Developing Anti-tick Vaccines

ATP-sensitive inward rectifier potassium channels regulate secretion of pro-feeding salivary proteins in the lone star tick (Amblyomma americanum)

Understanding the physiological and molecular regulation of tick feeding is necessary for developing intervention strategies to curb disease transmission by ticks. Pharmacological activation of ATP-gated inward rectifier potassium (KATP) channels reduced fluid secretion from isolated salivary gland and blood feeding in the lone star tick, Amblyomma americanum, yet the temporal expression pattern of KATP channel proteins remained unknown. KATP channels were highly expressed in type II and III acini in off-host stage and early feeding phase ticks, yet expression was reduced in later stages of feeding. We next assessed KATP channel regulation of the secreted proteome of tick saliva. LC-MS/MS analysis identified 40 differentially secreted tick saliva proteins after exposure to KATP activators or inhibitors. Secretion of previously validated tick saliva proteins that promote tick feeding, AV422, AAS27, and AAS41 were significantly reduced by upwards of 8 log units in ticks exposed to KATP channel activators when compared to untreated ticks. Importantly, activation of KATP channels inhibited tick feeding and vice versa for KATP channel inhibitors. Data indicate KATP channels regulate tick feeding biology by controlling secretion of pro-feeding proteins that are essential during early feeding phases, which provides insights into physiological and molecular regulation of tick feeding behavior.

A high-quality Ixodes scapularis genome advances tick science

Ixodes spp. and related ticks transmit prevalent infections, although knowledge of their biology and development of anti-tick measures have been hindered by the lack of a high-quality genome. In the present study, we present the assembly of a 2.23-Gb Ixodes scapularis genome by sequencing two haplotypes within one individual, complemented by chromosome-level scaffolding and full-length RNA isoform sequencing, yielding a fully reannotated genome featuring thousands of new protein-coding genes and various RNA species. Analyses of the repetitive DNA identified transposable elements, whereas the examination of tick-associated bacterial sequences yielded an improved Rickettsia buchneri genome. We demonstrate how the Ixodes genome advances tick science by contributing to new annotations, gene models and epigenetic functions, expansion of gene families, development of in-depth proteome catalogs and deciphering of genetic variations in wild ticks. Overall, we report critical genetic resources and biological insights impacting our understanding of tick biology and future interventions against tick-transmitted infections.

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

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

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

Prevention of tick-borne diseases: challenge to recent medicine

Abstract

Ticks represent important vectors and reservoirs of pathogens, causing a number of diseases in humans and animals, and significant damage to livestock every year. Modern research into protection against ticks and tick-borne diseases focuses mainly on the feeding stage, i.e. the period when ticks take their blood meal from their hosts during which pathogens are transmitted. Physiological functions in ticks, such as food intake, saliva production, reproduction, development, and others are under control of neuropeptides and peptide hormones which may be involved in pathogen transmission that cause Lyme borreliosis or tick-borne encephalitis. According to current knowledge, ticks are not reservoirs or vectors for the spread of COVID-19 disease. The search for new vaccination methods to protect against ticks and their transmissible pathogens is a challenge for current science in view of global changes, including the increasing migration of the human population.

Highlights

• Tick-borne diseases have an increasing incidence due to climate change and increased human migration

• To date, there is no evidence of transmission of coronavirus COVID-19 by tick as a vector

• To date, there are only a few modern, effective, and actively- used vaccines against ticks or tick-borne diseases

• Neuropeptides and their receptors expressed in ticks may be potentially used for vaccine design

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.

Vaccines Against Vector-Borne Diseases

Arthropod vectors account for a number of animal and human diseases, posing substantial threats to health and safety on a global scale. Ticks are considered as one of the most prominent vectors, as they can parasitize almost any vertebrate class and transmit a multitude of infectious diseases, particularly ones that affect humans and domestic animals. While various tick species elicit different tick-borne infections in specific geographic regions, single species can have widespread effects, such as blacklegged ticks, which are widely distributed across the eastern United States and can transmit a variety of infections, including Lyme borreliosis, anaplasmosis, relapsing fever disease, ehrlichiosis, babesiosis, and Powassan virus disease. Despite increasing awareness about ticks as serious disease vectors, effective vaccines against most tick-borne infections are not available. Previously, the successful development of an anti-tick vaccine for use in veterinary animals was based on an 86-kDa midgut antigen from Rhipicephalus (formerly Boophilus) microplus ticks. Herein we describe the fundamentals of vaccine development using protein antigens as model vaccinogen candidates, beginning with the cloning, expression, and purification of recombinant proteins, host immunization, and the assessment of protective efficacy in laboratory settings using a tick-borne murine model of Lyme borreliosis.

