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

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

Inorganic polyphosphate's role in energy production and mitochondrial permeability transition pore opening in tick mitochondria

Inorganic polyphosphate (polyP) is a biopolymer composed of phosphoanhydride-linked orthophosphate molecules. PolyP is engaged in a variety of cellular functions, including mitochondrial metabolism. Here, we examined the effects of polyP on electron transport chain enzymes and F1 Fo ATP synthase in tick embryos during embryonic development. The study found that polyPs containing medium and long chains (polyP15 and polyP65 ) enhanced the activity of complex I, complex II, complex III, and F1 Fo ATP synthase, while short polyP chains (polyP3 ) had no effect. The study also examined the activity of exopolyphosphatases (PPX) in various energy-demand situations. PPX activity was stimulated when ADP concentrations are high, characterizing a low-energy context. When complexes I-III and F1 Fo ATP synthase inhibitors were added in energized mitochondria, PPX activity decreased, whereas the mitochondrial uncoupler FCCP had no impact on PPX activity. Additionally, the study investigated the effect of polyP on mitochondrial swelling, finding that polyP causes mitochondrial swelling by increasing calcium effects on the mitochondrial permeability transition pore. The findings presented here to increase our understanding of the function of polyP in mitochondrial metabolism and its relationship to mitochondrial permeability transition pore opening in an arthropod model.

Meta-analysis of heritability estimates and genome-wide association for tick-borne haemoparasites in African cattle

The control of tick-borne haemoparasites in cattle largely relies on the use of acaricide drugs against the tick vectors, with some vaccination also being used against selected pathogens. These interventions can be difficult in Africa, where accessibility and cost of vaccines can be issues, and the increasing resistance of tick vectors to the widely used acaricides is a complication to disease control. A potential complementary control strategy could be the exploitation of any natural host genetic resistance to the pathogens. However, there are currently very few estimates of the extent of host resistance to tick-borne haemoparasites, and a significant contributing factor to this knowledge gap is likely to be the difficulty of collecting appropriate samples and data in the smallholder systems that predominate livestock production in low- and middle-income countries, particularly at scale. In this study, we have estimated the heritability for the presence/absence of several important haemoparasite species (including Anaplasma marginale, Babesia bigemina, Babesia bovis, and Ehrlichia ruminantium), as well as for relevant traits such as body weight and body condition score (BCS), in 1,694 cattle from four African countries (Burkina Faso, Ghana, Nigeria, and Tanzania). Heritability estimates within countries were mostly not significant, ranging from 0.05 to 0.84 across traits and countries, with standard errors between 0.07 and 0.91. However, the weighted mean of heritability estimates was moderate and significant for body weight and BCS (0.40 and 0.49, respectively), with significant heritabilities also observed for the presence of A. marginale (0.16) and E. ruminantium (0.19). In a meta-analysis of genome-wide association studies (GWAS) for these traits, two peaks were identified as reaching the suggestive significance threshold (p < 1.91 × 10-7 and p < 1.89 × 10-7, respectively): one on chromosome 24 for BCS and one on chromosome 8 for the E. ruminantium infection status. These findings indicate that there is likely to be a genetic basis that contributes to pathogen presence/absence for tick-borne haemoparasite species, which could potentially be exploited to improve cattle resistance in Africa to the economically important diseases caused by these pathogens.

A multiepitope chimeric antigen from Rhipicephalus microplus-secreted salivary proteins elicits anti-tick protective antibodies in rabbit

Rhipicephalus (Boophilus) microplus, the Cattle Fever Tick, causes significant economic losses in livestock in tropical and subtropical regions of the world. As the usual control strategy based on chemical acaricides presents different drawbacks, alternative control strategies have been considered for tick control. In recent decades, several tick proteins have been evaluated as targets for the development of anti-tick vaccines. Thus, in the present work, coding sequences from three different proteins present in tick saliva were employed together to construct a recombinant chimeric protein that was evaluated as an antigen in rabbit immunization. Then, the elicited antibodies were tested in a tick artificial feeding experiment to verify the protective effect against the parasites. In addition to Rhipicephalus microplus subtilisin inhibitor 7 (RmSI-7), a serine protease inhibitor member of the TIL (Trypsin Inhibitory Like) family, an interdomain region from the Kunitz inhibitor BmTI-A, and a new cysteine-rich AMP-like microplusin, called RmSEI (previously identified as an elastase inhibitor), were selected to compose the chimeric protein. Anti-chimeric IgG antibodies were able to affect R. microplus female egg production after artificial feeding. Moreover, antibodies elicited in infested tick-resistant and tick-susceptible cattle recognized the recombinant chimera. Additionally, the functional characterization of recombinant RmSEI was performed and revealed antimicrobial activity against gram-positive bacteria. Moreover, the antimicrobial protein was also recognized by antibodies elicited in sera from cattle previously exposed to R. microplus bites. Together, these data suggest that the chimeric protein composed of three salivary antigens is suitable for anti-tick vaccine development.

