioactive protein components. These not only enable blood feeding but also play a crucial role in regulating local infection at the bite site and the remote dissemination of MBVs as well as in remodeling the innate and adaptive immune responses of host vertebrates. Here, we review the physiological functions of mosquito salivary proteins (MSPs) in detail, the influence and the underlying mechanism of MSPs on the transmission of MBVs, and the current progress and issues that urgently need to be addressed in the research and development of MSP-based MBV transmission blocking vaccines.

A deeper insight into the sialome of male and female Culex quinquefasciatus mosquitoes

INTRODUCTION

During evolution, blood-feeding arthropods developed a complex salivary mixture that can interfere with host haemostatic and immune response, favoring blood acquisition and pathogen transmission. Therefore, a survey of the salivary gland contents can lead to the identification of molecules with potent pharmacological activity in addition to increase our understanding of the molecular mechanisms underlying the hematophagic behaviour of arthropods. The southern house mosquito, Culex quinquefasciatus, is a vector of several pathogenic agents, including viruses and filarial parasites that can affect humans and wild animals.

RESULTS

Previously, a Sanger-based transcriptome of the salivary glands (sialome) of adult C. quinquefasciatus females was published based on the sequencing of 503 clones organized into 281 clusters. Here, we revisited the southern mosquito sialome using an Illumina-based RNA-sequencing approach of both male and female salivary glands. Our analysis resulted in the identification of 7,539 coding DNA sequences (CDS) that were functionally annotated into 25 classes, in addition to 159 long non-coding RNA (LncRNA). Additionally, comparison of male and female libraries allowed the identification of female-enriched transcripts that are potentially related to blood acquisition and/or pathogen transmission.

CONCLUSION

Together, these findings represent an extended reference for the identification and characterization of the proteins containing relevant pharmacological activity in the salivary glands of C. quinquefasciatus mosquitoes.

Experimental infection of Aedes (Stegomyia) albopictus and Culex pipiens mosquitoes with Bluetongue virus

Bluetongue disease (BT), caused by Bluetongue virus (BTV), infects wild and domestic ruminants, causing severe economic damage in the cattle and sheep industry. Proven vectors of BTV are biting midges belonging to the Culicoides genus, but other arthropods are considered potential vectors, such as ticks, mosquitoes, wingless flies, and sand flies. The present study represents the first attempt to evaluate the vectorial capacity of Culex pipiens and Aedes albopictus for BTV. Mosquitoes were artificially fed with blood containing BTV serotype 1. Infection, dissemination and transmission rates were evaluated at 0, 3, 7, 14 and 21 days after an infected blood meal. Viral RNA was only detected up to 3 days post infection in the bodies of both species. This study indicates that the two Italian populations of Cx. pipiens and Ae. albopictus are not susceptible to BTV infection.

Mosquito Salivary Proteins and Arbovirus Infection: From Viral Enhancers to Potential Targets for Vaccines

Arthropod-borne viruses present important public health challenges worldwide. Viruses such as DENV, ZIKV, and WNV are of current concern due to an increasing incidence and an expanding geographic range, generating explosive outbreaks even in non-endemic areas. The clinical signs associated with infection from these arboviruses are often inapparent, mild, or nonspecific, but occasionally develop into serious complications marked by rapid onset, tremors, paralysis, hemorrhagic fever, neurological alterations, or death. They are predominately transmitted to humans through mosquito bite, during which saliva is inoculated into the skin to facilitate blood feeding. A new approach to prevent arboviral diseases has been proposed by the observation that arthropod saliva facilitates transmission of pathogens. Viruses released within mosquito saliva may more easily initiate host invasion 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, especially because of the lack of licensed vaccines against most of these viruses. This review aims to provide an overview of the effects on the host immune response by the mosquito salivary proteins and how these phenomena alter the infection outcome for different arboviruses, recent attempts to generate mosquito salivary-based vaccines against flavivirus including DENV, ZIKV, and WNV, and the potential benefits and pitfalls that this strategy involves.

Native structure of mosquito salivary protein uncovers domains relevant to pathogen transmission

Female mosquitoes inject saliva into vertebrate hosts during blood feeding. This process transmits mosquito-borne human pathogens that collectively cause ~1,000,000 deaths/year. Among the most abundant and conserved proteins secreted by female salivary glands is a high-molecular weight protein called salivary gland surface protein 1 (SGS1) that facilitates pathogen transmission, but its mechanism remains elusive. Here, we determine the native structure of SGS1 by the cryoID approach, showing that the 3364 amino-acid protein has a Tc toxin-like Rhs/YD shell, four receptor domains, and a set of C-terminal daisy-chained helices. These helices are partially shielded inside the Rhs/YD shell and poised to transform into predicted transmembrane helices. This transformation, and the numerous receptor domains on the surface of SGS1, are likely key in facilitating sporozoite/arbovirus invasion into the salivary glands and manipulating the host's immune response.

An insight into the female and male Sabethes cyaneus mosquito salivary glands transcriptome

Mosquitoes are responsible for the death and debilitation of millions of people every year due to the pathogens they can transmit while blood feeding. While a handful of mosquitoes, namely those in the Aedes, Anopheles, and Culex genus, are the dominant vectors, many other species belonging to different genus are also involved in various pathogen cycles. Sabethes cyaneus is one of the many poorly understood mosquito species involved in the sylvatic cycle of Yellow Fever Virus. Here, we report the expression profile differences between male and female of Sa.cyaneus salivary glands (SGs). We find that female Sa.cyaneus SGs have 165 up-regulated and 18 down-regulated genes compared to male SGs. Most of the up-regulated genes have unknown functions, however, odorant binding proteins, such as those in the D7 protein family, and mucins were among the top 30 genes. We also performed various in vitro activity assays of female SGs. In the activity analysis we found that female SG extracts inhibit coagulation by blocking factor Xa and has endonuclease activity. Knowledge about mosquitoes and their physiology are important for understanding how different species differ in their ability to feed on and transmits pathogens to humans. These results provide us with an insight into the Sabethes SG activity and gene expression that expands our understanding of mosquito salivary glands.

