Vaccination against ticks (Boophilus spp.): the experience with the Bm86-based vaccine Gavac

Counterattacking the tick bite: towards a rational design of anti-tick vaccines targeting pathogen transmission

Hematophagous arthropods are responsible for the transmission of a variety of pathogens that cause disease in humans and animals. Ticks of the Ixodes ricinus complex are vectors for some of the most frequently occurring human tick-borne diseases, particularly Lyme borreliosis and tick-borne encephalitis virus (TBEV). The search for vaccines against these diseases is ongoing. Efforts during the last few decades have primarily focused on understanding the biology of the transmitted viruses, bacteria and protozoans, with the goal of identifying targets for intervention. Successful vaccines have been developed against TBEV and Lyme borreliosis, although the latter is no longer available for humans. More recently, the focus of intervention has shifted back to where it was initially being studied which is the vector. State of the art technologies are being used for the identification of potential vaccine candidates for anti-tick vaccines that could be used either in humans or animals. The study of the interrelationship between ticks and the pathogens they transmit, including mechanisms of acquisition, persistence and transmission have come to the fore, as this knowledge may lead to the identification of critical elements of the pathogens' life-cycle that could be targeted by vaccines. Here, we review the status of our current knowledge on the triangular relationships between ticks, the pathogens they carry and the mammalian hosts, as well as methods that are being used to identify anti-tick vaccine candidates that can prevent the transmission of tick-borne pathogens.

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.

Differential expression analysis for subolesin in Rhipicephalus microplus infected with Anaplasma marginale

Rhipicephalus microplus (formerly Boophilus microplus) ticks are potential vectors of several pathogens of livestock especially in tropical and subtropical regions where may have substantial effects on economic development. Among tick-borne pathogens, Anaplasma marginale is considered one of the most important in domestic and wild ruminants worldwide. Different molecular mechanisms have been employed by both ticks and these intracellular pathogens, in order to be able to adapt and survive. Subolesin, originally called 4D8, is an evolutionarily well-preserved protein among ixodid tick species. This new antigen was found to be protective against tick infestations when used as a vaccine, as it has an essential role in tick blood digestion, development and infection of host cells by A. marginale. Recent studies have demonstrated that infection of both tick and vertebrate host cells with this microorganism changed gene expression. Therefore, the main objective of this study was to investigate subolesin expression in uninfected and A. marginale-infected R. microplus salivary glands by real-time reverse transcriptase (RT)-PCR. To analyze the differential expression of the recombinant protein subolesin, the gene was previously expressed from ticks infected with A. marginale. Results from this study revealed that, the expression of subolesin was significantly higher in salivary glands of infected R. microplus in comparison to uninfected ones.

Analysis of Bm86 conserved epitopes: is a global vaccine against Cattle Tick Rhipicephalus microplus possible?

The cattle tick Rhipicephalus microplus causes significant economic losses in agribusiness. Control of this tick is achieved mainly through the application of chemical acaricides, often resulting in contamination of animal food products and of the environment. Another major concern associated with acaricide use is the increasing reports of resistance of this tick vector against the active ingredients of many commercial products. An alternative control method is vaccination. However, the commercially available vaccine based on a protein homologous to Bm86 exhibits variations in efficacy relative to the different geographical locations. This study aimed to identify antigenic determinants of the sequences of proteins homologous to Bm86. Phylogenetic analyses were performed to determine the extent of divergence between different populations of R. microplus to identify the sequence that could be used as a universal vaccine against the multiple geographically distinct populations of R. microplus and related tick species. Considering the extensive sequence and functional polymorphism observed among strains of R. microplus from different geographical regions, we can conclude that it may be possible to achieve effective vaccination against these cattle ticks using a single universal Bm86-based antigen.

Comparison of Protein Gut Samples from Rhipicephalus spp. Using a Crude and an Innovative Preparation Method for Proteome Analysis

Tick populations are controlled through the application of chemical pesticides. However, the rise in chemical resistance has prompted the investigation of other control methods such as the use of tick vaccines. Proteomic analysis provides valuable information about the possible function and localization of proteins, as candidate vaccine proteins are often either secreted or localized on the cell-surface membrane. Progress in the utilization of proteomics for the identification of novel treatment targets has been significant. However, their use in tick-specific investigations is still quite novel, with the continual development of tick-specific methodologies essential. In this study, an innovative sample preparation method was utilized to isolate epithelial cells from tick midguts to identify the membrane-bound proteins. Proteomic analysis was conducted comparing crude and innovative sample preparation methods with 692 and 1242 tick-specific proteins, 108 and 314 surface proteins respectively, isolated from the midguts of semi-engorged Rhipicephalus microplus adult female ticks. This research reports a novel preparation protocol for the analysis of tick midgut proteins which reduces host protein contamination.

