A novel tick antigen shows high vaccine efficacy against the dog tick, Rhipicephalus sanguineus

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

IMPORTANCE

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS AND RELEVANCE

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

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.

Cross-species immunoprotective antigens (subolesin, ferritin 2 and P0) provide protection against Rhipicephalus sanguineus sensu lato

BACKGROUND

Tick control is mostly hampered by the rise of acaricide-resistant tick populations. Significant efforts have focused on developing alternative control methods, including cross-species protective and/or cocktail-based anti-tick vaccines, to achieve protection against various tick species.

METHODS

In this study, full-length open reading frames encoding subolesin (SUB) from Rhipicephalus microplus and ferritin 2 (FER2) from Hyalomma anatolicum as well as the partial 60S acidic ribosomal protein (P0) from R. microplus were cloned, expressed in Escherichia coli and used as vaccine antigens against Rhipicephalus sanguineus sensu lato (R. sanguineus s.l.) infestation in rabbits.

RESULTS

In silico analyses revealed that the SUB, P0 and FER2 proteins were antigenic and displayed limited similarity to the host's homologous proteins. The proteins shared identities of 97.5%, 100% and 89.5% with their SUB, P0 and FER2 R. sanguineus s.l. orthologous sequences, respectively. Antibodies against each recombinant protein cross-recognized the native proteins in the different tissues and developmental stages of R. sanguineus s.l. Overall efficacy of the SUB, FER2 and cocktail (SUB+FER2+P0) vaccines against R. sanguineus s.l. infestation was 86.3%, 95.9% and 90.9%, respectively.

CONCLUSIONS

Both mono-antigen and the cocktail anti-tick vaccines affected the biological parameters of R. sanguineus s.l. infestation in the rabbit model, which could be extrapolated to its infested host under natural conditions. These findings support the possibility of using mono-antigenic and cocktail-based vaccines for large-scale anti-tick vaccine development against multiple tick species.

Efficacy of the Vaccine Candidate Based on the P0 Peptide against Dermacentor nitens and Ixodes ricinus Ticks

The control of ticks through vaccination offers a sustainable alternative to the use of chemicals that cause contamination and the selection of resistant tick strains. However, only a limited number of anti-tick vaccines have reached commercial realization. In this sense, an antigen effective against different tick species is a desirable target for developing such vaccines. A peptide derived from the tick P0 protein (pP0) conjugated to a carrier protein has been demonstrated to be effective against the Rhipicephalus microplus, Rhipicephalus sanguineus, and Amblyomma mixtum tick species. The aim of this work was to assess the efficacy of this peptide when conjugated to the Bm86 protein against Dermacentor nitens and Ixodes ricinus ticks. An RNAi experiment using P0 dsRNA from I. ricinus showed a dramatic reduction in the feeding of injected female ticks on guinea pigs. In the follow-up vaccination experiments, rabbits were immunized with the pP0-Bm86 conjugate and challenged simultaneously with larvae, nymphs, and the adults of I. ricinus ticks. In the same way, horses were immunized with the pP0-Bm86 conjugate and challenged with D. nitens larva. The pP0-Bm86 conjugate showed efficacies of 63% and 55% against I. ricinus and D. nitens ticks, respectively. These results, combined with previous reports of efficacy for this conjugate, show the promising potential for its development as a broad-spectrum anti-tick vaccine.

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

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

Universal Tick Vaccines: Candidates and Remaining Challenges

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

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.

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.

The Bm86 Discovery: A Revolution in the Development of Anti-Tick Vaccines

The presence in nature of species with genetic resistance to ticks, or with acquired resistance after repeated tick infestations, has encouraged the scientific community to consider vaccination as an alternative to the unsustainable chemical control of ticks. After numerous attempts to artificially immunize hosts with tick extracts, the purification and characterization of the Bm86 antigen by Willadsen et al. in 1989 constituted a revolutionary step forward in the development of vaccines against ticks. Previously, innovative studies that had used tick gut extracts for the immunization of cattle against Rhipicepahalus microplus (previously named Boophilus microplus) ticks, with amazingly successful results, demonstrated the feasibility of using antigens other than salivary-gland-derived molecules to induce a strong anti-tick immunity. However, the practical application of an anti-tick vaccine required the isolation, identification, and purification of the responsible antigen, which was finally defined as the Bm86 protein. More than thirty years later, the only commercially available anti-tick vaccines are still based on this antigen, and all our current knowledge about the field application of immunological control based on vaccination against ticks has been obtained through the use of these vaccines.

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.

