Functional characterization of candidate antigens of Hyalomma anatolicum and evaluation of its cross-protective efficacy against Rhipicephalus microplus

Vaccinomics-driven selection and validation of protective salivary antigens from the argasid tick Ornithodoros moubata

Ornithodoros moubata serves as primary vector of African swine fever and tick-borne human relapsing fever in Africa. Developing an effective vaccine targeting this argasid tick would significantly enhance disease control measures. To identify potential vaccine targets, the recently characterised sialome of O. moubata was analysed using a vaccinomics approach. This led to the identification of a set of salivary secreted proteins predicted to be antigenic and implicated in the regulation of blood-feeding and host immune defences. The objective of this study was to evaluate the protective potential of seven of these proteins, namely Complement inhibitor (OmCI), Cyclophilin (OmCPH), Hypothetical protein 275 (OmH275), Peroxiredoxin (OmPXR), Calreticulin (OmCLR), Neprilysin (OmNEP), and Superoxide dismutase (OmSOD). These candidates were produced as recombinant proteins, formulated with Montanide adjuvant, and administered individually to different groups of rabbits. Adult and nymphal-3 specimens of O. moubata and Ornithodoros erraticus (the Mediterranean vector of ASF and TBRF) were allowed to feed on the vaccinated rabbits, and the ticks' feeding performance, survival, and reproduction rates were assessed. OmH275, OmPXR, OmCPH, and OmCLR conferred 20 %-32 % protection against O. moubata and/or O. erraticus, whereas OmCI, OmNEP, and OmSOD afforded 2 %-17 % protection against one or both tick species. Consequently, OmH275, OmPXR, OmCPH, and OmCLR were deemed suitable candidates for inclusion in the development of anti-Ornithodoros cocktail vaccines, while OmCI, OmNEP, and OmSOD were considered less promising for tick vaccine development. These findings validate the vaccinomics pipeline, identifying four of seven candidates (57 %) as viable antigens for Ornithodoros tick vaccines.

Cocktail vaccine for the management of Hyalomma anatolicum and Rhipicephalus microplus

Introduction

Globally, ticks rank second only to mosquitoes as vectors of deadly pathogens affecting humans and first in transmitting animal pathogens, presenting a significant challenge to human wellness and sustainability of livestock-based industries. Traditional tick control via chemical acaricides impacts on the environment and has led to the emergence of multi-acaricide-resistant tick populations. Use of immunoprophylactic, along with other components of integrated tick management, holds the potential to mitigate tick infestations in a sustainable manner. To control multi-species tick infestations, the concept of a cocktail vaccine comprising of more than one antigens has emerged as a viable solution due to the inconsistent efficacy of single antigen-based immunization protocol.

Methods

In this study, a dual antigen cocktail immunization protocol was developed targeting ferritin2 (FER2) and tropomyosin (TPM) proteins, which are associated with ticks' essential cellular and physiological functions, like blood iron homeostasis and muscle contractions.

Results

Dual gene silencing of FER2 and TPM genes in Hyalomma anatolicum resulted in a 75.3% reduction in infested ticks, a 95.4% decrease in egg masses, and a complete loss of egg hatching when compared to control ticks. Microscopically, an altered ovarian cellular architecture, marked by vacuolation and reduced nucleus-to-cytoplasmic ratio were noted in the gene knocked down ticks. An immunization with cocktails of 300 µg dose of each protein, rHaFER2 and rHaTPM was standardized in a rat model and was used to immunize cross-bred (Bos indicus x B. taurus) male cattle with Montanide ISA 50V2 adjuvant on days 0, 28, and 49. A significant (p < 0.001) IgG and IgG2 antibody response was observed in the immunized animals with high IgG levels sustained until day 119 post-primary immunization, showing a 4.1-fold increase over the pre-immunization period. The animals were challenged with larvae and adults of H. anatolicum and larvae of Rhipicephalus microplus. Immunization with the cocktail antigen resulted an efficacy of 70% and 76% against H. anatolicum larvae and adults, respectively, and 54% against R. microplus infestations. Compared to single-antigen immunization, the immunization with cocktail antigens demonstrated higher protection against R. microplus and H. anatolicum ticks. The results advance the development of cocktail vaccines to control multiple tick species.