Dipteran endoparasitoid Exorista bombycis utilizes antihemocyte components against host defense of silkworm Bombyx mori

Dipteran endoparasitoids avoid host immune response; however, antidefense components from the Dipterans are unknown. Infestation of commercial silkworm Bombyx mori Linnaeus (Lepidoptera: Bombycidae) by endoparasitoid Exorista bombycis Louis (Diptera: Tachinidae) induced immune reactions, cytotoxicity, granulation, degranulation, and augmented release of cytotoxic marker enzyme lactate dehydrogenase (LDH), and degranulation-mediator enzyme β-hexosaminidase in hemocytes. In this study, by reverse phase high-performance liquid chromatography, fractions of E. bombycis larval tissue protein with antihemocytic activity are separated. From the fraction, peptides of hemocyte aggregation inhibitor protein (HAIP) and pyridoxamine phosphate oxidase (PNPO) are identified by mass spectrometry. Interacting partners of HAIP and PNPO are retrieved that further enhance the virulence of the parasitoid. PNPO and HAIP genes showed a four- to seven fold increase in expression in the integument of the parasitoid larva. Together, the dipteran endoparasitoid E. bombycis exploit antihemocyte activity to inhibit host defense reactions in addition to defense evasion contemplated.

A deeper insight into the sialome of male and female Ochlerotatus triseriatus mosquitoes

Over the last 20 years, advancements in sequencing technologies have highlighted the unique composition of the salivary glands of blood-feeding arthropods. Further biochemical and structural data demonstrated that salivary proteins can disrupt host hemostasis, inflammation and immunity, which favors pathogen transmission. Previously, a Sanger-based sialome of adult Ochlerotatus triseriatus female salivary glands was published based on 731 expressed sequence tag (ESTs). Here, we revisited O. triseriatus salivary gland contents using an Illumina-based sequencing approach of both male and female tissues. In the current data set, we report 10,317 DNA coding sequences classified into several functional classes. The translated transcripts also served as a reference database for proteomic analysis of O. triseriatus female saliva, in which unique peptides from 101 proteins were found. Finally, comparison of male and female libraries allowed for the identification of female-enriched transcripts that are potentially related to blood acquisition and virus transmission.

Pipiserpin, a Culex factor Xa inhibitor, affects female reproductive capacity and serves as a potential target for mosquito control

BACKGROUND

Mosquito control is still the main prevention and control measure for numerous mosquito-borne diseases causing millions of deaths each year. New strategies for mosquito control are in demand. Proteases play an important role in mosquito physiology, therefore this study explored the inhibition of a serpin (serine protease inhibitor) in mosquitoes and its effect on reproductive capacity.

RESULTS

A factor Xa inhibitor homolog (named Pipiserpin) was amplified and identified in Culex pipiens pallens mosquitoes. We expressed a recombinant Pipiserpin protein in vitro against which a mouse antiserum was generated. We found that female mosquitoes expressed more Pipiserpin protein than male mosquitoes. After mating, female mosquitoes were fed with blood mixed with different amounts of antisera and results showed that consumption of Pipiserpin impeded ovary development and decreased eggs hatching rates compared to that of the pre-immune serum group.

CONCLUSION

We identified a Culex mosquito factor Xa inhibitor, Pipiserpin, which affects female reproductive potential. Our results suggest that Pipiserpin may be a novel target for mosquito population control. The conclusions from our study on Cx. pipiens pallens might serve as a reference for the development of control measures for other mosquitoes as well. © 2022 Society of Chemical Industry.

Human IgG responses to the Aedes albopictus 34k2 salivary protein: analyses in Réunion Island and Bolivia confirm its suitability as marker of host exposure to the tiger mosquito

BACKGROUND

The rapid worldwide spreading of Aedes aegypti and Aedes albopictus is expanding the risk of arboviral diseases transmission, pointing out the urgent need to improve monitoring and control of mosquito vector populations. Assessment of human-vector contact, currently estimated by classical entomological methods, is crucial to guide planning and implementation of control measures and evaluate transmission risk. Antibody responses to mosquito genus-specific salivary proteins are emerging as a convenient complementary tool for assessing host exposure to vectors. We previously showed that IgG responses to the Ae. albopictus 34k2 salivary protein (al34k2) allow detection of seasonal and geographic variation of human exposure to the tiger mosquito in two temperate areas of Northeast Italy. The main aim of this study was to confirm and extend these promising findings to tropical areas with ongoing arboviral transmission.

METHODS

IgG responses to al34k2 and to the Ae. aegypti orthologous protein ae34k2 were measured by ELISA in cohorts of subjects only exposed to Ae. albopictus (Réunion Island), only exposed to Ae. aegypti (Bolivia) or unexposed to both these vectors (North of France).

RESULTS AND CONCLUSION

Anti-al34k2 IgG levels were significantly higher in sera of individuals from Réunion Island than in unexposed controls, indicating that al34k2 may be a convenient and reliable proxy for whole saliva or salivary gland extracts as an indicator of human exposure to Ae. albopictus. Bolivian subjects, exposed to bites of Ae. aegypti, carried in their sera IgG recognizing the Ae. albopictus al34k2 protein, suggesting that this salivary antigen can also detect, even though with low sensitivity, human exposure to Ae. aegypti. On the contrary, due to the high background observed in unexposed controls, the recombinant ae34k2 appeared not suitable for the evaluation of human exposure to Aedes mosquitoes. Overall, this study confirmed the suitability of anti-al34k2 IgG responses as a specific biomarker of human exposure to Ae. albopictus and, to a certain extent, to Ae. aegypti. Immunoassays based on al34k2 are expected to be especially effective in areas where Ae. albopictus is the main arboviral vector but may also be useful in areas where Ae. albopictus and Ae. aegypti coexist.

