Saliva from nymph and adult females of Haemaphysalis longicornis: a proteomic study

Comprehensive antigen identification and comparative analysis: significant approaches for controlling Haemaphysalis longicornis ticks

IMPORTANCE

Ticks transmit severe human and animal diseases, posing global health and economic risks. Haemaphysalis longicornis spreads infections like Rickettsia, Theileria, and Anaplasma, exacerbating concerns. Conventional tick control, including chemical acaricides, faces challenges like toxicity, non-target effects, and resistance. Innovative, sustainable strategies are essential. Advances in tick antigen research have identified molecular targets, paving the way for anti-tick vaccines as a promising, eco-friendly alternative to manage H. longicornis infestations and reduce tick-borne disease transmission. This review explores recent discoveries in tick antigens, the development of recombinant proteins, and their knockdown effects on H. longicornis infestations.

OBSERVATIONS

Several novel antigens target essential physiological processes for tick survival. Reproductive and developmental antigens, such as subolesin and subolesin+cystatin, regulate immunity and reproduction, reducing blood feeding, oviposition, egg mass, and hatching rates. Knockdown of recombinant P27/30 impairs embryogenesis, significantly reducing larval survival. Chitinase inhibition disrupts molting, impairing nymph development. Metabolic enzymes like enolase and GSK-3β regulate homeostasis and energy production; their inhibition reduces feeding efficiency and survivability. Additionally, ribosomal protein S27 and troponin I-like protein, essential for protein synthesis and muscle contraction, respectively, impact tick growth and mobility. These antigens may serve as valuable vaccine targets for controlling H. longicornis.

CONCLUSIONS AND RELEVANCE

Anti-tick vaccines offer a cost-effective, sustainable alternative to chemical controls. Advances in transcriptomics, genomics, and proteomics have identified promising antigens, with subolesin, chitinase, troponin I-like protein, GSK-3β, and enolase demonstrating strong potential. Enolase, affecting immunity, reproduction, and pathogen transmission, emerges as the most effective target for reducing H. longicornis infestations.

Regulation of tick attachment and rapid engorgement via dopamine receptors in the Asian longhorned tick Haemaphysalis longicornis

Dopamine plays multifaceted roles in the physiology of insects and ticks, acting as a key neurotransmitter and modulator of various biological processes. In ticks, it plays a particularly important role in regulating salivary gland function, which is essential for successful tick feeding on hosts. Salivary secretion in ticks is orchestrated by the collection of saliva in the acinar lumen mediated by the dopamine receptor (D1) and the expulsion of collected saliva into the salivary duct mediated by the invertebrate specific D1-like dopamine receptor (InvD1L). However, the function of dopamine receptors in different feeding stages and other tissues remains unclear. In this study, D1 and InvD1L of Haemaphysalis longicornis (Haelo-D1 and Haelo-InvD1L, respectively) were found to be involved in tick attachment and the rapid phase of blood feeding. Both receptors were identified and profiled in the synganglion, salivary glands, and midgut of H. longicornis females across different feeding stages. Functional analyses revealed that both receptors were activated by dopamine in a concentration-dependent manner with distinct sensitivities. RNA interference (RNAi) targeting these receptors significantly reduced dopamine-mediated salivation and delayed tick attachment and blood feeding. Furthermore, RNAi prolonged rapid engorgement phases and reduced the final body weight of replete ticks. These results highlight the crucial roles of D1 and InvD1L in regulating salivary secretion in ixodid ticks and facilitating their attachment and rapid engorgement, thereby offering potential targets for novel tick control strategies aimed at disrupting feeding and reducing pathogen transmission.

Comprehensive review of Argulus infestations in aquaculture: Biological impacts and advanced management strategies

The aquaculture industry is hindered by various factors. One of the most noticeable factors is infection by parasites and pathogens. Argulus stands out as a prominent and economically significant ectoparasite in freshwater aquaculture. Argulus infestation causes severe immunomodulatory effects on its hosts by promoting argulosis, causing inflammation, extensive tissue damage, and death. Indian aquaculture sector faced a loss of 62.5 million USD due to Argulus infection. However, current control methods, such as pesticides, cause serious environmental damage. Herbal treatment methods are ineffective and have limitations. Hence, a more efficient and cost-effective control method is needed. In recent years, vaccine development has emerged as a promising avenue of research. Understanding the effect of the host-parasite relationship in the host immune system is essential to develop strategies for prevention, control, and management of argulosis. These interactions provide insights into the co-evolutionary dynamics between hosts and parasites. This review provides an overview of the current knowledge on the host-searching behaviour of Argulus, host-parasite interaction and control strategies. This review also highlights the need for further research and the development of sustainable control measures for Argulus infection.

Effect of Silencing subolesin and enolase impairs gene expression, engorgement and reproduction in Haemaphysalis longicornis (Acari: Ixodidae) ticks

IMPORTANCE

Haemaphysalis longicornis is an obligate blood-sucking ectoparasite that has gained attention due its role of transmitting medically and veterinary significant pathogens and it is the most common tick species in Republic of Korea. The preferred strategy for controlling ticks is a multi-antigenic vaccination. Testing the efficiency of a combination antigen is a promising method for creating a tick vaccine.

OBJECTIVE

The aim of the current research was to analyze the role of subolesin and enolase in feeding and reproduction of H. longicornis by gene silencing.

METHODS

In this study, we used RNA interference to silence salivary enolase and subolesin in H. longicornis. Unfed female ticks injected with double-stranded RNA targeting subolesin and enolase were attached and fed normally on the rabbit's ear. Real-time polymerase chain reaction was used to confirm the extent of knockdown.

RESULTS

Ticks in the subolesin or enolase dsRNA groups showed knockdown rates of 80% and 60% respectively. Ticks in the combination dsRNA (subolesin and enolase) group showed an 80% knockdown. Knockdown of subolesin and enolase resulted in significant depletion in feeding, blood engorgement weight, attachment rate, and egg laying. Silencing of both resulted in a significant (p < 0.05) reduction in tick engorgement, egg laying, egg hatching (15%), and reproduction.

CONCLUSIONS AND RELEVANCE

Our results suggest that subolesin and enolase are an exciting target for future tick control strategies.

Molecular cloning, identification, transcriptional analysis, and silencing of enolase on the life cycle of Haemaphysalis longicornis (Acari, Ixodidae) tick

Ticks, blood-sucking ectoparasites, spread diseases to humans and animals. Haemaphysalis longicornis is a significant vector for tick-borne diseases in medical and veterinary contexts. Identifying protective antigens in H. longicornis for an anti-tick vaccine is a key tick control strategy. Enolase, a multifunctional protein, significantly converts D-2-phosphoglycerate and phosphoenolpyruvate in glycolysis and gluconeogenesis in cell cytoplasm. This study cloned a complete open reading frame (ORF) of enolase from the H. longicornis tick and characterized its transcriptional and silencing effect. We amplified the full-length cDNA of the enolase gene using rapid amplification of cDNA ends. The complete cDNA, with an ORF of 1,297 nucleotides, encoded a 432-amino acid polypeptide. Enolase of the Jeju strain H. longicornis exhibited the highest sequence similarity with H. flava (98%), followed by Dermacentor silvarum (82%). The enolase motifs identified included N-terminal and C-terminal regions, magnesium binding sites, and several phosphorylation sites. Reverse transcription-polymerase chain reaction (RT-PCR) analysis indicated that enolase mRNA transcripts were expressed across all developmental stages of ticks and organs such as salivary gland and midgut. RT-PCR showed higher transcript levels in syn-ganglia, suggesting that synganglion nerves influence enolase,s role in tick salivary glands. We injected enolase double-stranded RNA into adult unfed female ticks, after which they were subsequently fed with normal unfed males until they spontaneously dropped off. RNA interference significantly (P<0.05) reduced feeding and reproduction, along with abnormalities in eggs (no embryos) and hatching. These findings suggest enolase is a promising target for future tick control strategies.

Comparative analysis of essential oil efficacy against the Asian longhorned tick Haemaphysalis longicornis (Acari: Ixodidae)

This study evaluated the potential repellent and acaricidal effects of 4 essential oils (clove, eucalyptus, lavender, and mint) against the Asian longhorned tick Haemaphysalis longicornis, a vector of various tick-borne diseases in medical and veterinary contexts. Selected for their potential repellent and acaricidal properties, the 4 essential oils were tested on adult and nymph H. longicornis ticks at different concentrations. The experiment assessed mortality rates and repellency, particularly during tick attachment to host skin. There was a significant increase (p<0.05) in tick mortality and repellency scores across all groups. At a 1% concentration, adult tick mortality ranged from 36% to 86%, while nymph mortality ranged from 6% to 97%. Clove oil exhibited notable efficacy, demonstrating high mortality rates of nymphs and adults. Clove oil also displayed strong repellency properties, with a repellency index of 0.05, surpassing those of mint, eucalyptus, and lavender oils. Clove oil showed the highest effectiveness in deterring nonattached adult ticks (90%) and nymphs (95%) when applied to skin. Clove oil was the most effective against adult and nymph ticks, achieving mortality rates of 86% and 97%, respectively, and led to the highest nonattachment rates when applied to skin. In conclusion, essential oils such as clove, eucalyptus, lavender, and mint oils present promising results for tick population control.