Interventions for the control of Crimean-Congo hemorrhagic fever and tick vectors

Crimean-Congo hemorrhagic fever (CCHF) is a zoonotic disease associated with its principal tick vector, Hyalomma spp. with increasing fatal incidence worldwide. Accordingly, CCHF is a World Health Organization-prioritized disease with the absence of effective preventive interventions and approved vaccines or effective treatments. This perspective raised from a multidisciplinary gap analysis considering a One Health approach beneficial for human and animal health and the environment exploring international collaborations, gaps and recommendations.

Human Tick-Borne Diseases and Advances in Anti-Tick Vaccine Approaches: A Comprehensive Review

This comprehensive review explores the field of anti-tick vaccines, addressing their significance in combating tick-borne diseases of public health concern. The main objectives are to provide a brief epidemiology of diseases affecting humans and a thorough understanding of tick biology, traditional tick control methods, the development and mechanisms of anti-tick vaccines, their efficacy in field applications, associated challenges, and future prospects. Tick-borne diseases (TBDs) pose a significant and escalating threat to global health and the livestock industries due to the widespread distribution of ticks and the multitude of pathogens they transmit. Traditional tick control methods, such as acaricides and repellents, have limitations, including environmental concerns and the emergence of tick resistance. Anti-tick vaccines offer a promising alternative by targeting specific tick proteins crucial for feeding and pathogen transmission. Developing vaccines with antigens based on these essential proteins is likely to disrupt these processes. Indeed, anti-tick vaccines have shown efficacy in laboratory and field trials successfully implemented in livestock, reducing the prevalence of TBDs. However, some challenges still remain, including vaccine efficacy on different hosts, polymorphisms in ticks of the same species, and the economic considerations of adopting large-scale vaccine strategies. Emerging technologies and approaches hold promise for improving anti-tick vaccine development and expanding their impact on public health and agriculture.

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.

Protective Efficacy of Multiple Epitope-Based Vaccine against Hyalomma anatolicum, Vector of Theileria annulata and Crimean-Congo Hemorrhagic Fever Virus

Hyalomma anatolicum is the principal vector for Theileria annulata, T. equi, and T. Lestoquardi in animals and the Crimean-Congo hemorrhagic fever virus in humans. Due to the gradual loss of efficacy of the available acaricides against field tick populations, the development of phytoacaricides and vaccines has been considered the two most critical components of the integrated tick management strategies. In the present study, in order to induce both cellular and humoral immune responses in the host against H. anatolicum, two multi-epitopic peptides (MEPs), i.e., VT1 and VT2, were designed. The immune-stimulating potential of the constructs was determined by in silicoinvestigation on allergenicity (non-allergen, antigenic (0.46 and 1.0046)), physicochemical properties (instability index 27.18 and 35.46), as well as the interaction of constructs with TLRs by docking and molecular dynamics analysis. The immunization efficacy of the MEPs mixed with 8% Montanide^TM gel 01 PR against H. anatolicum larvae was determined as 93.3% and 96.9% in VT1- and VT2-immunized rabbits, respectively. Against adults, the efficacy was 89.9% and 86.4% in VT1- and VT2-immunized rabbits, respectively. A significant (p < 0.001) reduction in the anti-inflammatory cytokine (IL-4) and significantly higher IgG response was observed in a VT1-immunized group of rabbits as compared with the response observed in the control group. However, in the case of the VT2-immunized rabbits, an elevated anti-VT2 IgG and pro-inflammatory cytokine (IL-2) (>30 fold) along with a decreased level of anti-inflammatory cytokine IL-4 (0.75 times) was noted. The efficacy of MEP and its potential immune stimulatory responses indicate that it might be useful for tick management.

The many faces of parasite calreticulin

Calreticulin from parasites and its vertebrate hosts share ~50% identity and many of its functions are equally conserved. However, the existing amino acid differences can affect its biological performance. Calreticulin plays an important role in Ca2+ homeostasis and as a chaperone involved in the correct folding of proteins within the endoplasmic reticulum. Outside the endoplasmic reticulum, calreticulin is involved in several immunological functions such as complement inhibition, enhancement of efferocytosis, and immune upregulation or inhibition. Several parasite calreticulins have been shown to limit immune responses and promote infectivity, while others are strong immunogens and have been used for the development of potential vaccines that limit parasite growth. Furthermore, calreticulin is essential in the dialogue between parasites and hosts, inducing Th1, Th2 or regulatory responses in a species-specific manner. In addition, calreticulin participates as initiator of endoplasmic reticulum stress in tumor cells and promotion of immunogenic cell death and removal by macrophages. Direct anti-tumoral activity has also been reported. The highly immunogenic and pleiotropic nature of parasite calreticulins, either as positive or negative regulators of the immune response, render these proteins as valuable tools to modulate immunopathologies and autoimmune disorders, as well as a potential treatment of neoplasms. Moreover, the disparities in the amino acid composition of parasite calreticulins might provide subtle variations in the mechanisms of action that could provide advantages as therapeutic tools. Here, we review the immunological roles of parasite calreticulins and discuss possible beneficial applications.