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

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

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

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

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

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

Cattle ticks and tick-borne diseases: a review of Uganda's situation

Herein we review the epidemiology of ticks and tick-borne diseases (TTBDs), their impact on livestock health and on the economy, control and associated challenges in Uganda. Ticks are leading vectors of economically important pathogens and are widespread in Uganda due to suitable climatic conditions. Besides the physical injury inflicted on the animal host, ticks transmit a number of pathogens that can cause morbidity and mortality of livestock if untreated, resulting in economic losses. Uganda suffers an aggregated annual loss (direct and indirect) of over USD 1.1 billion in the TTBDs complex. East Coast fever (ECF) caused by a protozoan haemoparasite, Theileria parva, is the most prevalent and economically important tick-borne disease (TBD) in Uganda and its vector, the brown ear tick (Rhipicephalus appendiculatus) widely distributed. Other prevalent TBDs in Uganda include anaplasmosis, babesiosis and heartwater. We highlight the role of agro-ecological zones (AEZs) and livestock management system in the distribution of TTBDs, citing warm and humid lowlands as being ideal habitats for ticks and endemic for TBDs. Control of TTBDs is a matter of great importance as far as animal health is concerned in Uganda. Indigenous cattle, which make up over 90% of the national herd are known to be more tolerant to TTBDs and most farms rely on endemic stability to TBDs for control. However, exotic cattle breeds are more capital intensive than indigenous breeds, but the increasing adoption of tick-susceptible exotic cattle breeds (especially dairy) in western and central Uganda demands intensive use of acaricides for tick control and prevention of TBDs. Such acaricide pressure has unfortunately led to selection of acaricide-resistant tick populations and the consequent acaricide resistance observed in the field. Vaccination against ECF, selective breeding for tick resistance and integrated tick control approaches that limit tick exposure, could be adopted to interrupt spread of acaricide resistance. We recommend increasing monitoring and surveillance for TTBDs and for emerging acaricide resistance, improved extension services and sensitization of farmers on tick control measures, appropriate acaricide use and the development and implementation of vaccines for the control of TTBDs as more sustainable and effective interventions. A tick control policy should be developed, taking into account variations of agro-ecological zones, farm circumstances and indigenous technical knowledge, and this should be incorporated into the overall animal health program.

Acaricidal activity of Artemisia herba-alba and Melia azedarach oil nanoemulsion against Hyalomma dromedarii and their toxicity on Swiss albino mice

Biopesticides such as essential oils (EOs) are considered an improvement for integrated pest control as they appear to be less toxic to the environment than chemical acaricides. The current study aimed to evaluate the acaricidal activity of Artemisia herba-alba and Melia azedarach oil loaded nano-emulsion as alternatives for chemical acaricides against the camel tick Hyalomma dromedarii, besides evaluating their toxic effect on Swiss albino mice. Transmission electron microscopy (TEM) and Fourier transform infrared spectroscopy (FTIR) were used for the characterization of loaded nano-emulsions.The immersion test was used for the bioassay of both loaded nanoemulsions on tick stages (egg, nymph, larva, and adult). Mortality percentages and LC₅₀ values of each tick stage were calculated. Reproductive performance for the survived engorged females after treatment was monitored. The toxicity of both loaded nano-emulsions was evaluated on Swiss albino mice by an oral dose of 1500 mg/kg/day for five successive days. The hematological, biochemical, and histopathological changes were evaluated. TEM characterization revealed spherical droplets for A. herba-alba and M. azedarach oil loaded nano-emulsion with droplet size ranging from 62 to 69 nm and 52-91 nm, respectively. FTIR revealed the absence of extra peaks in the loaded nano-emulsions that confirmed no chemical changes existed by ultrasonication. The LC₅₀ values of A. herba-alba and M. azedarach oil loaded nano-emulsion on embryonated eggs, larvae, engorged nymphs, and unfed adults were 0.3 and 1.1%, 0.7 and 1.7%, 0.3 and 0.4%, 4.4 and 22.2%, respectively. The egg productive index (EPI), egg number, and hatchability percentage were lower in the treated females compared with Butox 5% (deltamethrin) and control. The hematological picture and biochemical analysis revealed insignificant changes in the treatment group compared with the negative control group. The liver of the A. herba-alba and M. azedarach oil loaded nano-emulsion treated group exhibited vacuolar degeneration and infiltration of lymphocytic cells. The kidney of mice treated with A. herba-alba and M. azedarach oil loaded nano-emulsion showed hemolysis and slight degeneration of epithelial cells of tubules. It is concluded that A. herba-alba and M. azedarach oil loaded nano-emulsion have good acaricidal activity against camel tick H. dromedarii.

