Exploring the use of an anti-tick vaccine as a tool for the integrated eradication of the cattle fever tick, Rhipicephalus (Boophilus) annulatus

A reverse vaccinology approach identified novel recombinant tick proteins with protective efficacy against Rhipicephalus microplus infestation

The cattle tick, Rhipicephalus microplus, causes significant economic losses to the cattle industry. Tick control is predominately achieved via pesticide applications. However, alternative control methods such as vaccines are needed due to the tick's capacity to quickly develop pesticide resistance and to combat tick-borne diseases. We used an in silico reverse vaccinology approach to evaluate and rank open reading frames (ORFs) from the tick's transcriptome for their potential use as anti-R. microplus vaccine antigens. We manually annotated the 200 highest ranked antigens and selected 10 transcript ORFs as vaccine antigen candidates for expression in Pichia pastoris or insect cells. Six of the ten candidate antigens could be successfully expressed and purified in vitro as recombinant proteins with > 1 mg quantity. RT-PCR confirmed the expression of all six transcripts in tick RNA. However, only three of the six transcripts' corresponding ORFs could be confirmed as present in tick tissue protein extracts. Only four of the six vaccine candidate antigens were successfully expressed and purified in sufficient quantity (> 10 mg) for immunogenicity and efficacy trials in cattle. These four were designated BI-TS002, BI-TS004, BI-TS008, and BI-TS009 and sufficient annotation existed that showed sequence similarity to serine‑rich adhesin for platelets, glycine-rich cell wall structural membrane protein, SWM-1 tick serine protease inhibitor, and venom-like dermonecrotic toxins from ticks and spiders, respectively. Cattle immunized with BI-TS004, BI-TS008 and BI-TS009 yielded a statistically significant difference in antibody response post-immunization. This difference was noted on Days 42, 56, 70, and 84 post-immunization for BI-TS008 and BI-TS009, but only on Day 56 for BI-TS004. BI-TS008 and BI-TS009, were formulated with adjuvant and cattle stall tests conducted over a 175 day period to evaluate efficacy against R. microplus infestations. Both an adjuvant only negative control group and a positive control group using the commercially available GAVAC anti-tick vaccine were used. Efficacy was determined by comparing number of engorged adult female ticks, total egg mass weight, and egg hatchability produced from the immunized group to corresponding data from the adjuvant only negative control group. Thus, effects on engorged adult tick number, reproductive capacity, and fertility were measured. Both initial (designated Phase 1 and calculated from tick collections of Days 60-94 days post-first immunization) and long-term (designated Phase 2 and calculated from tick collections of Days 152-175 post-first immunization) efficacies were determined. The overall Phase 1 trial efficacies of BI-TS008, BI-TS009, and GAVAC were 68.3 %, 48.5 %, and 70.7 %, respectively. The overall Phase 2 trial efficacies of BI-TS008, BI-TS009, and GAVAC were 64.4 %, -30.1 %, and 45.1 %, respectively.

Inclusion of Anti-Tick Vaccines into an Integrated Tick Management Program in Mexico: A Public Policy Challenge

Acaricides are the most widely used method to control the cattle tick Rhipicephalus microplus. However, its use increases production costs, contaminates food and the environment, and directly affects animal and human health. The intensive use of chemical control has resulted in the selection of genes associated with resistance to acaricides, and consumers are increasingly less tolerant of food contamination. This scenario has increased the interest of different research groups around the world for anti-tick vaccine development, in order to reduce the environmental impact, the presence of residues in food, and the harmful effects on animal and human health. There is enough evidence that vaccination with tick antigens induces protection against tick infestations, reducing tick populations and acaricide treatments. Despite the need for an anti-tick vaccine in Mexico, vaccination against ticks has been limited to one vaccine that is used in some regions. The aim of this review is to contribute to the discussion on tick control issues and provide a reference for readers interested in the importance of using anti-tick vaccines encouraging concerted action on the part of Mexican animal health authorities, livestock organizations, cattle producers, and academics. Therefore, it is suggested that an anti-tick vaccine should be included as a part of an integrated tick management program in Mexico.