Co-Immunization Efficacy of Recombinant Antigens against Rhipicephalus microplus and Hyalomma anatolicum Tick Infestations

The immunoprophylactic management of ticks is the most effective option to control tick infestations and counter spread the acaricide resistance problem worldwide. Several researchers reported an inconsistent efficacy of the single antigen-based immunization of hosts against different tick species. In the present study, to develop a multi-target immunization protocol, proteins from Rhipicephalus microplus BM86 and Hyalomma anatolicum subolesin (SUB) and tropomyosin (TPM) were targeted to evaluate the cross-protective potential. The sequence identities of the BM86, SUB, and TPM coding genes amongst Indian tick isolates of targeted species were 95.6–99.8%, 98.7–99.6%, and 98.9–99.9%, respectively, while at the predicted amino acid level, the identities were 93.2 to 99.5, 97.6 to 99.4, and 98.2 to 99.3%. The targeted genes were expressed in the eukaryotic expression system, pKLAC2-Kluyveromyces lactis, and 100 µg each of purified recombinant protein (Bm86-89 kDa, SUB-21 kDa, and TPM-36 kDa) mixed with adjuvant was injected individually through the intramuscular route at different sites of the body on days 0, 30, and 60 to immunize cross-bred cattle. Post-immunization, a statistically significant (p < 0.001) antibody response (IgG, IgG1, and IgG2) in comparison to the control, starting from 15 to 140 days, against each antigen was recorded. Following multi-antigen immunization, the animals were challenged twice with the larvae of R. microplus and H. anatolicum and theadults of H. anatolicum, and a significant vaccine efficacy of 87.2% and 86.2% against H. anatolicum larvae and adults, respectively, and 86.7% against R. microplus was obtained. The current study provides significant support to develop a multi-antigen vaccine against cattle tick species.

The control of Hyalomma ticks, vectors of the Crimean–Congo hemorrhagic fever virus: Where are we now and where are we going?

At a time of major global, societal, and environmental changes, the shifting distribution of pathogen vectors represents a real danger in certain regions of the world as generating opportunities for emergency. For example, the recent arrival of the Hyalomma marginatum ticks in southern France and the concurrent appearance of cases of Crimean–Congo hemorrhagic fever (CCHF)—a disease vectored by this tick species—in neighboring Spain raises many concerns about the associated risks for the European continent. This context has created an urgent need for effective methods for control, surveillance, and risk assessment for ticks and tick-borne diseases with a particular concern regarding Hyalomma sp. Here, we then review the current body of knowledge on different methods of tick control—including chemical, biological, genetical, immunological, and ecological methods—and the latest developments in the field, with a focus on those that have been tested against ticks from the genus Hyalomma. In the absence of a fully and unique efficient approach, we demonstrated that integrated pest management combining several approaches adapted to the local context and species is currently the best strategy for tick control together with a rational use of acaricide. Continued efforts are needed to develop and implement new and innovative methods of tick control.

Disease-bearing Hyalomma ticks are an increasingly emerging threat to humans and livestock worldwide. Various chemical, biological, genetic, and ecological methods for tick control have been developed, with variable efficiencies. Today, the best tick control strategy involves an integrated pest management approach.