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.

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.

Resistance to Ticks and the Path to Anti-Tick and Transmission Blocking Vaccines

The medical and veterinary public health importance of ticks and tick-borne pathogens is increasing due to the expansion of the geographic ranges of both ticks and pathogens, increasing tick populations, growing incidence of tick-borne diseases, emerging tick transmitted pathogens, and continued challenges of achieving effective and sustained tick control. The past decades show an increasing interest in the immune-mediated control of tick infestations and pathogen transmission through the use of vaccines. Bovine tick resistance induced by repeated infestations was reported over a century ago. This review addresses the phenomena and immunological underpinning of resistance to tick infestation by livestock and laboratory animals; the scope of tick countermeasures to host immune defenses; and the impact of genomics, functional genomics, and proteomics on dissecting complex tick-host-pathogen interactions. From early studies utilizing tick tissue extracts to salivary gland derived molecules and components of physiologically important pathways in tick gut and other tissues, an increased understanding of these relationships, over time, impacted the evolution of anti-tick vaccine antigen selection. Novel antigens continue to emerge, including increased interest in the tick microbiome. Anti-tick and transmission blocking vaccines targeting pathogen reservoirs have the potential to disrupt enzootic cycles and reduce human, companion, domestic animal, and wildlife exposure to infected ticks.

Mialostatin, a Novel Midgut Cystatin from Ixodes ricinus Ticks: Crystal Structure and Regulation of Host Blood Digestion

The hard tick Ixodes ricinus is a vector of Lyme disease and tick-borne encephalitis. Host blood protein digestion, essential for tick development and reproduction, occurs in tick midgut digestive cells driven by cathepsin proteases. Little is known about the regulation of the digestive proteolytic machinery of I. ricinus. Here we characterize a novel cystatin-type protease inhibitor, mialostatin, from the I. ricinus midgut. Blood feeding rapidly induced mialostatin expression in the gut, which continued after tick detachment. Recombinant mialostatin inhibited a number of I. ricinus digestive cysteine cathepsins, with the greatest potency observed against cathepsin L isoforms, with which it co-localized in midgut digestive cells. The crystal structure of mialostatin was determined at 1.55 Å to explain its unique inhibitory specificity. Finally, mialostatin effectively blocked in vitro proteolysis of blood proteins by midgut cysteine cathepsins. Mialostatin is likely to be involved in the regulation of gut-associated proteolytic pathways, making midgut cystatins promising targets for tick control strategies.

Comparative Proteomic Analysis of Rhipicephalus sanguineus sensu lato (Acari: Ixodidae) Tropical and Temperate Lineages: Uncovering Differences During Ehrlichia canis Infection

The tick vector Rhipicephalus sanguineus is established as a complex of closely related species with high veterinary-medical significance, in which the presence of different genetic, morphological, and biological traits has resulted in the recognition of different lineages within taxa. One of the most striking differences in the "temperate" and "tropical" lineages of R. sanguineus (s.l.) is the vector competence to Ehrlichia canis, suggesting that these ticks tolerate and react differently to pathogen infection. The present study addresses the SG and MG proteome of the R. sanguineus tropical and temperate lineages and compares their proteomic profile during E. canis infection. Batches of nymphs from the two lineages were allowed to feed on naïve and experimentally E. canis infected dogs and after molting, adults were dissected, and salivary glands and midgut tissues separated. Samples were screened for the presence of E. canis before proteomic analyses. The representation of the proteins identified in infected and non-infected tissues of each lineage was compared and gene ontology used for protein classification. Results highlight important differences in those proteomic profiles that added to previous reported genetic, biological, behavioral, and morphological differences, strengthening the hypothesis of the existence of two different species. Comparing infected and non-infected tissues, the results show that, while in midgut tissues the response to E. canis infection is similar in the salivary glands, the two lineages show a different pattern of protein representation. Focusing on the proteins found only in the infected condition, the data suggests that the cement cone produced during tick feeding may be implicated in pathogen infection. This study adds useful information to the debate on the controversial R. sanguineus systematic status, to the discussion related with the different vectorial competence occurring between the two lineages and identifies potential targets for efficient tick and tick-borne disease control.