Functional aspects of evolution in a cluster of salivary protein genes from mosquitoes

The D7 proteins are highly expressed in the saliva of hematophagous Nematocera and bind biogenic amines and eicosanoid compounds produced by the host during blood feeding. These proteins are encoded by gene clusters expressing forms having one or two odorant-binding protein-like domains. Here we examine functional diversity within the D7 group in the genus Anopheles and make structural comparisons with D7 proteins from culicine mosquitoes in order to understand aspects of D7 functional evolution. Two domain long form (D7L) and one domain short form (D7S) proteins from anopheline and culicine mosquitoes were characterized to determine their ligand selectivity and binding pocket structures. We previously showed that a D7L protein from Anopheles stephensi, of the subgenus Cellia, could bind eicosanoids at a site in its N-terminal domain but could not bind biogenic amines in its C-terminal domain as does a D7L1 ortholog from the culicine species Aedes aegypti, raising the question of whether anopheline D7L proteins had lost their ability to bind biogenic amines. Here we find that D7L from anopheline species belonging to two other subgenera, Nyssorhynchus and Anopheles, can bind biogenic amines and have a structure much like the Ae. aegypti ortholog. The unusual D7L, D7L3, can also bind serotonin in the Cellia species An. gambiae. We also show through structural comparisons with culicine forms that the biogenic amine binding function of single domain D7S proteins in the genus Anopheles may have evolved through gene conversion of structurally similar proteins, which did not have biogenic amine binding capability. Collectively, the data indicate that D7L proteins had a biogenic amine and eicosanoid binding function in the common ancestor of anopheline and culicine mosquitoes, and that the D7S proteins may have acquired a biogenic amine binding function in anophelines through a gene conversion process.

Mosquito saliva enhances virus infection through sialokinin-dependent vascular leakage

Viruses transmitted by Aedes mosquitoes are an increasingly important global cause of disease. Defining common determinants of host susceptibility to this large group of heterogenous pathogens is key for informing the rational design of panviral medicines. Infection of the vertebrate host with these viruses is enhanced by mosquito saliva, a complex mixture of salivary-gland-derived factors and microbiota. We show that the enhancement of infection by saliva was dependent on vascular function and was independent of most antisaliva immune responses, including salivary microbiota. Instead, the Aedes gene product sialokinin mediated the enhancement of virus infection through a rapid reduction in endothelial barrier integrity. Sialokinin is unique within the insect world as having a vertebrate-like tachykinin sequence and is absent from Anopheles mosquitoes, which are incompetent for most arthropod-borne viruses, whose saliva was not proviral and did not induce similar vascular permeability. Therapeutic strategies targeting sialokinin have the potential to limit disease severity following infection with Aedes-mosquito-borne viruses.

MicroRNAs and other small RNAs in Aedes aegypti saliva and salivary glands following chikungunya virus infection

Mosquito saliva facilitates blood feeding through the anti-haemostatic, anti-inflammatory and immunomodulatory properties of its proteins. However, the potential contribution of non-coding RNAs to host manipulation is still poorly understood. We analysed small RNAs from Aedes aegypti saliva and salivary glands and show here that chikungunya virus-infection triggers both the siRNA and piRNA antiviral pathways with limited effects on miRNA expression profiles. Saliva appears enriched in specific miRNA subsets and its miRNA content is well conserved among mosquitoes and ticks, clearly pointing to a non-random sorting and occurrence. Finally, we provide evidence that miRNAs from Ae. aegypti saliva may target human immune and inflammatory pathways, as indicated by prediction analysis and searching for experimentally validated targets of identical human miRNAs. Overall, we believe these observations convincingly support a scenario where both proteins and miRNAs from mosquito saliva are injected into vertebrates during blood feeding and contribute to the complex vector-host-pathogen interactions.

Dengue virus infection modifies mosquito blood-feeding behavior to increase transmission to the host

Because dengue viruses are spread by mosquitoes during biting, transmission capacity depends on mosquito-biting behavior. For this reason, it is critical to understand how infection in mosquitoes influences biting. To answer this question, we deployed a multidisciplinary approach including high-resolution, multivariate biting behavior monitoring on mice, in vivo transmission assay, and mathematical modeling. We demonstrated that infected mosquitoes are more attracted to mice and bite more often to get the same amount of blood as uninfected mosquitoes. While the effect of increased attraction to host on transmission capacity is trivial, we showed that increased number of bites results in successive transmission. Eventually, we calculated that the infection-induced behavior changes tripled transmission capacity of mosquitoes.

Mosquito blood-feeding behavior is a key determinant of the epidemiology of dengue viruses (DENV), the most-prevalent mosquito-borne viruses. However, despite its importance, how DENV infection influences mosquito blood-feeding and, consequently, transmission remains unclear. Here, we developed a high-resolution, video-based assay to observe the blood-feeding behavior of Aedes aegypti mosquitoes on mice. We then applied multivariate analysis on the high-throughput, unbiased data generated from the assay to ordinate behavioral parameters into complex behaviors. We showed that DENV infection increases mosquito attraction to the host and hinders its biting efficiency, the latter resulting in the infected mosquitoes biting more to reach similar blood repletion as uninfected mosquitoes. To examine how increased biting influences DENV transmission to the host, we established an in vivo transmission model with immuno-competent mice and demonstrated that successive short probes result in multiple transmissions. Finally, to determine how DENV-induced alterations of host-seeking and biting behaviors influence dengue epidemiology, we integrated the behavioral data within a mathematical model. We calculated that the number of infected hosts per infected mosquito, as determined by the reproduction rate, tripled when mosquito behavior was influenced by DENV infection. Taken together, this multidisciplinary study details how DENV infection modulates mosquito blood-feeding behavior to increase vector capacity, proportionally aggravating DENV epidemiology. By elucidating the contribution of mosquito behavioral alterations on DENV transmission to the host, these results will inform epidemiological modeling to tailor improved interventions against dengue.