Impact of the Paper by Allen and Humphreys (1979) on Anti-Tick Vaccine Research

The classic paper by Allen and Humphreys "Immunisation of guinea pigs and cattle against ticks" Nature, 1979, 280: 491-493 led to a surge in the development of tick vaccines as a nonchemical method for prevention of tick infestations in susceptible hosts living in tick-endemic regions. Although observations of host resistance to ticks had been documented since the beginning of the last century, it was not until publication of this paper that the proof of concept of anti-tick vaccines was developed. The described experimental methods directly impacted further investigations on the discovery and evaluation of new anti-tick vaccines.

Overview of the Main Species of Ticks and Animal and Human Tick-Related Diseases in the Caribbean, Particularly in Haiti

The Caribbean region faces a wide diversity of ticks and tick-borne diseases (TBDs) in animals and humans. But to date, these have been the subject of few studies, resulting in a relative lack of knowledge of their epidemiology, pathogenicity, and the best prevention and control methods. Ticks are hematophagous mites, which feed on the blood of mammals, birds, and reptiles. They are subdivided into two large families: the Ixodidae or hard ticks and the Argasidae or soft ticks. Each collection of blood by ticks from infected hosts can lead to their infection, which will contaminate other previously unharmed animals and contribute to the spread of tick-borne diseases caused mainly by bacteria, viruses, and parasites. It seems important to us to draw up a state of knowledge on ticks. Some long-known tick species like Rhipicephalus, Dermacentor, and Amblyomma and diseases like Anaplasmosis and Babesiosis deserve to be better studied, and others are yet to be identified for further research. The study consists of a review of the various documents published on this theme by Haitian and foreign researchers. The data are analyzed to assess the spatiotemporal distribution of ticks and identify the pathogenic germs they harbor and the various pathologies they induce in the Caribbean and Haiti.

The Symbiotic Continuum Within Ticks: Opportunities for Disease Control

Among blood-sucking arthropods, ticks are recognized as being of prime global importance because of their role as vectors of pathogens affecting human and animal health. Ticks carry a variety of pathogenic, commensal, and symbiotic microorganisms. For the latter, studies are available concerning the detection of endosymbionts, but their role in the physiology and ecology of ticks remains largely unexplored. This review paper focuses on tick endosymbionts of the genera Coxiella, Rickettsia, Francisella, Midichloria, and Wolbachia, and their impact on ticks and tick-pathogen interactions that drive disease risk. Tick endosymbionts can affect tick physiology by influencing nutritional adaptation, fitness, and immunity. Further, symbionts may influence disease ecology, as they interact with tick-borne pathogens and can facilitate or compete with pathogen development within the vector tissues. Rickettsial symbionts are frequently found in ticks of the genera of Ixodes, Amblyomma, and Dermacentor with relatively lower occurrence in Rhipicephalus, Haemaphysalis, and Hyalomma ticks, while Coxiella-like endosymbionts (CLEs) were reported infecting almost all tick species tested. Francisella-like endosymbionts (FLEs) have been identified in tick genera such as Dermacentor, Amblyomma, Ornithodoros, Ixodes, and Hyalomma, whereas Wolbachia sp. has been detected in Ixodes, Amblyomma, Hyalomma, and Rhipicephalus tick genera. Notably, CLEs and FLEs are obligate endosymbionts essential for tick survival and development through the life cycle. American dog ticks showed greater motility when infected with Rickettsia, indirectly influencing infection risk, providing evidence of a relationship between tick endosymbionts and tick-vectored pathogens. The widespread occurrence of endosymbionts across the tick phylogeny and evidence of their functional roles in ticks and interference with tick-borne pathogens suggests a significant contribution to tick evolution and/or vector competence. We currently understand relatively little on how these endosymbionts influence tick parasitism, vector capacity, pathogen transmission and colonization, and ultimately on how they influence tick-borne disease dynamics. Filling this knowledge gap represents a major challenge for future research.

Fundamental Tick Vaccinomic Approach to Evade Host Autoimmune Reaction

Ticks are obligate hematophagous ectoparasites that infect domestic animals, humans, and wildlife. Ticks can transmit a wide range of pathogens (viruses, rickettsia, bacteria, parasites, etc.), and some of those are of zoonotic importance. Tick-borne diseases have a negative economic impact in several tropical and subtropical countries. With climate change, tick distribution and tick-associated pathogens have increased. Currently, tick control procedures have more environmental drawbacks and there are pitfalls in vaccination process. Since vaccinations have helped to prevent several diseases and infections, several vaccination trials are ongoing to control ticks and tick-borne pathogens. However, autoimmune reactions to vaccinations are reported as an adverse reaction since vaccines were used to protect against disease in humans and animals. The antibodies against the vaccine antigen might harm similar antigen in the host. Therefore, in this chapter, we attempt to shed light on the importance of raising awareness of possible adverse events associated with vaccinations and the methods that should be used to address this problem. In silico and lab work should be performed ahead of the vaccination process to evaluate the vaccine candidates and avoid the vaccination opposing consequences.