Rhipicephalus microplus thyropin-like protein: Structural and immunologic analyzes

Tick saliva has a pivotal function in parasitism. It has pharmacological and immunomodulatory properties, with several proteins reported in its composition. Thyroglobulin type-1 domain protease inhibitor (thyropin)-like proteins are found in tick saliva, but their function, properties and structures are poorly characterized. It has been reported that thyropins are capable of inhibiting cysteine peptidases present in antigen-presenting cells. To elucidate the role of thyropin-like proteins in ticks, we conducted in silico analysis and cloned an open reading frame from a thyropin-like protein found in Rhipicephalus microplus. The recombinant protein was successfully expressed, followed by immunological characterization and a vaccine trial against Rhipicephalus sanguineus in rabbits. Several differences are observed between thyropin-like proteins from hard and soft ticks, especially the number of thyroglobulin domains and predicted glycosylation pattern. Thyropin-like proteins also differ between postriata and metastriata ticks, the latter having a coil-domain at the C-terminal region and high number of predicted glycosylation sites. Overall, the data suggested divergence in thyropin-like proteins functions among ticks. The recombinant thyropin-like protein is immunogenic and the antibodies against it are able to recognize the native protein in tick saliva and tissues. While the recombinant protein does not elicit a protective response against R. sanguineus infestation, its characterization paves the way for further investigations aimed at determining the precise function of this protein in tick physiology.

Changes in saliva protein profile throughout Rhipicephalus microplus blood feeding

BACKGROUND

When feeding on a vertebrate host, ticks secrete saliva, which is a complex mixture of proteins, lipids, and other molecules. Tick saliva assists the vector in modulating host hemostasis, immunity, and tissue repair mechanisms. While helping the vector to feed, its saliva modifies the site where pathogens are inoculated and often facilitates the infection process. The objective of this study is to uncover the variation in protein composition of Rhipicephalus microplus saliva during blood feeding.

METHODS

Ticks were fed on calves, and adult females were collected, weighed, and divided in nine weight groups, representing the slow and rapid feeding phases of blood feeding. Tick saliva was collected, and mass spectrometry analyses were used to identify differentially secreted proteins. Bioinformatic tools were employed to predict the structural and functional features of the salivary proteins. Reciprocal best hit analyses were used to identify conserved families of salivary proteins secreted by other tick species.

RESULTS

Changes in the protein secretion profiles of R. microplus adult female saliva during the blood feeding were observed, characterizing the phenomenon known as "sialome switching." This observation validates the idea that the switch in protein expression may serve as a mechanism for evading host responses against tick feeding. Cattle tick saliva is predominantly rich in heme-binding proteins, secreted conserved proteins, lipocalins, and protease inhibitors, many of which are conserved and present in the saliva of other tick species. Additionally, another remarkable observation was the identification of host-derived proteins as a component of tick saliva.

CONCLUSIONS

Overall, this study brings new insights to understanding the dynamics of the proteomic profile of tick saliva, which is an important component of tick feeding biology. The results presented here, along with the disclosed sequences, contribute to our understanding of tick feeding biology and might aid in the identification of new targets for the development of novel anti-tick methods.

Tick innate immune responses to hematophagy and Ehrlichia infection at single-cell resolution

Introduction

Ticks rely on robust cellular and humoral responses to control microbial infection. However, several aspects of the tick's innate immune system remain uncharacterized, most notably that of the immune cells (called hemocytes), which are known to play a significant role in cellular and humoral responses. Despite the importance of hemocytes in regulating microbial infection, our understanding of their basic biology and molecular mechanisms remains limited. Therefore, we believe that a more detailed understanding of the role of hemocytes in the interactions between ticks and tick-borne microbes is crucial to illuminating their function in vector competence and to help identify novel targets for developing new strategies to block tick-borne pathogen transmission.

Methods

This study examined hemocytes from the lone star tick (Amblyomma americanum) at the transcriptomic level using the 10X genomics single-cell RNA sequencing platform to analyze hemocyte populations from unfed, partially blood-fed, and Ehrlichia chaffeensis-infected ticks. The functional role of differentially expressed hemocyte markers in hemocyte proliferation and Ehrlichia dissemination was determined using an RNA interference approach.

Results and discussion

Our data exhibit the identification of fourteen distinct hemocyte populations. Our results uncover seven distinct lineages present in uninfected and Ehrlichia-infected hemocyte clusters. The functional characterization of hemocytin, cystatin, fibronectin, and lipocalin demonstrate their role in hemocyte population changes, proliferation, and Ehrlichia dissemination.

Conclusion

Our results uncover the tick immune responses to Ehrlichia infection and hematophagy at a single-cell resolution. This work opens a new field of tick innate immunobiology to understand the role of hemocytes, particularly in response to prolonged blood-feeding (hematophagy), and tick-microbial interactions.

Ixodes scapularis nymph saliva protein blocks host inflammation and complement-mediated killing of Lyme disease agent, Borrelia burgdorferi

Tick serine protease inhibitors (serpins) play crucial roles in tick feeding and pathogen transmission. We demonstrate that Ixodes scapularis (Ixs) nymph tick saliva serpin (S) 41 (IxsS41), secreted by Borrelia burgdorferi (Bb)-infected ticks at high abundance, is involved in regulating tick evasion of host innate immunity and promoting host colonization by Bb. Recombinant (r) proteins were expressed in Pichia pastoris, and substrate hydrolysis assays were used to determine. Ex vivo (complement and hemostasis function related) and in vivo (paw edema and effect on Bb colonization of C3H/HeN mice organs) assays were conducted to validate function. We demonstrate that rIxsS41 inhibits chymase and cathepsin G, pro-inflammatory proteases that are released by mast cells and neutrophils, the first immune cells at the tick feeding site. Importantly, stoichiometry of inhibition analysis revealed that 2.2 and 2.8 molecules of rIxsS41 are needed to 100% inhibit 1 molecule of chymase and cathepsin G, respectively, suggesting that findings here are likely events at the tick feeding site. Furthermore, chymase-mediated paw edema, induced by the mast cell degranulator, compound 48/80 (C48/80), was blocked by rIxsS41. Likewise, rIxsS41 reduced membrane attack complex (MAC) deposition via the alternative and lectin complement activation pathways and dose-dependently protected Bb from complement killing. Additionally, co-inoculating C3H/HeN mice with Bb together with rIxsS41 or with a mixture (rIxsS41 and C48/80). Findings in this study suggest that IxsS41 markedly contributes to tick feeding and host colonization by Bb. Therefore, we conclude that IxsS41 is a potential candidate for an anti-tick vaccine to prevent transmission of the Lyme disease agent.

Rabbits as Animal Models for Anti-Tick Vaccine Development: A Global Scenario

Studies evaluating candidate tick-derived proteins as anti-tick vaccines in natural hosts have been limited due to high costs. To overcome this problem, animal models are used in immunization tests. The aim of this article was to review the use of rabbits as an experimental model for the evaluation of tick-derived proteins as vaccines. A total of 57 tick proteins were tested for their immunogenic potential using rabbits as models for vaccination. The most commonly used rabbit breeds were New Zealand (73.8%), Japanese white (19%), Californians (4.8%) and Flemish lop-eared (2.4%) rabbits. Anti-tick vaccines efficacy resulted in up to 99.9%. Haemaphysalis longicornis (17.9%) and Ornithodoros moubata (12.8%) were the most common tick models in vaccination trials. Experiments with rabbits have revealed that some proteins (CoAQP, OeAQP, OeAQP1, Bm86, GST-Hl, 64TRP, serpins and voraxin) can induce immune responses against various tick species. In addition, in some cases it was possible to determine that the vaccine efficacy in rabbits was similar to that of experiments performed on natural hosts (e.g., Bm86, IrFER2, RmFER2, serpins and serine protease inhibitor). In conclusion, results showed that prior to performing anti-tick vaccination trials using natural hosts, rabbits can be used as suitable experimental models for these studies.

Universal Tick Vaccines: Candidates and Remaining Challenges

Recent advancements in molecular biology, particularly regarding massively parallel sequencing technologies, have enabled scientists to gain more insight into the physiology of ticks. While there has been progress in identifying tick proteins and the pathways they are involved in, the specificities of tick-host interaction at the molecular level are not yet fully understood. Indeed, the development of effective commercial tick vaccines has been slower than expected. While omics studies have pointed to some potential vaccine immunogens, selecting suitable antigens for a multi-antigenic vaccine is very complex due to the participation of redundant molecules in biological pathways. The expansion of ticks and their pathogens into new territories and exposure to new hosts makes it necessary to evaluate vaccine efficacy in unusual and non-domestic host species. This situation makes ticks and tick-borne diseases an increasing threat to animal and human health globally, demanding an urgent availability of vaccines against multiple tick species and their pathogens. This review discusses the challenges and advancements in the search for universal tick vaccines, including promising new antigen candidates, and indicates future directions in this crucial research field.

Molecular Detection of Tick-Borne Bacterial and Protozoan Pathogens in Haemaphysalis longicornis (Acari: Ixodidae) Ticks from Free-Ranging Domestic Sheep in Hebei Province, China

Ticks and tick-borne pathogens significantly threaten human and animal health worldwide. Haemaphysalis longicornis is one of the dominant tick species in East Asia, including China. In the present study, 646 Ha. longicornis ticks were collected from free-ranging domestic sheep in the southern region of Hebei Province, China. Tick-borne pathogens of zoonotic and veterinary importance (i.e., Rickettsia, Anaplasma, Ehrlichia, Borrelia, Theileria, and Hepatozoon spp.) were detected in the ticks using PCR assays and sequence analysis. The prevalence rates of these pathogens were 5.1% (33/646), 15.9% (103/646), 1.2% (8/646), 17.0% (110/646), 0.15% (1/646), and 0.15% (1/646), respectively. For Rickettsia spp., R. japonica (n = 13), R. raoultii (n = 6), and Candidatus R. jingxinensis (n = 14) were detected for the first time in the province, while several Anaplasma spp. were also detected in the ticks, including A. bovis (n = 52), A. ovis (n = 31), A. phagocytophilum (n = 10), and A. capra (n = 10). A putative novel Ehrlichia spp. was also found with a prevalence of 1.2% in the area. The present study provides important data for effectively controlling ticks and tick-borne diseases in the Hebei Province region of China.

