Cross immunity with Haemaphysalis longicornis glutathione S-transferase reduces an experimental Rhipicephalus (Boophilus) microplus infestation

Immunologic characterization of the Bm05br protein using the Rhipicephalus linnaei (Audouin, 1826) species as a tick model

The identification and characterization of tick proteins allow us to discover new physiological targets useful for the development of tick control methods. Bm05br (Brazil Rhipicephalus microplus protein 05) is a protein with unknown function identified in the saliva of R. microplus. Rs05br (Brazil Rhipicephalus sanguineus protein 05), a protein with 99 % similarity to Bm05br, was identified in Rhipicephalus linnaei egg, larval, and nymphal stages, as well as in adult saliva. To improve the knowledge about both proteins, immunological characterization was performed, including antigenicity analysis, vaccination trials, and artificial feeding. The sequence and antigenicity analysis of Bm05br and Rs05br proteins showed that R. linnaei could serve as a tick model for cross-protection studies. The recombinant Bm05br protein was immunogenic. Anti-Bm05br antibodies recognized the homologous protein Rs05br in different stages, organs, and in the saliva of R. linnaei. Although rBm05br did not induce a protective response against infestation in R. linnaei in this study, further experiments could be developed taking into account new formulations and animal models for vaccination. These results also serve as a reference for future research on the function of these proteins in R. microplus and R. linnaei physiology, as well as other species of the genus Rhipicephalus.

Targeting Haemaphysalis longicornis serpin to prevent tick feeding and pathogen transmission

Serine proteinase inhibitors (serpins), identified from the hard tick Haemaphysalis longicornis of China, play significant roles in various animal physiological processes. In this study, we showed that H. longicornis serpins (Hlserpin-a and Hlserpin-b) were induced during blood-feeding in nymph ticks and exhibited anticoagulation activity in vitro. Silencing Hlserpins through RNA interference (RNAi) significantly impaired tick feeding. Immunization of mice with recombinant Hlserpins or passive transfer of Hlserpin antiserum significantly curtails the efficacy of tick feeding. Concurrently, the transmission of the Langat virus (LGTV) from ticks to mice witnessed a substantial decrease when Hlserpins were silenced. Our findings suggest that inhibiting Hlserpins can hamper tick engorgement and pathogen transmission, indicating the potential of Hlserpins as a vaccine to counter tick-borne diseases.

In Vivo Characterization of the Anti-Glutathione S-Transferase Antibody Using an In Vitro Mite Feeding Model

Poultry red mites (Dermanyssus gallinae, PRMs), tropical fowl mites (Ornithonyssus bursa, TFMs), and northern fowl mites (O. sylviarum, NFMs) are blood-feeding pests that debilitate poultry worldwide. Glutathione S-transferase (GST) plays an important role in the detoxification and drug metabolism of mites. However, research on avian mite GSTs as vaccine antigens is still lacking. Therefore, we aimed to evaluate the potential of avian mite GSTs for vaccine development. We identified GST genes from TFMs and NFMs. We prepared recombinant GST (rGST) from TFMs, NFMs, and PRMs, and assessed their protein functions. Moreover, we evaluated the cross-reactivity and acaricidal effect of immune plasma against each rGST on TFMs, NFMs, and PRMs. The deduced amino acid sequences of GSTs from TFMs and NFMs were 80% similar to those of the PRMs. The rGSTs exhibited catalytic activity in conjugating glutathione to the 1-chloro-2,4-dinitrobenzene substrate. Immune plasma against each rGST showed cross-reactivity with rGST from different mite species. Moreover, the survival rate of PRMs fed with immune plasma against the rGST of TFMs and NFMs was significantly lower than that of the control plasma. These results demonstrate the potential application of GST as an antigen for the development of a broad-spectrum vaccine against avian mites.

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.

Biochemical characterization of a novel sphingomyelinase-like protein from the Rhipicephalus microplus tick

Sphingomyelinase D is a toxin present in venomous spiders and bacteria and is associated with infection symptoms in patients affected by spider bites. It was observed that in Ixodes scapularis ticks, sphingomyelinase-like protein secreted in saliva can modulate the host immune response, affecting the transmission of flavivirus to the host via exosomes. In this work, a sphingomyelinase D-like protein (RmSMase) from R. microplus, a tick responsible for economic losses and a vector of pathogens for cattle, was investigated. The amino acid sequence revealed the lack of important residues for enzymatic activity, but the recombinant protein showed sphingomyelinase D activity. RmSMase shows Ca2+ and Mg2+ dependence in acidic pH, differing from IsSMase, which has Mg2+ dependence in neutral pH. Due to the difference between RmSMase and other SMases described, the data suggest that RmSMase belongs to SMase D class IIc. RmSMase mRNA transcription levels are upregulated during tick feeding, and the recombinant protein was recognized by host antibodies elicited after heavy tick infestation, indicating that RmSMase is present in tick saliva and may play a role in the tick feeding process.

Mining gene expression data for rational identification of novel drug targets and vaccine candidates against the cattle tick, Rhipicephalus microplus

Control of complex parasites via vaccination remains challenging, with the current combination of vaccines and small drugs remaining the choice for an integrated control strategy. Studies conducted to date, are providing evidence that multicomponent vaccines will be needed for the development of protective vaccines against endo- and ectoparasites, though multicomponent vaccines require an in-depth understanding of parasite biology which remains insufficient for ticks. With the rapid development and spread of acaricide resistance in ticks, new targets for acaricide development also remains to be identified, along with novel targets that can be exploited for the design of lead compounds. In this study, we analysed the differential gene expression of Rhipicephalus microplus ticks that were fed on cattle vaccinated with a multi-component vaccine (Bm86 and 3 putative Bm86-binding proteins). The data was scrutinised for the identification of vaccine targets, small drug targets and novel pathways that can be evaluated in future studies. Limitations associated with targeting novel proteins for vaccine and/or drug design is also discussed and placed into the context of challenges arising when targeting large protein families and intracellular localised proteins. Lastly, this study provide insight into how Bm86-based vaccines may reduce successful uptake and digestion of the bloodmeal and overall tick fecundity.

Elucidating structure and dynamics of glutathione S-transferase from Rhipicephalus (Boophilus) microplus

Rhipicephalus (Boophilus) microplus is tick parasite that affects the cattle industry worldwide. In R. (B.) microplus, acaricide resistance develops rapidly against many commercial acaricides. One of main resistance strategies is to enhance the metabolic detoxification mediated by R. (B.) microplus glutathione-S-transferase (RmGST). RmGST detoxifies acaricides by catalyzing the conjugation of glutathione to acaricides. Although structural and dynamic details of RmGST are expected to elucidate the biologic activity of this molecule, these data have not been available to date. Thus, Molecular Dynamics simulations were employed to study ligand-free RmGST at an atomic level. Like other m-class GSTs, the flexible m loop (m1) of RmGST was observed. M1 seems to shield the active sites from the bulk. A RmGST dimer is stabilized by the lock-and-key motif (F57 as "key") and hydrogen bonds of R82-E91 and R82-D98 at the dimer interface. Without substrates, conserved catalytic Y116 and N209 can interact with V112, G210 (for Y116) and F215 (for N209). Overall, most residues involving in RmGST function and stability are similar to other m-class GSTs. This implies similar structural stability and catalytic activity of RmGST to other GSTs. An insight obtained here will be useful for management of acaricide resistance and tick control.Communicated by Ramaswamy H. Sarma.