Low Genetic Polymorphism in the Immunogenic Sequences of Rhipicephalus microplus Clade C

Rhipicephalus microplus tick highly affects the veterinary sector throughout the world. Different tick control methods have been adopted, and the identification of tick-derived highly immunogenic sequences for the development of an anti-tick vaccine has emerged as a successful alternate. This study aimed to characterize immunogenic sequences from R. microplus ticks prevalent in Pakistan. Ticks collected in the field were morphologically identified and subjected to DNA and RNA extraction. Ticks were molecularly identified based on the partial mitochondrial cytochrome C oxidase subunit (cox) sequence and screened for piroplasms (Theileria/Babesia spp.), Rickettsia spp., and Anaplasma spp. PCR-based pathogens-free R. microplus-derived cDNA was used for the amplification of full-length cysteine protease inhibitor (cystatin 2b), cathepsin L-like cysteine proteinase (cathepsin-L), glutathione S-transferase (GST), ferritin 1, 60S acidic ribosomal protein (P0), aquaporin 2, ATAQ, and R. microplus 05 antigen (Rm05Uy) coding sequences. The cox sequence revealed 100% identity with the nucleotide sequences of Pakistan's formerly reported R. microplus, and full-length immunogenic sequences revealed maximum identities to the most similar sequences reported from India, China, Cuba, USA, Brazil, Egypt, Mexico, Israel, and Uruguay. Low nonsynonymous polymorphisms were observed in ATAQ (1.5%), cathepsin-L (0.6%), and aquaporin 2 (0.4%) sequences compared to the homologous sequences from Mexico, India, and the USA, respectively. Based on the cox sequence, R. microplus was phylogenetically assembled in clade C, which includes R. microplus from Pakistan, Myanmar, Malaysia, Thailand, Bangladesh, and India. In the phylogenetic trees, the cystatin 2b, cathepsin-L, ferritin 1, and aquaporin 2 sequences were clustered with the most similar available sequences of R. microplus, P0 with R. microplus, R. sanguineus and R. haemaphysaloides, and GST, ATAQ, and Rm05Uy with R. microplus and R. annulatus. This is the first report on the molecular characterization of clade C R. microplus-derived immunogenic sequences.

Prediction and validation of cross-protective candidate antigen of Hyalomma asiaticum cathepsin L between H. asiaticum and H. anatolicum

Hyalomma asiaticum and H. anatolicum are tick species in Eurasia and Africa with major medical and veterinary significance. Beside their direct pathogenic effects, H. asiaticum and H. anatolicum are vectors of important diseases of livestock and in some instances of zoonoses. In search of ways to address the increasing incidence of global acaricide resistance, tick control through vaccination is regarded as a sustainable alternative approach. Cathepsin L-like cysteine protease (CPL) is a potent hemoglobinase, and plays important roles in the digestion of blood acquired from a host. CPL from H. anatolicum (HanCPL) with high similarity (> 90%) for H. asiaticum CPL (HasCPL) were aligned by in silico analysis. After further in vitro validation, the anti-HasCPL sera have cross-reactivity between the different total native protein of life stages and tissues for H. asiaticum and H. anatolicum. Furthermore, we further confirmed that recombinant HasCPL (rHasCPL) immunized rabbits were partially cross-protected (54.8%) by H. anatolicum infestation.

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.

Protective efficacy of the peptide Subolesin antigen against the cattle tick Rhipicephalus microplus under natural infestation

The cattle tick Rhipicephalus microplus affect animal health, welfare, and cattle production in tropical and subtropical zones of the world. Anti-tick vaccines have been an effective alternative for cattle tick control instead of traditional chemical products. To date, Subolesin antigen has shown efficacy for the control of tick infestation in cattle, and previous studies showed that one peptide derived from this protein has demonstrated to elicit a strong and specific humoral immune response. Based on these findings, herein we characterized the efficacy of the peptide Subolesin for the control of cattle tick, R. microplus infestation under field conditions. Twenty-four female calves were assigned to four experimental groups and immunized with three subcutaneous doses of the peptide Subolesin, Bm86, both antigens (dual vaccine) and adjuvant/saline alone, respectively. Serum antibody levels (IgG) were assessed by ELISA and confirmed by Western blot; also, reproductive performance of naturally infested R. microplus was determined. The results showed that immunizations with the experimental antigens reduced tick infestations with vaccine's efficacy of 67 % (peptide Subolesin), 56 % (Bm86), and 49 % (dual vaccine) based on adult tick numbers, oviposition, and egg fertility between vaccinated and control animals. Peptide Subolesin-immunized calves developed a strong humoral immune response expressed by high anti-pSubolesin IgG levels, and the Western blot analysis confirmed that it is immunogenic. Cattle receiving Bm86 and dual vaccine showed less protection, although Bm86 was within the range reported previously. The negative correlation between antibody levels and reduction of naturally infested R. microplus strongly suggested that the effect of the vaccine was the result of the antibody response in immunized cattle. In conclusion, it was demonstrated that the peptide Subolesin induced a specific immune response in cattle under field conditions, resulting in reduced R. microplus populations in subsequent generations. Finally, integrated tick control must consider anti-tick vaccines as a cost-effective, sustainable, and successful tool for controlling cattle tick infestations.