Effects of histamine and antihistamine on the hard tick Haemaphysalis longicornis during blood sucking

At the time of host attachment, ticks are very sensitive to histamine, but during rapid blood sucking they paradoxically require histamine. Using a rabbit model, we studied the effects of histamine and antihistamine during attachment and fast-feeding in different life stages of Haemaphysalis longicorns. We examined how they responded to histamine and antihistamine by analyzing the detachment rate, histology of feeding lesions, and post-feeding behavior. A significant difference (P&lt;0.01) was found in the detachment rate between experimental and control treatments throughout the observation period. Ticks exhibited a higher detachment rate (30.1%) at 12 h after histamine application during attachment time and on antihistamine-treated skin (25.4%) at 96 h during fast-feeding. After feeding on histamine-treated rabbits, the fully engorged body weights of larvae and nymphs were 0.7±0.36 mg and 3.5±0.65 mg, respectively. An average increase in body weight of 0.6±0.05 mg and 3.2±0.30 mg was observed for larvae and nymphs compared to the respective control weights. Nymphs and adults engorged after antihistamine treatment had an average body weight of 1.3±0.54 mg and 54±0.81 mg, respectively. An average decrease in body weight was observed in antihistamine-treated H. longicornis compared with control nymphs (3.3±0.42 mg) and adults (174±1.78 mg). Skin biopsies were collected after treatment, and differential histopathological characteristics were found between the treatment and control groups. Tick-infested skin collected from rabbits in the antihistamine-treated group lacked erythrocytes in the feeding pool, indicating that antihistamine impaired tick fast-feeding stage.

Saliva proteome of partially- and fully-engorged adult female Haemaphysalis flava ticks

Tick saliva is a reservoir of bioactive proteins. Saliva protein compositions change dynamically during blood-feeding. Decipherment of protein profiles in different blood-feeding stages may bring deeper insight into tick feeding physiology and provide targets for immunologic control alternatives. However, having the infancy of tick genome sequencing, assembly, annotation, and limited knowledge of tick salivary proteins restrain the data interpretation. Here, we aimed to depict the saliva protein profile in partially- (PE) and fully-engorged (FE) Haemaphysalis flava ticks, with a special focus on the analysis of those uncharacterized proteins. Saliva was collected from PE and FE adult female H. flava ticks. Saliva proteins were analyzed by high-performance liquid chromatography-tandem mass spectrometry (HPLC/MS-MS). MS data were searched against an in-house salivary gland transcriptome library for identification of tick-derived proteins. Abundances of proteins were compared between PE and FE ticks. The uncharacterized proteins detected in saliva were further bioinformatically analyzed. In total, 614 proteins were identified including 94 host proteins and 520 tick-derived proteins. The 226 tick-derived high-confidence proteins were classified into 10 categories: transporters, enzymes, protease inhibitors, immunity-related proteins, lipocalins, glycine-rich proteins, muscle proteins, secreted proteins, uncharacterized proteins and others. A total of 98 proteins were shared in both PE and FE with 74 only in PE and 54 only in FE. Abundances of 24 shared proteins were significantly higher in PE. The profile of top 15 most abundant proteins was also different between PE and FE ticks. The 65 uncharacterized proteins detected in tick saliva were branched into subclusters 1 A, 1B, 2, 3 A, 3B and 3 C based on particular motifs like RGD, LRR, indicating their diverse predicted functions like anti-coagulation, regulation of innate immune, or other functions. This study provides and compares saliva proteomes of H. flava ticks in two feeding stages with special cluster analysis on the uncharacterized proteins. Further investigations are needed to confirm the roles of these uncharacterized proteins in ticks.

Daily patterns in parasite processes: diel variation in fish louse transcriptomes

Parasites, similar to all other organisms, time themselves to environmental cues using a molecular clock to generate and maintain rhythms. Chronotherapeutic (timed treatment) techniques based on such rhythms offer great potential for improving control of chronic, problematic parasites. Fish lice are a key disease threat in aquaculture, with current control insufficient. Assessing the rhythmicity of fish lice transcriptomes offers not only insight into the viability of chronotherapy, but the opportunity to identify new drug targets. Here, for the first known time in any crustacean parasite, diel changes in gene transcription are examined, revealing that approximately half of the Argulus foliaceus annotated transcriptome displays significant daily rhythmicity. We identified rhythmically transcribed putative clock genes including core clock/cycle and period/timeless pairs, alongside rhythms in feeding-associated genes and processes involving immune response, as well as fish louse drug targets. A substantial number of gene pathways showed peak transcription in hours immediately preceding onset of light, potentially in anticipation of peak host anti-parasite responses or in preparation for increased feeding activity. Genes related to immune haemocyte activity and chitin development were more highly transcribed 4 h post light onset, although inflammatory gene transcription was highest during dark periods. Our study provides an important resource for application of chronotherapy in fish lice; timed application could increase efficacy and/or reduce dose requirement, improving the current landscape of drug resistance and fish health while reducing the economic cost of infection.

Host Immune Responses to Salivary Components - A Critical Facet of Tick-Host Interactions

Tick sialome is comprised of a rich cocktail of bioactive molecules that function as a tool to disarm host immunity, assist blood-feeding, and play a vibrant role in pathogen transmission. The adaptation of the tick's blood-feeding behavior has lead to the evolution of bioactive molecules in its saliva to assist them to overwhelm hosts' defense mechanisms. During a blood meal, a tick secretes different salivary molecules including vasodilators, platelet aggregation inhibitors, anticoagulants, anti-inflammatory proteins, and inhibitors of complement activation; the salivary repertoire changes to meet various needs such as tick attachment, feeding, and modulation or impairment of the local dynamic and vigorous host responses. For instance, the tick's salivary immunomodulatory and cement proteins facilitate the tick's attachment to the host to enhance prolonged blood-feeding and to modulate the host's innate and adaptive immune responses. Recent advances implemented in the field of "omics" have substantially assisted our understanding of host immune modulation and immune inhibition against the molecular dynamics of tick salivary molecules in a crosstalk between the tick-host interface. A deep understanding of the tick salivary molecules, their substantial roles in multifactorial immunological cascades, variations in secretion, and host immune responses against these molecules is necessary to control these parasites. In this article, we reviewed updated knowledge about the molecular mechanisms underlying host responses to diverse elements in tick saliva throughout tick invasion, as well as host defense strategies. In conclusion, understanding the mechanisms involved in the complex interactions between the tick salivary components and host responses is essential to decipher the host defense mechanisms against the tick evasion strategies at tick-host interface which is promising in the development of effective anti-tick vaccines and drug therapeutics.

Phosphoproteomic Analysis of Haemaphysalis longicornis Saliva Reveals the Influential Contributions of Phosphoproteins to Blood-Feeding Success

Tick saliva, an essential chemical secretion of the tick salivary gland, is indispensable for tick survival owing to the physiological influence it exerts on the host defence mechanisms via the instrumentality of its cocktail of pharmacologically active molecules (proteins and peptides). Much research about tick salivary proteome has been performed, but how most of the individual salivary proteins are utilized by ticks to facilitate blood acquisition and pathogen transmission is not yet fully understood. In addition, the phosphorylation of some proteins plays a decisive role in their function. However, due to the low phosphorylation level of protein, especially for a small amount of protein, it is more difficult to study phosphorylation. Maybe, for this reason, the scarcity of works on the phosphorylated tick salivary proteomes still abound. Here, we performed a phosphoproteomic analysis of Haemaphysalis longicornis tick saliva via TiO₂ enrichment and the most advanced Thermo Fisher Orbitrap Exploris 480 mass spectrometer for identification. A total of 262 phosphorylated tick saliva proteins were identified and were subjected to functional annotation/enrichment analysis. Cellular and metabolic process terms accounted for the largest proportion of the saliva proteins, with the participation of these proteins in vital intracellular and extracellular transport-oriented processes such as vesicle-mediated transport, exocytic process, cell adhesion, and movement of cell/subcellular component. “Endocytosis”, “Protein processing in endoplasmic reticulum”, and “Purine metabolism” were the most significantly enriched pathways. The knockdown (RNAi) of Tudor domain-containing protein (TCP), actin-depolymerizing factors (ADF), programmed cell death protein (PD), and serine/threonine-protein kinase (SPK) resulted in the dissociation of collagen fibers and the pilosebaceous unit, increased inflammatory infiltrates/granulocytes (possibly heterophiles), and the depletion of the epithelium. Ticks injected with SPK dsRNA engorged normally but with a change in skin colour (possibly an autoimmune reaction) and the failure to produce eggs pointing to a possible role of SPK in reproduction and host immune modulation. Ticks injected with ADF dsRNA failed to acquire blood, underscoring the role of ADF in facilitating tick feeding. The results of this study showed the presence of phosphorylation in tick saliva and highlight the roles of salivary phosphoproteins in facilitating tick feeding.

A preliminary evaluation of tick cement-cone protein extract for a vaccine against Hyalomma infestation

BACKGROUND

Vaccines have been widely exploited to prevent tick-borne infections in cattle. Most vaccines have faced failure in the field because of inconsistency in an immune response. It is presumed that the cement-cone proteins of ticks that participate in the acquisition of blood meal for ticks possess strong immune-stimulating properties and, hence, could be a useful candidate in vaccine development.

AIMS

We evaluated cement-cone proteins of tick Hyalomma anatolicum as a vaccine candidate against infestations of H. anatolicum and H. aegyptium in cattle.

