Update on the proteomics of major arthropod vectors of human and animal pathogens

Immune Reactions of Vector Insects to Parasites and Pathogens

This overview initially describes insect immune reactions and then brings together present knowledge of the interactions of vector insects with their invading parasites and pathogens. It is a way of introducing this Special Issue with subsequent papers presenting the latest details of these interactions in each particular group of vectors. Hopefully, this paper will fill a void in the literature since brief descriptions of vector immunity have now been brought together in one publication and could form a starting point for those interested and new to this important area. Descriptions are given on the immune reactions of mosquitoes, blackflies, sandflies, tsetse flies, lice, fleas and triatomine bugs. Cellular and humoral defences are described separately but emphasis is made on the co-operation of these processes in the completed immune response. The paper also emphasises the need for great care in extracting haemocytes for subsequent study as appreciation of their fragile nature is often overlooked with the non-sterile media, smearing techniques and excessive centrifugation sometimes used. The potential vital role of eicosanoids in the instigation of many of the immune reactions described is also discussed. Finally, the priming of the immune system, mainly in mosquitoes, is considered and one possible mechanism is presented.

The global prevalence of parasites in non-biting flies as vectors: a systematic review and meta-analysis

BACKGROUND

Non-biting flies such as the house fly (Musca domestica), the Australian sheep blowfly (Lucilia cuprina) and the oriental latrine fly (Chrysomya megacephala) may carry many parasites. In the present study, we performed a systematic overview of the different species of parasites carried by non-biting flies, as well as of isolation methods, different geographical distribution, seasonality and risk assessment.

METHODS

A meta-analysis was carried out with the aim to review the global prevalence of parasite transmission in non-biting flies. A total sample size of 28,718 non-biting flies reported in studies worldwide satisfied the predetermined selection criteria and was included in the quantitative analysis.

RESULTS

The global prevalence of parasites in non-biting flies was 42.5% (95% confidence interval [CI] 31.9-53.2%; n = 15,888/28,718), with the highest prevalence found for non-biting flies in Africa (58.3%; 95% CI 47.4-69.3%; n = 9144/13,366). A total of 43% (95% CI 32.1-54.4%; n = 7234/15,282) of house flies (M. domestica), the fly species considered to be the most closely associated with humans and animals, were found with parasites. The prevalence of parasites in the intestine of non-biting flies was 37.1% (95% CI 22.7-51.5%; n = 1045/3817), which was significantly higher than the prevalence of parasites isolated from the body surface (35.1%; 95% CI 20.8-49.4%; n = 1199/3649; P < 0.01). Of the 27 reported parasites, a total of 20 known zoonotic parasites were identified, with an infection rate of 38.1% (95% CI 28.2-48.0%; n = 13,572/28,494).

CONCLUSIONS

This study provides a theoretical basis for the public health and ecological significance of parasites transmitted by non-biting flies.

Effects of Aedes aegypti salivary protein on duck Tembusu virus replication and transmission in salivary glands

Duck Tembusu virus (DTMUV) infection is an arthropod-borne viral disease that affects many poultry species, including ducks, chickens, and geese. Aedes aegypti mosquito is an important vector of DTMUV. This study sought to determine whether any individual Ae. aegypti salivary protein modulated DTMUV replication in the mosquito salivary gland. Ae. aegypti salivary gland protein of 34 kDa (AaSG34) was found to be expressed explicitly in mosquito salivary glands and was upregulated following DTMUV infection. Thus, AaSG34 was silenced in mosquitoes via RNA interference using double strand RNA (dsRNA), and the mosquitoes were then infected with DTMUV to elucidate their effects on DTMUV replication and transmission. Transcripts of the DTMUV genome in salivary glands and virus titer in saliva were significantly diminished when AaSG34 was silenced, indicating that its presence enhances DTMUV replication in the salivary glands and DTMUV dissemination to saliva. Furthermore, the expression of antimicrobial peptides (AMPs) was upregulated upon AaSG34 silenced. Our results demonstrate that AaSG34 may play a vital role in the suppression of antiviral immune responses to enhance DTMUV replication and transmission. We thus provide new information on the effect of the AaSG34 salivary protein on DTMUV replication in Ae. aegypti as the mechanism of blocking virus transmission to the host.