Vector microbiota manipulation by host antibodies: the forgotten strategy to develop transmission-blocking vaccines

Human and animal pathogens that are transmitted by arthropods are a global concern, particularly those vectored by ticks (e.g. Borrelia burgdorferi and tick-borne encephalitis virus) and mosquitoes (e.g. malaria and dengue virus). Breaking the circulation of pathogens in permanent foci by controlling vectors using acaricide-based approaches is threatened by the selection of acaricide resistance in vector populations, poor management practices and relaxing of control measures. Alternative strategies that can reduce vector populations and/or vector-mediated transmission are encouraged worldwide. In recent years, it has become clear that arthropod-associated microbiota are involved in many aspects of host physiology and vector competence, prompting research into vector microbiota manipulation. Here, we review how increased knowledge of microbial ecology and vector-host interactions is driving the emergence of new concepts and tools for vector and pathogen control. We focus on the immune functions of host antibodies taken in the blood meal as they can target pathogens and microbiota bacteria within hematophagous arthropods. Anti-microbiota vaccines are presented as a tool to manipulate the vector microbiota and interfere with the development of pathogens within their vectors. Since the importance of some bacterial taxa for colonization of vector-borne pathogens is well known, the disruption of the vector microbiota by host antibodies opens the possibility to develop novel transmission-blocking vaccines.

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.

Synthesis, LC-MS/MS analysis, and biological evaluation of two vaccine candidates against ticks based on the antigenic P0 peptide from R. sanguineus linked to the p64K carrier protein from Neisseria meningitidis

A peptide from the P0 acidic ribosomal protein (pP0) of ticks conjugated to keyhole limpet hemocyanin from Megathura crenulata has shown to be effective against different tick species when used in host vaccination. Turning this peptide into a commercial anti-tick vaccine will depend on finding the appropriate, technically and economically feasible way to present it to the host immune system. Two conjugates (p64K-Cys¹pP0 and p64K-βAla¹pP0) were synthesized using the p64K carrier protein from Neisseria meningitidis produced in Escherichia coli, the same cross-linking reagent, and two analogues of pP0. The SDS-PAGE analysis of p64K-Cys¹pP0 showed a heterogeneous conjugate compared to p64K-βAla¹pP0 that was detected as a protein band at 91kDa. The pP0/p64K ratio determined by MALDI-MS for p64K-Cys¹pP0 ranged from 1 to 8, being 3-5 the predominant ratio, while in the case of p64K-βAla¹pP0 this ratio was 5-7. Cys¹pP0 was partially linked to 35 out of 39 Lys residues and the N-terminal end, while βAla¹pP0 was mostly linked to the six free cysteine residues, to the N-terminal end, and, in a lesser extent, to Lys residues. The assignment of the conjugation sites and side reactions were based on the identification of type 2 peptides. Rabbit immunizations showed the best anti-pP0 titers and the highest efficacy against Rhipicephalus sanguineus ticks when the p64K-Cys¹pP0 was used as vaccine antigen. The presence of high molecular mass aggregates observed in the SDS-PAGE analysis of p64K-Cys¹pP0 could be responsible for a better immune response against pP0 and consequently for its better efficacy as an anti-tick vaccine.

Evaluation on two types of paramyosin vaccines for the control of Haemaphysalis longicornis infestations in rabbits

BACKGROUND

Haemaphysalis longicornis is an obligate hematophagous ectoparasite that transmits a variety of pathogens causing life-threatening diseases in humans and animals. Paramyosin (Pmy) is not only an invertebrate-specific myofibrillar protein but also an important immunomodulatory protein. Therefore, it is one of the ideal candidate antigens for vaccines.

METHODS

We conducted two vaccine trials to evaluate the protective efficacy of Pmy recombinant protein (rPmy) and peptide vaccine (KLH-LEE). Each rabbit was immunized with three doses of rPmy or KLH-LEE adjuvanted with Freund's complete/incomplete at 500 μg/dose at 2-week intervals before challenge with 40 female H. longicornis/rabbit. PBS plus adjuvant, Trx or KLH was used as control group. The antibodies of rabbits were detected by ELISA. Then, female ticks were fed on the rabbits until detachment.