Characterization of cysteine proteases from poultry red mite, tropical fowl mite, and northern fowl mite to assess the feasibility of developing a broadly efficacious vaccine against multiple mite species

Infestation with poultry red mites (PRM, Dermanyssus gallinae) causes anemia, reduced egg production, and death in serious cases, resulting in significant economic losses to the poultry industry. As a novel strategy for controlling PRMs, vaccine approaches have been focused upon and several candidate vaccine antigens against PRMs have been reported. Tropical (TFM, Ornithonyssus bursa) and northern (NFM, Ornithonyssus sylviarum) fowl mites are also hematophagous and cause poultry industry problems similar to those caused by PRM. Therefore, ideal antigens for anti-PRM vaccines are molecules that cross-react with TFMs and NFMs, producing pesticidal effects similar to those against PRMs. In this study, to investigate the potential feasibility of developing vaccines with broad efficacy across mite species, we identified and characterized cysteine proteases (CPs) of TFMs and NFMs, which were previously reported to be effective vaccine antigens of PRMs. The open reading frames of CPs from TFMs and NFMs had the same sequences, which was 73.0% similar to that of PRMs. Phylogenetic analysis revealed that the CPs of TFMs and NFMs clustered in the same clade as CPs of PRMs. To assess protein functionality, we generated recombinant peptidase domains of CPs (rCP-PDs), revealing all rCP-PDs showed CP-like activities. Importantly, the plasma obtained from chickens immunized with each rCP-PD cross-reacted with rCP-PDs of different mites. Finally, all immune plasma of rCP-PDs reduced the survival rate of PRMs, even when the plasma was collected from chickens immunized with rCP-PDs derived from TFM and NFM. Therefore, CP antigen is a promising, broadly efficacious vaccine candidate against different avian mites.

Egg protein profile and dynamics during embryogenesis in Haemaphysalis flava ticks

Tick eggs contain all essential proteins for embryogenesis, and egg proteins are a potential reservoir of tick-protective antigens. However, the protein profile and dynamics during embryonic development remain unknown. This study aimed to depict the protein profile and dynamics in tick embryogenesis, further providing protein candidates for targeted interventions. Eggs from Haemaphysalis flava ticks were incubated at 28 °C and 85% relative humidity. On days 0 (newly laid eggs without incubation), 7, 14 and 21, eggs were collected, dewaxed and subject to protein extraction. Extracted proteins were digested by filter-aided sample preparation and analyzed by liquid chromatography-tandem mass spectrometry (LC/MS-MS). MS data were searched against an in-house H. flava protein database for tick-derived protein identification. Abundances of 40 selected high-confidence proteins were further quantified by LC-parallel reaction monitoring (PRM)/MS analysis throughout egg incubation. A total of 93 high-confidence proteins were identified in eggs on 0-day incubation. Identified proteins belonged to seven functional categories: transporters, enzymes, proteinase inhibitors, immunity-related proteins, cytoskeletal proteins, heat shock proteins and uncharacterized proteins. The enzyme category contained the most types of proteins. Neutrophil elastase inhibitors represented the most abundant proteins in terms of intensity-based absolute-protein-quantification. LC-PRM/MS revealed that the abundances of 20 proteins increased including enolase, calreticulin, actin, GAPDH et cetera, and the abundances of 11 proteins decreased including vitellogenins, neutrophil elastase inhibitor, carboxypeptidase Q, et cetera from 0- to 21-day incubation. This study provides the most comprehensive egg protein profile and dynamics during tick embryogenesis. Further investigations are needed to test the tick-control efficacy by targeting the egg proteins.

Potential of ferritin 2 as an antigen for the development of a universal vaccine for avian mites, poultry red mites, tropical fowl mites, and northern fowl mites

Introduction

Poultry red mites (PRMs, Dermanyssus gallinae), blood-sucking ectoparasites, are a threat to the poultry industry because of reduced production caused by infestation. In addition, tropical fowl mites (TFMs, Ornithonyssus bursa) and northern fowl mites (NFMs, Ornithonyssus sylviarum) are hematophagous, distributed in various regions, genetically and morphologically close to PRMs, and cause similar problems to the poultry industry. Vaccine approaches have been studied for PRM control, and several molecules have been identified in PRMs as candidates for effective vaccine antigens. The development of an anti-PRM vaccine as a universal vaccine with broad efficacy against avian mites could improve the productivity of poultry farms worldwide. Molecules that are highly conserved among avian mites and have critical functions in the physiology and growth of mites could be ideal antigen candidates for the development of universal vaccines. Ferritin 2 (FER2), an iron-binding protein, is critical for the reproduction and survival of PRMs and has been reported as a useful vaccine antigen for the control of PRMs and a candidate for the universal vaccine antigen in some tick species.

Method and results

Herein, we identified and characterized FER2 in TFMs and NFM. Compared with the sequence of PRM, the ferroxidase centers of the heavy chain subunits were conserved in FER2 of TFMs and NFMs. Phylogenetic analysis revealed that FER2 belongs to clusters of secretory ferritins of mites and other arthropods. Recombinant FER2 (rFER2) proteins from PRMs, TFMs, and NFMs exhibited iron-binding abilities. Immunization with each rFER2 induced strong antibody responses in chickens, and each immune plasma cross-reacted with rFER2 from different mites. Moreover, mortality rates of PRMs fed with immune plasma against rFER2 from TFMs or NFMs, in addition to PRMs, were higher than those of control plasma.

Discussion

rFER2 from each avian mite exhibited anti-PRM effects. This data suggests that it has the potential to be used as an antigen candidate for a universal vaccine against avian mites. Further studies are needed to access the usefulness of FER2 as a universal vaccine for the control of avian mites.

Recent Advances in Tick Antigen Discovery and Anti-Tick Vaccine Development

Ticks can seriously affect human and animal health around the globe, causing significant economic losses each year. Chemical acaricides are widely used to control ticks, which negatively impact the environment and result in the emergence of acaricide-resistant tick populations. A vaccine is considered as one of the best alternative approaches to control ticks and tick-borne diseases, as it is less expensive and more effective than chemical controls. Many antigen-based vaccines have been developed as a result of current advances in transcriptomics, genomics, and proteomic techniques. A few of these (e.g., Gavac® and TickGARD®) are commercially available and are commonly used in different countries. Furthermore, a significant number of novel antigens are being investigated with the perspective of developing new anti-tick vaccines. However, more research is required to develop new and more efficient antigen-based vaccines, including on assessing the efficiency of various epitopes against different tick species to confirm their cross-reactivity and their high immunogenicity. In this review, we discuss the recent advancements in the development of antigen-based vaccines (traditional and RNA-based) and provide a brief overview of recent discoveries of novel antigens, along with their sources, characteristics, and the methods used to test their efficiency.

Tick Vaccines and Concealed versus Exposed Antigens

Anti-tick vaccines development mainly depends on the identification of suitable antigens, which ideally should have different features. These should be key molecules in tick biology, encoded by a single gene, expressed across life stages and tick tissues, capable of inducing B and T cells to promote an immunological response without allergenic, hemolytic, and toxic effects; and should not be homologous to the mammalian host. The discussion regarding this subject and the usefulness of “exposed” and “concealed” antigens was effectively explored in the publication by Nuttall et al. (2006). The present commentary intends to debate the relevance of such study in the field of tick immunological control.