Demographic patterns of human antibody levels to Simulium damnosum s.l. saliva in onchocerciasis-endemic areas: An indicator of exposure to vector bites

BACKGROUND

In onchocerciasis endemic areas in Africa, heterogenous biting rates by blackfly vectors on humans are assumed to partially explain age- and sex-dependent infection patterns with Onchocerca volvulus. To underpin these assumptions and further improve predictions made by onchocerciasis transmission models, demographic patterns in antibody responses to salivary antigens of Simulium damnosum s.l. are evaluated as a measure of blackfly exposure.

METHODOLOGY/PRINCIPAL FINDINGS

Recently developed IgG and IgM anti-saliva immunoassays for S. damnosum s.l. were applied to blood samples collected from residents in four onchocerciasis endemic villages in Ghana. Demographic patterns in antibody levels according to village, sex and age were explored by fitting generalized linear models. Antibody levels varied between villages but showed consistent patterns with age and sex. Both IgG and IgM responses declined with increasing age. IgG responses were generally lower in males than in females and exhibited a steeper decline in adult males than in adult females. No sex-specific difference was observed in IgM responses.

CONCLUSIONS/SIGNIFICANCE

The decline in age-specific antibody patterns suggested development of immunotolerance or desensitization to blackfly saliva antigen in response to persistent exposure. The variation between sexes, and between adults and youngsters may reflect differences in behaviour influencing cumulative exposure. These measures of antibody acquisition and decay could be incorporated into onchocerciasis transmission models towards informing onchocerciasis control, elimination, and surveillance.

High resolution proteomics of Aedes aegypti salivary glands infected with either dengue, Zika or chikungunya viruses identify new virus specific and broad antiviral factors

Arboviruses such as dengue (DENV), Zika (ZIKV) and chikungunya (CHIKV) viruses infect close to half a billion people per year, and are primarily transmitted through Aedes aegypti bites. Infection-induced changes in mosquito salivary glands (SG) influence transmission by inducing antiviral immunity, which restricts virus replication in the vector, and by altering saliva composition, which influences skin infection. Here, we profiled SG proteome responses to DENV serotype 2 (DENV2), ZIKV and CHIKV infections by using high-resolution isobaric-tagged quantitative proteomics. We identified 218 proteins with putative functions in immunity, blood-feeding or related to the cellular machinery. We observed that 58, 27 and 29 proteins were regulated by DENV2, ZIKV and CHIKV infections, respectively. While the regulation patterns were mostly virus-specific, we separately depleted four uncharacterized proteins that were upregulated by all three viral infections to determine their effects on these viral infections. Our study suggests that gamma-interferon responsive lysosomal thiol-like (GILT-like) has an anti-ZIKV effect, adenosine deaminase (ADA) has an anti-CHIKV effect, salivary gland surface protein 1 (SGS1) has a pro-ZIKV effect and salivary gland broad-spectrum antiviral protein (SGBAP) has an antiviral effect against all three viruses. The comprehensive description of SG responses to three global pathogenic viruses and the identification of new restriction factors improves our understanding of the molecular mechanisms influencing transmission.

Ixodes ricinus Salivary Serpin Iripin-8 Inhibits the Intrinsic Pathway of Coagulation and Complement

Tick saliva is a rich source of antihemostatic, anti-inflammatory, and immunomodulatory molecules that actively help the tick to finish its blood meal. Moreover, these molecules facilitate the transmission of tick-borne pathogens. Here we present the functional and structural characterization of Iripin-8, a salivary serpin from the tick Ixodes ricinus, a European vector of tick-borne encephalitis and Lyme disease. Iripin-8 displayed blood-meal-induced mRNA expression that peaked in nymphs and the salivary glands of adult females. Iripin-8 inhibited multiple proteases involved in blood coagulation and blocked the intrinsic and common pathways of the coagulation cascade in vitro. Moreover, Iripin-8 inhibited erythrocyte lysis by complement, and Iripin-8 knockdown by RNA interference in tick nymphs delayed the feeding time. Finally, we resolved the crystal structure of Iripin-8 at 1.89 Å resolution to reveal an unusually long and rigid reactive center loop that is conserved in several tick species. The P1 Arg residue is held in place distant from the serpin body by a conserved poly-Pro element on the P′ side. Several PEG molecules bind to Iripin-8, including one in a deep cavity, perhaps indicating the presence of a small-molecule binding site. This is the first crystal structure of a tick serpin in the native state, and Iripin-8 is a tick serpin with a conserved reactive center loop that possesses antihemostatic activity that may mediate interference with host innate immunity.

Evaluation of Total Female and Male Aedes aegypti Proteomes Reveals Significant Predictive Protein-Protein Interactions, Functional Ontologies, and Differentially Abundant Proteins

Simple Summary

Aedes aegypti is a significant vector for flavivirus diseases. Only the female mosquito transmits pathogens, while the male plays a vital role in mating and species continuity. In this study, female and male Ae. aegypti proteins were analysed using a mass analyser. Then, we identified proteins for the examination of protein-protein interactions, functional enrichment, and differential protein abundance analysis. This study identified 422 and 682 proteins exclusive to male and female Ae. aegypti, respectively, with 608 proteins found in both sexes. The most significant protein-protein interaction clusters and functional enrichments were observed in the biological process, molecular function, and cellular component for the proteins of both sexes. The abundance of the proteins differed, with one protein showing an increase (elongation factor 1 α, EF1α) and two showing reductions (actin family) in females versus males. The study highlights the protein differences in male and female Ae. aegypti, and future research could further investigate their roles in mosquito–viral interactions for blocking disease transmission.

Abstract

Aedes aegypti is a significant vector for many tropical and subtropical flavivirus diseases. Only the female mosquito transmits pathogens, while the male plays a vital role in mating and species continuity. This study explored the total proteomes of females and males based on the physiological and genetic differences of female and male mosquitoes. Protein extracts from mosquitoes were analysed using LC–ESI–MS/MS for protein identification, protein interaction network analysis, functional ontology enrichment, and differential protein abundance analyses. Protein identification revealed 422 and 682 proteins exclusive to males and females, respectively, with 608 common proteins found in both sexes. The most significant PPIs (<1.0 × 10⁻¹⁶) were for common proteins, followed by proteins exclusive to females (<1.0 × 10⁻¹⁶) and males (1.58 × 10⁻¹²). Significant functional enrichments were observed in the biological process, molecular function, and cellular component for the male and female proteins. The abundance of the proteins differed, with one protein showing an increase (elongation factor 1 α, EF1α) and two showing reductions (actin family) in females versus males. Overall, the study verified the total proteomes differences between male and female Ae. aegypti based on protein identification and interactions, functional ontologies, and differentially abundant proteins. Some of the identified proteins merit further investigation to elucidate their roles in blocking viral transmission.