RESULTS

ELISA results showed that both vaccines induced rabbits to produce antibodies. Compared with the Trx group, the engorgement weight, oviposition and hatchability of the rPmy group decreased by 8.87%, 26.83% and 38.86%, respectively. On the other hand, engorgement weight, oviposition and hatchability of female ticks in the KLH-LEE group correspondingly resulted in 27.03%, 53.15% and 38.40% reduction compared with that of the KLH group. Considering the cumulative effect of vaccination on the evaluated parameters, results showed 60.37% efficacy of the rPmy vaccine formulation and 70.86% efficacy in the KLH-LEE group.

CONCLUSIONS

Pmy and particularly epitope LEE have potential for further development of an effective candidate vaccine to protect the host against tick infection. GRAPHIC ABSTARCT.

Vaccine approaches applied to controlling dog ticks

Ticks are considered the most important vectors in veterinary medicine with a profound impact on animal health worldwide, as well as being key vectors of diseases affecting household pets. The leading strategy applied to dog tick control is the continued use of acaricides. However, this approach is not sustainable due to surging tick resistance, growing public concern over pesticide residues in food and in the environment, and the rising costs associated with their development. In contrast, tick vaccines are a cost-effective and environmentally friendly alternative against tick-borne diseases by controlling vector infestations and reducing pathogen transmission. These premises have encouraged researchers to develop an effective vaccine against ticks, with several proteins having been characterized and used in native, synthetic, and recombinant forms as antigens in immunizations. The growing interaction between domestic pets and people underscores the importance of developing new tick control measures that require effective screening platforms applied to vaccine development. However, as reviewed in this paper, very little progress has been made in controlling ectoparasite infestations in pets using the vaccine approach. The control of tick infestations and pathogen transmission could be obtained through immunization programs aimed at reducing the tick population and interfering in the pathogenic transmission that affects human and animal health on a global scale.

Ticks and Tick-Borne Diseases in Cuba, Half a Century of Scientific Research

Ticks and the vast array of pathogens they transmit, including bacteria, viruses, protozoa, and helminths, constitute a growing burden for human and animal health worldwide. In Cuba, the major tropical island in the Caribbean, ticks are an important cause of vector-borne diseases affecting livestock production, pet animal health and, to a lesser extent, human health. The higher number of tick species in the country belong to the Argasidae family and, probably less known, is the presence of an autochthonous tick species in the island, Ixodes capromydis. Herein, we provide a comprehensive review of the ticks and tick-borne pathogens (TBPs) affecting animal and human health in Cuba. The review covers research results including ecophysiology of ticks, the epidemiology of TBPs, and the diagnostic tools used currently in the country for the surveillance of TBPs. We also introduce the programs implemented in the country for tick control and the biotechnology research applied to the development of anti-tick vaccines.

Functional and Mass Spectrometric Evaluation of an Anti-Tick Antigen Based on the P0 Peptide Conjugated to Bm86 Protein

A synthetic 20 amino acid peptide of the ribosomal protein P0 from ticks, when conjugated to keyhole limpet hemocyanin from Megathura crenulata and used as an immunogen against Rhipicephalus microplus and Rhipicephalus sanguineus s.l. species, has shown efficacies of around 90%. There is also experimental evidence of a high efficacy of this conjugate against Amblyomma mixtum and Ixodes ricinus species, which suggest that this antigen could be a good broad-spectrum anti-tick vaccine candidate. In this study, the P0 peptide (pP0) was chemically conjugated to Bm86 as a carrier protein. SDS-PAGE analysis of this conjugate demonstrated that it is highly heterogeneous in size, carrying from 1 to 18 molecules of pP0 per molecule of Bm86. Forty-nine out of the 54 lysine residues and the N-terminal end of Bm86 were found partially linked to pP0 by using LC-MS/MS analysis and the combination of four different softwares. Several post-translational modifications of Bm86 protein were also identified by mass spectrometry. High immunogenicity and efficacy were achieved when dogs and cattle were vaccinated with the pP0-Bm86 conjugate and challenged with R. sanguineus s.l. and R. microplus, respectively. These results encourage the development of this antigen with promising possibilities as an anti-tick vaccine.