METHODS

The cement-cone proteins were extracted from H. anatolicum to develop stage-reactive and immunogenic cross-reactive vaccine against the infestation of two species of ticks H. anatolicum and H. aegyptium. The immune response of the vaccine was tested against cement-cone proteins starved, partially fed, and richly fed ticks.

RESULTS

The findings of the present study demonstrated the cross-reactivity among the two species of ticks that belonged to the same genus (Hyalomma). The antigenic similarity between the two ticks species suggests that a common antigen may possibly be suitable for a vaccine against the two different species of ticks. The results have also indicated that the 23 kDa cement-cone protein of H. anatolicum and H. aegyptium may be responsible for the induction, or elicitation of immunogenic, common stage reactive, and cross-reactive host immune responses with consistent intensity throughout the life stages of ticks.

CONCLUSION

The vaccine based upon cement-cone proteins of ticks may be a useful deterrent against tick-borne infections in cattle in countries like Pakistan.

Ticks and antibodies: May parasite density and tick evasion influence the outcomes following immunization protocols?

Ticks are a major concern to human health and livestock worldwide, being responsible for economic losses that go beyond billions of US dollars per year. This scenario instigates the development of vaccines against these ectoparasites, emphasized by the fact that the main method of controlling ticks still relies on the use of acaricides, what increases costs and may affect the environment as well as human and animal health. The first commercial vaccines against ectoparasites were produced against the tick Rhipicephalus microplus and their efficacy were based on antibodies. Many additional attempts have been conducted to produce protective immune responses against ticks by immunization with specific antigens and the antibody response has usually been the main target of evaluation. But some controversy still populates the roles possibly performed by humoral responses in tick-mammalian host relationships. This review focuses on the analysis of specific aspects concerning antibodies and ticks, especially the influence of parasite density and evasion/modulation. The immunization trials already described against R. microplus were also compiled and analyzed based on the characteristics of the molecules tested, protocols of immunization and tick challenge. Within these issues, it is discussed if or when antibody levels can be directly correlated with the development of tick resistance, and whether anti-tick protective immune responses generated by infestations may become ineffective under a different tick density. Also, higher titers of antibodies can be correlated with protection or susceptibility to tick infestations, what may be altered following continuous or repeated infestations and differ greatly comparing hosts with distinct genetic backgrounds. Regarding evasion, ticks present a sophisticated mechanism for dealing with antibodies, including Immunoglobulin Binding Proteins (IGBPs), that capture, transport and inject them back into the host, while keeping their properties within the parasite. The comparison of immunization protocols shows a total of 22 molecules already tested in cattle vaccination trials against R. microplus, with the predominance of concealed and dual antigens as well as marked differences in tick challenge schemes. The presence of an antibody evasion apparatus and variable levels of tick resistance when facing different densities of parasites are concerns that should be considered when testing vaccine candidates. Ultimately, more refinement may be necessary to effectively design a cocktail vaccine with tick molecules, which may be needed to be altered and combined in non-competing immune contexts to be universally secure and protective.

Exploring immunogenicity of tick salivary AV422 protein in persons exposed to ticks: prospects for utilization

In order to determine whether conserved tick salivary protein AV422 is immunogenic, the goal of our study was to detect specific IgG response within at-risk populations. Study groups included 76 individuals, differing in occurrence of recently recorded tick bites and health status. Western blotting with recombinant (r) protein derived from Ixodes ricinus (Ir) was performed. IgG response to Borrelia/Rickettsia, as indicators of previous tick infestations, was also assessed. Additionally, a detailed in silico AV422 protein sequence analysis was performed, followed by modelling of the interactions between peptides and corresponding MHC II molecules by molecular docking. Anti-rIrAV422 seroprevalences among individuals exposed to ticks were high (62.5, 57.9 and 66.7%) and anti-Borrelia/Rickettsia seroprevalences were 54.2, 15.8 and 44.4% among individuals with/without recent tick bite and patients suspected of tick-borne disease, respectively. In silico analysis of AV422 protein sequence showed a high level of conservation across tick genera, including also the predicted antigenic determinants specific for T and B cells. Docking to the restricted MHC II molecules was performed for all predicted AV422 T cell epitopes, and the most potent (highly immunogenic) epitope determinants were suggested. The epitope prediction reveals that tick salivary protein AV422 may elicit humoral immune response in humans, which is consistent with the high anti-rIrAV422 seroprevalence in tested at-risk subjects. Tick-borne diseases are a growing public health concern worldwide, and AV422 is potentially useful in clinical practice and epidemiological studies.

Characterization of AV422 from Haemaphysalis flava ticks in vitro

Ticks are hematophagous ectoparasites and cause a major public health threat worldwide. Development of anti-tick vaccines is regarded to be an optimal alternative for tick control. AV422, a unique protein in ticks, is secreted into hosts during blood-feeding, but its roles are not confirmed in Haemaphysalis flava ticks. We retrieved a gene fragment encoding AV422 from a transcriptome dataset of H. flava, and based on it, we reconstructed the full length of AV422 from H. flava (Hf-AV422) by rapid amplification of cDNA ends. Expression profiles of Hf-AV422 in whole ticks and organs of different engorgement levels were determined by qPCR. Then its opening reading frame (ORF) was expressed in Escherichia coli strain BL21 (DE3). The prothrombin time (PT), activated partial thromboplastin time (APTT) and thrombin time (TT) assays were conducted to test anticoagulant activities of the purified recombinant protein (rHf-AV422). The full length of AV422 was 1152 bp. Hf-AV422 showed to be conserved as indicated by multiple sequence alignment. Expression of Hf-AV422 was significantly higher in salivary glands and cuticles than in ovaries. Its expression in whole ticks decreased during engorgement with the highest levels in 1/4 engorged ticks. rHf-AV422 prolonged PT, APTT and TT when incubated with rabbit plasma. Our data demonstrated that Hf-AV422 is a conserved salivary protein with anticoagulant activity. Further studies are needed to test in detail its functional properties to ensure it an adequate antigen candidate for the development of broad-spectrum vaccines against ticks.

Incompetence of the Asian Longhorned Tick (Acari: Ixodidae) in Transmitting the Agent of Human Granulocytic Anaplasmosis in the United States

The Asian longhorned tick, Haemaphysalis longicornis Neumann (Acari: Ixodidae), was recently introduced into the United States and is now established in at least 15 states. Considering its ability for parthenogenetic propagation and propensity for creating high-density populations, there is concern that this tick may become involved in transmission cycles of endemic tick-borne human pathogens. Human granulocytic anaplasmosis (HGA) caused by Anaplasma phagocytophilum is one of the more common tick-borne diseases in the United States, especially in the northeastern and midwestern states. There is considerable geographical overlap between HGA cases and the currently known distribution of H. longicornis, which creates a potential for this tick to encounter A. phagocytophilum while feeding on naturally infected vertebrate hosts. Therefore, we evaluated the ability of H. longicornis to acquire and transmit the agent of HGA under laboratory conditions and compared it to the vector competence of I. scapularis. Haemaphysalis longicornis nymphs acquired the pathogen with the bloodmeal while feeding on infected domestic goats, but transstadial transmission was inefficient and PCR-positive adult ticks were unable to transmit the pathogen to naïve goats. Results of this study indicate that the Asian longhorned tick is not likely to play a significant role in the epidemiology of HGA in the United States.

The genus Anaplasma: drawing back the curtain on tick-pathogen interactions

Tick-borne illnesses pose a serious concern to human and veterinary health and their prevalence is on the rise. The interactions between ticks and the pathogens they carry are largely undefined. However, the genus Anaplasma, a group of tick-borne bacteria, has been instrumental in uncovering novel paradigms in tick biology. The emergence of sophisticated technologies and the convergence of entomology with microbiology, immunology, metabolism and systems biology has brought tick-Anaplasma interactions to the forefront of vector biology with broader implications for the infectious disease community. Here, we discuss the use of Anaplasma as an instrument for the elucidation of novel principles in arthropod-microbe interactions. We offer an outlook of the primary areas of study, outstanding questions and future research directions.

A U.S. isolate of Theileria orientalis, Ikeda genotype, is transmitted to cattle by the invasive Asian longhorned tick, Haemaphysalis longicornis

Background

Theileria orientalis is a tick-borne hemoparasite that causes anemia, ill thrift, and death in cattle globally. The Ikeda strain of T.orientalis is more virulent than other strains, leading to severe clinical signs and death of up to 5% of affected animals. Within the Asia–Pacific region, where it affects 25% of Australian cattle, T.orientalis Ikeda has a significant economic impact on the cattle industry. In 2017, T.orientalis Ikeda was detected in a cattle herd in Albermarle County, Virginia, United States. Months earlier, the U.S. was alerted to the invasion of the Asian longhorned tick, Haemaphysalis longicornis, throughout the eastern U.S. Abundant H.longicornis ticks were identified on cattle in the T.orientalis-affected herd in VA, and a subset of ticks from the environment were PCR-positive for T.orientalis Ikeda. A strain of T.orientalis from a previous U.S. outbreak was not transmissible by H.longicornis; however, H.longicornis is the primary tick vector of T.orientalis Ikeda in other regions of the world. Thus, the objective of this study was to determine whether invasive H.longicornis ticks in the U.S. are competent vectors of T.orientalis Ikeda.

Methods

Nymphal H.longicornis ticks were fed on a splenectomized calf infected with the VA-U.S.-T.orientalis Ikeda strain. After molting, a subset of adult ticks from this cohort were dissected, and salivary glands assayed for T.orientalis Ikeda via qPCR. The remaining adult ticks from the group were allowed to feed on three calves. Calves were subsequently monitored for T.orientalis Ikeda infection via blood smear cytology and PCR.