Tick saliva-induced programmed death-1 and PD-ligand 1 and its related host immunosuppression

The tick Rhipicephalus microplus is a harmful parasite of cattle that causes considerable economic losses to the cattle breeding industry. Although R. microplus saliva (Rm-saliva) contains several immunosuppressants, any association between Rm-saliva and the expression of immunoinhibitory molecules, such as programmed death (PD)-1 and PD-ligand 1 (PD-L1), has not been described. In this study, flow cytometric analyses revealed that Rm-saliva upregulated PD-1 expression in T cells and PD-L1 expression in CD14⁺ and CD11c⁺ cells in cattle. Additionally, Rm-saliva decreased CD69 expression in T cells and Th1 cytokine production from peripheral blood mononuclear cells. Furthermore, PD-L1 blockade increased IFN-γ production in the presence of Rm-saliva, suggesting that Rm-saliva suppresses Th1 responses via the PD-1/PD-L1 pathway. To reveal the upregulation mechanism of PD-1/PD-L1 by Rm-saliva, we analyzed the function of prostaglandin E₂ (PGE₂), which is known as an inducer of PD-L1 expression, in Rm-saliva. We found that Rm-saliva contained a high concentration of PGE₂, and PGE₂ treatment induced PD-L1 expression in CD14⁺ cells in vitro. Immunohistochemical analyses revealed that PGE₂ and PD-L1 expression was upregulated in tick-attached skin in cattle. These data suggest that PGE₂ in Rm-saliva has the potential to induce the expression of immunoinhibitory molecules in host immune cells.

Repellency effect of Pilocarpus spicatus A. St.-Hil essential oil and nanoemulsion against Rhipicephalus microplus larvae

Rhipicephalus microplus, the cattle tick, is a major cause of economic losses in bovine production. Due to the widespread acaricidal resistance to commercially available products, as well as their toxicity and environmental impact, alternative control methods are required. Nanoformulations produced from plant extracts as bioactive substances are very promising as innovative acaricidal agents. Thus, the aim of this study was to evaluate the in vitro repellent activity of Pilocarpus spicatus essential oil and its nanoemulsion against R. microplus, using larval repellent test (RT). The essential oil was extracted by hydrodistillation, using a Clevenger-type apparatus. The nanoemulsion was prepared with 5% essential oil, 5% tween 80, and 90% water, using the phase inversion method (50 mg/mL). Limonene was the major component (46.8%) of the essential oil, as determined by gas chromatography-mass spectrometry (GC/MS) and confirmed by flame ionization detection (GC/FID). According to the RT results, the essential oil had a repellent activity greater than 69%, from concentrations of 3.12 mg/mL (69.81 ± 10%) to 50 mg/mL (98.10 ± 0.6%), whereas the nanoemulsion at 50 mg/mL presented repellent activities of 97.14 ± 1.37% and 97.89 ± 0.52% 6 and 10 h after treatment, respectively. These values regarding to total repellency were very close to those calculated for mortality corrected by Abbott's formula. The phase inversion method preserved the chemical and physical characteristics of the essential oil since both reached an equal repellent effect at the same concentration. Therefore, P. spicatus essential oil and nanoemulsion had excellent repellent activities against R. microplus larvae, demonstrating its potential for future use as an alternative for tick control.