Identification and Characterization of Immunodominant Proteins from Tick Tissue Extracts Inducing a Protective Immune Response against Ixodes ricinus in Cattle

Ixodes ricinus is the main vector of tick-borne diseases in Europe. An immunization trial of calves with soluble extracts of I. ricinus salivary glands (SGE) or midgut (ME) previously showed a strong response against subsequent tick challenge, resulting in diminished tick feeding success. Immune sera from these trials were used for the co-immunoprecipitation of tick tissue extracts, followed by LC-MS/MS analyses. This resulted in the identification of 46 immunodominant proteins that were differentially recognized by the serum of immunized calves. Some of these proteins had previously also drawn attention as potential anti-tick vaccine candidates using other approaches. Selected proteins were studied in more detail by measuring their relative expression in tick tissues and RNA interference (RNAi) studies. The strongest RNAi phenotypes were observed for MG6 (A0A147BXB7), a protein containing eight fibronectin type III domains predominantly expressed in tick midgut and ovaries of feeding females, and SG2 (A0A0K8RKT7), a glutathione-S-transferase that was found to be upregulated in all investigated tissues upon feeding. The results demonstrated that co-immunoprecipitation of tick proteins with host immune sera followed by protein identification using LC-MS/MS is a valid approach to identify antigen–antibody interactions, and could be integrated into anti-tick vaccine discovery pipelines.

Analysis of Genetic Diversity in Indian Isolates of Rhipicephalus microplus Based on Bm86 Gene Sequence

The control of cattle tick, Rhipicephalus microplus, is focused on repeated use of acaricides. However, due to growing acaricide resistance and residues problem, immunization of animals along with limited use of effective acaricides is considered a suitable option for the control of tick infestations. To date, more than fifty vaccine candidates have been identified and tested worldwide, but two vaccines were developed using the extensively studied candidate, Bm86. The main reason for limited vaccine commercialization in other countries is genetic diversity in the Bm86 gene leading to considerable variation in vaccine efficacy. India, with 193.46 million cattle population distributed in 28 states and 9 union territories, is suffering from multiple tick infestation dominated by R. microplus. As R. microplus has developed multi-acaricide resistance, an efficacious vaccine may provide a sustainable intervention for tick control. Preliminary experiments revealed that the presently available commercial vaccine based on the BM86 gene is not efficacious against Indian strain. In concert with the principle of reverse vaccinology, genetic polymorphism of the Bm86 gene within Indian isolates of R. microplus was studied. A 578 bp conserved nucleotide sequences of Bm86 from 65 R. microplus isolates collected from 9 Indian states was sequenced and revealed 95.6-99.8% and 93.2-99.5% identity in nucleotides and amino acids sequences, respectively. The identities of nucleotides and deduced amino acids were 94.7-99.8% and 91.8-99.5%, respectively, between full-length sequence (orf) of the Bm86 gene of IVRI-I strain and published sequences of vaccine strains. Six nucleotides deletion were observed in Indian Bm86 sequences. Four B-cell epitopes (D519-K554, H563-Q587, C598-T606, T609-K623), which are present in the conserved region of the IVRI-I Bm86 sequence, were selected. The results confirm that the use of available commercial Bm86 vaccines is not a suitable option against Indian isolates of R. microplus. A country-specific multi-epitope Bm86 vaccine consisting of four specific B-cell epitopes along with candidate molecules, subolesin and tropomyosin in chimeric/co-immunization format may provide a sustainable option for implementation in an integrated tick management system.

Recombinant interferon-gamma promotes immunoglobulin G and cytokine memory responses to cathepsin L-like cysteine proteinase of Hyalomma asiaticum and the efficacy of anti-tick