Complex Roles of Neutrophils during Arboviral Infections

Arboviruses are known to cause large-scale epidemics in many parts of the world. These arthropod-borne viruses are a large group consisting of viruses from a wide range of families. The ability of their vector to enhance viral pathogenesis and transmission makes the development of treatments against these viruses challenging. Neutrophils are generally the first leukocytes to be recruited to a site of infection, playing a major role in regulating inflammation and, as a result, viral replication and dissemination. However, the underlying mechanisms through which neutrophils control the progression of inflammation and disease remain to be fully understood. In this review, we highlight the major findings from recent years regarding the role of neutrophils during arboviral infections. We discuss the complex nature of neutrophils in mediating not only protection, but also augmenting disease pathology. Better understanding of neutrophil pathways involved in effective protection against arboviral infections can help identify potential targets for therapeutics.

A salivary protein of Aedes aegypti promotes dengue-2 virus replication and transmission

Although dengue is the most prevalent arthropod-borne viral disease in humans, no effective medication or vaccine is presently available. Previous studies suggested that mosquito salivary proteins influence infection by the dengue virus (DENV) in the mammalian host. However, the effects of salivary proteins on DENV replication within the Aedes aegypti mosquito remain largely unknown. In this study, we investigated the effect of a specific salivary protein (named AaSG34) on DENV serotype 2 (DENV2) replication and transmission. We showed that transcripts of AaSG34 were upregulated in the salivary glands of Aedes aegypti mosquitoes after a meal of blood infected with DENV2. Transcripts of the dengue viral genome and envelop protein in the salivary glands were significantly diminished after an infectious blood meal when AaSG34 was silenced. The effect of AaSG34 on DENV2 transmission was investigated in Stat1-deficient mice. The intradermal inoculation of infectious mosquito saliva induced hemorrhaging in the Stat1-deficient mice; however, saliva from the AaSG34-silenced mosquitoes did not induce hemorrhaging, suggesting that AaSG34 enhances DENV2 transmission. This is the first report to demonstrate that the protein AaSG34 promotes DENV2 replication in mosquito salivary glands and enhances the transmission of the virus to the mammalian host.

Proteome analysis of Duck Tembusu virus (DTMUV)-infected BHK-21 cells

Duck Tembusu virus (DTMUV) is a newly emerging pathogenic flavivirus that has caused huge economic losses to the duck industry in China since 2010. Moreover, the infection has spread rapidly, posing a potential public health concern. In this study, iTRAQ approach was first used to quantitatively identify differentially expressed cellular proteins in DTMUV-infected BHK-21 cells which are usually employed to produce veterinary vaccines for DTMUV, as well as other flaviviruses by serial passage. We identified 192 differentially expressed cellular proteins, including 11 upregulated and eight downregulated proteins at 24 h postinfection (hpi), as well as 25 upregulated and 151 downregulated proteins at 48 hpi, of which TLR9, DDX3X, and DDX5 may play important roles in virus propagation. Further, DDX3X could inhibit DTMUV replication by modulating the IFN pathway via TBK1. In conclusion, our study is the first to analyze the protein profile of DTMUV-infected cells by quantitative proteomics. We believe that our findings provide valuable information in better understanding the host response to DTMUV infection. These findings are particularly important in the development of vaccine-based strategies.

New approaches and omics tools for mining of vaccine candidates against vector-borne diseases

Vector-borne diseases (VBDs) present a major threat to human and animal health, as well as place a substantial burden on livestock production. As a way of sustainable VBD control, focus is set on vaccine development. Advances in genomics and other "omics" over the past two decades have given rise to a "third generation" of vaccines based on technologies such as reverse vaccinology, functional genomics, immunomics, structural vaccinology and the systems biology approach. The application of omics approaches is shortening the time required to develop the vaccines and increasing the probability of discovery of potential vaccine candidates. Herein, we review the development of new generation vaccines for VBDs, and discuss technological advancement and overall challenges in the vaccine development pipeline. Special emphasis is placed on the development of anti-tick vaccines that can quell both vectors and pathogens.