Blood transcriptome profile induced by an efficacious vaccine formulated with salivary antigens from cattle ticks

Ticks cause massive damage to livestock and vaccines are one sustainable alternative for the acaricide poisons currently heavily used to control infestations. An experimental vaccine adjuvanted with alum and composed by four recombinant salivary antigens mined with reverse vaccinology from a transcriptome of salivary glands from Rhipicephalus microplus ticks was previously shown to present an overall efficacy of 73.2% and cause a significant decrease of tick loads in artificially tick-infested, immunized heifers; this decrease was accompanied by increased levels of antigen-specific IgG1 and IgG2 antibodies, which were boosted during a challenge infestation. In order to gain insights into the systemic effects induced by the vaccine and by the tick challenge we now report the gene expression profile of these hosts' whole-blood leukocytes with RNA-seq followed by functional analyses. These analyses show that vaccination induced unique responses to infestations; genes upregulated in the comparisons were enriched for processes associated with chemotaxis, cell adhesion, T-cell responses and wound repair. Blood transcriptional modules were enriched for activation of dendritic cells, cell cycle, phosphatidylinositol signaling, and platelets. Together, the results indicate that by neutralizing the tick's salivary mediators of parasitism with vaccine-induced antibodies, the bovine host is able to mount normal homeostatic responses that hinder tick attachment and haematophagy and that the tick otherwise suppresses with its saliva.

Inhibition of energy metabolism by 3-bromopyruvate in the hard tick Rhipicephalus microplus

The cattle tick R. microplus is the biggest obstacle to livestock rearing in tropical countries. It is responsible for billions of dollars in losses every year, affecting meat and milk production, beef and dairy cattle, and the leather industry. The lack of knowledge and strategies to combat the tick only increases the losses, it leads to successive and uncontrolled applications of acaricides, favouring the selection of strains resistant to commercially available chemical treatments. In this paper, we tested 3‑bromopyruvate (3‑BrPA), an alkylating agent with a high affinity for cysteine residues, on the R. microplus metabolism. We found that 3-BrPA was able to induce cell death in an assay using BME26 strain cell cultures derived from embryos, it was also able to reduce cellular respiration in developing embryos. 3-BrPA is a nonspecific inhibitor, affecting enzymes of different metabolic pathways in R. microplus. In our experiments, we demonstrated that 3-BrPA was able to affect the glycolytic enzyme hexokinase, reducing its activity by approximately 50%; and it strongly inhibited triose phosphate isomerase, which is an enzyme involved in both glycolysis and gluconeogenesis. Also, the mitochondrial respiratory chain was affected, NADH cytochrome c reductase (complex I-III) and succinate cytochrome c reductase (complex II-III) were strongly inhibited by 3-BrPA. Glutamate dehydrogenase was also affected by 3-BrPA, showing a gradual inhibition of activity in all the 3-BrPA concentrations tested. Altogether, these results show that 3-BrPA is a harmful compound to the tick organism.

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.

Novel and Selective Rhipicephalus microplus Triosephosphate Isomerase Inhibitors with Acaricidal Activity

The cattle tick Rhipicephalus microplus is one of the most important ectoparasites causing significant economic losses for the cattle industry. The major tool of control is reducing the number of ticks, applying acaricides in cattle. However, overuse has led to selection of resistant populations of R. microplus to most of these products, some even to more than one active principle. Thus, exploration for new molecules with acaricidal activity in R. microplus has become necessary. Triosephosphate isomerase (TIM) is an essential enzyme in R. microplus metabolism and could be an interesting target for the development of new methods for tick control. In this work, we screened 227 compounds, from our in-house chemo-library, against TIM from R. microplus. Four compounds (50, 98, 14, and 161) selectively inhibited this enzyme with IC₅₀ values between 25 and 50 μM. They were also able to diminish cellular viability of BME26 embryonic cells by more than 50% at 50 μM. A molecular docking study showed that the compounds bind in different regions of the protein; compound 14 interacts with the dimer interface. Furthermore, compound 14 affected the survival of partially engorged females, fed artificially, using the capillary technique. This molecule is simple, easy to produce, and important biological data—including toxicological information—are available for it. Our results imply a promising role for compound 14 as a prototype for development of a new acaricidal involving selective TIM inhibition.

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.

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.

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.