Universal Tick Vaccines: Candidates and Remaining Challenges

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

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

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

Interaction between anti-tick vaccine and a macrocyclic lactone improves acaricidal efficacy against Rhipicephalus (Boophilus) microplus (Canestrini) (Acari: Ixodidae) in experimentally infested cattle

The southern cattle fever tick (SCFT) Rhipicephalus (Boophilus) microplus, is considered the most important ectoparasite of livestock in the world because of high financial losses associated with direct feeding and transmission of the hemoparasites Babesia bovis, B. bigemina, and Anaplasma marginale. Unfortunately, SCFT in many parts of the world have evolved resistance to all market-available pesticides thus driving development of new control technologies. Vaccination against ticks using the tick gut protein Bm86 has been shown to be effective against acaricide-resistant ticks. This technique has been successfully implemented in Puerto Rico for the control of acaricide-resistant R. microplus on dairy and beef cattle. Observations from Puerto Rico indicate a potentially positive interaction between anti-tick vaccination when used in conjunction with systemic acaricide treatment. In this project, controlled animal studies were completed directly comparing efficacy of anti-tick vaccination with and without systemic acaricide. Results show that the Bm86 anti-tick vaccine in combination with the macrocyclic lactone, Moxidectin, expressed a synergistic interaction, providing greater and longer efficacy than either treatment alone.

Predicting the potential distribution of the cattle fever tick Rhipicephalus annulatus (Acari: Ixodidae) using ecological niche modeling

Rhipicephalus annulatus is a tick species of veterinary importance due to its potential to transmit babesiosis to cattle. This species has a Holarctic distribution with some Afrotropical records and is one-host species of veterinary importance. This study was carried out from September 2021 to February 2022 at 6 Egyptian collection sites, and a total of 1150 cattle were scanned randomly to collect ticks. A total of 1095 tick specimens were collected and identified as R. annulatus using taxonomic keys. Males were found on all parts of the cattle except the head and around the eyes, but females were found on all parts; in addition, the highest number of specimens was gathered from the udder, (neck and chest), and belly. Maximum entropy (MaxEnt) modeling was used to predict the potential global distribution of R. annulatus. The MaxEnt model performed better than random with an average test area under the curve (AUC) value of 0.96, and model predictions were significantly better than random and gave (AUC) ratios above the null expectations in the partial receiver operating characteristic (pROC) analyses (P < 0.001). Based on correlation analyses, a set of 9 variables was selected for species from 15 bioclimatic and 5 normalized difference vegetation index (NDVI) variables. The study showed that the current distribution of R. annulatus is estimated to occur across Asia, Africa, Europe, South America, and North America. Annual mean temperature (Bio1) and median NDVI had the highest effect on the distribution of this species. The environmentally suitable habitat for R. annulatus sharply increased with increasing annual mean temperature (Bio1). These results can be used for making effective control planning decisions in areas suitable to this vector of many diseases worldwide.

Characterization of two Cuban colonies of Rhipicephalus microplus ticks

Rhipicephalus microplus (Canestrini, 1888) is one of the species with medical and economic relevance that has been reported in the list of Cuban tick species. Some morphological characterizations about the R. microplus species in Cuba have been published; however, molecular studies are lacking. Molecular phylogenetic analyses have grouped R. annulatus, R. australis and three clades of R. microplus in a complex named R. microplus. The present study aimed to characterize two R. microplus tick isolates, established as colonies at the Cuban National Laboratory of Parasitology. Morphological characterization of adult specimens was carried out by using Scanning Electron Microscopy. The sequences of mitochondrial genes: 12S rRNA, 16S rRNA and the subunit I of cytochrome c oxidase (coxI) and one nuclear sequence: internal transcribed spacer 2 (its2) were used for phylogenetic analyses. The life cycle under laboratory conditions for both isolates was also characterized. Tick specimens of both colonies showed morphological characteristics comparable with those distinctive for the R. microplus species. Phylogenies based on mitochondrial gene sequences identified congruently the Cuban tick colonies within the clade A of R. microplus. The life cycle of both isolates under laboratory conditions lasted 65 ± 5 days and the reproductive performance of female ticks of each colony also were similar with approximately 2500 larvae obtained from fully engorged female ticks. This study constitutes the first molecular characterization of ticks from the R. microplus species in Cuba.