Inspiring Anti-Tick Vaccine Research, Development and Deployment in Tropical Africa for the Control of Cattle Ticks: Review and Insights

Ticks are worldwide ectoparasites to humans and animals, and are associated with numerous health and economic effects. Threatening over 80% of the global cattle population, tick and tick-borne diseases (TTBDs) particularly constrain livestock production in the East, Central and Southern Africa. This, therefore, makes their control critical to the sustainability of the animal industry in the region. Since ticks are developing resistance against acaricides, anti-tick vaccines (ATVs) have been proposed as an environmentally friendly control alternative. Whereas they have been used in Latin America and Australia to reduce tick populations, pathogenic infections and number of acaricide treatments, commercially registered ATVs have not been adopted in tropical Africa for tick control. This is majorly due to their limited protection against economically important tick species of Africa and lack of research. Recent advances in various omics technologies and reverse vaccinology have enabled the identification of many candidate anti-tick antigens (ATAs), and are likely to usher in the next generation of vaccines, for which Africa should prepare to embrace. Herein, we highlight some scientific principles and approaches that have been used to identify ATAs, outline characteristics of a desirable ATA for vaccine design and propose the need for African governments to investment in ATV research to develop vaccines relevant to local tick species (personalized vaccines). We have also discussed the prospect of incorporating anti-tick vaccines into the integrated TTBDs control strategies in the sub-Saharan Africa, citing the case of Uganda.

Molecular targets for the development of new acaricides against Rhipicephalus microplus: a review

The cattle tick Rhipicephalus microplus is an ectoparasite with high economic importance to bovine culture, mainly in tropical and subtropical regions. The resistance of the tick from the commercial acaricides has hindered its control, thus motivating the search for new strategies. The purpose of this study was to perform a critical review about the main molecular targets of R. microplus that are useful for the discovery of new acaricides. Bibliographic search was conducted in the databases PubMed, ScienceDirect and CAB Direct, using the following descriptors: ‘Rhipicephalus microplus’, ‘Boophilus microplus’, ‘molecular targets’ and ‘action’, published between 2010 and 2021. Out of the 212 publications identified, 17 articles were selected for study inclusion. This review described 14 molecular targets and among these 4 are targets from commercial acaricides. Most of them are enzymes to catalyse important reactions to tick survival, related to energetic metabolism, mechanisms of biotransformation and neurotransmission. The data will be helpful in the development of new more effective and selective acaricides.

Recombinant cysteine proteinase as anti-tick targeting Hyalomma asiaticum infestation

Cysteine proteases are involved in the digestion of host blood and the degradation of yolk proteins of arthropod ectoparasites. In this study, a cathepsin L-like cysteine proteinase gene (HasCPL) of Hyalomma asiaticum was cloned, and recombinant (r)HasCPL protein was generated for immunization study. Bioinformatic analysis confirmed HasCPL was a member of the papain family (clan CA) and have high sequence identities with CPLs of other Ixodid ticks. The efficacy of immunization against H. asiaticum infestations in rabbits was assessed. Rabbits (n = 3) were immunized three times with rHasCPL before challenged with 250 larvae per rabbit four weeks post-immunization. A high antibody titer was detected in immunized rabbits in comparison to control. Western blot analysis detected CPLs in midgut, salivary gland, and ovary. Increase of rejection percentage of larvae were noted in ticks fed on immunized animals in comparison to control. Overall, a 55.09% protection against larva ticks was noted.

Anti-Tick Vaccines: Current Advances and Future Prospects

Ticks are increasingly a global public health and veterinary concern. They transmit numerous pathogens that are of veterinary and public health importance. Acaricides, livestock breeding for tick resistance, tick handpicking, pasture spelling, and anti-tick vaccines (ATVs) are in use for the control of ticks and tick-borne diseases (TTBDs); acaricides and ATVs being the most and least used TTBD control methods respectively. The overuse and misuse of acaricides has inadvertently selected for tick strains that are resistant to acaricides. Furthermore, vaccines are rare and not commercially available in sub-Saharan Africa (SSA). It doesn't help that many of the other methods are labor-intensive and found impractical especially for larger farm operations. The success of TTBD control is therefore dependent on integrating all the currently available methods. Vaccines have been shown to be cheap and effective. However, their large-scale deployment for TTBD control in SSA is hindered by commercial unavailability of efficacious anti-tick vaccines against sub-Saharan African tick strains. Thanks to advances in genomics, transcriptomics, and proteomics technologies, many promising anti-tick vaccine antigens (ATVA) have been identified. However, few of them have been investigated for their potential as ATV candidates. Reverse vaccinology (RV) can be leveraged to accelerate ATV discovery. It is cheap and shortens the lead time from ATVA discovery to vaccine production. This chapter provides a brief overview of recent advances in ATV development, ATVs, ATV effector mechanisms, and anti-tick RV. Additionally, it provides a detailed outline of vaccine antigen selection and analysis using computational methods.

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.

Rhipicephalus microplus: An overview of vaccine antigens against the cattle tick

Rhipicephalus microplus, popularly known as the cattle tick, is the most important tick of livestock as it is responsible for significant economic losses. The use of chemical acaricides is still the most widely used control method despite its known disadvantages. Vaccination would be a safe alternative for the control of R. microplus and holds advantages over the use of chemical acaricides as it is environmental-friendly and leaves no residues in meat or milk. Two vaccines based on the Bm86 protein were commercialized, TickGARD® and Gavac®, with varying reported efficacies in different countries. The use of other vaccines, such as Tick Vac®, Go-Tick®, and Bovimune Ixovac® have been restricted to some countries. Several other proteins have been analyzed as possible antigens for more effective vaccines against R. microplus, including peptidases, serine proteinase inhibitors, glutathione S-transferases, metalloproteases, and ribosomal proteins, with efficacies ranging from 14% to 96%. Nonetheless, more research is needed to develop safe and efficient tick vaccines, such as the evaluation of the efficacy of antigens against other tick species to verify cross-reactivity and inclusion of additional antigens to promote the blocking of the infection and spreading of tick-borne diseases. This review summarizes the discoveries of candidate antigens for R. microplus tick vaccines as well as the methods used to test their efficacy.

Identification and functional analysis of ferritin 2 from the Taiga tick Ixodes persulcatus Schulze

Ferritin 2 (FER2) is an iron storage protein, which has been shown to be critical for iron homeostasis during blood feeding and reproduction in ticks and is therefore suitable as a component for anti-tick vaccines. In this study, we identified the FER2 of Ixodes persulcatus, a major vector for zoonotic diseases such as Lyme borreliosis and tick-borne relapsing fever in Japan, and investigated its functions. Ixodes persulcatus-derived ferritin 2 (Ip-FER2) showed concentration-dependent iron-binding ability and high amino acid conservation, consistent with FER2s of other tick species. Vaccines containing the recombinant Ip-FER2 elicited a significant reduction of the engorgement weight of adult I. persulcatus. Interestingly, the reduction of engorgement weight was also observed in Ixodes ovatus, a sympatric species of I. persulcatus. In silico analyses of FER2 sequences of I. persulcatus and other ticks showed a greater similarity with I. scapularis and I. ricinus and lesser similarity with Hyalomma anatolicum, Haemaphysalis longicornis, Rhipicephalus microplus, and R. appendiculatus. Moreover, it was observed that the tick FER2 sequences possess conserved regions within the primary structures, and in silico epitope mapping analysis revealed that antigenic regions were also conserved, particularly among Ixodes spp ticks. In conclusion, the data support further protective tick vaccination applications using the Ip-FER2 antigens identified herein.