Acaricidal properties of the essential oil from Zanthoxylum caribaeum against Rhipicephalus microplus

Zanthoxylum caribaeum Lamarck (Rutaceae) is plant species with a variety of medical applications, including insecticidal activity. This study determined the bioacaricidal activity of the essential oil from Z. caribaeum leaves against engorged Rhipicephalus (Boophilus) microplus (Canestrini, 1887) females using the adult immersion test. For this purpose, three serial concentrations (5.0, 2.5, and 1.25%, vol:vol, in 1% dimetilsulfoxide) of the essential oil were used. Essential oil 5% caused 65% mortality on the first day after treatment, 85% on the second day, and 100% mortality by the fifth day. To our knowledge, this is the first demonstration of the acaricidal activity of the essential oil from Z. caribaeum leaves against cattle ticks.

Eficácia acaricida do óleo de citronela contra o Rhipicephalus (Boophilus) microplus

O Rhipicephalus (Boophilus) microplus é o carrapato bovino mais importante no Brasil. Para o controle do carrapato, vários estudos com plantas têm sido desenvolvidos numa tentativa de encontrar extratos com propriedades acaricidas. Esta pesquisa foi conduzida com o objetivo de avaliar o efeito in vitro e in vivo do óleo de citronela (Cymbopogon winterianus Jowitt) sobre o carrapato bovino. Na experimentação in vitro foi utilizado o grupo controle negativo e oito concentrações de óleo de citronela e óleo mineral (0,5; 1; 2; 5; 10; 20; 50; 100%), em fêmeas ingurgitadas de carrapatos. A eficácia carrapaticida para o óleo de citronela foi de 0; 34,5; 43; 48; 82; 99; 99; 100 e 100%, respectivamente; para o óleo mineral foram observados resultados irregulares na eficácia acaricida. Para a experimentação in vivo foram constituídos três grupos: controle negativo; óleo de citronela a 8,6% - nível estimado mediante análise de regressão, correspondendo a 95% de eficácia acaricida da pesquisa in vitro e amitraz a 0,025%, com dezoito vacas da raça Holandesa. Antes, média dos dias -3, -2, -1 e após a aplicação do produto, 1, 2, 3, 5, 7, 10, 14 e 21 dias, foram contadas fêmeas ingurgitadas de carrapato. Na 1ª e na 2ª ordenha após a aplicação dos tratamentos, foram avaliadas variáveis fisiológicas (controle negativo x tratamento fitoterápico). A eficácia carrapaticida foi de 0; 91,3 e 60%, respectivamente, 21 dias após o tratamento. Os valores das variáveis fisiológicas avaliadas foram similares entre os tratamentos.

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.

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.

A Rhipicephalus (Boophilus) microplus cathepsin with dual peptidase and antimicrobial activity

The cattle tick, Rhipicephalus (Boophilus) microplus, is a haematophagous arthropod responsible for considerable losses in the livestock industry. Immunological control with vaccines is a promising alternative to replace chemical acaricides. Due to their importance in parasite physiology, cysteine endopeptidases are potential targets. In a previous study, native Vitellin Degrading Cysteine Endopeptidase (VTDCE) was successfully tested as a vaccine antigen for bovines against R. microplus. In this work, nucleotide and amino acid VTDCE sequences were obtained from cDNA databanks, based on data from Edman sequencing and mass spectrometry. Subsequently, cloning and expression, purification, immunological and biochemical characterisation of the recombinant protein were performed to determine the biological importance of VTDCE. By Western blot, polyclonal antibodies produced against recombinant VTDCE recognised native VTDCE. Interestingly, molecular analysis showed that the VTDCE sequence has similarity to antimicrobial peptides. Indeed, experimental results revealed that VTDCE has an antimicrobial activity which is independent of endopeptidase activity. We believe that this is the first known study to show that an arthropod enzyme has antimicrobial activity.

Cattle tick vaccines: many candidate antigens, but will a commercially viable product emerge?

The cattle tick, Rhipicephalus microplus, is arguably the world's most economically important external parasite of cattle. Sustainable cattle tick control strategies are required to maximise the productivity of cattle in both large production operations and small family farms. Commercially available synthetic acaricides are commonly used in control and eradication programs, but indiscriminate practices in their application have resulted in the rapid evolution of resistance among populations in tropical and subtropical regions where the invasive R. microplus thrives. The need for novel technologies that could be used alone or in combination with commercially available synthetic acaricides is driving a resurgence of cattle tick vaccine discovery research efforts by various groups globally. The aim is to deliver a next-generation vaccine that has an improved efficacy profile over the existing Bm86-based cattle tick vaccine product. We present a short review of these projects and offer our opinion on what constitutes a good target antigen and vaccine, and what might influence the market success of candidate vaccines. The previous experience with Bm86-based vaccines offers perspective on marketing and producer acceptance aspects that a next-generation cattle tick vaccine product must meet for successful commercialisation.