Experimental Infection of Calves with Transfected Attenuated Babesia bovis Expressing the Rhipicephalus microplus Bm86 Antigen and eGFP Marker: Preliminary Studies towards a Dual Anti-Tick/Babesia Vaccine

Bovine babesiosis, caused by Babesia bovis and B. bigemina, is a major tick-borne disease of cattle with global economic impact. The disease can be prevented using integrated control measures including attenuated Babesia vaccines, babesicidal drugs, and tick control approaches. Vaccination of cattle with the Rhipicephalus microplus Bm86-based recombinant vaccine reduces the fitness of R. microplus and R. annulatus, but several booster inoculations are required to maintain protection. Herein, we generated a stable transfected strain of B. bovis expressing an enhanced GFP (eGFP) and a chimeric version of Bm86 (B. bovis/Bm86/eGFP). The eGFP was expressed in the parasite cytoplasm, whereas Bm86 was displayed on the surface of merozoites. Three splenectomized calves experimentally infected with B. bovis/Bm86/eGFP showed mild signs of acute disease and developed long-lasting antibody responses to B. bovis and native Bm86. No evidence of sequestration of parasites in the cerebral capillaries was found upon postmortem analysis, confirming attenuation of the strain. This is the first report of transfected B. bovis expressing the tick antigen Bm86 on the merozoite surface that elicits an antibody response to native Bm86. These results represent a proof of concept for a novel live, attenuated, tagged dual-vaccine approach to attempt simultaneous control of babesiosis and tick infestation.

Multiple Antigenic Peptide-Based Vaccines Targeting Ixodes ricinus Neuropeptides Induce a Specific Antibody Response but Do Not Impact Tick Infestation

Synthetic peptide vaccines were designed to target the neuropeptides innervating Ixodes ricinus salivary glands and hindgut and they were tested for their capacity to afford protective immunity against nymphs or larvae and Anaplasma phagocytophilum-infected nymph infestation, in mice and sheep, respectively. In both models, the assembly of SIFamide (SIFa) or myoinhibitory peptide (MIP) neuropeptides into multiple antigenic peptide constructs (MAPs) elicited a robust IgG antibody response following immunization. Nevertheless, no observable detrimental impact on nymphs was evidenced in mice, and, unfortunately, the number of engorged nymphs on sheep was insufficient for firm conclusions to be drawn, including for bacterial transmission. Regarding larvae, while vaccination of the sheep did not globally diminish tick feeding success or development, analyses of animals at the individual level revealed a negative correlation between anti-SIFa and MIP antibody levels and larva-to-nymph molting success for both antigens. Our results provide a proof of principle and precedent for the use of MAPs for the induction of immunity against tick peptide molecules. Although the present study did not provide the expected level of protection, it inaugurates a new strategy for protection against ticks based on the immunological targeting of key components of their nervous system.

Towards a Sustainable One Health Approach to Crimean-Congo Hemorrhagic Fever Prevention: Focus Areas and Gaps in Knowledge

Crimean–Congo hemorrhagic fever virus (CCHFV) infection is identified in the 2018 World Health Organization Research and Development Blueprint and the National Institute of Allergy and Infectious Diseases (NIH/NIAID) priority A list due to its high risk to public health and national security. Tick-borne CCHFV is widespread, found in Europe, Asia, Africa, the Middle East, and the Indian subcontinent. It circulates between ticks and several vertebrate hosts without causing overt disease, and thus can be present in areas without being noticed by the public. As a result, the potential for zoonotic spillover from ticks and animals to humans is high. In contrast to other emerging viruses, human-to-human transmission of CCHFV is typically limited; therefore, prevention of spillover events should be prioritized when considering countermeasures. Several factors in the transmission dynamics of CCHFV, including a complex transmission cycle that involves both ticks and vertebrate hosts, lend themselves to a One Health approach for the prevention and control of the disease that are often overlooked by current strategies. Here, we examine critical focus areas to help mitigate CCHFV spillover, including surveillance, risk assessment, and risk reduction strategies concentrated on humans, animals, and ticks; highlight gaps in knowledge; and discuss considerations for a more sustainable One Health approach to disease control.