Research on Integrated Management for Cattle Fever Ticks and Bovine Babesiosis in the United States and Mexico: Current Status and Opportunities for Binational Coordination

Bovine babesiosis is a reportable transboundary animal disease caused by Babesia bovis and Babesiabigemina in the Americas where these apicomplexan protozoa are transmitted by the invasive cattle fever ticks Rhipicephalus (Boophilus) microplus and Rhipicephalus(Boophilus) annulatus. In countries like Mexico where cattle fever ticks remain endemic, bovine babesiosis is detrimental to cattle health and results in a significant economic cost to the livestock industry. These cattle disease vectors continue to threaten the U.S. cattle industry despite their elimination through efforts of the Cattle Fever Tick Eradication Program. Mexico and the U.S. share a common interest in managing cattle fever ticks through their economically important binational cattle trade. Here, we report the outcomes of a meeting where stakeholders from Mexico and the U.S. representing the livestock and pharmaceutical industry, regulatory agencies, and research institutions gathered to discuss research and knowledge gaps requiring attention to advance progressive management strategies for bovine babesiosis and cattle fever ticks. Research recommendations and other actionable activities reflect commitment among meeting participants to seize opportunities for collaborative efforts. Addressing these research gaps is expected to yield scientific knowledge benefitting the interdependent livestock industries of Mexico and the U.S. through its translation into enhanced biosecurity against the economic and animal health impacts of bovine babesiosis and cattle fever ticks.

Modeling tick vaccines: a key tool to improve protection efficacy

Introduction: The development of more effective vaccines for the control of tick infestations and pathogen transmission is essential for prevention and control of tick-borne diseases worldwide. Recently, the application of omics technologies has advanced the identification of tick protective antigens. However, other factors such as vaccine formulation and implementation need to be addressed, and tick vaccine modeling will contribute to improve the efficacy of vaccination strategies.Areas covered: In this review, we summarized current information on tick vaccine correlates of protection and modeling, and proposed new approaches to improve vaccine evaluation and implementation using as a proof-of-concept the Hyalomma marginatum-Crimean-Congo hemorrhagic fever virus model due to its high mortality rate and potentially growing impact on human health.Expert opinion: Vaccines are required as an effective and environmentally sound intervention for the control of tick-borne diseases affecting human and animal health worldwide. Despite recent advances in the identification of candidate tick protective antigens, research on vaccine formulation and implementation need to be addressed to improve tick vaccine control efficacy. As shown here, modeling of the vaccination strategies against ticks and transmitted pathogens will contribute to vaccine development by guiding the selection of appropriate antigen combinations, target hosts, and vaccination time schedule.

Vitellogenin Receptor as a Target for Tick Control: A Mini-Review

While much effort has been put into understanding vitellogenesis in insects and other organisms, much less is known of this process in ticks. There are several steps that facilitate yolk formation in developing oocytes of which the vitellogenin receptor (VgR) is a key component. The tick VgR binds vitellogenin (Vg) circulating in the hemolymph to initiate receptor-mediated endocytosis and its transformation into vitellin (Vn). The conversion of Vg into Vn, the final form of the yolk protein, occurs inside oocytes of the female tick ovary. Vn is critical to tick embryos since it serves as the nutritional source for their development, survival, and reproduction. Recent studies also suggest that pathogenic microbes, i.e., Babesia spp., that rely on ticks for propagation and dissemination likely "hitchhike" onto Vg molecules as they enter developing oocytes through the VgR. Suppressing VgR messenger RNA synthesis via RNA interference (RNAi) completely blocked Babesia spp. transmission into developing tick oocytes, thereby inhibiting vertical transmission of these pathogenic microbes from female to eggs. To date, VgRs from only four tick species, Dermacentor variabilis, Rhipicephalus microplus, Amblyomma hebraeum, and Haemaphysalis longicornis, have been fully sequenced and characterized. In contrast, many more VgRs have been described in various insect species. VgR is a critical component in egg formation and maturation that can serve as a precise target for tick control. However, additional research will help identify unique residues within the receptor that are specific to ticks or other arthropod disease vectors while avoiding cross-reactivity with non-target species. Detailed knowledge of the molecular structure and functional role of tick VgRs will enable development of novel vaccines to control ticks and tick-borne diseases.

Simulation tools for assessment of tick suppression treatments of Rhipicephalus (Boophilus) microplus on non-lactating dairy cattle in Puerto Rico

BACKGROUND

The southern cattle fever tick (SCFT), Rhipicephalus (Boophilus) microplus, remains endemic in Puerto Rico. Systematic treatment programmes greatly reduced and even eradicated temporarily this tick from the island. However, a systemic treatment programme that includes integrated management practices for livestock against SCFT remains to be established in the island. We describe a spatially-explicit, individual-based model that simulates climate-livestock-SCFT-landscape interactions. This model was developed as an investigative tool to aid in a research project on integrated management of the SCFT that took place in Puerto Rico between 2014 and 2017. We used the model to assess the efficacy of tick suppression and probability of tick elimination when applying safer acaricides at 3-week intervals to different proportions of a herd of non-lactating dairy cattle.