Among bloodsucking arthropods, hard tick is a vector of transmitting the most diverse human and animal pathogens, leading to an increasing number of manifestations worldwide. The development of the anti-tick vaccine has the potential to be an environmentally friendly and cost-effective option for tick management. We have previously demonstrated the induction of both humoral and cellular response against Hyalomma asiaticum (H. asiaticum) following immunization with recombinant cathepsin L-like cysteine protease from H. asiaticum tick (rHasCPL), and could control tick infestations. Interferon-gamma (IFN-γ), is an immunomodulatory factor that plays an important role in the regulation of adaptive immunity against infection. In the present study, recombinant BALB/c mouse IFN-γ (rMus-IFN-γ) was cloned and expressed using a prokaryotic expression system, and verified by Western blotting and IFN-γ-ELISA kit analysis. Female BALB/c mice (n = 12) were used for immunization using rHasCPL (100 μg) plus IFN-γ as adjuvant (10 μg). In immunized female BALB/c mice, the levels of anti-CPL antibodies as well as cytokines were determined using ELISA analysis. Protective efficacy of immunization was evaluated by larvae H. asiaticum challenge of immunized female BALB/c mice. Using rMus-IFN-γ as an adjuvant to rHasCPL vaccine (CPL + IFN-γ) promoted specific antibody IgG (IgG1 > IgG2a) and increased production of IFN-γ and IL-4 compared to immune rHasCPL group (CPL). The protected rate of immunized mice from tick challenge was significantly higher after immunization with CPL + IFN-γ (85.11 %) than with CPL (63.28 %). Immunization using CPL + IFN-γ promoted the activation of anti-HasCPL humoral and cellular immune responses, and could provide better protection against H. asiaticum infestation. This approach may could help develop a candidate vaccine for control tick infestations.

A review on Hyalomma species infestations on human and animals and progress on management strategies

The Hyalomma species of ticks have gained additional attention due to their role in the transmission of Theileria annulata infection in animals and the Crimean-Congo Haemorrhagic Fever (CCHF) virus in humans. Apart from these, many other pathogens viz., other species of Theileria, a few species of Babesia, Rickettsia and viruses are either maintained or transmitted by this tick species. The medium to large size species with longer proboscis has inflicted additional burden on the overall impact of tick infestations. Being a multi-host species, management of the species is very challenging. Presently, the traditional method of tick management using chemical acaricides is found insufficient and unsustainable. Henceforth, the overall burden of tick infestations and tick-borne diseases are increasing gradually. After the successful development of vaccines against cattle tick, Rhipicephalus microplus, the anti-Hyalomma vaccine is considered a feasible and sustainable management option. In the recent past research on herbal acaricides and its possible application for tick control seems promising. Other eco-friendly methods are still under experimental stage. The present review is focused on impact of Hyalomma species infestation on human and animal health with special emphasis on progress on its sustainable management.

Prediction, mapping and validation of tick glutathione S-transferase B-cell epitopes

In search of ways to address the increasing incidence of global acaricide resistance, tick control through vaccination is regarded as a sustainable alternative approach. Recently, a novel cocktail antigen tick-vaccine was developed based on the recombinant glutathione S-transferase (rGST) anti-sera cross-reaction to glutathione S-transferases of Rhipicephalus appendiculatus (GST-Ra), Amblyomma variegatum (GST-Av), Haemaphysalis longicornis (GST-Hl), Rhipicephalus decoloratus (GST-Rd) and Rhipicephalus microplus (GST-Rm). Therefore, the current study aimed to predict the shared B-cell epitopes within the GST sequences of these tick species. Prediction of B-cell epitopes and proteasomal cleavage sites were performed using immunoinformatics algorithms. The conserved epitopes predicted within the sequences were mapped on the homodimers of the respective tick GSTs, and the corresponding peptides were independently used for rabbit immunization experiments. Based on the dot blot assay, the immunogenicity of the peptides and their potential to be recognized by corresponding rGST anti-sera raised by rabbit immunization in a previous work were investigated. This study revealed that the predicted conserved B-cell epitopes within the five tick GST sequences were localized on the surface of the respective GST homodimers. The epitopes of GST-Ra, GST-Rd, GST-Av, and GST-Hl were also shown to contain a seven residue-long peptide sequence with no proteasomal cleavage sites, whereas proteasomal digestion of GST-Rm was predicted to yield a 4-residue fragment. Given that a few proteasomal cleavage sites were found within the conserved epitope sequences of the four GSTs, the sequences could also contain a T-cell epitope. Finally, the peptide and rGST anti-sera reacted against the corresponding peptide, confirming their immunogenicity. These data support the claim that the rGSTs, used in the previous study, contain conserved B-cell epitopes, which elucidates why the rGST anti-sera cross-reacted to non-homologous tick GSTs. Taken together, the data suggest that the B-cell epitopes predicted in this study could be useful for constituting epitope-based GST tick vaccines.