Results

After acquisition feeding on a VA-U.S.-T.orientalis Ikeda-infected calf as nymphs, a subset of molted adult tick salivary glands tested positive by qPCR for T.orientalis Ikeda. Adult ticks from the same cohort successfully transmitted T.orientalis Ikeda to 3/3 naïve calves, each of which developed parasitemia reaching 0.4–0.9%.

Conclusions

Our findings demonstrate that U.S. H.longicornis ticks are competent vectors of the VA-U.S.-T.orientalis Ikeda strain. This data provides important information for the U.S. cattle industry regarding the potential spread of this parasite and the necessity of enhanced surveillance and control measures.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04659-9.

Borrelia burgdorferi infection modifies protein content in saliva of Ixodes scapularis nymphs

BACKGROUND

Lyme disease (LD) caused by Borrelia burgdorferi is the most prevalent tick-borne disease. There is evidence that vaccines based on tick proteins that promote tick transmission of B. burgdorferi could prevent LD. As Ixodes scapularis nymph tick bites are responsible for most LD cases, this study sought to identify nymph tick saliva proteins associated with B. burgdorferi transmission using LC-MS/MS. Tick saliva was collected using a non-invasive method of stimulating ticks (uninfected and infected: unfed, and every 12 h during feeding through 72 h, and fully-fed) to salivate into 2% pilocarpine-PBS for protein identification using LC-MS/MS.

RESULTS

We identified a combined 747 tick saliva proteins of uninfected and B. burgdorferi infected ticks that were classified into 25 functional categories: housekeeping-like (48%), unknown function (18%), protease inhibitors (9%), immune-related (6%), proteases (8%), extracellular matrix (7%), and small categories that account for <5% each. Notably, B. burgdorferi infected ticks secreted high number of saliva proteins (n=645) than uninfected ticks (n=376). Counter-intuitively, antimicrobial peptides, which function to block bacterial infection at tick feeding site were suppressed 23-85 folds in B. burgdorferi infected ticks. Similar to glycolysis enzymes being enhanced in mammalian cells exposed to B. burgdorferi : eight of the 10-glycolysis pathway enzymes were secreted at high abundance by B. burgdorferi infected ticks. Of significance, rabbits exposed to B. burgdorferi infected ticks acquired potent immunity that caused 40-60% mortality of B. burgdorferi infected ticks during the second infestation compared to 15-28% for the uninfected. This might be explained by ELISA data that show that high expression levels of immunogenic proteins in B. burgdorferi infected ticks.

CONCLUSION

Data here suggest that B. burgdorferi infection modified protein content in tick saliva to promote its survival at the tick feeding site. For instance, enzymes; copper/zinc superoxide dismutase that led to production of H2O2 that is toxic to B. burgdorferi were suppressed, while, catalase and thioredoxin that neutralize H2O2, and pyruvate kinase which yields pyruvate that protects Bb from H2O2 killing were enhanced. We conclude data here is an important resource for discovery of effective antigens for a vaccine to prevent LD.

Iripin-3, a New Salivary Protein Isolated From Ixodes ricinus Ticks, Displays Immunomodulatory and Anti-Hemostatic Properties In Vitro

Tick saliva is a rich source of pharmacologically and immunologically active molecules. These salivary components are indispensable for successful blood feeding on vertebrate hosts and are believed to facilitate the transmission of tick-borne pathogens. Here we present the functional and structural characterization of Iripin-3, a protein expressed in the salivary glands of the tick Ixodes ricinus, a European vector of tick-borne encephalitis and Lyme disease. Belonging to the serpin superfamily of protease inhibitors, Iripin-3 strongly inhibited the proteolytic activity of serine proteases kallikrein and matriptase. In an in vitro setup, Iripin-3 was capable of modulating the adaptive immune response as evidenced by reduced survival of mouse splenocytes, impaired proliferation of CD4+ T lymphocytes, suppression of the T helper type 1 immune response, and induction of regulatory T cell differentiation. Apart from altering acquired immunity, Iripin-3 also inhibited the extrinsic blood coagulation pathway and reduced the production of pro-inflammatory cytokine interleukin-6 by lipopolysaccharide-stimulated bone marrow-derived macrophages. In addition to its functional characterization, we present the crystal structure of cleaved Iripin-3 at 1.95 Å resolution. Iripin-3 proved to be a pluripotent salivary serpin with immunomodulatory and anti-hemostatic properties that could facilitate tick feeding via the suppression of host anti-tick defenses. Physiological relevance of Iripin-3 activities observed in vitro needs to be supported by appropriate in vivo experiments.

The Central Role of Salivary Metalloproteases in Host Acquired Resistance to Tick Feeding

During feeding on vertebrate hosts, ticks secrete saliva composed of a rich cocktail of bioactive molecules modulating host immune responses. Although most of the proteinaceous fraction of tick saliva is of little immunogenicity, repeated feeding of ticks on mammalian hosts may lead to impairment of tick feeding, preventing full engorgement. Here, we challenged rabbits with repeated feeding of both Ixodes ricinus nymphs and adults and observed the formation of specific antibodies against several tick salivary proteins. Repeated feeding of both I. ricinus stages led to a gradual decrease in engorged weights. To identify the salivary antigens, isolated immunoglobulins from repeatedly infested rabbits were utilized for a protein pull-down from the saliva of pilocarpine-treated ticks. Eluted antigens were first identified by peptide mass fingerprinting with the aid of available I. ricinus salivary gland transcriptomes originating from early phases of tick feeding. To increase the authenticity of immunogens identified, we also performed, for the first time, de novo assembly of the sialome from I. ricinus females fed for six days, a timepoint used for pilocarpine-salivation. The most dominant I. ricinus salivary immunogens identified in our study were zinc-dependent metalloproteases of three different families. To corroborate the role of metalloproteases at the tick/host interface, we fed ticks micro-injected with a zinc metalloprotease inhibitor, phosphoramidon, on a rabbit. These ticks clearly failed to initiate feeding and to engorge. However, neither feeding to ticks immune blood of repeatedly infested rabbits, nor phosphoramidon injection into ticks, prevented their engorgement when fed in vitro on an artificial membrane system. These data show that Zn metalloproteases play a decisive role in the success of tick feeding, mediated by complex molecular interactions between the host immune, inflammatory, and hemostatic processes, which are absent in in vitro feeding. This basic concept warrants further investigation and reconsideration of the current strategies towards the development of an effective “anti-tick” vaccine.

Tick salivary gland transcriptomics and proteomics

'Omics' technologies have facilitated the identification of hundreds to thousands of tick molecules that mediate tick feeding and play a role in the transmission of tick-borne diseases. Deep sequencing methodologies have played a key role in this knowledge accumulation, profoundly facilitating the study of the biology of disease vectors lacking reference genomes. For example, the nucleotide sequences of the entire set of tick salivary effectors, the so-called tick 'sialome', now contain at least one order of magnitude more transcript sequences compared to similar projects based on Sanger sequencing. Tick feeding is a complex and dynamic process, and while the dynamic 'sialome' is thought to mediate tick feeding success, exactly how transcriptome dynamics relate to tick-host-pathogen interactions is still largely unknown. The identification and, importantly, the functional analysis of the tick 'sialome' is expected to shed light on this 'black box'. This information will be crucial for developing strategies to block pathogen transmission, not only for anti-tick vaccine development but also the discovery and development of new, pharmacologically active compounds for human diseases.

Proteomic Analysis of Exosome-Like Vesicles Isolated From Saliva of the Tick Haemaphysalis longicornis

Extracellular vesicles (EVs), are considered as vehicles of cellular communication. Parasites usually release EVs in their excretory-secretory products to modulate host environment. However, little is known about the secretion of EVs by ticks. In this study, we show for the first time that the tick Haemaphysalis longicornis secretes EVs in saliva that resembles exosomes. EVs were purified from pilocarpine induced saliva of partially engorged H. longicornis ticks. Electron microscopy analysis revealed the presence of exosome-like vesicles with a size of 100 nm. Proteomic analysis by LC-MS/MS identified a total of 356 proteins in tick-derived EVs. Proteome data of tick-derived EVs was validated by Western blot analysis. Immunodetection of Hsp70 and GAPDH proteins indicated that the proteomics data of tick-derived EVs were highly reliable. Bioinformatics analysis (Gene Ontology) indicated association of certain biological and molecular functions with proteins which may be helpful during tick development. Likewise, KEGG database revealed involvement of vesicular proteins in proton transport, detoxification, ECM-receptor interaction, ribosome, RNA transport, ABC transporters, and oxidative phosphorylation. The results of this study provide evidence that EVs are being secreted in tick saliva and suggest that tick saliva-derived EVs could play important roles in host-parasite relationships. Moreover, EVs could be a useful tool in development of vaccines or therapeutics against ticks.

Quantitative Visions of Reality at the Tick-Host Interface: Biochemistry, Genomics, Proteomics, and Transcriptomics as Measures of Complete Inventories of the Tick Sialoverse

Species have definitive genomes. Even so, the transcriptional and translational products of the genome are dynamic and subject to change over time. This is especially true for the proteins secreted by ticks at the tick-host feeding interface that represent a complex system known as the sialoverse. The sialoverse represent all of the proteins derived from tick salivary glands for all tick species that may be involved in tick-host interaction and the modulation of the host's defense mechanisms. The current study contemplates the advances made over time to understand and describe the complexity present in the sialoverse. Technological advances at given periods in time allowed detection of functions, genes, and proteins enabling a deeper insight into the complexity of the sialoverse and a concomitant expansion in complexity with as yet, no end in sight. The importance of systematic classification of the sialoverse is highlighted with the realization that our coverage of transcriptome and proteome space remains incomplete, but that complete descriptions may be possible in the future. Even so, analysis and integration of the sialoverse into a comprehensive understanding of tick-host interactions may require further technological advances given the high level of expected complexity that remains to be uncovered.