Cocktail Anti-Tick Vaccines: The Unforeseen Constraints and Approaches toward Enhanced Efficacies

Ticks are second to mosquitoes as vectors of disease. Ticks affect livestock industries in Asia, Africa and Australia at ~$1.13 billion USD per annum. For instance, 80% of the global cattle population is at risk of infestation by the Rhipicephalus microplus species-complex, which in 2016 was estimated to cause $22-30 billion USD annual losses. Although the management of tick populations mainly relies on the application of acaricides, this raises concerns due to tick resistance and accumulation of chemical residues in milk, meat, and the environment. To counteract acaricide-resistant tick populations, immunological tick control is regarded among the most promising sustainable strategies. Indeed, immense efforts have been devoted toward identifying tick vaccine antigens. Until now, Bm86-based vaccines have been the most effective under field conditions, but they have shown mixed success worldwide. Currently, of the two Bm86 vaccines commercialized in the 1990s (GavacTM in Cuba and TickGARDPLUSTM in Australia), only GavacTM is available. There is thus growing consensus that combining antigens could broaden the protection range and enhance the efficacies of tick vaccines. Yet, the anticipated outcomes have not been achieved under field conditions. Therefore, this review demystifies the potential limitations and proposes ways of sustaining enhanced cocktail tick vaccine efficacy.

Understanding Tick Biology and Its Implications in Anti-tick and Transmission Blocking Vaccines Against Tick-Borne Pathogens

Ticks are obligate blood-feeding ectoparasites that transmit a wide variety of pathogens to animals and humans in many parts of the world. Currently, tick control methods primarily rely on the application of chemical acaricides, which results in the development of resistance among tick populations and environmental contamination. Therefore, an alternative tick control method, such as vaccines have been shown to be a feasible strategy that offers a sustainable, safe, effective, and environment-friendly solution. Nevertheless, novel control methods are hindered by a lack of understanding of tick biology, tick-pathogen-host interface, and identification of effective antigens in the development of vaccines. This review highlights the current knowledge and data on some of the tick-protective antigens that have been identified for the formulation of anti-tick vaccines along with the effects of these vaccines on the control of tick-borne diseases.

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.

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.

Rhipicephalus microplus cystatin as a potential cross-protective tick vaccine against Rhipicephalus appendiculatus

Rhipicephalus appendiculatus, the brown ear tick, is an important disease vector of livestock in eastern, central and southern Africa. Rhipicephalus appendiculatus acaricide resistance requires the search for alternative methods for its control. Cystatins constitute a superfamily of cysteine peptidase inhibitors vital for tick blood feeding and development. These inhibitors were proposed as antigens in anti-tick vaccines. In this work, we applied structural and biochemical approaches to characterize a new cystatin named R. appendiculatus cystatin 2a (Racys2a). Structural modeling showed that this new protein possesses characteristic type 2 cystatin motifs, besides conservation of other structural patterns along the protein. Peptidase inhibitory assays with recombinant Racys2a showed modulation of tick and host cathepsins involved in blood digestion and immune system responses, respectively. A heterologous tick challenge with R. appendiculatus in rabbits immunized with recombinant Rhipicephalus microplus cystatin 2c (rBmcys2c) was performed to determine cross-reactivity. Histological staining showed that rBmcys2c vaccination caused damage to the gut, salivary gland and ovary tissues in R. appendiculatus. Furthermore, cystatin vaccine reduced the number of fully engorged adult females in 11.5 %. Consequently, strategies to increase the protection rate are necessary, including the selection of two or more antigens to compose a vaccine cocktail.

Constituting a glutathione S-transferase-cocktail vaccine against tick infestation

Cocktail vaccines are proposed as an attractive way to increase protection efficacy against specific tick species. Furthermore, such vaccines made with different tick antigens have the potential of cross-protecting against a broad range of tick species. However, there are still limitations to the selection of immunogen candidates. Acknowledging that glutathione S-transferases (GSTs) have been exploited as vaccines against ticks and other parasites, this study aimed to analyze a GST-cocktail vaccine as a potential broad-spectrum tick vaccine. To constitute the GST-cocktail vaccine, five tick species of economic importance for livestock industry were studied (Rhipicephalus appendiculatus, Rhipicephalus decoloratus, Rhipicephalus microplus, Amblyomma variegatum, and Haemaphysalis longicornis). Tick GST ORF sequences were cloned, and the recombinant GSTs were produced in Escherichia coli. rGSTs were purified and inoculated into rabbits, and the immunological response was characterized. The humoral response against rGST-Rd and rGST-Av showed a stronger cross-reactivity against heterologous rGSTs compared to rGST-Hl, rGST-Ra, and rGST-Rm. Therefore, rGST-Rd and rGST-Av were selected for constituting an experimental rGST-cocktail vaccine. Vaccination experiment in rabbits showed that rGST-cocktail caused 35% reduction in female numbers in a Rhipicephalus sanguineus infestation. This study brings forward an approach to selecting immunogens for cocktail vaccines, and the results highlight rGST-Rd and rGST-Av as potentially useful tools for the development of a broad-spectrum tick vaccine.

CYTED Network to develop an immunogen compatible with integrated management strategies for tick control in cattle

INCOGARR is a thematic network recently approved to be financially supported by the Ibero-American Program of Science and Technology for Development (CYTED). The objectives of this Network are the design and evaluation of an efficient and feasible anti-tick vaccine candidate from the technical and economical points of view and also sharing experiences in the immunological control of ticks as part of an Integrated Control Program. The Network consists of seven laboratories and one company from six countries. The first meeting of the Network took place with the representation of each laboratory involved. In the meeting, general and specific objectives and activities of the Network were discussed and it was a very nice example of international collaboration to address an unsolved worldwide topic on tick control in which laboratories with different competencies and expertise join their efforts in a common goal.

Inducible glutathione S-transferase (IrGST1) from the tick Ixodes ricinus is a haem-binding protein

Blood-feeding parasites are inadvertently exposed to high doses of potentially cytotoxic haem liberated upon host blood digestion. Detoxification of free haem is a special challenge for ticks, which digest haemoglobin intracellularly. Ticks lack a haem catabolic mechanism, mediated by haem oxygenase, and need to dispose of vast majority of acquired haem via its accumulation in haemosomes. The knowledge of individual molecules involved in the maintenance of haem homeostasis in ticks is still rather limited. RNA-seq analyses of the Ixodes ricinus midguts from blood- and serum-fed females identified an abundant transcript of glutathione S-transferase (gst) to be substantially up-regulated in the presence of red blood cells in the diet. Here, we have determined the full sequence of this encoding gene, ir-gst1, and found that it is homologous to the delta-/epsilon-class of GSTs. Phylogenetic analyses across related chelicerates revealed that only one clear IrGST1 orthologue could be found in each available transcriptome from hard and soft ticks. These orthologues create a well-supported clade clearly separated from other ticks' or mites' delta-/epsilon-class GSTs and most likely evolved as an adaptation to tick blood-feeding life style. We have confirmed that IrGST1 expression is induced by dietary haem(oglobin), and not by iron or other components of host blood. Kinetic properties of recombinant IrGST1 were evaluated by model and natural GST substrates. The enzyme was also shown to bind haemin in vitro as evidenced by inhibition assay, VIS spectrophotometry, gel filtration, and affinity chromatography. In the native state, IrGST1 forms a dimer which further polymerises upon binding of excessive amount of haemin molecules. Due to susceptibility of ticks to haem as a signalling molecule, we speculate that the expression of IrGST1 in tick midgut functions as intracellular buffer of labile haem pool to ameliorate its cytotoxic effects upon haemoglobin intracellular hydrolysis.