Genetic diversity of the ATAQ gene in Rhipicephalus microplus collected in Mexico and implications as anti-tick vaccine

The cattle tick Rhipicephalus microplus has a large impact on cattle production due to its bloodsucking habit and transmission of pathogens that cause babesiosis and anaplasmosis. Application of acaricides constitutes the major control method but is often accompanied by serious drawbacks, including environmental contamination and an increase in acaricide resistance by ticks. The recent development of anti-tick vaccines has provided positive results in the post-genomic era, owing to the rise of reverse vaccinological and bioinformatics approaches to analyze and identify candidate protective antigens for use against ticks. The ATAQ protein is considered a novel antigen for the control of the cattle tick R. microplus; it is expressed in midguts and Malpighian tubules of all ticks from the Rhipicephalus genus. However, genetic diversity studies are required. Here, the ATAQ gene was sequenced of seven R. microplus tick isolates from different regions in Mexico to understand the genetic diversity. The results showed that sequence identity among the Mexican isolates ranged between 98 and 100% and 97.8-100% at the nucleotide and protein levels, respectively. Alignments of deduced amino acid sequences from different R. microplus ATAQ isolates in Mexico revealed a high degree of conservation. However, the Mexican isolates differed from the R. microplus "Mozambique" strain, at 20 amino acid residues. Finally, the analysis of more R. microplus isolates, and possibly of other Rhipicephalus species, to determine the genetic diversity in the ATAQ locus is essential to suggest this antigen as a vaccine candidate that might control tick infestations.

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.

Investigation into limiting dilution and tick transmissibility phenotypes associated with attenuation of the S24 vaccine strain

Background

Babesia bovis is the causal agent of Asiatic redwater, transmitted by the pandemic tick Rhipicephalus (Boophilus) microplus. Disease control may target the tick vector using acaricides or anti-tick vaccines, or the parasite using chemoprophylaxis or anti-parasite vaccines. Current anti-parasite vaccines comprise live blood vaccines using attenuated B. bovis strains. Attenuation is attained by rapid passage that may result in different phenotypes such as reduced virulence, non-transmissibility by the tick vector, inability to sequester in the host (lack of limiting dilution) and limited genetic diversity. Attenuation and phenotypes may be linked to selection of subpopulations during rapid passage. The South African B. bovis S24 vaccine strain comprise a subpopulation that present low virulence, non-transmissibility, lack of limiting dilution phenotype and the presence of a single A558 Bv80 allele. The S24 strain could be co-transmitted with a field strain (05-100) suggesting sexual recombination. The present study investigated the change in phenotype for the S24 vaccine strain during rapid passage and co-transmission.

Methods

Vaccine phenotype change during passage as well as co-transmissibility was monitored using Bv80 allele specific PCR, limiting dilution and Illumina-based genome sequencing.

Results

The S24 population could not be rescued from the S16 passage as previously attained suggesting that selection of the S24 vaccine strain was a serendipitous and stochastic event. Passage from S16 to S24 also resulted in loss of the limiting dilution phenotype. Genome sequencing indicated sexual recombination during co-transmission with the 05-100 field strain. Analysis of the recombinant strain indicate that VESA1, smORF and SBP2 family members are present and may be responsible for the limiting dilution phenotypes, while various regions may also be responsible for the tick transmission phenotype.

Conclusions

The molecular basis for tick transmission and limiting dilution phenotypes may be defined in future using selection based on these traits in combination with sexual recombination.

Babesiosis Vaccines: Lessons Learned, Challenges Ahead, and Future Glimpses

The incidence and prevalence of babesiosis in animals and humans is increasing, yet prevention, control, or treatment measures remain limited and ineffective. Despite a growing body of new knowledge of the biology, pathogenicity, and virulence of Babesia parasites, there is still no well-defined, adequately effective and easily deployable vaccine. While numerous published studies suggest that the development of such anti-Babesia vaccines should be feasible, many others identify significant challenges that need to be overcome in order to succeed. Here, we review historic and recent attempts in babesiosis vaccine discovery to avoid past pitfalls, learn new lessons, and provide a roadmap to guide the development of next-generation babesiosis vaccines.