A chemical conjugate of the tick P0 peptide is efficacious against Amblyomma mixtum

After Rhipicephalus microplus, the most important tick species affecting livestock industry in Cuba belong to the Amblyomma genus. There are few reports of effective vaccine antigens for these species. Recently, vaccination and challenge trials using a peptide from the P0 acidic ribosomal protein of R. microplus ticks (pP0) as antigen have shown an efficacy around 90% against tick species from the Rhipicephalus genus. Given the high degree of sequence conservation among tick species, pP0 could be an antigen of versatile use in anti-tick vaccine formulations. In this paper, seven rabbits were immunized with a chemical conjugate of pP0 to keyhole limpet haemocyanin. Rabbits were challenged with an average of 1,900 Amblyomma mixtum larvae from a Cuban tick strain. The average number of recovered fed larvae and the viability of larvae in the moulting process were significantly lower in vaccinated animals compared with the control group. The overall vaccine efficacy of the P0 peptide antigen is 54% according to the calculated parameters.

Cross protection induced by combined Subolesin-based DNA and protein immunizations against adult Haemaphysalis longicornis

Vaccination against ticks is an environmentally friendly alternative control method compared to chemical acaricide applications. Subolesin is a conserved protein in ticks, which can provide protection against some tick species. In this study, we evaluated the capacity of cocktail vaccination with Subolesin and ribosomal acidic protein 0 (P0) peptide against adults of Haemaphysalis longicornis. Priming with DNA vaccine expressing subolesin, followed by boosters of a single antigen (rRhSub) or a chimeric polypeptide (rRhSub/P0), provided cross protection. This treatment resulted in significant mortality, reduced blood ingestion and reduced reproduction in H. longicornis adults. Vaccination efficacies of 79.3% and 86.6% are reported in groups supplemented with rRhSub and rRhSub/P0, respectively. Conserved antigens, such as subolesin, formulated as DNA vaccine and enhanced with chimeric polypeptides, could be used as an anti-tick vaccine application, especially for control of infestation involving several tick species.

In silico selection of functionally important proteins from the mialome of Ornithodoros erraticus ticks and assessment of their protective efficacy as vaccine targets

BACKGROUND

New candidate protective antigens for tick vaccine development may be identified by selecting and testing antigen candidates that play key biological functions. After blood-feeding, tick midgut overexpresses proteins that play essential functions in tick survival and disease transmission. Herein, Ornithodoros erraticus midgut transcriptomic and proteomic data were examined in order to select functionally significant antigens upregulated after feeding to be tested as vaccine candidate antigens.

METHODS

Transcripts annotated as chitinases, tetraspanins, ribosomal protein P0 and secreted proteins/peptides were mined from the recently published O. erraticus midgut transcriptome and filtered in a second selection step using criteria based on upregulation after feeding, predicted antigenicity and expression in the midgut proteome. Five theoretical candidate antigens were selected, obtained as recombinant proteins and used to immunise rabbits: one chitinase (CHI), two tetraspanins (TSPs), the ribosomal protein P0 (RPP0) and one secreted protein PK-4 (PK4).

RESULTS

Rabbit vaccination with individual recombinant candidates induced strong humoral responses that mainly reduced nymph moulting and female reproduction, providing 30.2% (CHI), 56% (TSPs), 57.5% (RPP0) and 57.8% (PK4) protection to O. erraticus infestations and 19.6% (CHI), 11.1% (TSPs), 0% (RPP0) and 8.1% (PK4) cross-protection to infestations by the African tick Ornithodoros moubata. The joint vaccine efficacy of the candidates was assessed in a second vaccine trial reaching 66.3% protection to O. erraticus and 25.6% cross-protection to O. moubata.

CONCLUSIONS

These results (i) indicate that argasid chitinases and RPP0 are promising protective antigens, as has already been demonstrated for ixodid chitinases and RPP0, and could be included in vaccines targeting multiple tick species; (ii) reveal novel protective antigens tetraspanins and secreted protein PK-4, never tested before as protective antigens in ticks; and (iii) demonstrate that multi-antigenic vaccines increased vaccine efficacy compared with individual antigens. Lastly, our data emphasize the value of the tick midgut as a source of protective candidate antigens in argasids for tick control.