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.

Characterization and expression analysis of a newly identified glutathione S-transferase of the hard tick Haemaphysalis longicornis during blood-feeding

Background

Ticks are obligate hematophagous parasites important economically and to health. Ticks consume large amounts of blood for their survival and reproduction; however, large amounts of iron in blood could lead to oxidative stress. Ticks use several molecules such as glutathione S-transferases (GSTs), ferritins, and peroxiredoxins to cope with oxidative stress. This study aimed to identify and characterize the GSTs of the hard tick Haemaphysalis longicornis in order to determine if they have a role in coping with oxidative stress.

Methods

Genes encoding GSTs of H. longicornis were isolated from the midgut CDNA library. Genes have been cloned and recombinant GSTs have been expressed. The enzymatic activities, enzyme kinetic constants, and optimal pH of the recombinant GSTs toward 1-chloro-2,4-dinitrobenzene (CDNB) were determined. The gene transcription and protein expression profiles were determined in the whole ticks and internal organs, and developmental stages using real time RT-PCR and Western blotting during blood feeding. The localization of GST proteins in organs was also observed using immunofluorescent antibody test (IFAT).

Results

We have isolated two genes encoding GSTs (HlGST and HlGST2). The enzymatic activity toward CDNB is 9.75 ± 3.04 units/mg protein for recombinant HlGST and 11.63 ± 4.08 units/mg protein for recombinant HlGST2. Kinetic analysis of recombinant HlGST showed K_m values of 0.82 ± 0.14 mM and 0.64 ± 0.32 mM for the function of CDNB and GSH, respectively. Meanwhile, recombinant HlGST2 has K_m values of 0.61 ± 0.20 mM and 0.53 ± 0.02 mM for the function of CDNB and GSH, respectively. The optimum pH of recombinant HlGST and recombinant HlGST2 activity was 7.5–8.0. Transcription of both GSTs increases in different developmental stages and organs during blood-feeding. GST proteins are upregulated during blood-feeding but decreased upon engorgement in whole ticks and in some organs, such as the midgut and hemocytes. Interestingly, salivary glands, ovaries, and fat bodies showed decreasing protein expression during blood-feeding to engorgement. Varying localization of GSTs in the midgut, salivary glands, fat bodies, ovaries, and hemocytes was observed depending on the feeding state, especially in the midgut and salivary glands.

Conclusions

In summary, a novel GST of H. longicornis has been identified. Characterization of the GSTs showed that GSTs have positive correlation with the degree and localization of oxidative stress during blood-feeding. This could indicate their protective role during oxidative stress.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-2667-1) contains supplementary material, which is available to authorized users.

Molecular and structural characterization of novel cystatins from the taiga tick Ixodes persulcatus

Cystatins are cysteine peptidase inhibitors that in ticks mediate processes such as blood feeding and digestion. The ixodid tick Ixodes persulcatus is endemic to the Eurasia, where it is the principal vector of Lyme borreliosis. To date, no I. persulcatus cystatin has been characterized. In the present work, we describe three novel cystatins from I. persulcatus, named JpIpcys2a, JpIpcys2b and JpIpcys2c. In addition, the potential of tick cystatins as cross-protective antigens was evaluated by vaccination of hamsters using BrBmcys2c, a cystatin from Rhipicephalus microplus, against I. persulcatus infestation. Sequence analysis showed that motifs that are characteristic of cystatins type 2 are fully conserved in JpIpcys2b, while mutations are present in both JpIpcys2a and JpIpcys2c. Protein-protein docking simulations further revealed that JpIpcys2a, JpIpcys2b and JpIpcys2c showed conserved binding sites to human cathepsins L, all of them covering the active site cleft. Cystatin transcripts were detected in different I. persulcatus tissues and instars, showing their ubiquitous expression during I. persulcatus development. Serological analysis showed that although hamsters immunized with BrBmcys2c developed a humoral immune response, this response was not adequate to protect against a heterologous challenge with I. persulcatus adult ticks. The lack of cross-protection provided by BrBmcys2c immunization is perhaps linked to the fact that cystatins cluster into multigene protein families that are expressed differentially and exhibit functional redundancy. How to target such small proteins that are secreted in low quantities remains a challenge in the development of suitable anti-tick vaccine antigens.

Transfected Babesia bovis Expressing a Tick GST as a Live Vector Vaccine

The Rhipicephalus microplus tick is a notorious blood-feeding ectoparasite of livestock, especially cattle, responsible for massive losses in animal production. It is the main vector for transmission of pathogenic bacteria and parasites, including Babesia bovis, an intraerythrocytic apicomplexan protozoan parasite responsible for bovine Babesiosis. This study describes the development and testing of a live B. bovis vaccine expressing the protective tick antigen glutathione-S-transferase from Haemaphysalis longicornis (HlGST). The B. bovis S74-T3B parasites were electroporated with a plasmid containing the bidirectional Ef-1α (elongation factor 1 alpha) promoter of B. bovis controlling expression of two independent genes, the selectable marker GFP-BSD (green fluorescent protein–blasticidin deaminase), and HlGST fused to the MSA-1 (merozoite surface antigen 1) signal peptide from B. bovis. Electroporation followed by blasticidin selection resulted in the emergence of a mixed B. bovis transfected line (termed HlGST) in in vitro cultures, containing parasites with distinct patterns of insertion of both exogenous genes, either in or outside the Ef-1α locus. A B. bovis clonal line termed HlGST-Cln expressing intracellular GFP and HlGST in the surface of merozoites was then derived from the mixed parasite line HlGST using a fluorescent activated cell sorter. Two independent calf immunization trials were performed via intravenous inoculation of the HlGST-Cln and a previously described control consisting of an irrelevant transfected clonal line of B. bovis designated GFP-Cln. The control GFP-Cln line contains a copy of the GFP-BSD gene inserted into the Ef-1α locus of B. bovis in an identical fashion as the HIGST-Cln parasites. All animals inoculated with the HlGST-Cln and GFP-Cln transfected parasites developed mild babesiosis. Tick egg fertility and fully engorged female tick weight was reduced significantly in R. microplus feeding on HlGST-Cln-immunized calves. Collectively, these data show the efficacy of a transfected HlGST-Cln B. bovis parasite to induce detectable anti-glutathione-S-transferase antibodies and a reduction in tick size and fecundity of R. microplus feeding in experimentally inoculated animals.

The cattle tick Rhipicephalus microplus is a hematophagous ectoparasite, responsible for the transmission of lethal parasites such as Babesia sp, limiting cattle production in tropical and subtropical regions of the world. There is an urgent emerging need for improved methods of control for these currently neglected tick and tick borne diseases. It is hypothesized that a dual attenuated-live vector vaccine containing a stably transfected tick antigen elicits protective immune responses against the parasite and the tick vector in vaccinated cattle. Live Babesia vaccines based on attenuated parasites are the only effective method available for preventing acute babesiosis. On the other hand, glutathione-S-transferase from Haemaphysalis longicornis (HlGST) is a known effective antigen against Rhipicephalus microplus, the most common vector for B. bovis. This study describes the development and testing of a transfected, B. bovis vaccine expressing HlGST against the tick R. microplus. A B. bovis clonal line designated HlGST-Cln expressing HlGST and GFP/BSD, and separately a control transfected B. bovis clonal line expressing only GFP/BSD was used to vaccinate calves in two independent experiments. All immunized calves developed mild babesiosis, and only calves immunized with the HlGST-Cln parasite line generated anti-HlGST antibodies. Tick egg fertility and fully engorged female tick weight were reduced significantly in R. microplus feeding on HlGST-Cln-vaccinated calves. Taken together, these data demonstrates the ability of transfected B. bovis to elicit antibodies against a heterologous tick antigen in cattle and to induce partial protection in the vaccinated animals against the cattle tick for the first time, representing a step toward the goal to produce a live vector anti-tick vaccine.