Oral Vaccination With a Formulation Combining Rhipicephalus microplus Subolesin With Heat Inactivated Mycobacterium bovis Reduces Tick Infestations in Cattle

Vaccines are an environmentally friendly alternative to acaracides for the control of tick infestations, to reduce the risk for tick-borne diseases affecting human and animal health worldwide, and to improve animal welfare and production. Subolesin (SUB, also known as 4D8) is the functional homolog of Akirin2 involved in the regulation of development and innate immune response, and a proven protective antigen for the control of ectoparasite infestations and pathogen infection. Oral vaccination combining protein antigens with immunostimulants has proven efficacy with increased host welfare and safety, but has not been used for the control of tick infestations. Here we describe the efficacy of oral vaccination with a formulation combining Rhipicephalus microplus SUB and heat inactivated Mycobacterium bovis (IV) on cattle tick infestations and fertility. The levels of IgG antibody titers against SUB and M. bovis P22, and the expression of selected immune response genes were determined and analyzed as possible correlates of protection. We demonstrated that oral immunization with the SUB+IV formulation resulted in 51% reduction in the number of female ticks and 30% reduction in fertility with an overall efficacy of 65% in the control of R. microplus infestations by considering the cumulative effect on reducing tick survival and fertility in cattle. The akr2, IL-1β, and C3 mRNA levels together with antibody levels against SUB correlated with vaccine efficacy. The effect of the oral immunization with SUB+IV in cattle on tick survival and fertility is essential to reduce tick infestations, and extended previous results on the effect of R. microplus SUB for the control of cattle tick infestations. These results support the development of oral vaccines formulations for the control of tick infestations and the incidence of tick-borne diseases.

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

INTRODUCTION

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

Epidemiology, Pathogenesis, and Control of a Tick-Borne Disease- Kyasanur Forest Disease: Current Status and Future Directions

In South Asia, Haemaphysalis spinigera tick transmits Kyasanur Forest Disease Virus (KFDV), a flavivirus that causes severe hemorrhagic fever with neurological manifestations such as mental disturbances, severe headache, tremors, and vision deficits in infected human beings with a fatality rate of 3-10%. The disease was first reported in March 1957 from Kyasanur forest of Karnataka (India) from sick and dying monkeys. Since then, between 400 and 500 humans cases per year have been recorded; monkeys and small mammals are common hosts of this virus. KFDV can cause epizootics with high fatality in primates and is a level-4 virus according to the international biosafety rules. The density of tick vectors in a given year correlates with the incidence of human disease. The virus is a positive strand RNA virus and its genome was discovered to code for one polyprotein that is cleaved post-translationally into 3 structural proteins (Capsid protein, Envelope Glycoprotein M and Envelope Glycoprotein E) and 7 non-structural proteins (NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5). KFDV has a high degree of sequence homology with most members of the TBEV serocomplex. Alkhurma virus is a KFDV variant sharing a sequence similarity of 97%. KFDV is classified as a NIAID Category C priority pathogen due to its extreme pathogenicity and lack of US FDA approved vaccines and therapeutics; also, the infectious dose is currently unknown for KFD. In India, formalin-inactivated KFDV vaccine produced in chick embryo fibroblast is being used. Nevertheless, further efforts are required to enhance its long-term efficacy. KFDV remains an understudied virus and there remains a lack of insight into its pathogenesis; moreover, specific treatment to the disease is not available to date. Environmental and climatic factors involved in disseminating Kyasanur Forest Disease are required to be fully explored. There should be a mapping of endemic areas and cross-border veterinary surveillance needs to be developed in high-risk regions. The involvement of both animal and health sector is pivotal for circumscribing the spread of this disease to new areas.

Controlling ticks and tick-borne diseases…looking forward

Tick-borne diseases (TBDs) represent a growing burden for human and animal health worldwide. Several approaches including the use of chemicals with repellency and parasiticidal activity, habitat management, genetic selection of hosts with higher resistance to ticks, and vaccines have been implemented for reducing the risk of TBDs. However, the application of latest gene editing technologies in combination with vaccines likely combining tick and pathogen derived antigens and other control measures should result in the development of effective, safe, and environmentally sound integrated control programs for the prevention and control of TBDs. This paper is not a review of current approaches for the control of ticks and TBDs, but an opinion about future directions in this area.