Promiscuous T cell epitopes boosts specific IgM immune response against a P0 peptide antigen from sea lice in different teleost species

The development of vaccines employing conserved protein antigens, for instance ribosomal protein P0, has as disadvantage the high degree of identity between pathogen and host proteins due to possible induction of tolerance or auto antibodies in the host organism. To overcome this drawback, peptide-based vaccines have been designed with a proved high efficacy. The use of defined peptides as antigens has the problem that they are generally poor immunogenic unless coupled to a carrier protein. Several studies have established the potential for promiscuous T cell epitopes incorporated into chimeric peptides to enhance the immunogenicity in mammals. On the contrary, studies about the role of these epitopes on teleost immune system are scarce. Therefore, the main objective of our present study was to evaluate the potential of promiscuous T cell epitopes to boost specific IgM immune response in teleost fish against a peptide antigen. With this aim, we used a peptide of 35 amino acids from the ribosomal P0 protein of Lepeophtheirus salmonis, an important parasite in salmon aquaculture. We fused this peptide to the C-terminal of T cell epitopes from tetanus toxin and measles virus and produced the chimeric protein in Escherichia coli. Following vaccination, IgM antibody production was monitored in different immunization schemes in Tilapia, African catfish and Atlantic salmon. The results demonstrated for first time that the addition of T cell epitopes at the N-terminal of a target peptide increased IgM specific response in different teleost species, revealing the potential of this approach to develop peptide-based vaccines for aquaculture. The results are also of great importance in the context of vaccine development against sea lice using ribosomal protein P0 as antigen taking into account the key role of P0 in protein synthesis and other essential physiological processes.

Evaluation of vaccine candidates purified from the adult ticks of Ornithodoros savignyi (Acari: Argasidae) and Hyalomma dromedarii (Acari: Ixodidae) against tick infestations

Ticks cause anemia, toxicosis, growth delay, and transmit infectious diseases in animals and humans. The current study aimed to evaluate the immunoprophylactic properties of two vaccine candidates to develop vaccine against tick infestations. These two vaccine candidates were specific fraction from the adults of the soft tick Ornithodoros savignyi and cross-reactive fraction from the adults of the hard tick Hyalomma dromedarii. Both specific and cross-reactive fractions were isolated by Cyanogen Bromide-activated Sepharose-4B affinity column chromatography. Both candidates proved their cross-reactivity by enzyme linked immunosorbent assay and Western blot. Characterization of the two vaccines by SDS-PAGE showed that the O. savignyi specific fraction consists of four bands; 97, 85, 66 and 11.5 kDa compared with nine bands associated with its crude antigen (196-11.5 kDa). The H. dromedarii cross-reactive vaccine candidate consists of three bands; 97, 66 and 45 kDa compared to eight bands of its crude antigen (196-21 kDa). Two common bands of 97 and 66 kDa between two candidates showed immunogenic cross-reactivity with the developed antisera of both infestations by Western blot. Immunization of rabbits intramuscularly with two doses of the fractions separately (40 µg/kg) led to immunological and parasitological changes. Immunologically; the level of immunoglobulins in vaccinated rabbits increased significantly compared with control infested non-vaccinated rabbits. These immunoglobulins are probably responsible for the protective effect of both candidates. Parasitologically, immunized rabbits showed protection against infestation by adult ticks as proved by significant feeding rejection percentage and significant reduction in egg and engorgement weights of H. dromedarii. While insignificant protection was observed against O. savignyi ticks infestation in feeding rejection and reduction in engorgement weight. In conclusion, this study suggests promising immunoprophylactic potentials of the purified fractions against tick infestations in rabbits through induction of IgG responses. The protective effect of both vaccine candidates deserves further evaluation in other hosts and against other tick infestations.

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.

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.

Liposome mediated double-stranded RNA delivery to silence ribosomal protein P0 in the tick Rhipicephalus haemaphysaloides

Control of ticks has been achieved primarily by the application of acaricides, which has drawbacks such as environmental contamination leading to the selection of pesticide-resistant ticks. The potential of dsRNA to suppress genes critical for tick survival due to its sequence specificity suggests that dsRNAs could be developed as tailor-made pesticides. In this study, the dsRNA of P0 gene from the tick, Rhipicephalus haemaphysaloides, was evaluated as a potential anti-tick agent. Effects of using different dsRNA delivery methods were tested by quantitative RT-PCR and tick bioassays to determine survival, feeding and reproduction. The results showed that P0 dsRNAs could be effectively delivered into ticks and silenced by incubating with liposomes. Incubation time was found to be the most important factor in dsRNA delivery and gene silencing compared with liposome types and dsRNA concentration. The effects of P0 dsRNA treatment on ticks were found to be significant on blood feeding, molting or reproduction. These data show that anti-tick agents based on dsRNAs could have potential use in tick control.