Type I hypersensitivity promotes Aedes aegypti blood feeding

Mosquitoes play a major role in human disease by serving as vectors of pathogenic microorganisms. Mosquitoes inject saliva into host skin during the probing process. Mosquito saliva contains a number of proteins that facilitate blood feeding by preventing hemostasis. Mosquito saliva also contains potent allergens that induce type I hypersensitivity reactions in some individuals. Type I hypersensitivity reactions in skin involve IgE-mediated degranulation of mast cells, which leads to vasodilation and an itch sensation. We hypothesized that hypersensitivity to mosquito saliva influences blood feeding. To test this hypothesis, we recruited human subjects who consented to Aedes aegypti bites. We measured their first sensation of itch, the strength of their itch sensation, the number of times mosquitoes attempted to feed, the number of times mosquitoes probed their skin, feeding time, engorgement status, and wheal diameter. Here we show that hypersensitive subjects had a stronger itch sensation, and that the time to first itch sensation was inversely correlated with wheal diameter; however, mosquitoes tended to probe less and engorge more on these subjects. Follow-up experiments testing the impact of oral antihistamine treatment on mosquito feeding parameters failed to reveal a statistically significant result. Histamine also failed to promote blood feeding on an artificial membrane feeder. This study suggests that mosquito saliva-induced type I hypersensitivity promotes blood feeding but that this may be independent from histamine or histamine signaling.

AeMOPE-1, a Novel Salivary Peptide From Aedes aegypti, Selectively Modulates Activation of Murine Macrophages and Ameliorates Experimental Colitis

The sialotranscriptomes of Aedes aegypti revealed a transcript overexpressed in female salivary glands that codes a mature 7.8 kDa peptide. The peptide, specific to the Aedes genus, has a unique sequence, presents a putative secretory nature and its function is unknown. Here, we confirmed that the peptide is highly expressed in the salivary glands of female mosquitoes when compared to the salivary glands of males, and its secretion in mosquito saliva is able to sensitize the vertebrate host by inducing the production of specific antibodies. The synthetic version of the peptide downmodulated nitric oxide production by activated peritoneal murine macrophages. The fractionation of a Ae. aegypti salivary preparation revealed that the fractions containing the naturally secreted peptide reproduced the nitric oxide downmodulation. The synthetic peptide also selectively interfered with cytokine production by murine macrophages, inhibiting the production of IL-6, IL-12p40 and CCL2 without affecting TNF-α or IL-10 production. Likewise, intracellular proteins associated with macrophage activation were also distinctively modulated: while iNOS and NF-κB p65 expression were diminished, IκBα and p38 MAPK expression did not change in the presence of the peptide. The anti-inflammatory properties of the synthetic peptide were tested in vivo on a dextran sulfate sodium-induced colitis model. The therapeutic administration of the Ae. aegypti peptide reduced the leukocytosis, macrophage activity and nitric oxide levels in the gut, as well as the expression of cytokines associated with the disease, resulting in amelioration of its clinical signs. Given its biological properties in vitro and in vivo, the molecule was termed Aedes-specific MOdulatory PEptide (AeMOPE-1). Thus, AeMOPE-1 is a novel mosquito-derived immunobiologic with potential to treat immune-mediated disorders.

Protein and phytohormone profiles of Mahanarva spectabilis salivary glands infesting different forages

Given the importance of pastures for feeding cattle, the study of factors that affect their productivity is essential to get plant material of higher nutritional quality. Thus, the study of insect-plant interaction is important for the development of control strategies. Pasture spittlebugs affect forage grasses causing severe damage. We tested hormone and protein profiles differentially expressed in the salivary glands of Mahanarva spectabilis when fed with different pasture genotypes. The LC/MS approaches combined with bioinformatics tools were used to identify the mains biological processes in the salivary glands. The grouping revealed a greater number of proteins involved in biological processes of metabolic synthesis, biotic/abiotic stress, and ion transport across the membrane. The proteomic profiles were altered when insects were fed with different grasses. We also detected phytohormones in the salivary glands involved in the modulation of defense responses in host plants. These results allowed the analysis of important biological processes such as cell homeostasis, stress proteins, nucleic acid metabolism, regulation of muscle contraction, and transport and export of biomolecules. This represents an important advance in the understanding of the plant-pest interaction and can contribute to the choice of target elicitors, which allow effective strategies in the control of pasture spittlebugs.

Phylogenetic analyses suggest centipede venom arsenals were repeatedly stocked by horizontal gene transfer

Venoms have evolved over a hundred times in animals. Venom toxins are thought to evolve mostly by recruitment of endogenous proteins with physiological functions. Here we report phylogenetic analyses of venom proteome-annotated venom gland transcriptome data, assisted by genomic analyses, to show that centipede venoms have recruited at least five gene families from bacterial and fungal donors, involving at least eight horizontal gene transfer events. These results establish centipedes as currently the only known animals with venoms used in predation and defence that contain multiple gene families derived from horizontal gene transfer. The results also provide the first evidence for the implication of horizontal gene transfer in the evolutionary origin of venom in an animal lineage. Three of the bacterial gene families encode virulence factors, suggesting that horizontal gene transfer can provide a fast track channel for the evolution of novelty by the exaptation of bacterial weapons into animal venoms.