An overview on different aspects of hypodermosis: Current status and future prospects

Livestock plays a vital role in economic development of a nation and is being used in agriculture for draft power, production of farmyard manure as well as milk and meat production. Bovine hypodermosis is the top culprit among all parasitic infections across the world. Hypodermosis is an endemic disease in the mountainous areas/plain areas and is regularly observed in the northern hemisphere of the globe affecting cattle, deer, yaks and buffaloes. There is a wide variation in geographical distribution of Hypoderma spp. during the years 1945-2015. The manuscript includes a geospatial study that tries to maps the global distribution of hypodermosis in different areas of the world in order to detect hotspots or endemic areas that may be a potential source for disease spread. This information's are very useful to predict the potential high risk areas that are prone to disease outbreak. The present review aims to evaluate the global distribution, molecular discrimination, diagnostics and vaccination of hypodermosis, focusing on its current status and future perspectives towards the management of the disease and its control strategies.

Strategies for new and improved vaccines against ticks and tick-borne diseases

Ticks infest a variety of animal species and transmit pathogens causing disease in both humans and animals worldwide. Tick-host-pathogen interactions have evolved through dynamic processes that accommodated the genetic traits of the hosts, pathogens transmitted and the vector tick species that mediate their development and survival. New approaches for tick control are dependent on defining molecular interactions between hosts, ticks and pathogens to allow for discovery of key molecules that could be tested in vaccines or new generation therapeutics for intervention of tick-pathogen cycles. Currently, tick vaccines constitute an effective and environmentally sound approach for the control of ticks and the transmission of the associated tick-borne diseases. New candidate protective antigens will most likely be identified by focusing on proteins with relevant biological function in the feeding, reproduction, development, immune response, subversion of host immunity of the tick vector and/or molecules vital for pathogen infection and transmission. This review addresses different approaches and strategies used for the discovery of protective antigens, including focusing on relevant tick biological functions and proteins, reverse genetics, vaccinomics and tick protein evolution and interactomics. New and improved tick vaccines will most likely contain multiple antigens to control tick infestations and pathogen infection and transmission.

A review of reverse vaccinology approaches for the development of vaccines against ticks and tick borne diseases

The field of reverse vaccinology developed as an outcome of the genome sequence revolution. Following the introduction of live vaccinations in the western world by Edward Jenner in 1798 and the coining of the phrase 'vaccine', in 1881 Pasteur developed a rational design for vaccines. Pasteur proposed that in order to make a vaccine that one should 'isolate, inactivate and inject the microorganism' and these basic rules of vaccinology were largely followed for the next 100 years leading to the elimination of several highly infectious diseases. However, new technologies were needed to conquer many pathogens which could not be eliminated using these traditional technologies. Thus increasingly, computers were used to mine genome sequences to rationally design recombinant vaccines. Several vaccines for bacterial and viral diseases (i.e. meningococcus and HIV) have been developed, however the on-going challenge for parasite vaccines has been due to their comparatively larger genomes. Understanding the immune response is important in reverse vaccinology studies as this knowledge will influence how the genome mining is to be conducted. Vaccine candidates for anaplasmosis, cowdriosis, theileriosis, leishmaniasis, malaria, schistosomiasis, and the cattle tick have been identified using reverse vaccinology approaches. Some challenges for parasite vaccine development include the ability to address antigenic variability as well the understanding of the complex interplay between antibody, mucosal and/or T cell immune responses. To understand the complex parasite interactions with the livestock host, there is the limitation where algorithms for epitope mining using the human genome cannot directly be adapted for bovine, for example the prediction of peptide binding to major histocompatibility complex motifs. As the number of genomes for both hosts and parasites increase, the development of new algorithms for pan-genomic mining will continue to impact the future of parasite and ricketsial (and other tick borne pathogens) disease vaccine development.

Acaricidal properties of vetiver essential oil from Chrysopogon zizanioides (Poaceae) against the tick species Amblyomma cajennense and Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

Ticks are arthropods widely distributed in tropical and subtropical regions, which can transmit infectious agents also responsible for zoonoses. Excessive use of conventional acaricides has resulted in the onset of drug resistance by these parasites, thus the need to use alternative methods for their control. This study evaluated the acaricidal activities of Chrysopogon zizanioides (vetiver) essential oils containing different zizanoic and khuzimol (high and low acidity) acid concentrations on Amblyomma cajennense and Rhipicephalus microplus (Acari: Ixodidae). To this aims, toxicity tests of different concentrations of examined essential oils were conducted on adult females and larval stages. Results showed that the essential oils of C. zizanioides with high and low acidity reduced oviposition of females, eggs hatch and larval survival, being more effective than some commercial products widely used to control these ectoparasites. These results indicate that the C. zizanoides essential oils are promising candidates as acaricidal agents and represent also an add value to vetiver oil with high acidity, which is commercially undervalued in the cosmetic industry.

New salivary anti-haemostatics containing protective epitopes from Ornithodoros moubata ticks: Assessment of their individual and combined vaccine efficacy

Ornithodoros moubata is the main vector of the pathogens causing African swine fever and human relapsing fever in Africa. The development of an efficient vaccine against this tick would facilitate its control and the prevention of the diseases it transmits to a considerable extent. Previous efforts to identify vaccine target candidates led us to the discovery of novel salivary proteins that probably act as anti-haemostatics at the host-tick interface, including a secreted phospholipase A2 (PLA2), a 7DB-like protein (7DB-like), a riboprotein 60S L10 (RP-60S), an apyrase (APY), and a new platelet aggregation inhibitor peptide, designated mougrin (MOU). In this work, the corresponding recombinant proteins were expressed in Escherichia coli and their individual vaccine efficacy was tested in rabbit vaccination trials. All of them, except the less immunogenic RP-60S, induced strong humoral responses that reduced tick feeding and survival, providing vaccine efficacies of 44.2%, 43.2% and 27.2%, 19.9% and 17.3% for PLA2, APY, MOU, RP-60S and 7DB-like, respectively. In the case of the more protective recombinant antigens (PLA2, APY and MOU), the immunodominant protective linear B-cell epitopes were identified and their combined vaccine efficacy was tested in a second vaccine trial using different adjuvants. In comparison with the best efficacy of individual antigens, the multicomponent vaccine increased vaccine efficacy by 13.6%, indicating additive protective effects rather than a synergistic effect. Tick saliva inoculated during natural tick-host contacts had a boosting effect on vaccinated animals, increasing specific antibody levels and protection.

Characterisation of Dermanyssus gallinae glutathione S-transferases and their potential as acaricide detoxification proteins

BACKGROUND

Glutathione S-transferases (GSTs) facilitate detoxification of drugs by catalysing the conjugation of the reduced glutathione (GSH) to electrophilic xenobiotic substrates and therefore have a function in multi-drug resistance. As a result, knowledge of GSTs can inform both drug resistance in, and novel interventions for, the control of endo- and ectoparasite species. Acaricide resistance and the need for novel control methods are both pressing needs for Dermanyssus gallinae, a highly economically important haematophagous ectoparasite of poultry.