Proteomic profiling of the midgut contents of Haemaphysalis flava

Scant information is available regarding the proteins involved in blood meal processing in ticks. Here, we aimed to highlight the midgut proteins involved in preventing blood meal coagulation, and in facilitating intracellular digestion in the tick Haemaphysalis flava. Proteins were extracted from the midgut contents of fully engorged and partially engorged ticks. We used liquid chromatography tandem-mass spectrometry (LC-MS/MS) analysis to identify 131 unique peptides, and 102 proteins. Of these, 15 proteins, each with at least two unique peptides, were recognized with high confidence. We also retrieved 18 unigenes from our previous published transcriptomic libraries of the midguts and salivary glands of H. flava, and inferred the primary structures of nine proteins and fragments of five proteins. There were 23 and 21 unique proteins in the midgut contents of fully engorged and partially engorged ticks, respectively. We detected 58 shared proteins in the midgut contents of both fully engorged and partially engorged ticks. Of these, seven were significantly differentially expressed between fully engorged and partially engorged ticks: actin, calmodulin, elongation factor-1α, hsp90, multifunctional chaperone, tubulin α, and tubulin β. Our results demonstrated that the proteome of the midgut contents, combined with the transcriptome of the midgut, was a viable method for the reinforcement of protein identification. This method will facilitate further study of blood meal processing by ticks, as well as the identification of clues for tick infestation control. The existence of numerous proteins detected in the midgut contents also highlight the complexity of blood digestion in ticks; this area is in need of further investigation.

Ticks and Tick-Borne Pathogens of the Caribbean: Current Understanding and Future Directions for More Comprehensive Surveillance

Ticks are obligate hematophagous arthropods of significant importance to human and veterinary medicine. They transmit a vast array of pathogens, including bacteria, viruses, protozoa, and helminths. Most epidemiological data on ticks and tick-borne pathogens (TBPs) in the West Indies are limited to common livestock pathogens such as Ehrlichia ruminantium, Babesia spp. (i.e., B. bovis and B. bigemina), and Anaplasma marginale, and less information is available on companion animal pathogens. Of note, human tick-borne diseases (TBDs) remain almost completely uncharacterized in the West Indies. Information on TBP presence in wildlife is also missing. Herein, we provide a comprehensive review of the ticks and TBPs affecting human and animal health in the Caribbean, and introduce the challenges associated with understanding TBD epidemiology and implementing successful TBD management in this region. In particular, we stress the need for innovative and versatile surveillance tools using high-throughput pathogen detection (e.g., high-throughput real-time microfluidic PCR). The use of such tools in large epidemiological surveys will likely improve TBD prevention and control programs in the Caribbean.

Deciphering Babesia-Vector Interactions

Understanding host-pathogen-tick interactions remains a vitally important issue that might be better understood by basic research focused on each of the dyad interplays. Pathogens gain access to either the vector or host during tick feeding when ticks are confronted with strong hemostatic, inflammatory and immune responses. A prominent example of this is the Babesia spp.—tick—vertebrate host relationship. Babesia spp. are intraerythrocytic apicomplexan organisms spread worldwide, with a complex life cycle. The presence of transovarial transmission in almost all the Babesia species is the main difference between their life cycle and that of other piroplasmida. With more than 100 species described so far, Babesia are the second most commonly found blood parasite of mammals after trypanosomes. The prevalence of Babesia spp. infection is increasing worldwide and is currently classified as an emerging zoonosis. Babesia microti and Babesia divergens are the most frequent etiological agents associated with human babesiosis in North America and Europe, respectively. Although the Babesia-tick system has been extensively researched, the currently available prophylactic and control methods are not efficient, and chemotherapeutic treatment is limited. Studying the molecular changes induced by the presence of Babesia in the vector will not only elucidate the strategies used by the protozoa to overcome mechanical and immune barriers, but will also contribute toward the discovery of important tick molecules that have a role in vector capacity. This review provides an overview of the identified molecules involved in Babesia-tick interactions, with an emphasis on the fundamentally important ones for pathogen acquisition and transmission.

Expression and determination of immunization dose of recombinant tropomyosin protein of Hyalomma anatolicum for the development of anti-tick vaccine

Present investigation was carried out to standardize the immunization dose of one recombinant antigen in rat model before conducting large animal experimentation. Tropomyosin (TPM), a muscle associated and highly conserved protein found in all species of invertebrates, was cloned, expressed in prokaryotic system and the downstream process was standardized. SDS-PAGE analysis showed a distinct band of approximately 51 kDa Western blot analysis using specific sera gave a strong reaction of approximately the same size as that of SDSPAGE. For standardization of immunization dose, the rTPM at three different dosages viz., 150, 300, 450 μg was used to immunize wister rats and the antibody response was titrated by ELISA. Applying ANOVA, highly significantdifference in anti-rTPM titre was recorded between the animals injected with 300 μg total dose (TD) and other dosages selected for the study. The significantly high antibody tire at 1:25600 dilution observed in animals immunized with 300 μg TD was selected for further study on in vivo immunization of calves and experimental challenge by the tick stages.