Characterization of a glycine-rich protein from Rhipicephalus microplus: tissue expression, gene silencing and immune recognition

Salivary molecules, as glycine-rich proteins (GRPs), are essential to tick attachment and feeding on the host and are suggested to be involved in the host's immune system evasion, therefore representing natural candidates in the search for protective vaccine antigens. This work shows the molecular characterization of a GRP from Rhipicephalus microplus (RmGRP). The cDNA and putative amino acid sequences were analysed, as well as the transcription level in tick tissues/developmental stages, showing the highest levels of gene expression in 1-day-old larvae and salivary glands of fully engorged females. RmGRP gene silencing resulted in a lower hatching rate of larvae from treated females. In addition, recombinant RmGRP (rRmGRP) was recognized by sera from naturally and experimentally infested bovines, displaying considerable differences among the individuals tested. rRmGRP was recognized by anti-saliva and anti-salivary glands sera, while anti-rRmGRP serum recognized RmGRP in saliva and salivary glands, indicating its secretion into the host. The data collected indicate that RmGRP may present roles other than in the tick–host relationship, especially in embryo development. In addition, the high expression in adult females, antigenicity and presence of shared characteristics with other tick protective GRPs turns RmGRP a potential candidate to compose an anti-tick vaccine cocktail.

Immunofluorescent detection in the ovary of host antibodies against a secretory ferritin injected into female Haemaphysalis longicornis ticks

Due to the continuous threat of ticks and tick-borne diseases to human and animal health worldwide, and the drawbacks of chemical acaricide application, many researchers are exploring vaccination as an alternative tick control method. Earlier studies have shown that host antibodies can circulate in the ticks, but it has not been confirmed whether these antibodies can be passed on to the eggs. We previously reported that ticks infesting rabbits immunized with a recombinant secretory ferritin of Haemaphysalis longicornis (HlFER2) had reduced egg production and hatching. Here we attempted to detect the presence of antibodies against HlFER2 in the ovary and eggs of female ticks through immunofluorescent visualization. Purified anti-HlFER2 antibodies or rabbit IgG for control was directly injected to engorged female H. longicornis. Ovaries and eggs after oviposition were collected and prepared for an indirect immunofluorescent antibody test. Positive fluorescence was detected in ovaries one day post-injection of anti-HlFER2 antibodies. Through silencing of Hlfer2 gene, we also determined whether the injected antibodies can specifically bind to native HlFER2. Immunofluorescence was observed in the oocytes of dsLuciferase control ticks injected with anti-HlFER2 antibodies, but not in the oocytes of Hlfer2-silenced ticks also injected with anti-HlFER2 antibodies. Our current findings suggest that host antibodies can be passed on to the oocytes, which is significant in formulating a vaccine that can disrupt tick reproduction.

Experimental efficacy of a vaccine against Rhipicephalus australis

Despite several decades of chemical use the cattle tick, Rhipicephalus australis, still represents an important threat for breeders of tick susceptible cattle under tropical conditions. The intense use of acaricides has lead to the development of multi-resistant strains of ticks and alternative means of control need to be developed to maintain control. A vaccine against ticks, based on the Boophilus microplus Bm86 protein, is one of the promising alternative means of tick control. In this investigation, an experimental vaccine was developed based on the orthologous R. australis Bm86 sequence identified from local R. australis strains and a recombinant protein expressed in Escherichia coli. The efficacy of this vaccine against a local strain of R. australis was assessed under controlled conditions. Vaccinated cattle presented 40.3% fewer ticks than unvaccinated cattle and tick reproductive performance was also affected by the vaccine. Ticks that engorged on vaccinated animals laid 51.2% less egg mass and tick fertility decreased by 18.8% compared to the control group. The use of the vaccine reduced the tick population by 74.2% at each generation. The tick vaccine can be used in an integrated tick control program.

Evaluation of three adjuvants with respect to both adverse effects and the efficacy of antibody production to the Bm86 protein

Cattle tick infestations remain an important burden for farmers in tropical area like in New Caledonia. With the development of acaricide resistance, tick vaccines should be an attractive alternative to control ticks but their efficacy needs to be improved. In this study three adjuvants were studied in an experimental tick vaccine with a Bm86 protein to assess their performance in terms of antibody productions and adverse reactions following vaccinations. The water-in-oil adjuvant ISA 61 VG led to higher antibody titers compared to a water-in-oil-in-water adjuvant ISA 201 VG and an aqueous polymeric adjuvant Montanide Gel 01. Vaccinations with these three adjuvants did not produce severe general reaction but an increase in skin thickness was observed especially with both oil-based emulsions. These results indicated that the water-in-oil adjuvant is the most interesting to use for this vaccine but local adverse reactions remain an issue.

Mining a differential sialotranscriptome of Rhipicephalus microplus guides antigen discovery to formulate a vaccine that reduces tick infestations

BACKGROUND

Ticks cause massive damage to livestock and vaccines are one sustainable substitute for the acaricides currently heavily used to control infestations. To guide antigen discovery for a vaccine that targets the gamut of parasitic strategies mediated by tick saliva and enables immunological memory, we exploited a transcriptome constructed from salivary glands from all stages of Rhipicephalus microplus ticks feeding on genetically tick-resistant and susceptible bovines.