Identification and characterization of vaccine candidates against Hyalomma anatolicum-Vector of Crimean-Congo haemorrhagic fever virus

Crimean-Congo haemorrhagic fever (CCHF) is a tick borne viral disease reported from different parts of the world. The distribution of the CCHF cases are linked with the distribution of the principal vector, Hyalomma anatolicum in the ecosystem. Presently, vector control is mainly dependent on repeated application of acaricides, results in partial efficacy and generated acaricide resistant tick strains. Amongst the different components of integrated management programme, immunization of hosts is considered as one of the sustainable component. To restrict CCHF virus spreading, use of anti-Hyalomma vaccines appears as a viable solution. Accordingly, present study was under taken to characterize and evaluate vaccine potential of two conserved molecules, ferritin2 (FER2) and tropomyosin (TPM). Silencing of the genes conferred a cumulative reduction (rejection + unable to engorge) of 61.3% in FER2 and 70.2% in TPM respectively. Furthermore, 44.2% and 72.7% reduction in engorgement weight, 63.6% and 94.9% reduction in egg masses in FER2 and TPM silenced ticks in comparison to LUC-control group was recorded. The recombinant protein, rHaFER2 was characterized as 35 kDa protein with pI of 5.84 and possesses iron binding domains. While rHaTPM is a 51kDa protein with pI of 4.94 having calcium binding domains. Immunization of cross-bred calves by rHaFER2 conferred 51.7% and 51.2% protection against larvae and adults of H. anatolicum challenge infestations. While rHaTPM conferred 63.7% and 66.4% protection against larvae and adults infestations, respectively. The results were comparable with the data generated by RNAi and it clearly showed the possibility for the development of anti-hyalomma vaccine to manage CCHF virus and Theileria annulata infection in human and animals.

Functional Evolution of Subolesin/Akirin

The Subolesin/Akirin constitutes a good model for the study of functional evolution because these proteins have been conserved throughout the metazoan and play a role in the regulation of different biological processes. Here, we investigated the evolutionary history of Subolesin/Akirin with recent results on their structure, protein-protein interactions and function in different species to provide insights into the functional evolution of these regulatory proteins, and their potential as vaccine antigens for the control of ectoparasite infestations and pathogen infection. The results suggest that Subolesin/Akirin evolved conserving not only its sequence and structure, but also its function and role in cell interactome and regulome in response to pathogen infection and other biological processes. This functional conservation provides a platform for further characterization of the function of these regulatory proteins, and how their evolution can meet species-specific demands. Furthermore, the conserved functional evolution of Subolesin/Akirin correlates with the protective capacity shown by these proteins in vaccine formulations for the control of different arthropod and pathogen species. These results encourage further research to characterize the structure and function of these proteins, and to develop new vaccine formulations by combining Subolesin/Akirin with interacting proteins for the control of multiple ectoparasite infestations and pathogen infection.

An insight into the ecobiology, vector significance and control of Hyalomma ticks (Acari: Ixodidae): A review

Ticks (Acari:Ixodoidea) are important ectoparasites infesting livestock and human populations around the globe. Ticks can cause damage directly by affecting the site of infestation, or indirectly as vectors of a wide range of protozoa, bacteria and viruses which ultimately lead to lowered productivity of livestock populations. Hyalomma is a genus of hard ticks, having more than 30 species well-adapted to hot, humid and cold climates. Habitat diversity, vector ability, and emerging problem of acaricidal resistance in enzootic regions typify this genus in various countries around the world. This paper reviews the epidemiology, associated risk factors (temperature, climate, age, sex, breed etc.), vector role, vector-pathogen association, and reported control strategies of genus Hyalomma. The various proteins in saliva of Hyalomma secreted into the blood stream of host and the prolonged attachment are responsible for the successful engorgement of female ticks in spite of host immune defense system. The various immunological approaches that have been tried by researchers in order to cause tick rejection are also discussed. In addition, the novel biological control approaches involving the use of entomo-pathogenic nematodes and Bacillus thuringiensis (B. thuringiensis) serovar thuringiensis H14; an endotoxin, for their acaricidal effect on different species and life cycle stages of Hyalomma are also presented.