Aedes aegypti post-emergence transcriptome: Unveiling the molecular basis for the hematophagic and gonotrophic capacitation

The adult females of Aedes aegypti mosquitoes are facultative hematophagous insects but they are unable to feed on blood right after pupae emergence. The maturation process that takes place during the first post-emergence days, hereafter named hematophagic and gonotrophic capacitation, comprises a set of molecular and physiological changes that prepare the females for the first gonotrophic cycle. Notwithstanding, the molecular bases underlying mosquito hematophagic and gonotrophic capacitation remain obscure. Here, we investigated the molecular and biochemical changes in adult Ae. aegypti along the first four days post-emergence, prior to a blood meal. We performed a RNA-Seq analysis of the head and body, comparing male and female gene expression time courses. A total of 811 and 203 genes were differentially expressed, respectively in the body and head, and both body parts showed early, mid, and late female-specific expression profiles. Female-specific up-regulation of genes involved in muscle development and the oxidative phosphorylation pathway were remarkable features observed in the head. Functional assessment of mitochondrial oxygen consumption in heads showed a gradual increase in respiratory capacity and ATP-linked respiration as a consequence of induced mitochondrial biogenesis and content over time. This pattern strongly suggests that boosting oxidative phosphorylation in heads is a required step towards blood sucking habit. Several salivary gland genes, proteases, and genes involved in DNA replication and repair, ribosome biogenesis, and juvenile hormone signaling were up-regulated specifically in the female body, which may reflect the gonotrophic capacitation. This comprehensive description of molecular and biochemical mechanisms of the hematophagic and gonotrophic capacitation in mosquitoes unravels potentially new targets for vector control.

Dengue Virus Infection of Aedes aegypti Alters Extracellular Vesicle Protein Cargo to Enhance Virus Transmission

Dengue is the most burdensome vector-borne viral disease in the world. Dengue virus (DENV), the etiological cause of dengue, is transmitted primarily by the Aedes aegypti mosquito. Like any arbovirus, the transmission cycle of dengue involves the complex interactions of a multitude of human and mosquito factors. One point during this transmission cycle that is rich in these interactions is the biting event by the mosquito, upon which its saliva is injected into the host. A number of components in mosquito saliva have been shown to play a pivotal role in the transmission of dengue, however one such component that is not as well characterized is extracellular vesicles. Here, using high-performance liquid chromatography in tandem with mass spectrometry, we show that dengue infection altered the protein cargo of Aedes aegypti extracellular vesicles, resulting in the packaging of proteins with infection-enhancing ability. Our results support the presence of an infection-dependent pro-viral protein packaging strategy that uses the differential packaging of pro-viral proteins in extracellular vesicles of Ae. aegypti saliva to promote transmission. These studies represent the first investigation into the function of Ae. aegypti extracellular vesicle cargo during dengue infection.

Aedes Mosquito Salivary Components and Their Effect on the Immune Response to Arboviruses

Vector-borne diseases are responsible for over a billion infections each year and nearly one million deaths. Mosquito-borne dengue virus, West Nile, Japanese encephalitis, Zika, Chikungunya, and Rift Valley Fever viruses constitute major public health problems in regions with high densities of arthropod vectors. During the initial step of the transmission cycle, vector, host, and virus converge at the bite site, where local immune cells interact with the vector's saliva. Hematophagous mosquito saliva is a mixture of bioactive components known to modulate vertebrate hemostasis, immunity, and inflammation during the insect's feeding process. The capacity of mosquito saliva to modulate the host immune response has been well-studied over the last few decades and has led to the consensus that the presence of saliva is linked to the enhancement of virus transmission, host susceptibility, disease progression, viremia levels, and mortality. We review some of the major aspects of the interactions between mosquito saliva and the host immune response that may be useful for future studies on the control of arboviruses.

IgG Antibody Responses to the Aedes albopictus 34k2 Salivary Protein as Novel Candidate Marker of Human Exposure to the Tiger Mosquito

Mosquitoes of the Aedes genus transmit arboviruses of great importance to human health as dengue, chikungunya, Zika and yellow fever. The tiger mosquito Aedes albopictus can play an important role as arboviral vector, especially when Aedes aegypti is absent or present at low levels. Remarkably, the rapid worldwide spreading of the tiger mosquito is expanding the risk of arboviral transmission also to temperate areas, and the autochthonous cases of chikungunya, dengue and Zika in Europe emphasize the need for improved monitoring and control. Proteomic and transcriptomic studies on blood feeding arthropod salivary proteins paved the way toward the exploitation of genus-specific mosquito salivary proteins for the development of novel tools to evaluate human exposure to mosquito bites. We previously found that the culicine-specific 34k2 salivary protein from Ae. albopictus (al34k2) evokes specific IgG responses in experimentally exposed mice, and provided preliminary evidence of its immunogenicity to humans. In this study we measured IgG responses to al34k2 and to Ae. albopictus salivary gland protein extracts (SGE) in individuals naturally exposed to the tiger mosquito. Sera were collected in two areas of Northeast Italy (Padova and Belluno) during two different time periods: at the end of the low- and shortly after the high-density mosquito seasons. Anti-SGE and anti-al34k2 IgG levels increased after the summer period of exposure to mosquito bites and were higher in Padova as compared to Belluno. An age-dependent decrease of anti-saliva IgG responses was found especially in Padova, an area with at least 25 years history of Ae. albopictus colonization. Moreover, a weak correlation between anti-saliva IgG levels and individual perception of mosquito bites by study participants was found. Finally, determination of anti-al34k2 IgG1 and IgG4 levels indicated a large predominance of IgG1 antibodies. Overall, this study provides a convincing indication that antibody responses to al34k2 may be regarded as a reliable candidate marker to detect temporal and/or spatial variation of human exposure to Ae. albopictus; a serological tool of this kind may prove useful both for epidemiological studies and to estimate the effectiveness of anti-vectorial measures.