RESULTS

Different levels of host anti-tick immunity affected gene expression in tick salivary glands; we thus selected four proteins encoded by genes weakly expressed in ticks attempting to feed on resistant hosts or otherwise abundantly expressed in ticks fed on susceptible hosts; these sialoproteins mediate four functions of parasitism deployed by male ticks and that do not induce antibodies in naturally infected, susceptible bovines. We then evaluated in tick-susceptible heifers an alum-adjuvanted vaccine formulated with recombinant proteins. Parasite performance (i.e. weight and numbers of females finishing their parasitic cycle) and titres of antigen-specific antibodies were significantly reduced or increased, respectively, in vaccinated versus control heifers, conferring an efficacy of 73.2%; two of the antigens were strong immunogens, rich in predicted T-cell epitopes and challenge infestations boosted antibody responses against them.

CONCLUSION

Mining sialotranscriptomes guided by the immunity of tick-resistant hosts selected important targets and infestations boosted immune memory against salivary antigens.

A new method for in vitro feeding of Rhipicephalus australis (formerly Rhipicephalus microplus) larvae: a valuable tool for tick vaccine development

BACKGROUND

Rhipicephalus microplus is a hard tick that has a major impact on cattle health in tropical and subtropical regions because it feeds on cattle and is implicated in the transmission of pathogens that cause diseases such as bovine anaplasmosis and babesiosis. Presently, acaricides are used to control tick infestation but this is becoming increasingly less effective due to the emergence of tick strains that are resistant to one or more classes of acaricides. Anti-tick vaccines are a promising alternative to control tick infestation in cattle. The life-cycle and host preference of R. microplus, however, makes vaccine research in cattle costly and would therefore greatly benefit from an in vitro screening system.

METHODS

To this aim, a stacked 24-well in vitro feeding system was designed in which the blood meal was administered in a chamber on top of the compartment containing the ticks, exploiting their anti-gravitational tendency. Both compartments were separated by a special feeding membrane, which was made by applying a silicone mixture to a gold beater's skin (baudruche membrane) with a paint roller to create a slightly uneven surface of 17-40 μm variable thickness. To further stimulate feeding, the membrane was treated with bovine hair extract and the unit was placed at 37 °C with 90% RH and 5% CO2.

RESULTS

Using this set-up with Rhipicephalus australis (formerly Rhipicephalus microplus), a larval engorgement rate of up to 71% could be achieved. The larvae could successfully feed on blood, but also on serum. The latter allows easy screening of the effect of sera that are raised against tick proteins on feeding. As an example, serum from cattle that were vaccinated with the Bm86 midgut protein of R. microplus significantly reduced larval engorgement rates by 42%.

CONCLUSION

The in vitro feeding system's high throughput design and its ability to measure statistically significant anti-tick effects in sera from immunized cattle enables screening of multiple vaccine candidates in a cost-effective manner.

Tick repellents and acaricides of botanical origin: a green roadmap to control tick-borne diseases?

Arthropods are dangerous vectors of agents of deadly diseases, which may hit as epidemics or pandemics in the increasing world population of humans and animals. Among them, ticks transmit more pathogen species than any other group of blood-feeding arthropods worldwide. Thus, the effective and eco-friendly control of tick vectors in a constantly changing environment is a crucial challenge. A number of novel routes have been attempted to prevent and control tick-borne diseases, including the development of (i) vaccines against viruses vectored by ticks; (ii) pheromone-based control tools, with special reference to the "lure and kill" techniques; (iii) biological control programmes relying on ticks' natural enemies and pathogens; and (iv) the integrated pest management practices aimed at reducing tick interactions with livestock. However, the extensive employment of acaricides and tick repellents still remains the two most effective and ready-to-use strategies. Unfortunately, the first one is limited by the rapid development of resistance in ticks, as well as by serious environmental concerns. On the other hand, the exploitation of plants as sources of effective tick repellents is often promising. Here, we reviewed current knowledge concerning the effectiveness of plant extracts as acaricides or repellents against tick vectors of public health importance, with special reference to Ixodes ricinus, Ixodes persulcatus, Amblyomma cajennense, Haemaphysalis bispinosa, Haemaphysalis longicornis, Hyalomma anatolicum, Hyalomma marginatum rufipes, Rhipicephalus appendiculatus, Rhipicephalus (Boophilus) microplus, Rhipicephalus pulchellus, Rhipicephalus sanguineus and Rhipicephalus turanicus. Eighty-three plant species from 35 botanical families were selected. The most frequent botanical families exploited as sources of acaricides and repellents against ticks were Asteraceae (15 % of the selected studies), Fabaceae (9 %), Lamiaceae (10 %), Meliaceae (5 %), Solanaceae (6 %) and Verbenaceae (5 %). Regression equation analyses showed that the literature grew by approximately 20 % per year (period: 2005-2015). Lastly, in the final section, insights for future research are discussed. We focused on some caveats for future data collection and analysis. Current critical points mainly deal with (a) not uniform methods used, which prevent proper comparison of the results; (b) inaccurate tested concentrations, frequently 100 % concentration corresponded to the gross extract, where the exact amounts of extracted substances are unknown; and (c) not homogeneous size of tested tick instars and species. Overall, the knowledge summarized in this review may be helpful for comparative screening among extensive numbers of plant-borne preparations, in order to develop newer and safer tick control tools.