Multiple Modes of Action of the Squamocin in the Midgut Cells of Aedes aegypti Larvae

Annonaceous acetogenins are botanical compounds with good potential for use as insecticides. In the vector, Aedes aegypti (L.) (Diptera: Culicidae), squamocin (acetogenin) has been reported to be a larvicide and cytotoxic, but the modes of action of this molecule are still poorly understood. This study evaluated the changes in the cell morphology, and in the expression of genes, for autophagy (Atg1 and Atg8), for membrane ion transporter V-ATPase, and for water channel aquaporin-4 (Aqp4) in the midgut of A. aegypti larvae exposed to squamocin from Annona mucosa Jacq. (Annonaceae). Squamocin showed cytotoxic action with changes in the midgut epithelium and digestive cells of A. aegypti larvae, increase in the expression for autophagy gene Atg1 and Atg8, decrease in the expression of V-ATPase, decrease in the expression of Aqp4 gene in LC20 and inhibition of Apq4 genes in the midgut of this vector in LC50. These multiple modes of action for squamocin are described for the first time in insects, and they are important because different sites of action of squamocin from A. mucosa may reduce the possibility of resistance of A. aegypti to this molecule.

Proteomics characterization of tick-host-pathogen interactions

Ticks are blood-feeding arthropod ectoparasites of wild and domestic animals that transmit disease-causing pathogens to humans and animals worldwide and a good model for the characterization of tick-host-pathogen interactions. Tick-host-pathogen interactions consist of dynamic processes involving genetic traits of hosts, pathogens, and ticks that mediate their development and survival. Proteomics provides information on the protein content of cells and tissues that may differ from results at the transcriptomics level and may be relevant for basic biological studies and vaccine antigen discovery. In this chapter, we describe various methods for protein extraction and for proteomics analysis in ticks based on one-dimensional gel electrophoresis to characterize tick-host-pathogen interactions. Particularly relevant for this characterization is the use of blood-fed ticks. Therefore, we put special emphasis on working with replete ticks collected after feeding on vertebrate hosts.

Transmission-Blocking Vaccines: Focus on Anti-Vector Vaccines against Tick-Borne Diseases

Tick-borne diseases are a potential threat that account for significant morbidity and mortality in human population worldwide. Vaccines are not available to treat several of the tick-borne diseases. With the emergence and resurgence of several tick-borne diseases, emphasis on the development of transmission-blocking vaccines remains increasing. In this review, we provide a snap shot on some of the potential candidates for the development of anti-vector vaccines (a form of transmission-blocking vaccines) against wide range of hard and soft ticks that include Ixodes, Haemaphysalis, Dermacentor, Amblyomma, Rhipicephalus and Ornithodoros species.

Role of skin immune cells on the host susceptibility to mosquito-borne viruses

Due to climate change and the propagation of competent arthropods worldwide, arboviruses have become pathogens of major medical importance. Early transmission to vertebrates is initiated by skin puncture and deposition of virus together with arthropod saliva in the epidermis and dermis. Saliva components have the capacity to modulate skin cell responses by enhancing and/or counteracting initial replication and establishment of systemic viral infection. Here, we review the nature of the cells targeted by arboviruses at the skin level and discuss the type of cellular responses elicited by these pathogens in light of the immunomodulatory properties of arthropod vector-derived salivary factors injected at the inoculation site. Understanding cutaneous arbovirus-host interactions may provide new clues for the design of future therapeutics.

Hijacking of host cellular functions by an intracellular parasite, the microsporidian Anncaliia algerae

Intracellular pathogens including bacteria, viruses and protozoa hijack host cell functions to access nutrients and to bypass cellular defenses and immune responses. These strategies have been acquired through selective pressure and allowed pathogens to reach an appropriate cellular niche for their survival and growth. To get new insights on how parasites hijack host cellular functions, we developed a SILAC (Stable Isotope Labeling by Amino Acids in Cell culture) quantitative proteomics workflow. Our study focused on deciphering the cross-talk in a host-parasite association, involving human foreskin fibroblasts (HFF) and the microsporidia Anncaliia algerae, a fungus related parasite with an obligate intracellular lifestyle and a strong host dependency. The host-parasite cross-talk was analyzed at five post-infection times 1, 6, 12 and 24 hours post-infection (hpi) and 8 days post-infection (dpi). A significant up-regulation of four interferon-induced proteins with tetratricopeptide repeats IFIT1, IFIT2, IFIT3 and MX1 was observed at 8 dpi suggesting a type 1 interferon (IFN) host response. Quantitative alteration of host proteins involved in biological functions such as signaling (STAT1, Ras) and reduction of the translation activity (EIF3) confirmed a host type 1 IFN response. Interestingly, the SILAC approach also allowed the detection of 148 A. algerae proteins during the kinetics of infection. Among these proteins many are involved in parasite proliferation, and an over-representation of putative secreted effectors proteins was observed. Finally our survey also suggests that A. algerae could use a transposable element as a lure strategy to escape the host innate immune system.