Tick-Host Range Adaptation: Changes in Protein Profiles in Unfed Adult Ixodes scapularis and Amblyomma americanum Saliva Stimulated to Feed on Different Hosts

Understanding the molecular basis of how ticks adapt to feed on different animal hosts is central to understanding tick and tick-borne disease (TBD) epidemiology. There is evidence that ticks differentially express specific sets of genes when stimulated to start feeding. This study was initiated to investigate if ticks such as Ixodes scapularis and Amblyomma americanum that are adapted to feed on multiple hosts utilized the same sets of proteins to prepare for feeding. We exposed I. scapularis and A. americanum to feeding stimuli of different hosts (rabbit, human, and dog) by keeping unfed adult ticks enclosed in a perforated microfuge in close contact with host skin, but not allowing ticks to attach on host. Our data suggest that ticks of the same species differentially express tick saliva proteins (TSPs) when stimulated to start feeding on different hosts. SDS-PAGE and silver staining analysis revealed unique electrophoretic profiles in saliva of I. scapularis and A. americanum that were stimulated to feed on different hosts: rabbit, human, and dog. LC-MS/MS sequencing and pairwise analysis demonstrated that I. scapularis and A. americanum ticks expressed unique protein profiles in their saliva when stimulated to start feeding on different hosts: rabbit, dog, or human. Specifically, our data revealed TSPs that were unique to each treatment and those that were shared between treatments. Overall, we identified a total of 276 and 340 non-redundant I. scapularis and A. americanum TSPs, which we have classified into 28 functional classes including: secreted conserved proteins (unknown functions), proteinase inhibitors, lipocalins, extracellular matrix/cell adhesion, heme/iron metabolism, signal transduction and immunity-related proteins being the most predominant in saliva of unfed ticks. With exception of research on vaccines against Rhipicephalus microplus, which its natural host, cattle, research on vaccine against other ticks relies feeding ticks on laboratory animals. Data here suggest that relying on lab animal tick feeding data to select target antigens could result in prioritizing irrelevant anti-tick vaccine targets that are expressed when ticks feed on laboratory animals. This study provides the platform that could be utilized to identify relevant target anti-tick vaccine antigens, and will facilitate early stage tick feeding research.

Evaluation of ribosomal P0 peptide as a vaccine candidate against Argulus siamensis in Labeo rohita

Argulusspp. are important ectoparasites of fish, and the current approach of their control using chemical pesticides has numerous drawbacks. Vaccination is a promising alternative but identification of protective antigens is a limiting step. The ribosomal protein P0, essential for protein synthesis, has been studied as a vaccine candidate. We generated sequence information of the P0 protein of the ectoparasiteArgulus siamensisand the hostLabeo rohita. The region of the parasite P0 protein with less sequence similarity with that of the host P0 protein and high predicted antigenicity was used for peptide synthesis. The peptide was conjugated with keyhole limpet hemocyanin (KLH) for immunization of rohu at a dose of 1.5 μg/g body weight. Dot blot assays confirmed production of antibodies against pP0-KLH in immunized fish. We evaluated the efficiency of pP0-KLH as a vaccine antigen by challenge of the immunized fish withA.siamensis. Although there was no significant difference in parasite load between both groups, a reduced and delayed mortality of 59% (15 days post-infection) in immunized group was noticed as compared to 75% mortality (within 7–15 days post-infection) in control group. The partial protection observed indicated the need for further optimization of this molecule to develop it into a vaccine candidate.

Immunogenic potential of Rhipicephalus (Boophilus) microplus aquaporin 1 against Rhipicephalus sanguineus in domestic dogs

Abstract This study evaluated a recombinant aquaporin 1 protein of Rhipicephalus (Boophilus) microplus (RmAQP1) as antigen in a vaccine against R. sanguineus. Five dogs were immunized with RmAQP1 (10 µg) + adjuvant (Montanide) (G1), and five were inoculated with adjuvant only (G2), three times. Twenty-one days after the last immunization, animals of both groups were challenged with R. sanguineus larvae, nymphs and adults, and their biotic potential was compared. Blood samples were collected before each immunization and every 28 days after the last immunization for 10 weeks. Serum antibody titers (IgG) were assessed by ELISA. We observed that: engorgement period of adult females from G1 was 12% shorter than G2; larvae from G1 had 8.7% longer engorgement period than G2 and weighed 7.2% less; nymphs from G1 had 4.5% shorter engorgement period than G2 and weighed 3.6% less; although the antibody titers increased following the second immunization, they rapidly decreased after the third immunization. Results indicated low immunoprotection of RmAQP1 against adult R. sanguineus ticks, and possible efficacy on larvae and nymphs fed on immunized dogs. Further studies should be performed for a full evaluation of the immunoprotection of RmAQP1 against R. sanguineus infestations in dogs.