Extensive polymorphism of Ra86 genes in field populations of Rhipicephalus appendiculatus from Kenya

Commercial vaccines based on recombinant forms of the Bm86 tick gut antigen are used to control the southern cattle tick, Rhipicephalus microplus, a 1-host species, in Australia and Latin America. We describe herein sequence polymorphism in genes encoding Ra86 homologues of Bm86 in the brown ear tick, Rhipicephalus appendiculatus, isolated from four Kenyan field populations and one laboratory colony. Sequencing of 19 Ra86 sequences defined two alleles differentiated by indels, encoding 693 amino acids (aa) and 654 aa respectively, from the Muguga laboratory reference strain. Ra86 sequences were also determined from gut cDNA from four field populations of R. appendiculatus collected in different livestock production systems in Kenya. Analysis of approximately 20 Ra86 sequences from each of the four field sites in central and Western Kenya; Makuyu, Kiambu, Kakamega and Uasin Gishu, revealed three additional size types differentiated by 39-49 amino acid indels resulting in a total of 5 indel-defined genotypes. The 693 aa type 5 was isolated only from the laboratory tick stock; genotypes 1, 2 and 3 were identified in ticks from the four Kenyan field sites and appeared to be derivatives of the shorter RA86 genotype found in Muguga laboratory stock genotype 4. By contrast no large indels have yet been observed between R. microplus sequences from Australia, South America or Africa. Evidence that selection contributes to the observed sequence variation was provided by analysis of ratio of synonymous and non-synonymous substitutions and application of the selective neutrality and neutral evolution tests to the primary data. Phylogenetic analysis clustered sequences from all Ra86 size types and Bm86, into four major clades based on amino acid substitutions, but there was no evidence that these groupings correlated with geographical separation of R. appendiculatus populations.

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.

Comparative in vitro anti-tick efficacy of commercially available products and newly developed phyto-formulations against field collected and resistant tick lines of Rhipicephalus (Boophilus) microplus

Rhipicephalus (Boophilus) microplus is considered as one of the most widely distributed tick species ecto-parasitizing on livestock and causes fatal diseases with significant production loss. To address the problem of controlling acaricide resistant tick infestations on animals, attention has been paid to develop eco-friendly phyto-acaricides. The present study was undertaken to evaluate the comparative anti-tick activities of commercially available herbal and chemical products with chemically characterized phyto-formulations developed recently against field ticks and resistant tick lines of R. (B.) microplus. The chemical product Butox^® Vet was found nearly passive against all the tested resistant tick lines. However, one of the commercial polyherbal product, Zerokeet^® showed an efficacy (E%) of 41.8-75.4 % ([Formula: see text]) using recommended dilution (1:2) against field ticks and resistant tick lines. However, the other commercial product, Erina^® EP has very limited efficacy against all the tested tick. In comparison, the newly developed phyto-formulation, NBA/13/B/2 and NAC-01 conferred an E% of 82.4-91.3 % ([Formula: see text]) and 62.3-94.6 % ([Formula: see text]), respectively, against tested resistant ticks. Results indicated higher marketing potentiality of newly developed formulation in the existing tick problem scenario.

Types of Recombinant Vaccines

The original scientific strategy behind vaccinology has historically been to “isolate, inactivate, and inject,” first invoked by Louis Pasteur.

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.

Identification of potential plant extracts for anti-tick activity against acaricide resistant cattle ticks, Rhipicephalus (Boophilus) microplus (Acari: Ixodidae)

To develop an eco-friendly tick control method, seven plant extracts were prepared using 50 and 95% ethanol and evaluated for acaricidal activity against cattle tick, Rhipicephalus (Boophilus) microplus. The adult immersion test was adopted for testing different extracts. Based on 72 h screening criterion, 95% ethanolic extracts of Datura metel fruits and Argemone mexicana whole plant were found effective showing more than 50% mortality of treated ticks. The 95% ethanolic extracts of D. metel fruits and A. mexicana whole plant exhibited acaricidal and reproductive inhibitory effects on treated ticks. The LC90 values of D. metel and A. mexicana extracts were determined as 7.13 and 11.3%, respectively. However, although both the extracts were found efficacious against deltamethrin-resistant IVRI-4 and multi-acaricide resistant IVRI-5 lines of R. (B.) microplus, they caused less mortality than treated ticks of the reference IVRI-I line. Phytochemical studies indicated the presence of alkaloids and glucosides in D. metel fruits and alkaloids, terpenoids, flavonoids and phenolics in A. mexicana whole plant extracts. The results indicated that these botanicals may play an important role in reducing the use of chemicals for tick control and possibly to manage resistant tick population in environment friendly manner.

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.