Interactomics and tick vaccine development: new directions for the control of tick-borne diseases

INTRODUCTION

Ticks are obligate hematophagous arthropod ectoparasites that transmit pathogens responsible for a growing number of tick-borne diseases (TBDs) throughout the world. Vaccines have been shown to be the most efficient, cost-effective, and environmentally friendly approach for the control of ticks and the prevention of TBDs. Although at its infancy, interactomics has shown the possibilities that the knowledge of the interactome offers in understanding tick biology and the molecular mechanisms involved in pathogen infection and transmission. Furthermore, interactomics has provided information for the identification of candidate vaccine protective antigens. Areas covered: In this special report, we review the different approaches used for the study of protein-protein physical and functional interactions, and summarize the application of interactomics to the characterization of tick biology and tick-host-pathogen interactions, and the possibilities that offers to vaccine development for the control of ticks and TBDs. Expert commentary: The combination of interacting proteins in antigen formulations may increase vaccine efficacy. In the near future, the combination of interactomics with other omics approaches such as transcriptomics, proteomics, metabolomics, and regulomics together with intelligent Big Data analytic techniques will improve the high throughput discovery and characterization of vaccine protective antigens for the prevention and control of TBDs.

De novo assembly and analysis of midgut transcriptome of the argasid tick Ornithodoros erraticus and identification of genes differentially expressed after blood feeding

Ticks are hematophagous vectors of great medical and veterinary importance because they transmit numerous pathogenic microorganisms to humans and animals. The argasid Ornithodoros erraticus is the main vector of tick-borne human relapsing fever and African swine fever in the Mediterranean Basin. Tick enterocytes express bioactive molecules that perform key functions in blood digestion, feeding, toxic waste processing and pathogen transmission. To explore new strategies for tick control, in this work we have obtained and compared the midgut transcriptomes of O. erraticus female ticks before and after a blood meal and identified the genes whose expression is differentially regulated after feeding. The transcript sequences were annotated, functionally and structurally characterised and their expression levels compared between both physiological conditions (unfed females and fed females at 2 days post-engorgement). Up to 29,025 transcripts were assembled, and 9290 of them corresponded to differentially expressed genes (DEGs) after feeding. Of these, 4656 genes were upregulated and nearly the same number of genes was downregulated in fed females compared to unfed females. BLASTN and BLASTX analyses of the 29,025 transcripts allowed the annotation of 9072 transcripts/proteins. Among them, the most numerous were those with catalytic and binding activities and those involved in diverse metabolic pathways and cellular processes. The analyses of functional groups of upregulated DEGs potentially related to the digestion of proteins, carbohydrates and lipids, and the genes involved in the defence response and response to oxidative stress, confirm that these processes are narrowly regulated in ticks, highlighting their complexity and importance in tick biology. The expression patterns of six genes throughout the blood digestion period revealed significant differences between these patterns, strongly suggesting that the transcriptome composition is highly dynamic and subjected to important variation along the trophogonic cycle. This may guide future studies aimed at improving the understanding of the molecular physiology of tick digestion and digestion-related processes. The current work provides a more robust and comprehensive understanding of the argasid tick digestive system.

Metazoan Parasite Vaccines: Present Status and Future Prospects

Eukaryotic parasites and pathogens continue to cause some of the most detrimental and difficult to treat diseases (or disease states) in both humans and animals, while also continuously expanding into non-endemic countries. Combined with the ever growing number of reports on drug-resistance and the lack of effective treatment programs for many metazoan diseases, the impact that these organisms will have on quality of life remain a global challenge. Vaccination as an effective prophylactic treatment has been demonstrated for well over 200 years for bacterial and viral diseases. From the earliest variolation procedures to the cutting edge technologies employed today, many protective preparations have been successfully developed for use in both medical and veterinary applications. In spite of the successes of these applications in the discovery of subunit vaccines against prokaryotic pathogens, not many targets have been successfully developed into vaccines directed against metazoan parasites. With the current increase in -omics technologies and metadata for eukaryotic parasites, target discovery for vaccine development can be expedited. However, a good understanding of the host/vector/pathogen interface is needed to understand the underlying biological, biochemical and immunological components that will confer a protective response in the host animal. Therefore, systems biology is rapidly coming of age in the pursuit of effective parasite vaccines. Despite the difficulties, a number of approaches have been developed and applied to parasitic helminths and arthropods. This review will focus on key aspects of vaccine development that require attention in the battle against these metazoan parasites, as well as successes in the field of vaccine development for helminthiases and ectoparasites. Lastly, we propose future direction of applying successes in pursuit of next generation vaccines.