Antigen fingerprinting of polyclonal antibodies raised in immunized chickens with tick total proteins: a reservoir for the discovery of novel antigens

Identification of tick-protective antigens remains the limiting step in vaccine development. The authors have generated several B cell epitope candidates by fingerprinting Rhipicephalus (Boophilus) microplus proteins that were characterized through bioselection of random peptide phage display libraries against polyclonal antibodies antitick proteins. From 280 clones selected and sequenced, 107 distinct reactive clones were validated by dot-blot assays. Eight consensus motifs were generated, and the most frequent ones were PXXKXH, NXXKXXL, and HTS (68.2%, 65%, and 42%, respectively). The consensus sequences identified potential vaccine targets by alignment with the protein database of R. microplus, which may have putative roles in the host response. Sequences that did not align with known proteins but shared extensive homology among each other were classified as conformational epitopes. Sequence alignments also recognized multiple targets, and the most predominant proteins were identified. Finally, immunized mice sera recognized tick proteins, demonstrating that functional epitope profiles can be identified through selection of phage-displayed peptide libraries with hyperimmune sera and revealing that the epitope-displaying phages can be used as potential vaccine immunogens.

Effect of Metarhizium anisopliae fungus on off-host Rhipicephalus (Boophilus) microplus from tick-infested pasture under cattle grazing in Brazil

This work aimed to assess the effect of the fungus Metarhizium anisopliae on off-host Rhipicephalus (Boophilus) microplus from tick-infested Brachiaria decumbens pasture undergoing cattle grazing. For this purpose a naturally tick-infested Brachiaria decumbens pasture of 60 m × 100 m with twelve grazing Holstein Friesian-Nelore (Bos indicus) cross breed bovines was sprayed 12 times, 21 days apart with an aqueous conidial suspension of the E9 isolate of M. anisopliae fungus. Control pasture was treated with conidial suspension vehicle only. Efficacy of treatment was evaluated by tick larvae counts on the pasture and that of engorged female ticks on grazing cattle. Fungus persistence on grass stems as well as soil pasture was assessed after each spray. Efficacy of fungus against ticks was also measured by an in vitro immersion test. Whereas in vitro test showed a clear pathogenic effect of the fungus on ticks, no pathogenic effect over R. (B.) microplus ticks was detected in the field trial by spraying pasture with fungal suspension. Fungus from the suspension could be recovered from both the grass stem as well as the soil of sprayed pasture, even though the numbers obtained varied distinctly and could only be recovered shortly after spray. Pasture environments with exposure to sun and rain, seem to be very detrimental to the fungus, thus suspensions which provide fungus with protection or more resistant isolates to these should be looked for. In order to achieve high fungal efficacy against tick under field conditions, accurate laboratory assays, optimization of application strategy and knowledge of interactions between fungal strains and environmental factors are warranted.

Effect of GSK-3 activity, enzymatic inhibition and gene silencing by RNAi on tick oviposition and egg hatching

Glycogen synthase kinase-3 (GSK-3) is classically described as a key enzyme involved in glycogen metabolism in mammals. It has been shown to be highly conserved among several organisms, mainly in the catalytic domain region. This enzyme has already been described in Rhipicephalus (Boophilus) microplus and the ovaries of females appeared to be the major site of GSK-3 transcription. The treatment with GSK-3 specific inhibitor (alsterpaullone, bromo-indirubin-oxime 6 and indirubin-3-oxime) caused a reduction in oviposition and egg hatching in completely engorged female ticks. The effect was more pronounced in partially engorged females when alsterpaullone was administrated by artificial capillary feeding. Moreover, GSK-3 gene silencing by RNAi in partially engorged females reduced significantly both oviposition and hatching. The study of tick embryogenesis and proteins that participate in this process has been suggested as an important means for the development of novel strategies for parasite control. GSK-3 is an essential protein involved in embryonic processes and for this reason it has already been suggested as a possible antigen candidate for tick control.