METHODS

A transcriptomic database representing D. gallinae was examined and 11 contig sequences were identified with GST BlastX identities. The transcripts represented by 3 contigs, designated Deg-GST-1, -2 and -3, were fully sequenced and further characterized by phylogenetic analysis. Recombinant versions of Deg-GST-1, -2 and -3 (rDeg-GST) were enzymically active and acaricide-binding properties of the rDeg-GSTs were established by evaluating the ability of selected acaricides to inhibit the enzymatic activity of rDeg-GSTs.

RESULTS

6 of the identified GSTs belonged to the mu class, followed by 3 kappa, 1 omega and 1 delta class molecules. Deg-GST-1 and -3 clearly partitioned with orthologous mu class GSTs and Deg-GST-2 partitioned with delta class GSTs. Phoxim, permethrin and abamectin significantly inhibited rDeg-GST-1 activity by 56, 35 and 17% respectively. Phoxim also inhibited rDeg-2-GST (14.8%) and rDeg-GST-3 (20.6%) activities.

CONCLUSIONS

Deg-GSTs may have important roles in the detoxification of pesticides and, with the increased occurrence of acaricide resistance in this species worldwide, Deg-GSTs are attractive targets for novel interventions.

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

BACKGROUND

Haemaphysalis longicornis is a major vector of Theileria spp., Anaplasma phagocytophilum, Babesia spp. and Coxiella burnetti in East Asian countries. All life stages of ixodid ticks have a destructive pool-feeding style in which they create a pool-feeding site by lacerating host tissue and secreting a variety of biologically active compounds that allows the tick to evade host responses, enabling the uptake of a blood meal. The identification and functional characterization of tick saliva proteins can be useful to elucidate the molecular mechanisms involved in tick development and to conceive new anti-tick control methods.

METHODS

H. longicornis tick saliva was collected from fully engorged nymphs and fully engorged adults induced by dopamine or pilocarpine, respectively. Saliva was digested with trypsin for LC-MS/MS sequencing and peptides were searched against tick and rabbit sequences.

RESULTS

A total of 275 proteins were identified, of which 135 were tick and 100 were rabbit proteins. Of the tick proteins, 30 proteins were identified exclusively in fully engorged nymph saliva, 74 in fully engorged adult females, and 31 were detected in both stages. The identified tick proteins include heme/iron metabolism-related proteins, oxidation/detoxification proteins, enzymes, proteinase inhibitors, tick-specific protein families, and cytoskeletal proteins. Proteins involved in signal transduction, transport and metabolism of carbohydrate, energy, nucleotide, amino acids and lipids were also detected. Of the rabbit proteins, 13 were present in nymph saliva, 48 in adult saliva, and 30 were present in both. The host proteins include immunoglobulins, complement system proteins, antimicrobial proteins, serum albumin, peroxiredoxin, serotransferrin, apolipoprotein, hemopexin, proteinase inhibitors, and hemoglobin/red blood cells-related products.

CONCLUSIONS

This study allows the identification of H. longicornis saliva proteins. In spontaneously detached tick saliva various proteins were identified, although results obtained with saliva of fully engorged ticks need to be carefully interpreted. However, it is interesting to note that proteins identified in this study were also described in other tick saliva proteomes using partially engorged tick saliva, including hemelipoprotein, proteases, protease inhibitors, proteins related to structural functions, transporter activity, metabolic processes, and others. In conclusion, these data can provide a deeper understanding to the biology of H. longicornis.

Transmembrane proteins--Mining the cattle tick transcriptome

Managing the spread and load of pathogen-transmitting ticks is an important task worldwide. The cattle tick, Rhipicephalus microplus, not only impacts the economy through losses in dairy and meat production, but also raises concerns for human health in regards to the potential of certain transmitted pathogens becoming zoonotic. However, novel strategies to control R. microplus are hindered by lack of understanding tick biology and the discovery of suitable vaccine or acaricide targets. The importance of transmembrane proteins as vaccine targets are well known, as is the case in tick vaccines with Bm86 as antigen. In this study, we describe the localization and functional annotation of 878 putative transmembrane proteins. Thirty proteins could be confirmed in the R. microplus gut using LC-MS/MS analysis and their roles in tick biology are discussed. To the best of our knowledge, 19 targets have not been reported before in any proteomics study in various tick species and the possibility of using the identified proteins as targets for tick control are discussed. Although tissue expression of identified putative proteins through expansive proteomics is necessary, this study demonstrates the possibility of using bioinformatics for the identification of targets for further evaluation in tick control strategies.

Vaccination with cyclin-dependent kinase tick antigen confers protection against Ixodes infestation

Among arthropods, ticks lead as vectors of animal diseases and rank second to mosquitoes in transmitting human pathogens. Cyclin-dependent kinases (CDK) participate in cell cycle control in eukaryotes. CDKs are serine/threonine protein kinases and these catalytic subunits are activated or inactivated at specific stages of the cell cycle. To determine the potential of using CDKs as anti-tick vaccine antigens, hamsters were immunized with recombinant Ixodes persulcatus CDK10, followed by a homologous tick challenge. Though it was not exactly unexpected, IpCDK10 vaccination significantly impaired tick blood feeding and fecundity, which manifested as low engorgement weights, poor oviposition, and a reduction in 80% of hatching rates. These findings may underpin the development of more efficacious anti-tick vaccines based on the targeting of cell cycle control proteins.

High efficacy of a 20 amino acid peptide of the acidic ribosomal protein P0 against the cattle tick, Rhipicephalus microplus

Current strategies to control cattle ticks use integrated control programs (ICP) that include vaccination. Reduction in the use of chemicals and in the cost of tick control, the delay or elimination of acaricide resistance and the decreasing of environmental pollution are the advantages of using these programs. This integrated program is potentially applicable to all genotypes of chemical resistant ticks. However, the problem here is to improve the efficacy of anti-tick vaccines. The P0 protein is a structural component of the ribosome of all organisms. We have identified an immunogenic region of ribosomal protein P0 from Rhipicephalus spp. ticks that is not very conserved compared to the orthologous protein in their hosts. A synthetic 20 amino acid peptide from this sequence was effective as a vaccine against Rhipicephalus sanguineus infestations in an immunization and challenge experiment using rabbits. In this paper, the same peptide used as vaccine against the cattle tick Rhipicephalus Boophilus microplus shows a significant diminution in the number of engorged females recovered, in the weight of females and the weight of egg masses. The number of eggs hatched was also significantly reduced for the vaccinated group, with an overall effectivity for the antigen pP0 of 96%. These results, together with the conserved sequence of the P0 peptide among ticks, suggest that this antigen could be a good broad spectrum vaccine candidate. It would be expected to be active against many species of ticks and thus has promise in an ICP for effective control of ticks and thereby to improve the efficiency and productivity of the livestock industry.

Rhipicephalus microplus and Ixodes ovatus cystatins in tick blood digestion and evasion of host immune response

BACKGROUND

Cystatins are a group of cysteine protease inhibitors responsible for physiological proteolysis regulation and present in a wide range of organisms. Studies about this class of inhibitors in parasites have contributed to clarify their roles in important physiological processes, like blood digestion and modulation of host immune response during blood feeding. Thus, cystatins are a subject of research on the development of new parasite control methods. Additionally, the characterization of proteins shared by different parasite species represents a valuable strategy to find potential targets in multi-species control methods. However, cystatin functions in ticks remain undetermined, especially in Rhipicephalus microplus and Ixodes ovatus, two species that affect livestock and human health, respectively.