Integrated analysis of sialotranscriptome and sialoproteome of the brown dog tick Rhipicephalus sanguineus (s.l.): Insights into gene expression during blood feeding

Tick salivary glands secrete a complex saliva into their hosts which modulates vertebrate hemostasis, immunity and tissue repair mechanisms. Transcriptomic studies revealed a large number of transcripts coding for structural and secreted protein products in a single tick species. These transcripts are organized in several large families according to their products. Not all transcripts are expressed at the same time, transcription profile switches at intervals, characterizing the phenomenon of "sialome switching". In this work, using transcriptomic and proteomic analysis we explored the sialome of Rhipicephalus sanguineus (s.l.) adult female ticks feeding on a rabbit. The correlations between transcriptional and translational results in the different groups were evaluated, confirming the "sialome switching" and validating the idea that the expression switch may serve as a mechanism of escape from the host immunity. Recombination breakpoints were identified in lipocalin and metalloprotease families, indicating this mechanism could be a possible source of diversity in the tick sialome. Another remarkable observation was the identification of host-derived proteins as a component of tick salivary gland content. These results and disclosed sequences contribute to our understanding of tick feeding biology, to the development of novel anti-tick methods, and to the discovery of novel pharmacologically active products. SIGNIFICANCE: Ticks are a burden by themselves to humans and animals, and vectors of viral, bacterial, protozoal and helminthic diseases. Their saliva has anti-clotting, anti-platelet, vasodilatory and immunomodulatory activities that allows successful feeding and pathogen transmission. Previous transcriptomic studies indicate ticks to have over one thousand transcripts coding for secreted salivary proteins. These transcripts code for proteins of diverse families, but not all are transcribed simultaneously, but rather transiently, in a succession. Here we explored the salivary transcriptome and proteome of the brown dog tick, Rhipicephalus sanguineus. A protein database of over 20 thousand sequences was "de novo" assembled from over 600 million nucleotide reads, from where over two thousand polypeptides were identified by mass spectrometry. The proteomic data was shown to vary in time with the transcription profiles, validating the idea that the expression switch may serve as a mechanism of escape from the host immunity. Analysis of the transcripts coding for lipocalin and metalloproteases indicate their genes to contain signals of breakpoint recombination suggesting a new mechanism responsible for the large diversity in tick salivary proteins. These results and the disclosed sequences contribute to our understanding of the success ticks enjoy as ectoparasites, to the development of novel anti-tick methods, and to the discovery of novel pharmacologically active products.

Changes in Protein Phosphorylation during Salivary Gland Degeneration in Haemaphysalis longicornis

The ticks feed large amount of blood from their hosts and transmit pathogens to the victims. The salivary gland plays an important role in the blood feeding. When the female ticks are near engorgement, the salivary gland gradually loses its functions and begins to rapidly degenerate. In this study, data-independent acquisition quantitative proteomics was used to study changes in the phosphorylation modification of proteins during salivary gland degeneration in Haemaphysalis longicornis. In this quantitative study, 400 phosphorylated proteins and 850 phosphorylation modification sites were identified. Trough RNA interference experiments, we found that among the proteins with changes in phosphorylation, apoptosis-promoting Hippo protein played a role in salivary gland degeneration.

Tick and Host Derived Compounds Detected in the Cement Complex Substance

Ticks are obligate hematophagous arthropods and vectors of pathogens affecting human and animal health worldwide. Cement is a complex protein polymerization substance secreted by ticks with antimicrobial properties and a possible role in host attachment, sealing the feeding lesion, facilitating feeding and pathogen transmission, and protection from host immune and inflammatory responses. The biochemical properties of tick cement during feeding have not been fully characterized. In this study, we characterized the proteome of Rhipicephalus microplus salivary glands (sialome) and cement (cementome) together with their physicochemical properties at different adult female parasitic stages. The results showed the combination of tick and host derived proteins and other biomolecules such as α-Gal in cement composition, which varied during the feeding process. We propose that these compounds may synergize in cement formation, solidification and maintenance to facilitate attachment, feeding, interference with host immune response and detachment. These results advanced our knowledge of the complex tick cement composition and suggested that tick and host derived compounds modulate cement properties throughout tick feeding.

Identification of proteins from the secretory/excretory products (SEPs) of the branchiuran ectoparasite Argulus foliaceus (Linnaeus, 1758) reveals unique secreted proteins amongst haematophagous ecdysozoa

BACKGROUND

It is hypothesised that being a blood-feeding ectoparasite, Argulus foliaceus (Linnaeus, 1758), uses similar mechanisms for digestion and host immune evasion to those used by other haematophagous ecdysozoa, including caligid copepods (e.g. sea louse). We recently described and characterised glands associated with the feeding appendages of A. foliaceus using histological techniques. The work described in the present study is the first undertaken with the objective of identifying and partially characterising the components secreted from these glands using a proteomic approach.

METHODS

Argulus foliaceus parasites were sampled from the skin of rainbow trout (Oncorhynchus mykiss), from Loch Fad on the Isle of Bute, Scotland, UK. The proteins from A. foliaceus secretory/excretory products (SEPs) were collected from the supernatant of artificial freshwater conditioned with active adult parasites (n = 5-9 per ml; n = 560 total). Proteins within the SEPs were identified and characterised using LC-ESI-MS/MS analysis. Data are available via ProteomeXchange with identifier PXD016226.

RESULTS

Data mining of a protein database translated from an A. foliaceus dataset using ProteinScape allowed identification of 27 predicted protein sequences from the A. foliaceus SEPs, each protein matching the criteria of 2 peptides with at least 4 contiguous amino acids. Nine proteins had no matching sequence through OmicsBox (Blast2GO) analysis searches suggesting that Argulus spp. may additionally have unique proteins present in their SEPs. SignalP 5.0 software, identified 13 proteins with a signal sequence suggestive of signal peptides and supportive of secreted proteins being identified. Notably, the functional characteristics of identified A. foliaceus proteins/domains have also been described from the salivary glands and saliva of other blood-feeding arthropods such as ticks. Identified proteins included: transporters, peroxidases, metalloproteases, proteases and serine protease inhibitors which are known to play roles in parasite immune evasion/induction (e.g. astacin), immunomodulation (e.g. serpin) and digestion (e.g. trypsin).

CONCLUSIONS

To our knowledge, the present study represents the first proteomic analysis undertaken for SEPs from any branchiuran fish louse. Here we reveal possible functional roles of A. foliaceus SEPs in digestion and immunomodulation, with a number of protein families shared with other haematophagous ectoparasites. A number of apparently unique secreted proteins were identified compared to other haematophagous ecdysozoa.

Time-resolved proteomic profile of Amblyomma americanum tick saliva during feeding

Amblyomma americanum ticks transmit more than a third of human tick-borne disease (TBD) agents in the United States. Tick saliva proteins are critical to success of ticks as vectors of TBD agents, and thus might serve as targets in tick antigen-based vaccines to prevent TBD infections. We describe a systems biology approach to identify, by LC-MS/MS, saliva proteins (tick = 1182, rabbit = 335) that A. americanum ticks likely inject into the host every 24 h during the first 8 days of feeding, and towards the end of feeding. Searching against entries in GenBank grouped tick and rabbit proteins into 27 and 25 functional categories. Aside from housekeeping-like proteins, majority of tick saliva proteins belong to the tick-specific (no homology to non-tick organisms: 32%), protease inhibitors (13%), proteases (8%), glycine-rich proteins (6%) and lipocalins (4%) categories. Global secretion dynamics analysis suggests that majority (74%) of proteins in this study are associated with regulating initial tick feeding functions and transmission of pathogens as they are secreted within 24–48 h of tick attachment. Comparative analysis of the A. americanum tick saliva proteome to five other tick saliva proteomes identified 284 conserved tick saliva proteins: we speculate that these regulate critical tick feeding functions and might serve as tick vaccine antigens. We discuss our findings in the context of understanding A. americanum tick feeding physiology as a means through which we can find effective targets for a vaccine against tick feeding.

The lone star tick, Amblyomma americanum, is a medically important species in US that transmits 5 of the 16 reported tick-borne disease agents. Most recently, bites of this tick were associated with red meat allergies in humans. Vaccination of animals against tick feeding has been shown to be a sustainable and an effective alternative to current acaricide based tick control method which has several limitations. The pre-requisite to tick vaccine development is to understand the molecular basis of tick feeding physiology. Toward this goal, this study has identified proteins that A. americanum ticks inject into the host at different phases of its feeding cycle. This data set has identified proteins that A. americanum inject into the host within 24–48 h of feeding before it starts to transmit pathogens. Of high importance, we identified 284 proteins that are present in saliva of other tick species, which we suspect regulate important role(s) in tick feeding success and might represent rich source target antigens for a tick vaccine. Overall, this study provides a foundation to understand the molecular mechanisms regulating tick feeding physiology.