Vaccines against bovine babesiosis: where we are now and possible roads ahead

Bovine babesiosis caused by the tick-transmitted haemoprotozoans Babesia bovis, Babesia bigemina and Babesia divergens commonly results in substantial cattle morbidity and mortality in vast world areas. Although existing live vaccines confer protection, they have considerable disadvantages. Therefore, particularly in countries where large numbers of cattle are at risk, important research is directed towards improved vaccination strategies. Here a comprehensive overview of currently used live vaccines and of the status quo of experimental vaccine trials is presented. In addition, pertinent research fields potentially contributing to the development of novel non-live and/or live vaccines are discussed, including parasite antigens involved in host cell invasion and in pathogen-tick interactions, as well as the protective immunity against infection. The mining of available parasite genomes is continuously enlarging the array of potential vaccine candidates and, additionally, the recent development of a transfection tool for Babesia can significantly contribute to vaccine design. However, the complication and high cost of vaccination trials hinder Babesia vaccine research, and have so far seriously limited the systematic examination of antigen candidates and prevented an in-depth testing of formulations using different immunomodulators and antigen delivery systems.

Influence of pH control in the formation of inclusion bodies during production of recombinant sphingomyelinase-D in Escherichia coli

BACKGROUND

Inclusion bodies (IBs) are aggregated proteins that form clusters when protein is overexpressed in heterologous expression systems. IBs have been considered as non-usable proteins, but recently they are being used as functional materials, catalytic particles, drug delivery agents, immunogenic structures, and as a raw material in recombinant therapeutic protein purification. However, few studies have been made to understand how culture conditions affect the protein aggregation and the physicochemical characteristics that lead them to cluster. The objective of our research was to understand how pH affects the physicochemical properties of IBs formed by the recombinant sphingomyelinase-D of tick expressed in E. coli BL21-Gold (DE3) by evaluating two pH culture strategies.

RESULTS

Uncontrolled pH culture conditions favored recombinant sphingomyelinase-D aggregation and IB formation. The IBs of sphingomyelinase-D produced under controlled pH at 7.5 and after 24 h were smaller (<500 nm) than those produced under uncontrolled pH conditions (>500 nm). Furthermore, the composition, conformation and β-structure formation of the aggregates were different. Under controlled pH conditions in comparison to uncontrolled conditions, the produced IBs presented higher resistance to denaturants and proteinase-K degradation, presented β-structure, but apparently as time passes the IBs become compacted and less sensitive to amyloid dye binding.

CONCLUSIONS

The manipulation of the pH has an impact on IB formation and their physicochemical characteristics. Particularly, uncontrolled pH conditions favored the protein aggregation and sphingomyelinase-D IB formation. The evidence may lead to find methodologies for bioprocesses to obtain biomaterials with particular characteristics, extending the application possibilities of the inclusion bodies.

Rhipicephalus (Boophilus) microplus tick in vitro feeding methods for functional (dsRNA) and vaccine candidate (antibody) screening

Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) ticks cause economic losses for cattle industries throughout tropical and subtropical regions of the world estimated at $US2.5 billion annually. Lack of access to efficacious long-lasting vaccination regimes and increases in tick acaricide resistance have led to the investigation of targets for the development of novel tick vaccines and treatments. In vitro tick feeding has been used for many tick species to study the effect of new acaricides on the transmission of tick-borne pathogens. Few studies have reported the use of in vitro feeding for functional genomic studies using RNA interference and/or the effect of specific anti-tick antibodies. In particular, in vitro feeding reports for the cattle tick are limited due to its relatively short hypostome. Previously published methods were further modified to broaden optimal tick sizes/weights, feeding sources including bovine and ovine serum, optimisation of commercially available blood anti-coagulant tubes, and IgG concentrations for effective antibody delivery. Ticks are fed overnight and monitored for ∼5-6 weeks to determine egg output and success of larval emergence using a humidified incubator. Lithium-heparin blood tubes provided the most reliable anti-coagulant for bovine blood feeding compared with commercial citrated (CPDA) and EDTA tubes. Although >30mg semi-engorged ticks fed more reliably, ticks as small as 15mg also fed to repletion to lay viable eggs. Ticks which gained less than ∼10mg during in vitro feeding typically did not lay eggs. One mg/ml IgG from Bm86-vaccinated cattle produced a potent anti-tick effect in vitro (83% efficacy) similar to that observed in vivo. Alternatively, feeding of dsRNA targeting Bm86 did not demonstrate anti-tick effects (11% efficacy) compared with the potent effects of ubiquitin dsRNA. This study optimises R. microplus tick in vitro feeding methods which support the development of cattle tick vaccines and treatments.