Mitochondrial metabolic genes provide phylogeographic relationships of global collections of Aedes aegypti (Diptera: Culicidae)

Phylogeographic relationships among global collections of the mosquito Aedes aegypti were evaluated using the mitochondrial Cytochrome C Oxidase 1 (CO1) and NADH dehydrogenase subunit 4 (ND4) genes including new sequences from Sri Lanka. Phylogeographic analysis estimated that Ae. aegypti arose as a species ~614 thousand years ago (kya) in the late Pleistocene. At 545 kya an “early” East African clade arose that continued to differentiate in East Africa, and eventually gave rise to three lineages one of which is distributed throughout all tropical and subtropical regions, a second that contains Southeast Asian/Sri Lankan mosquitoes and a third that contains mostly New World mosquitoes. West African collections were not represented in this early clade. The late clade continued to differentiate throughout Africa and gave rise to a lineage that spread globally. The most recent branches of the late clade are represented by South-East Asia and India/Pakistan collections. Analysis of migration rates suggests abundant gene flow between India/Pakistan and the rest of the world with the exception of Africa.

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.

A long noncoding RNA acts as a post-transcriptional regulator of heat shock protein (HSP70) synthesis in the cold hardy Diamesa tonsa under heat shock

Cold stenothermal insects living in glacier-fed streams are stressed by temperature variations resulting from glacial retreat during global warming. The molecular aspects of insect response to environmental stresses remain largely unexplored. The aim of this study was to expand our knowledge of how a cold stenothermal organism controls gene expression at the transcriptional, translational, and protein level under warming conditions. Using the chironomid Diamesa tonsa as target species and a combination of RACE, qPCR, polysomal profiling, western blotting, and bioinformatics techniques, we discovered a new molecular pathway leading to previously overlooked adaptive strategies to stress. We obtained and characterized the complete cDNA sequences of three heat shock inducible 70 (hsp70) and two members of heat-shock cognate 70 (hsc70). Strikingly, we showed that a novel pseudo-hsp70 gene encoding a putative long noncoding RNA (lncRNA) which is transcribed during thermal stress, acting as a ribosome sponge to provide post-transcriptional control of HSP70 protein levels. The expression of the pseudo-hsp70 gene and its function suggest the existence of a new and unexpected mechanism to cope with thermal stress: lowering the pace of protein production to save energy and optimize resources for recovery.

A serine protease-associated lectin in the cytolytic system of blowfly (Chrysomya megacephala) larvae: Evidence and characterization

Cytolytic activity against invading microorganisms is one of the innate forms of immunity in invertebrates. A serine protease-associated sialic acid-specific cytolytic lectin was purified using glutaraldehyde-fixed ox erythrocytes from the larval extract of blowfly (Chrysomya megacephala). The purified lectin lysed vertebrate erythrocytes with effective haemolysis of ox red blood cells (RBCs) in an isotonic medium. The degree of haemolytic (HL) activity of the purified cytolytic lectin depended on its concentration, pH, temperature, and calcium ions. It was sensitive to ethylenediaminetetraacetic acid. The native molecular mass of the C-type lectin was 260 ± 26 kDa, comprising four different polypeptide subunits of 75 kDa (pI ~8), 69 kDa (pI ~7.0), 61 kDa (pI ~5.3), and 55 kDa (pI ~4.6). The association between the C-type lectin and serine protease was confirmed by MALDI-TOF-MS analysis that revealed its homology in the same spectral peak as well as the proteases and phenylmethylsulphonyl fluoride inhibition of HL activity. Haemolysis inhibition by N-acetylneuraminic acid and other sugars revealed the properties of the lectin. The purified lectin distorted the integrity of ox RBCs and Paenalcaligenes hermetiae. This in vitro study documents the presence of a cytolytic system in blowfly (C. megacephala) larvae for the clearance of invading microbial pathogens in their feeding niche.

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.

AgBR1 antibodies delay lethal Aedes aegypti-borne West Nile virus infection in mice

West Nile virus (WNV) is transmitted by mosquitoes and can cause severe disease, including meningoencephalitis. AgBR1 is a mosquito salivary protein that enhances Aedes aegypti mosquito-borne Zika virus pathogenesis in mice. Here, we show that AgBR1 antibodies reduce the initial West Nile viral load and delay lethal infection after feeding by an infected Aedes aegypti mosquito. Targeting AgBR1 may therefore be incorporated into strategies to prevent mosquito-transmitted West Nile virus infection.

The salivary transcriptome of Limnobdella mexicana (Annelida: Clitellata: Praobdellidae) and orthology determination of major leech anticoagulants

Bloodfeeding requires several adaptations that allow the parasite to feed efficiently. Leeches and other hematophagous animals have developed different mechanisms to inhibit hemostasis, one of the main barriers imposed by their hosts. Limnobdella mexicana is a member of the leech family Praobdellidae, a family of host generalists known for their preference to attach on mucosal membranes of mammals, such as those in nasopharyngeal cavities, bladders and ocular orbits. Previous studies have hypothesized a positive relationship between diversity of anticoagulants and diversity of hosts in bloodfeeding leeches. However, orthology determination of putative anticoagulants and the lack of standardization of sequencing effort and method hinder comparisons between publicly available transcriptomes generated in different laboratories. In the present study, we examine the first transcriptome of a praobdellid leech and identify 15 putative anticoagulants using a phylogeny-based inference approach, amino-acid conservation, Pfam domains and BLAST searches. Our phylogenetic analyses suggest that the ancestral leech was able to inhibit factor Xa and that some hirudins that have been reported in previous studies on leech anticoagulants may not be orthologous with the archetypal hirudin.

Aedes-Chikungunya Virus Interaction: Key Role of Vector Midguts Microbiota and Its Saliva in the Host Infection

Aedes mosquitoes are important vectors for emerging diseases caused by arboviruses, such as chikungunya (CHIKV). These viruses’ main transmitting species are Aedes aegypti and Ae. albopictus, which are present in tropical and temperate climatic areas all over the globe. Knowledge of vector characteristics is fundamentally important to the understanding of virus transmission. Only female mosquitoes are able to transmit CHIKV to the vertebrate host since they are hematophagous. In addition, mosquito microbiota is fundamentally important to virus infection in the mosquito. Microorganisms are able to modulate viral transmission in the mosquito, such as bacteria of the Wolbachia genus, which are capable of preventing viral infection, or protozoans of the Ascogregarina species, which are capable of facilitating virus transmission between mosquitoes and larvae. The competence of the mosquito is also important in the transmission of the virus to the vertebrate host, since their saliva has several substances with biological effects, such as immunomodulators and anticoagulants, which are able to modulate the host’s response to the virus, interfering in its pathogenicity and virulence. Understanding the Aedes vector-chikungunya interaction is fundamentally important since it can enable the search for new methods of combating the virus’ transmission.