Caracterization of glutathione S-transferase of Dermacantor marginatus and effect of the recombinant antigen as a potential anti-tick vaccine

Dermacentor marginatus is one of the main tick species in northwestern China, and is a vector of various tick-borne pathogens. Tick control method largely depends on chemical agents, but the disadvantages of using such approach would cause environmental damage and the risk of developing tick resistance to acaricides. Vaccination of tick protective antigen is an eco-friendly approach which is an alternative and promising method to mitigate tick infestation in livestock. In the study, a mu-class glutathione S-transferase (GST) sequence of D. marginatus was cloned and the recombinant protein (rDmGST) was expressed. Transcriptional level of the GST was measured together with native GST activity of the tick. Finally, A vaccine trial on rabbits against D. marginatus was proceeded to evaluate the anti-tick effect of rDmGST. Results reveled that the CDs of the D. margiantus glutathione S-transferase mu 1 gene has 669 base pair nucleotide sequence encoding a 223 amino acid. The deduced GST protein sequence had over 95 % similarity with that of D. variabilis. The rDmGST was efficiently expressed soluble and purified by His trap affinity chromatography. Enzyme activity of native GST and transcriptional profiles of the GST showed up-regulation in different stages and organs of D. marginaus during blood feeding. Polyclonal antibody reacted with rDmGST in Western blotting. Tick challenge on rDmGST inoculated rabbits showed reductions in adult female engorgement rate, total egg mass and egg hatching rate with an overall vaccine efficacy of 43.69 %. The results of the experiment indicated the GST has potential value to be an effective protective antigen of D. marginatus.

A Peroxiredoxin From the Haemaphysalis longicornis Tick Affects Langat Virus Replication in a Hamster Cell Line

Ticks are hematophagous arthropods, and their blood feeding on vertebrate hosts is essential for their development. The vertebrate blood contains high levels of free iron that can react with oxygen in ticks, resulting in the production of hydrogen peroxide (H₂O₂), one of the reactive oxygen species. Peroxiredoxins (Prxs), H₂O₂-scavenging enzymes, take on an important role in the ticks' oxidative stress coping mechanism. Ticks also transmit several disease-causing pathogens, including tick-borne encephalitis virus (TBEV), in animals and humans. Therefore, the control of ticks and tick-borne pathogens is a key issue that needs to be addressed. Infection with an arthropod-borne flavivirus is known to induce oxidative stress in insect cells. We hypothesize that vector-derived Prxs could have an effect on the infection and/or replication of flaviviruses in the hosts, since ticks Prxs are possibly transmitted from ticks to their hosts. In this study, we established stable strains of baby hamster kidney (BHK) cells expressing two types of H₂O₂-scavenging Prxs from the hard tick Haemaphysalis longicornis (BHK-HlPrx and BHK-HlPrx2 cells). Although the infection of TBEV surrogate Langat virus (LGTV) did not induce H₂O₂ production in normal BHK cells, the mortality rate and the virus titer of LGTV infected BHK-HlPrx cells increased. In addition, HlPrx proteins in BHK cells can facilitate LGTV replication in cells, while HlPrx2 proteins in BHK cells cannot. The results also demonstrated that this facilitation of LGTV replication by the 1-Cys Prx in the BHK cells is not by scavenging H₂O₂ but by an unknown mechanism. In order to understand this mechanism, more studies using tick-derived cells and ticks are necessary.

Salivary gland proteome analysis of developing adult female Haemaphysalis longicornis ticks: molecular motor and TCA cycle-related proteins play an important role throughout development

Background

Ticks are notorious blood-feeding arthropods that can spread a variety of deadly diseases. The salivary gland is an important organ for ticks to feed on blood, and this organ begins to develop rapidly when ixodid ticks suck blood. When these ticks reach a critical weight, the salivary glands stop developing and begin to degenerate. The expression levels of a large number of proteins during the development and degeneration of salivary glands change, which regulate the biological functions of the salivary glands. Furthermore, to the best of our knowledge, there are only a few reports on the role of molecular motor and TCA cycle-related proteins in the salivary glands of ticks.

Results

We used iTRAQ quantitative proteomics to study the dynamic changes in salivary gland proteins in female Haemaphysalis longicornis at four feeding stages: unfed, partially fed, semi-engorged and engorged. Using bioinformatics methods to analyze the dynamic changes of a large number of proteins, we found that molecular motor and TCA cycle-related proteins play an important role in the physiological changes of the salivary glands. The results of RNAi experiments showed that when dynein, kinesin, isocitrate dehydrogenase and citrate synthase were knocked down independently, the weight of the engorged female ticks decreased by 63.5%, 54.9%, 42.6% and 48.6%, respectively, and oviposition amounts decreased by 83.1%, 76.0%, 50.8%, and 55.9%, respectively, and the size of type III acini of females salivary glands decreased by 35.6%, 33.3%, 28.9%, and 20.0%, respectively.

Conclusions

The results showed that the expression of different types of proteins change in different characteristics in salivary glands during the unfed to engorged process of female ticks. Corresponding expression changes of these proteins at different developmental stages of female ticks are very important to ensure the orderly development of the organ. By analyzing these changes, some proteins, such as molecular motor and TCA cycle-related proteins, were screened and RNAi carried out. When these mRNAs were knocked down, the female ticks cannot develop normally. The research results provide a new protein target for the control of ticks and tick-borne diseases.

Molecular cloning, expression and impact of ribosomal protein S-27 silencing in Haemaphysalis longicornis (Acari: Ixodidae)

Ticks, obligatory blood-feeding arthropods, are a major pathogen vector in humans and animals worldwide. Anti-tick vaccines are an exciting alternative to chemical acaricides for controlling these disease-transmitting vectors. However, identification of protective antigens for anti-tick vaccine development is challenging. Different ribosomal proteins play multifunctional roles in tick survival and feeding. Here, we first report the cloning and molecular characterization of ribosomal protein S27 (RPS-27) from the hard tick Haemaphysalis longicornis. We identified a complete open reading frame (ORF) of RPS-27: a 255-bp (base pair) cDNA encoding a mature protein of 84 amino-acid residues with a 9.4-kDa predicted molecular mass. Amino-acid sequence analysis revealed that RPS-27 was highly conserved among different tick and vertebrate animals with identity ranges of 97-98% and 60-85%, respectively. Phylogenetic tree analysis showed that RPS-27 from different tick species clustered together. Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that the RPS-27 mRNA transcript was expressed in all life stages. At the tissue level, it was more highly expressed in the salivary gland than in the midgut for both the fed and unfed conditions, which indicates a role for RPS-27 in tick feeding. In vitro analysis showed that recombinant RPS-27 (10-RPS-27) was successfully expressed in a pGEMEX-2 vector with an estimated 45-kDa molecular mass. The functional importance of RPS-27 was determined by gene silencing through RNA interference (RNAi). RPS-27 silencing showed a significant (P < 0.05) reduction of feeding abilityand engorgement weight after the blood meal in both nymph and adult female ticks and also significantly (P < 0.05) reduced molting rate in nymph. In addition, RPS-27 silencing in eggs led to abnormalities in shape and hatching. Taken together, our results suggest that RPS-27 is an important molecule that plays multiple roles in the tick life cycle including in both feeding and reproduction. Therefore, RPS-27 is an exciting target for future tick control strategies.

Amblyomma americanum serpin 27 (AAS27) is a tick salivary anti-inflammatory protein secreted into the host during feeding

Ticks successfully feed and transmit pathogens by injecting pharmacological compounds in saliva to thwart host defenses. We have previously used LC-MS/MS to identify proteins that are present in saliva of unfed Amblyomma americanum ticks that were exposed to different hosts. Here we show that A. americanum serine protease inhibitor (serpin) 27 (AAS27) is an immunogenic saliva protein that is injected into the host within the first day of tick feeding and is an anti-inflammatory protein that might act by blocking plasmin and trypsin functions. Although AAS27 is injected into the host throughout tick feeding, qRT-PCR and western blotting analyses indicate that the respective transcript and protein are present in high amounts within the first 24 h of tick feeding. Biochemical screening of Pichia pastoris-expressed recombinant (r) AAS27 against mammalian proteases related to host defense shows it is an inhibitor of trypsin and plasmin, with stoichiometry of inhibition indices of 3.5 and 3.8, respectively. Consistent with typical inhibitory serpins, rAAS27 formed heat- and SDS-stable irreversible complexes with both proteases. We further demonstrate that rAAS27 inhibits trypsin with ka of 6.46 ± 1.24 x 104 M-1 s-1, comparable to serpins of other tick species. We show that native AAS27 is part of the repertoire of proteins responsible for the inhibitory activity against trypsin in crude tick saliva. AAS27 is likely utilized by the tick to evade the hosts inflammation defense since rAAS27 blocks both formalin and compound 48/80-induced inflammation in rats. Tick immune sera of rabbits that had acquired resistance against tick feeding following repeated infestations with A. americanum or Ixodes scapularis ticks reacts with rAAS27. Of significant interest, antibody to rAAS27 blocks this serpin inhibitory functions. Taken together, we conclude that AAS27 is an anti-inflammatory protein secreted into the host during feeding and may represent a potential candidate for development of an anti-tick vaccine.

Proteomic analysis of saliva from partially and fully engorged adult female Rhipicephalus microplus (Acari: Ixodidae)

Rhipicephalus microplus salivary gland secretes a number of complex bioactive proteins during feeding. These components are important in feeding and affect anti-coagulation, anti-inflammation and also have anti-microbial effects. In this study, tick saliva was collected from partially engorged female (PEF) and fully engorged female (FEF) ticks. Liquid chromatography tandem-mass spectrometry (LC-MS/MS) and isobaric tags for relative and absolute quantification (iTRAQ) were used to identify and quantify R. microplus salivary proteins. A total of 322 unique peptides were detected and 151 proteins were characterized in both PEF and FEF. Of these, 41 proteins are considered as high-confidence proteins. Fifteen high-confidence proteins were upregulated and six high-confidence proteins were downregulated (p < 0.05; PEF:FEF ratio ≥ 1.2 or PEF:FEF ratio ≤ 0.83); 17 high-confidence proteins are slightly changed (PEF:FEF ratio > 0.83 and < 1.2). These high-confidence proteins are involved in several physiological roles, including egg development, transportation of proteins, immunity and anti-microorganism, anti-coagulant, and adhesion. In comparison with PEF, the number of upregulated proteins exceeded the number of proteins downregulated. Salivary protein may be induced by the blood-meal and these proteins contribute to successful feeding.