Targeted surface expression of an exogenous antigen in stably transfected Babesia bovis

Babesia bovis is a tick-borne intraerythocytic protozoan responsible for acute disease in cattle which can be controlled by vaccination with attenuated B. bovis strains. Emerging B. bovis transfection technologies may increase the usefulness of these live vaccines. One use of transfected B. bovis parasites may be as a vaccine delivery platform. Previous transfection methods for B. bovis were limited by single expression sites and intracellular expression of transfected antigens. This study describes a novel transfection system in which two exogenous genes are expressed: one for selection and the other for a selected antigen designed to be delivered to the surface of the parasites. The strategy for duplicating the number of transfected genes was based on the use of the putative bidirectional promoter of the B. bovis 1.4 Kb ef-1α intergenic region. The ability of this region to regulate two independent expression sites was demonstrated using a luciferase assay on transiently transfected B. bovis parasites and then incorporated into a stable transfection plasmid to control independent expression of the selectable marker GFP-BSD and another gene of interest. A chimeric gene was synthetized using sequences from the protective B-cell epitopes of Rhipicephalus microplus tick antigen Bm86 along with sequences from the surface exposed B. bovis major surface antigen-1. This chimeric gene was then cloned into the additional expression site of the transfection plasmid. Transfection of the B. bovis Mo7 strain with this plasmid resulted in stable insertion into the ef-1α locus and simultaneous expression of both exogenous genes. Expression of the Bm86 epitopes on the surface of transfected merozoites was demonstrated using immunofluorescence analyses. The ability to independently express multiple genes by the inclusion of a bidirectional promoter and the achievement of surface expression of foreign epitopes advances the potential of transfected B. bovis as a future vaccine delivery platform.

Sequence characterization and immunogenicity of cystatins from the cattle tick Rhipicephalus (Boophilus) microplus

Various classes of endopeptidases and their inhibitors facilitate blood feeding and digestion in ticks. Cystatins, a family of tight-binding and reversible inhibitors of cysteine endopeptidases, have recently been found in several tick tissues. Moreover, vaccine trials using tick cystatins have been found to induce protective immune responses against tick infestation. However, the mode of action of tick cystatins is still poorly understood, limiting the elucidation of their physiological role. Against this background, we have investigated sequence characteristics and immunogenic properties of 5 putative cystatins from Rhipicephalus (Boophilus) microplus from Brazil and Uruguay. The similarity of the deduced amino acid sequences among cystatins from the Brazilian tick strain was 27-42%, all of which had a secretory signal peptide. The cystatin motif (QxVxG), a glycine in the N-terminal region, and the PW motif in the second hairpin loop in the C-terminal region are highly conserved in all 5 cystatins identified in this study. Four cysteine residues in the C terminus characteristic of type 2 cystatins are also present. qRT-PCR revealed differential expression patterns among the 5 cystatins identified, as well as variation in mRNA transcripts present in egg, larva, gut, salivary glands, ovary, and fat body tissues. One R. microplus cystatin showed 97-100% amino acid similarity between Brazilian and Uruguayan isolates. Furthermore, by in silico analysis, antigenic amino acid regions from R. microplus cystatins showed high degrees of homology (54-92%) among Rhipicephalus spp. cystatins. Three Brazilian R. microplus cystatins were expressed in Escherichia coli, and immunogenicity of the recombinant proteins were determined by vaccinating mice. Western blotting using mice sera indicated cross-reactivity between the cystatins, suggesting shared epitopes. The present characterization of Rhipicephalus spp. cystatins represents an empirical approach in an effort to evaluate the physiological role of cystatins in a larger context of targeting them for use in future tick control strategies.

Tick vaccines and the control of tick-borne pathogens

Ticks are obligate hematophagous ectoparasites that transmit a wide variety of pathogens to humans and animals. The incidence of tick-borne diseases has increased worldwide in both humans and domestic animals over the past years resulting in greater interest in the study of tick-host-pathogen interactions. Advances in vector and pathogen genomics and proteomics have moved forward our knowledge of the vector-pathogen interactions that take place during the colonization and transmission of arthropod-borne microbes. Tick-borne pathogens adapt from the vector to the mammalian host by differential gene expression thus modulating host processes. In recent years, studies have shown that targeting tick proteins by vaccination can not only reduce tick feeding and reproduction, but also the infection and transmission of pathogens from the tick to the vertebrate host. In this article, we review the tick-protective antigens that have been identified for the formulation of tick vaccines and the effect of these vaccines on the control of tick-borne pathogens.

Screening and molecular cloning of a protective antigen from the midgut of Haemaphysalis longicornis

Vaccination is considered a promising alternative for controlling tick infestations. Haemaphysalis longicornis midgut proteins separated by SDS-PAGE and transferred to polyvinylidene difluoride (PVDF) membrane were screened for protective value against bites. The western blot demonstrated the immunogenicity of 92 kDa protein (P92). The analysis of the P92 amino acid sequence by LC-MS/MS indicated that it was a H. longicornis paramyosin (Hl-Pmy). The full lenghth cDNA of Hl-Pmy was obtained by rapid amplification of cDNA ends (RACE) which consisted of 2,783 bp with a 161 bp 3' untranslated region. Sequence alignment of tick paramyosin (Pmy) showed that Hl-Pmy shared a high level of conservation among ticks. Comparison with the protective epitope sequence of other invertebrate Pmy, it was calculated that the protective epitope of Hl-Pmy was a peptide (LEEAEGSSETVVEMNKKRDTE) named LEE, which was close to the N-terminal of Hl-Pmy protein. The secondary structure analysis suggested that LEE had non-helical segments within an α-helical structure. These results provide the basis for developing a vaccine against biting H. longicornis ticks.