METHODS

Here we report the inhibitory profile of two R. microplus (BrBmcys2b and BrBmcys2c) and one I. ovatus (JpIocys2a) cystatins to commercial cathepsins B, C, and L. The presence of native cystatins in R. microplus tissues was analyzed using sera against recombinant BrBmcys2b and BrBmcys2c. Also, a peptide from JpIocys2a was synthesized for rabbit immunization, and this serum was used to analyze the cross antigenicity between R. microplus and I. ovatus cystatins.

RESULTS

Enzymatic inhibition profile of tick cystatins shows a distinct modulation for cathepsins related to tick blood digestion and evasion of host immune response. Furthermore, BrBmcys2b was detected in saliva and different tissues along tick stages, while BrBmcys2c was detected mainly in gut from partially engorged R. microplus females, demonstrating a distinct pattern of cystatin expression, secretion and traffic between tick tissues. Moreover, phylogenetic analysis suggests that JpIocys2a belongs to the group of tick gut secreted cystatins. Finally, cross-antigenicity assays revealed that antibodies against the JpIocys2a peptide recognize native and recombinant R. microplus cystatins.

CONCLUSION

The presence of these proteins in different tissues and their ability to differentially inhibit cathepsins suggest distinct roles for JpIocys2a, BrBmcys2b, and BrBmcys2c in blood digestion, egg and larvae development, and modulation of host immune response in tick physiology. The cross-antigenicity between native and recombinant cystatins supports further experiments using JpIocys2a, BrBmcys2b, and BrBmcys2c as vaccine antigens.

The immunobiology of myiasis infections--whatever happened to vaccination?

The current state of myiasis vaccine technologies are reviewed mainly in the primary research genera of Lucilia and Hypoderma. The importance of myiasis flies as primary causes of morbidity and mortality in agricultural species and man has not diminished despite the existence of good control strategies. However, the development of vaccines against myiasis infections has been relatively quiescent for more than 10 years despite the rapid development of genomic and proteomic analysis and of skills in data interpretation. The value of vaccine research in an era of chemical primacy is analysed. In fact, recent findings of drug resistance and the impact of animal welfare concerns should mean a renewed interest in alternative controls. The reasons that this has not been true to date are explored and new possibilities discussed.

Immunoprotective potential of a Rhipicephalus (Boophilus) microplus metalloprotease

Ticks have serious impacts on animal and human health, causing significant economic losses in cattle breeding. Besides damage due to the hematophagous behavior, they transmit several pathogens. Low cost and environmental safety have made vaccines a promising alternative control method against tick infestation. Metalloproteases (MPs) have been shown to be essential for diverse biological functions in hematophagous organisms, inhibiting blood clotting, degrading extracellular matrix proteins, and inhibiting host tissue repair via anti-angiogenic activity. In this study, we analyzed the immunoprotective potential of a recombinant MP against Rhipicephalus (Boophilus) microplus infestation. First, a cDNA encoding R. microplus amino acids sequence with highly conserved regions of the metzincin (reprolysin) group of MP was identified (BrRm-MP4). After expression and purification, recombinant BrRm-MP4 was used as a vaccinal antigen against R. microplus infestation in cattle (Bos taurus taurus). All vaccinated bovines developed immune response to the antigen, resulting in increased antibody level throughout the immunization protocol. Immunization with rBrRm-MP4 reduced tick feeding success, decreasing the number of engorged females and their reproduction potential, representing a 60% overall protection. These results show that rBrRm-MP4 provides protection against tick infestation, placing it is a potential candidate for an anti-tick vaccine.

A 24-48 h fed Amblyomma americanum tick saliva immuno-proteome

BACKGROUND

Multiple tick saliva proteins, the majority of which are unknown, confer tick resistance in repeatedly infested animals. The objective of this study was to identify the 24-48 h fed Amblyomma americanum tick saliva immuno-proteome. The 24-48 h tick-feeding phase is critical to tick parasitism as it precedes important events in tick biology, blood meal feeding and disease agent transmission. Fed male, 24 and 96 h fed female phage display cDNA expression libraries were biopanned using rabbit antibodies to 24 and 48 h fed A. americanum female tick saliva proteins. Biopanned immuno-cDNA libraries were subjected to next generation sequencing, de novo assembly, and bioinformatic analysis.

RESULTS

More than 800 transcripts that code for 24-48 h fed A. americanum immuno-proteins are described. Of the 895 immuno-proteins, 52% (464/895) were provisionally identified based on matches in GenBank. Of these, ~19% (86/464) show high level of identity to other tick hypothetical proteins, and the rest include putative proteases (serine, cysteine, leukotriene A-4 hydrolase, carboxypeptidases, and metalloproteases), protease inhibitors (serine and cysteine protease inhibitors, tick carboxypeptidase inhibitor), and transporters and/or ligand binding proteins (histamine binding/lipocalin, fatty acid binding, calreticulin, hemelipoprotein, IgG binding protein, ferritin, insulin-like growth factor binding proteins, and evasin). Others include enzymes (glutathione transferase, cytochrome oxidase, protein disulfide isomerase), ribosomal proteins, and those of miscellaneous functions (histamine release factor, selenoproteins, tetraspanin, defensin, heat shock proteins).

CONCLUSIONS

Data here demonstrate that A. americanum secretes a complex cocktail of immunogenic tick saliva proteins during the first 24-48 h of feeding. Of significance, previously validated immunogenic tick saliva proteins including AV422 protein, calreticulin, histamine release factor, histamine binding/lipocalins, selenoproteins, and paramyosin were identified in this screen, supporting the specificity of the approach in this study. While descriptive, this study opens opportunities for in-depth tick feeding physiology studies.

Glutathione S-transferase affects permethrin detoxification in the brown dog tick, Rhipicephalus sanguineus

Control of ticks on dogs is often done by application of repellents that contain permethrin as the active ingredient. In this research, we studied the role of a glutathione S-transferase (GST) gene in detoxification of permethrin by ticks using a gene silencing method RNA interference (RNAi). The brown dog tick, Rhipicephalus sanguineus, used in these studies, has a notable host preference for dogs, but also infests other mammals. In this research, R. sanguineus females were injected with gst double-stranded RNA (dsRNA) to effect gene silencing by RNAi and then exposed to sublethal doses of permethrin. Sixty hours after injection, the females were allowed to feed on sheep. The female ticks subjected to RNAi proved to be more susceptible to permethrin than the untreated controls. The effect of gene silencing was most notable in the highest dose group (50.3 ppm) in which all ticks died, while in the corresponding controls that were not subjected to RNAi this dose was not lethal. The acaricide treatment of the ticks resulted in a change in tick attachment behavior. Acaricide-treated ticks attached in a scattered pattern in contrast to the control ticks that attached and fed tightly clustered together. The time required for repletion for both the injected and non-injected females exposed to the higher permethrin level was shorter than that observed in the lower-dose groups and unexposed controls, and this more rapid attachment and feeding would likely favor more rapid transmission of pathogens. However, engorgement and egg mass weights were not significantly different among the experimental groups. This research demonstrated that the silencing of the gst gene increased the tick's susceptibility to permethrin. Overall, these results have contributed to our understanding of the detoxification mechanism of ticks and provide new considerations for the formulation of treatment strategies.