Comparative proteomics for the characterization of the most relevant Amblyomma tick species as vectors of zoonotic pathogens worldwide

Ticks transmit zoonotic pathogens worldwide. Nevertheless, very little information is available on their genome, transcriptome and proteome. Herein, we characterized the proteome of Amblyomma americanum adults and nymphs because of their role in pathogen transmission and compared the proteome of A. americanum, A. cajennense and A. variegatum adult ticks. We also used de novo sequencing proteomics data for the analysis of the phylogenetic relationships between the three Amblyomma spp. in a proof of concept for phyloproteomics. The results showed that host and tick proteins involved in blood digestion, heme detoxification, development and innate immunity were differentially represented between adults and nymphs. Although these ticks were unfed, over-represented host proteins may supply nutrients during off-host periods. Tick proteins involved in tick attachment, feeding, heat shock response, protease inhibition and heme detoxification were differentially represented between Amblyomma spp., suggesting adaptation processes to biotic and abiotic factors. These results suggested that phyloproteomics might be a useful tool for the phylogenetic analysis of tick species in which sequence data is a limiting factor and demonstrate the possibilities of proteomics studies for the characterization of relevant tick vector species and provide new relevant information to understand the physiology, development and evolution of these tick species.

BIOLOGICAL SIGNIFICANCE

This is the first report on the proteome of the most important Amblyomma tick species for their relevance as vectors of zoonotic pathogens worldwide. Nevertheless, very little information is available on the genome, transcriptome and proteome of these vector ectoparasites. The results reported herein provide new relevant information to understand the physiology, development and evolution of these tick species. Phyloproteomics using de novo protein sequencing was assayed as a new approach for the phylogenetic analysis of tick species in which sequence data is a limiting factor.This article is part of a Special Issue entitled: Proteomics of non-model organisms.

Decoding the ubiquitin-mediated pathway of arthropod disease vectors

Protein regulation by ubiquitin has been extensively described in model organisms. However, characterization of the ubiquitin machinery in disease vectors remains mostly unknown. This fundamental gap in knowledge presents a concern because new therapeutics are needed to control vector-borne diseases, and targeting the ubiquitin machinery as a means for disease intervention has been already adopted in the clinic. In this study, we employed a bioinformatics approach to uncover the ubiquitin-mediated pathway in the genomes of Anopheles gambiae, Aedes aegypti, Culex quinquefasciatus, Ixodes scapularis, Pediculus humanus and Rhodnius prolixus. We observed that (1) disease vectors encode a lower percentage of ubiquitin-related genes when compared to Drosophila melanogaster, Mus musculus and Homo sapiens but not Saccharomyces cerevisiae; (2) overall, there are more proteins categorized as E3 ubiquitin ligases when compared to E2-conjugating or E1-activating enzymes; (3) the ubiquitin machinery within the three mosquito genomes is highly similar; (4) ubiquitin genes are more than doubled in the Chagas disease vector (R. prolixus) when compared to other arthropod vectors; (5) the deer tick I. scapularis and the body louse (P. humanus) genomes carry low numbers of E1-activating enzymes and HECT-type E3 ubiquitin ligases; (6) R. prolixus have low numbers of RING-type E3 ubiquitin ligases; and (7) C. quinquefasciatus present elevated numbers of predicted F-box E3 ubiquitin ligases, JAB and UCH deubiquitinases. Taken together, these findings provide novel opportunities to study the interaction between a pathogen and an arthropod vector.

Differential proteomics of Aedes albopictus salivary gland, midgut and C6/36 cell induced by dengue virus infection

The interaction between dengue virus (DENV) and vector mosquitoes are still poorly understood at present. In this study, 2-D DIGE combined with MS was used to analyze the differential proteomes of Aedes albopictus salivary gland, midgut and C6/36 cells induced by DENV-2. Our results indicated that the virus infection regulated several functional classes of proteins. Among them, 26 were successfully analyzed by real-time RT-PCR. The mRNA levels of 15 were the highest in salivary gland, 2 in midgut and none in C6/36 cells, however, 18 were the least in fat body compared to other organs. Interestingly, the changes of differential proteins mRNA were the most obvious in fat body post-infection. Chaperone, cytoskeleton and energy metabolism enzyme were the most down- or up- regulated proteins after DENV-2 infection. The abundant expression of these proteins in salivary gland may relate to its high susceptibility.