Borrelia burgdorferi and tick proteins supporting pathogen persistence in the vector

Borrelia burgdorferi, a pathogen transmitted by Ixodes ticks, is responsible for a prevalent illness known as Lyme disease, and a vaccine for human use is unavailable. Recently, genome sequences of several B. burgdorferi strains and Ixodes scapularis ticks have been determined. In addition, remarkable progress has been made in developing molecular genetic tools to study the pathogen and vector, including their intricate relationship. These developments are helping unravel the mechanisms by which Lyme disease pathogens survive in a complex enzootic infection cycle. Notable discoveries have already contributed to understanding the spirochete gene regulation accounting for the temporal and spatial expression of B. burgdorferi genes during distinct phases of the lifecycle. A number of pathogen and vector gene products have also been identified that contribute to microbial virulence and/or persistence. These research directions will enrich our knowledge of vector-borne infections and contribute towards the development of preventative strategies against Lyme disease.

Immune Response of Bos indicus Cattle against the Anti-Tick Antigen Bm91 Derived from Local Rhipicephalus (Boophilus) microplus Ticks and Its Effect on Tick Reproduction under Natural Infestation

Antigens of anti-tick vaccines are more efficacious for homologous challenge with local tick strains. cDNA clones encoding for Bm91 from local Rhipicephalus (Boophilus) microplus strains were developed to immunize Bos indicus cattle under field conditions. Three groups of six animals each were injected with the antigen Bm91, saline, and adjuvant, respectively. Animals were immunized three times at 3-week intervals and a fourth time after six months. The anti-Bm91 antibody level, measured by ELISA, was monitored for 7 months and the reproductive performance of naturally infested R. (B.) microplus was determined. Bm91-immunized animals developed a strong immune response expressed by high anti-Bm91 levels remaining on high levels until the end of the study. Western blot analysis confirmed that Bm91 is immunogenic. Compared to control animals, the reproductive efficiency index and the egg viability were 6% and 8%, respectively, lower in the Bm91 group (P < 0.05). In conclusion, it was demonstrated that Bm91 induced a long-lasting immune response. However, the effect on the tick reproduction was not sufficient for an efficient tick control. Further studies under field conditions are warranted to enhance the effect on the tick reproduction by optimizing the immunization regimen, alone or in combination with other vaccine candidate antigens.

Inhibition of enzyme activity of Rhipicephalus (Boophilus) microplus triosephosphate isomerase and BME26 cell growth by monoclonal antibodies

In the present work, we produced two monoclonal antibodies (BrBm37 and BrBm38) and tested their action against the triosephosphate isomerase of Rhipicephalus (Boophilus) microplus (RmTIM). These antibodies recognize epitopes on both the native and recombinant forms of the protein. rRmTIM inhibition by BrBm37 was up to 85% whereas that of BrBrm38 was 98%, depending on the antibody-enzyme ratio. RmTIM activity was lower in ovarian, gut, and fat body tissue extracts treated with BrBm37 or BrBm38 mAbs. The proliferation of the embryonic tick cell line (BME26) was inhibited by BrBm37 and BrBm38 mAbs. In summary, the results reveal that it is possible to interfere with the RmTIM function using antibodies, even in intact cells.

Efficacy of Hyalomma scupense (Hd86) antigen against Hyalomma excavatum and H. scupense tick infestations in cattle

The Rhipicephalus microplus recombinant Bm86-based tick vaccines have shown their efficacy for the control of several Hyalomma cattle ticks genera, namely H. dromedarii and H. anatolicum. However, H. scupense species, the most important tick in North Africa has never been studied. Vaccination trials using either a recombinant Bm86-based vaccine or a recombinant Hd86-based vaccine (the Bm86 ortholog in H. scupense) were conducted in cattle against immature and adult H. scupense ticks and adult H. excavatum ticks. The results showed a 59.19% reduction in the number of scupense nymphs engorging on Hd86 vaccinated cattle. However, cattle vaccination with Bm86 or Hd86 did not have an effect on H. scupense or H. excavatum adult ticks infestations. These results showed that Hd86 vaccines are selectively effective against H. scupense immature instars and emphasize on an integrated anti-tick vaccine control in North Africa.