Design of the ATAQ peptide and its evaluation as an immunogen to develop a Rhipicephalus vaccine

Tick infestation may cause several problems including affecting domestic animal health and reducing the production of meat and milk, among others. Resistance to several classes of acaricides have been reported, forcing researchers to search for alternative measures, such as vaccines against ticks, to ensure tick control while having no or at least low negative impacts on the environment and public health. However, the current commercially available vaccines in different strains of Rhipicephalus microplus are reported to be of low efficacy. Fortunately, reverse vaccinology approaches have shown positive results in the new generation of vaccines. On this basis, a synthetic peptide from the ATAQ protein, which is present in the gut and Malpighi tubes of R. microplus, was synthesized. The ATAQ proteins were isolated, characterized and sequenced from several species of the genus Rhipicephalus. The alignment showed 93.3% identity among DNA sequences of ATAQs from these species. Because of this, immunization trials with this peptide were conducted on mice, rabbits and cattle to evaluate the humoral immune response and the efficacy against Rhipicephalus sanguineus in addition to R. microplus. Based on recent results, we conclude that reverse vaccinology is a promising approach because it is more accurate and faster than conventional methods in the detection of potential antigens to use in anti-tick vaccines. It is not only applicable against R. microplus but also against tick species that play important roles in spreading other diseases. ATAQ proteins should be considered as the antigen in new trials to develop a multi-antigenic vaccine. Although these peptides behave as hapten and are not able to be recognized by the immune system on its own, using carriers and adjuvants helps its presentation and induces strong immune responses. Furthermore, an efficiency of 35% reduction in overall life cycle parameters was reported for R. microplus (98% for ELISA responder animals) and 47% for R. sanguineus. Although not yet enough to prevent the environment to infestation of ticks, this still constitutes a promising strategy that could be applied to integrated measures on tick control and in new research that develops anti-tick vaccines.

Developing Anti-tick Vaccines

Ticks are responsible for the transmission of viral, bacterial, and protozoal diseases of man and animals and also produce significant economic losses to cattle industry. The use of acaricides constitutes a major component of integrated tick control strategies. However, this is accompanied by the selection of acaricide-resistant ticks and contamination of environment and milk and meat products with drug residues. These issues highlight the need for alternative approaches to control tick infestations and have triggered the search for tick protective antigens for vaccine development. Vaccination as a tick control method has been practiced since the introduction of TickGARD and Gavac that were developed using the midgut glycoprotein Bm86 as antigen. Gavac within integrated tick management systems has proven to reduce the number of acaricidal applications per year that are required to control some strains of R. microplus ticks in different geographical regions. Nevertheless, it has limited or no efficacy against other tick species. These issues have stimulated research for additional tick protective antigens with critical functions in the tick. This chapter presents methodologies for the design and test of molecules as antigens against ticks. Considerations about different methods for the tick control compared to the immunological methods, the desirable characteristics for an anti-tick vaccine and the obstacles encountered for developing this kind of vaccines are discussed. Detailed methodologies for the establishment of a biological model to test new molecules as immunogens against ticks and to perform challenge trials with this model are presented. General considerations in the efficacy calculation for any anti-tick vaccine are also discussed.

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.

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.

Application of M13 phage display for identifying immunogenic proteins from tick (Ixodes scapularis) saliva

Background

Ticks act as vectors for a large number of different pathogens, perhaps most notably Borrelia burgdorferi, the causative agent of Lyme disease. The most prominent tick vector in the United States is the blacklegged tick, Ixodes scapularis. Tick bites are of special public health concern since there are no vaccines available against most tick-transmitted pathogens. Based on the observation that certain non-natural host animals such as guinea pigs or humans can develop adaptive immune responses to tick bites, anti-tick vaccination is a potential approach to tackle health risks associated with tick bites.

Results

The aim of this study was to use an oligopeptide phage display strategy to identify immunogenic salivary gland proteins from I. scapularis that are recognized by human immune sera. Oligopeptide libraries were generated from salivary gland mRNA of 18 h fed nymphal I. scapularis. Eight immunogenic oligopeptides were selected using human immune sera. Three selected immunogenic oligopeptides were cloned and produced as recombinant proteins. The immunogenic character of an identified metalloprotease (MP1) was validated with human sera. This enzyme has been described previously and was hypothesized as immunogenic which was confirmed in this study. Interestingly, it also has close homologs in other Ixodes species.

Conclusion

An immunogenic protein of I. scapularis was identified by oligopeptide phage display. MP1 is a potential candidate for vaccine development.

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.

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

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

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.