The Use of Tick Salivary Proteins as Novel Therapeutics

The last three decades of research into tick salivary components have revealed several proteins with important pharmacological and immunological activities. Two primary interests have driven research into tick salivary secretions: the search for suitable pathogen transmission blocking or “anti-tick” vaccine candidates and the search for novel therapeutics derived from tick salivary components. Intensive basic research in the field of tick salivary gland transcriptomics and proteomics has identified several major protein families that play important roles in tick feeding and overcoming vertebrate anti-tick responses. Moreover, these families contain members with unrealized therapeutic potential. Here we review the major tick salivary protein families exploitable in medical applications such as immunomodulation, inhibition of hemostasis and inflammation. Moreover, we discuss the potential, opportunities, and challenges in searching for novel tick-derived drugs.

Chemical Equilibrium at the Tick-Host Feeding Interface:A Critical Examination of Biological Relevance in Hematophagous Behavior

Ticks secrete hundreds to thousands of proteins into the feeding site, that presumably all play important functions in the modulation of host defense mechanisms. The current review considers the assumption that tick proteins have functional relevance during feeding. The feeding site may be described as a closed system and could be treated as an ideal equilibrium system, thereby allowing modeling of tick-host interactions in an equilibrium state. In this equilibrium state, the concentration of host and tick proteins and their affinities will determine functional relevance at the tick-host interface. Using this approach, many characterized tick proteins may have functional relevant concentrations and affinities at the feeding site. Conversely, the feeding site is not an ideal closed system, but is dynamic and changing, leading to possible overestimation of tick protein concentration at the feeding site and consequently an overestimation of functional relevance. Ticks have evolved different possible strategies to deal with this dynamic environment and overcome the barrier that equilibrium kinetics poses to tick feeding. Even so, cognisance of the limitations that equilibrium binding place on deductions of functional relevance should serve as an important incentive to determine both the concentration and affinity of tick proteins proposed to be functional at the feeding site.

Message in a vesicle - trans-kingdom intercommunication at the vector-host interface

Vector-borne diseases cause over 700,000 deaths annually and represent 17% of all infectious illnesses worldwide. This public health menace highlights the importance of understanding how arthropod vectors, microbes and their mammalian hosts interact. Currently, an emphasis of the scientific enterprise is at the vector-host interface where human pathogens are acquired and transmitted. At this spatial junction, arthropod effector molecules are secreted, enabling microbial pathogenesis and disease. Extracellular vesicles manipulate signaling networks by carrying proteins, lipids, carbohydrates and regulatory nucleic acids. Therefore, they are well positioned to aid in cell-to-cell communication and mediate molecular interactions. This Review briefly discusses exosome and microvesicle biogenesis, their cargo, and the role that nanovesicles play during pathogen spread, host colonization and disease pathogenesis. We then focus on the role of extracellular vesicles in dictating microbial pathogenesis and host immunity during transmission of vector-borne pathogens.

A microRNA profile of saliva and role of miR-375 in Haemaphysalis longicornis (Ixodida: Ixodidae)

Background

Tick saliva contains many bioactive molecules that are involved in attachment to the host, blood-feeding and transmission of pathogens. MicroRNAs (miRNAs) are a class of short non-coding RNAs with a length of 19–24 nucleotides. They act as regulators of gene expression by binding to their target mRNA at the post-transcriptional level and control a variety of cellular functions, including regulation of growth, metabolism and development. The detection and characterizations of miRNAs from tick saliva may help explain the molecular mechanisms involved in the interaction between ticks, pathogens and hosts. They may also contribute to the discovery of vaccines, which can control ticks and the pathogens they transmit.

Results

An RNA library was generated from the saliva of fed adult Haemaphysalis longicornis ticks, containing 17.4 million clean reads of 18–30 nucleotides. Overall, 319 known miRNAs and 1 novel miRNA were found. The 10 most abundantly expressed miRNAs present in tick saliva were miR-100_2, miR-315, miR-184_1, miR-100-5p_2, miR-5307, miR-184-3p_3, Let-7-5p_6, miR-71_5, miR-1-3p_6 and miR-10-5p_2. miR-375, one of the abundantly expressed, was subjected to quantitative real-time PCR analysis (qRT-PCR) in various tick developmental stages, as well as in different tissues isolated from adult ticks. The expression of miR-375 in different tick development stages was highest in unfed nymphs and lowest in the egg stage. In the tissues of adult ticks, miR-375 was most highly expressed in the salivary gland. To investigate the possible role of miR-375, Ant-375 was used to inhibit the miR-375. The treated group (Ant-375) had a reduced number of eggs (t₍₁₀₎ = 2.652, P = 0.0242), eggs that were partially desiccated, and reduced egg hatchability (t₍₁₀₎ = 2.272, P = 0.044) compared to Ms-Ant and the non-injected control.

Conclusions

This is the first study to investigate the miRNA profile in tick saliva and the role of miR-375 in H. longicornis. The identification and characterization of miRNA in tick saliva may help to reveal the molecular mechanisms of interactions among ticks, pathogens and hosts, and suggest new vaccine strategies to control tick-borne diseases.

Electronic supplementary material

The online version of this article (10.1186/s13071-019-3318-x) contains supplementary material, which is available to authorized users.

Secretome Analysis and In Planta Expression of Salivary Proteins Identify Candidate Effectors from the Brown Planthopper Nilaparvata lugens

The brown planthopper (BPH), Nilaparvata lugens (Stål), is a phloem sap-feeding insect. During feeding on rice plants, BPH secretes salivary proteins with potential effector functions, which may play a critical role in the plant-insect interactions. However, a limited number of BPH effector proteins have been identified to date. Here, we sequenced the salivary gland transcriptomes of five BPH populations and subsequently established a N. lugens secretome consisting of 1,140 protein-encoding genes. Secretome analysis revealed the presence of both conserved and rapidly evolving salivary proteins. A screen for potential effectors that elicit responses in the plant was performed via the transient expression analysis of 64 BPH salivary proteins in Nicotiana benthamiana leaves and rice protoplasts. The salivary proteins Nl12, Nl16, Nl28, and Nl43 induced cell death, whereas Nl40 induced chlorosis and Nl32 induced a dwarf phenotype in N. benthamiana, indicating effector properties of these proteins. Ectopic expression of the six salivary proteins in N. benthamiana upregulated expression of defense-related genes and callose deposition. Tissue expression analysis showed a higher expression level of the six candidate effectors in salivary glands than in other tissues. Subcellular localization and analysis of the domain required for cell death showed a diverse structure of the six effectors. Nl28, Nl40, and Nl43 are N. lugens specific; in contrast, Nl12, Nl16, and Nl32 are conserved among insects. The Nl40 family has numerous isoforms produced by alternative splicing, exemplifying rapid evolution and expansion of effector proteins in the BPH. Our results suggest a potential large effector repertoire in BPH and a higher level of effector conservation exist in BPH compared with that in plant pathogens.

Comprehensive Analysis of the Global Protein Changes That Occur During Salivary Gland Degeneration in Female Ixodid Ticks Haemaphysalis longicornis

Ticks are notorious blood-sucking arthropods that can spread a variety of pathogens and cause great harm to the health of humans, wildlife and domestic animals. The salivary glands of female ticks degenerate rapidly when the ticks reach critical weight or become engorged, which can be caused by hormones and by the synergistic effects of multiple proteins. To explore the complex molecular mechanisms of salivary gland degeneration in ticks, this study applies iTRAQ quantitative proteomic technology for the first time to study changes in protein expression in the salivary glands of female Haemaphysalis longicornis during the process of degeneration and to search for proteins that play an important role in salivary gland degeneration. It was found that the expression of some proteins associated with energy production was continuously down-regulated during salivary gland degeneration, while some proteins associated with DNA or protein degradation were consistently up-regulated. Furthermore, the expression of some proteins related to cell apoptosis or autophagy was also changed. These proteins were knocked down by RNAi to observe the phenotypic and physiological changes in female ticks. The results showed that the time required for engorgement and the mortality rates of the female ticks increased after RNAi of F0F1-type ATP synthase, NADH-ubiquinone oxidoreductase, cytochrome C, or apoptosis-inducing factor (AIF). The corresponding engorged weights, oviposition amounts, and egg hatching rates of the female ticks decreased after RNAi. Interference of the expression of AIF in engorged ticks by RNAi showed that the degeneration of salivary glands of female ticks was slowed down.

Host-specific expression of Ixodes scapularis salivary genes

Ixodes scapularis vectors several pathogens including Borrelia burgdorferi, the agent of Lyme disease. Nymphal and larval stages, and the pathogens transmitted by I. scapularis are maintained in a zoonotic cycle involving rodent reservoir hosts, predominantly Peromyscus leucopus. Humans are not reservoir hosts, however, accidental encounters of infected ticks with humans, results in pathogen transmission to the human host. Laboratory models of non-reservoir hosts such as guinea pigs develop a strong immune response to tick salivary proteins and reject ticks upon repeated tick infestations. Anecdotal and scientific evidence suggests that humans that get frequent tick bites might also develop resistance to ticks. Mus musculus, the laboratory model of natural host, does not develop resistance to I. scapularis upon repeated tick infestations. Addressing this dichotomy in vector-host interaction, we present data that suggest that the salivary transcriptome and proteome composition is different in mouse and guinea pig-fed I. scapularis, and that these differences might contribute to differences in host immune responses. These findings reveal a new insight into vector-host interactions and offer a functional paradigm to better understand the phenomenon of acquired tick-resistance.