Bovine immunoprotection against Rhipicephalus (Boophilus) microplus with recombinant Bm86-Campo Grande antigen

The southern cattle fever tick, Rhipicephalus (Boophilus) microplus, is no doubt the most economically important ectoparasite of cattle globally. The inappropriate use of chemical acaricides has driven the evolution of resistance in populations of R. (B.) microplus. Anti-tick vaccines represent a technology that can be combined with acaricides in integrated control programs to mitigate the impact of R. (B.) microplus. The recombinant form of Bm86 antigen from the Campo Grande (rBm86-CG) strain of R. (B.) microplus was produced using the Pichiapastoris expression system to test its ability to immunoprotect cattle against tick infestation. Secretion of rBm86-CG by P. pastoris through the bioprocess reported here simplified purification of the antigen. A specific humoral immune response was detected by ELISA in vaccinated cattle. Immunoblot results revealed that polyclonal antibodies from vaccinated cattle recognized a protein in larval extracts with a molecular weight corresponding to Bm86. The rBm86-CG antigen showed 31% efficacy against the Campo Grande strain of R. (B.) microplus infesting vaccinated cattle. The rBm86-CG is an antigen that could be used in a polyvalent vaccine as part of an integrated program for the control of R. (B.) microplus in the region that includes Mato Grosso do Sul.

Integrated Strategy for Sustainable Cattle Fever Tick Eradication in USA is Required to Mitigate the Impact of Global Change

The ticks Rhipicephalus (Boophilus) annulatus and R. (B.) microplus, commonly known as cattle and southern cattle tick, respectively, impede the development and sustainability of livestock industries throughout tropical and other world regions. They affect animal productivity and wellbeing directly through their obligate blood-feeding habit and indirectly by serving as vectors of the infectious agents causing bovine babesiosis and anaplasmosis. The monumental scientific discovery of certain arthropod species as vectors of infectious agents is associated with the history of research on bovine babesiosis and R. annulatus. Together, R. microplus and R. annulatus are referred to as cattle fever ticks (CFT). Bovine babesiosis became a regulated foreign animal disease in the United States of America (U.S.) through efforts of the Cattle Fever Tick Eradication Program (CFTEP) established in 1906. The U.S. was declared free of CFT in 1943, with the exception of a permanent quarantine zone in south Texas along the border with Mexico. This achievement contributed greatly to the development and productivity of animal agriculture in the U.S. The permanent quarantine zone buffers CFT incursions from Mexico where both ticks and babesiosis are endemic. Until recently, the elimination of CFT outbreaks relied solely on the use of coumaphos, an organophosphate acaricide, in dipping vats or as a spray to treat livestock, or the vacation of pastures. However, ecological, societal, and economical changes are shifting the paradigm of systematically treating livestock to eradicate CFT. Keeping the U.S. CFT-free is a critical animal health issue affecting the economic stability of livestock and wildlife enterprises. Here, we describe vulnerabilities associated with global change forces challenging the CFTEP. The concept of integrated CFT eradication is discussed in reference to global change.

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

Ticks are acaridae ectoparasites that, while taking a blood meal, can transmit viruses, bacteria, protozoa and filarial nematodes, which cause a variety of human and animal illnesses. The use of chemical pesticides constitutes the primary measure for control of these ectoparasites. However, the intensive use of these chemicals has drawbacks such as the contamination of food, environmental pollution and development of resistance by ectoparasites. Vaccination is considered a promising alternative for controlling infestations by ectoparasites. Although emerging tick proteins have been identified recently, and have been proposed as potential targets for generating protective molecules, only a limited number of them have been evaluated in vaccine trials. More than 80 proteins are found in eukaryotic ribosomes. The protein P0 is essential for the assembly of the 60S ribosomal subunit. We have identified an immunogenic region of the ribosomal protein P0 from Rhipicephalus sp. ticks that is not very conserved compared to host P0. The efficacy of a 20 amino acid synthetic peptide from this sequence was assayed as a vaccine antigen against Rhipicephalus sanguineus infestations in an immunization and challenge experiment on rabbits. A remarkable diminution in the viability of newly molted nymphs from larvae fed on vaccinated rabbits was observed. The number of adults and the number of eggs hatching were significantly reduced, with an overall efficacy of 90%. Our results demonstrated that immunization with an immunogenic peptide of tick protein P0 greatly reduced survival of ticks, suggesting that it has promise as an effective tick control agent.

Rhipicephalus (Boophilus) microplus: expression and characterization of Bm86-CG in Pichia pastoris

The cattle tick Rhipicephalus (Boophilus) microplus is responsible for great economic losses. It is mainly controlled chemically, with limitations regarding development of resistance to the chemicals. Vaccines may help control this parasite, thereby reducing tick pesticide use. In this light, we performed subcloning of the gene of the protein Bm86-GC, the homologue protein that currently forms the basis of vaccines (Gavac(TM) and TickGard(PLUS)) that have been developed against cattle ticks. The subcloning was done in the pPIC9 expression vector, for transformation in the yeast Pichia pastoris. This protein was characterized by expression of the recombinant Mut+ strain, which expressed greater quantities of protein. The expressed protein (rBm86-CG) was recognized in the Western-blot assay using anti-Gavac, anti-TickGard, anti-larval extract and anti-rBm86-CG polyclonal sera. The serum produced in cattle vaccinated with the antigen CG rBm86 presented high antibody titers and recognized the native protein. The rBm86-GC has potential relevance as an immunogen for vaccine formulation against cattle ticks.