Vertical transmission of Zika virus in Culex quinquefasciatus Say and Aedes aegypti (L.) mosquitoes

Several mosquito species have been described as vectors for the Zika virus (ZIKV), such as those in the Aedes, Anopheles, Mansonia and Culex genera. Our previous survey studies were found the ZIKV RNA positive in both male, female and larvae of Culex quinquefasciatus Say and Aedes aegypti (L.) mosquitoes collected from active ZIKV infected patients' homes in Thailand. Therefore, the aims of this study were to investigate whether ZIKV could be vertically transmitted in Cx. quinquefasciatus, Ae. aegypti and Ae. albopictus. Laboratory and field colonies of these mosquito species were maintained and artificially fed with ZIKV in human blood. Fully engorged mosquitoes (F₀) were selected and reared for the vertical transmission study. The subsequent mosquito generations were fed with human blood without the virus. ZIKV in the mosquitoes was detected by hemi-nested RT-PCR and sequencing. C6/36 cells were used to isolate ZIKV from samples that tested positive by hemi-nested RT-PCR. Moreover, ZIKV was identified by immunocytochemical staining 7 days after infection in several organs of infected F₀ females, including the salivary glands, midguts, yoke granules and facet cells of the eye. The localization of the ZIKV antigen was identified by the presence of the specific antibody in the salivary glands, midguts, yoke granules and facet cells. ZIKV was detected in female and male Cx. quinquefasciatus until the F₆ and F₂ generations, respectively. The isolated virus showed cytopathic effects in C6/36 cells by 5 days postinfection. The results suggested that the vertical transmission of ZIKV occurs in Cx. quinquefasciatus in the laboratory. However, we were able to detect the presence of ZIKV in Ae. aegypti in only the F₁ generation in both male and female mosquitoes, and Ae. albopictus mosquitoes were not able to vertically transmit the virus at all. Data obtained from this study could be valuable for developing a better understanding of the role of Cx. quinquefasciatus as a potential vector for ZIKV transmission in Thailand and may be useful in creating more effective mosquito vector control strategies in the future.

Protein expression in female salivary glands of pyrethroid-susceptible and resistant strains of Aedes aegypti mosquitoes

BACKGROUND

A group of insecticides called pyrethroids has been used extensively worldwide and development of pyrethroid resistance within mosquito populations, especially in Aedes aegypti, has rapidly spread through populations. In this study, SDS-PAGE, 2-DE coupled with NanoLC-MS, and bioinformatics were used to analyze the female salivary gland proteins of pyrethroid-susceptible (PMD) and pyrethroid-resistant (PMD-R and UPK-R) strains of Ae. aegypti mosquitoes for the first time.

RESULTS

SDS-PAGE analysis revealed that among the three strains at least nine major proteins were detected but one protein band (20 kDa) was found only in the PMD strain. Two-dimensional gel electrophoresis analysis revealed 19 similarly expressed proteins in the salivary glands of the three strains involved in blood-feeding process, stress response, immunogenic response, and metabolic process and five additional major protein spots differentially expressed in the susceptible and resistant strains. Comparative analysis of the expression volume of each protein spot between the PMD and the PMD-R strains showed three downregulated proteins of the PMD-R mosquitoes. For UPK-R strains, six major proteins were downregulated when compared to the PMD strain. Additionally, four downregulated proteins were found in the UPK-R when compared to the PMD-R strain. These results suggest that pyrethroids might induce alteration of salivary gland proteins in resistant mosquitoes. Network analysis by STITCH database 5.0 showed that SRPN23 interacted with sodium and calcium ions, suggesting that SRPN23 might be involved in insecticide resistance.

CONCLUSIONS

Information obtained from this study will be useful for further studies on the roles of differentially expressed salivary gland proteins in resistance to insecticides and viral transmission.

An insight into the sialotranscriptome and virome of Amazonian anophelines

Background

Saliva of mosquitoes contains anti-platelet, anti-clotting, vasodilatory, anti-complement and anti-inflammatory substances that help the blood feeding process. The salivary polypeptides are at a fast pace of evolution possibly due to their relative lack of structural constraint and possibly also by positive selection on their genes leading to evasion of host immune pressure.

Results

In this study, we used deep mRNA sequence to uncover for the first time the sialomes of four Amazonian anophelines species (Anopheles braziliensis, A. marajorara, A. nuneztovari and A. triannulatus) and extend the knowledge of the A. darlingi sialome. Two libraries were generated from A. darlingi mosquitoes, sampled from two localities separated ~ 1100 km apart. A total of 60,016 sequences were submitted to GenBank, which will help discovery of novel pharmacologically active polypeptides and the design of specific immunological markers of mosquito exposure. Additionally, in these analyses we identified and characterized novel phasmaviruses and anpheviruses associated to the sialomes of A. triannulatus, A. marajorara and A. darlingi species.

Conclusions

Besides their pharmacological properties, which may be exploited for the development of new drugs (e.g. anti-thrombotics), salivary proteins of blood feeding arthropods may be turned into tools to prevent and/or better control vector borne diseases; for example, through the development of vaccines or biomarkers to evaluate human exposure to vector bites. The sialotranscriptome study reported here provided novel data on four New World anopheline species and allowed to extend our knowledge on the salivary repertoire of A. darlingi. Additionally, we discovered novel viruses following analysis of the transcriptomes, a procedure that should become standard within future RNAseq studies.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5545-0) contains supplementary material, which is available to authorized users.