RESULTS

Probabilities of eliminating host-seeking larvae from the simulated system decreased from ≈ 1 to ≈ 0 as the percentage of cattle treated decreased from 65 to 45, with elimination probabilities ≈ 1 at higher treatment percentages and ≈ 0 at lower treatment percentages. For treatment percentages between 65% and 45%, a more rapid decline in elimination probabilities was predicted by the version of the model that produced higher densities of host-seeking larvae. Number of weeks after the first acaricide application to elimination of host-seeking larvae was variable among replicate simulations within treatment percentages, with within-treatment variation increasing markedly at treatment percentages ≤ 65. Number of weeks after first application to elimination generally varied between 30 and 40 weeks for those treatment percentages with elimination probabilities ≈ 1.

CONCLUSIONS

Explicit simulation of the spatial and temporal dynamics of off-host (host-seeking) larvae in response to control methods should be an essential element of research that involves the evaluation of integrated SCFT management programmes. This approach could provide the basis to evaluate novel control technologies and to develop protocols for their cost-effective use with other treatment methods.

Probability of Rhipicephalus microplus introduction into farms by cattle movement using a Bayesian Belief Network

Attempts to eliminate Rhipicephalus microplus from Uruguay have been unsuccessful, and, currently, the country is divided into two areas: a tick-free area and a tick-infested area. In the tick-infested area, different farms face different situations. Some farms are in regions where, due to environmental conditions or a lack of infrastructure, it is difficult to eliminate R. microplus, and the only option is to control it. In contrast, other farms can attempt complete removal. Before deciding whether a farmer should attempt to eliminate R. microplus, the probability of reintroduction must be evaluated. The objective of this study was to develop a probabilistic model based on a Bayesian Belief Network (BBN) to assess the likelihood of a farm becoming infested with R. microplus via the introduction of tick-infested cattle. Only the tick-infested area was considered in the development of this model. Nine variables related to environmental conditions and biosecurity measures, with a focus on cattle movement, were considered. Three different sources of data were used to populate the BBN model: data from the literature; a representative national survey from 2016; and a survey developed to identify biosecurity practices on farms. Model sensitivity and specificity were assessed, and an overall accuracy of 92% was obtained. The model was applied to 33 farms located in the tick-infested area. For one farm, the probability of introduction of R. microplus was 1%; for three farms, the probability was between 21% and 34%; for seven farms, it was between 66% and 76%; and for 22 farms, the probability was greater than 83%. This model was useful for estimating the probability of the introduction of R. microplus into farms, making it possible to assess the impact that the evaluated biosecurity measures have on the probability of introduction and, thus, guiding more objective decision making about the control or elimination of R. microplus from farms.

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.

Comparative Hemolymph Proteomic and Enzymatic Analyses of Two Strains of Rhipicephalus (Boophilus) microplus Ticks Resistant and Susceptible to Ixodicides

The cattle tick Rhipicephalus (Boophilus) microplus is one of the most harmful ectoparasites affecting bovines worldwide. It represents a major threat to livestock industry due to the economic losses caused and diseases associated with these ticks. The most important tick control strategy has been the use of ixodicides, resulting in chemically resistant tick populations. It is necessary to understand the mechanisms that result in resistance so as to create new strategies increasing the lifespan of ixodicides or finding alternative targets to produce new acaricides. In this paper, in order to obtain an insight into the mechanisms that govern ixodicides resistance, we will compare the hemolymph proteome of two tick R. microplus strains, one susceptible (MJ) and one resistant (SA) to ixodicides, using HPLC and 2D electrophoresis. Significant differences were found in protein content between strains using HPLC. 2D electrophoresis revealed that 68 hemolymph protein spots were common between strains; however, 26 spots were unique to the susceptible strain MJ and 5 to the resistant strain SA. The most distinctive protein spots on the preparative gels were selected for further analyses. Nine protein spots were identified by mass fingerprinting, 
revealing proteins that may have a role in the ixodicides resistance or susceptibility. In this paper, we present the tick hemolymph proteome revealing a set of proteins which suggest a possible role in tick detoxification.

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.

TRANSLATING ECOLOGY, PHYSIOLOGY, BIOCHEMISTRY, AND POPULATION GENETICS RESEARCH TO MEET THE CHALLENGE OF TICK AND TICK-BORNE DISEASES IN NORTH AMERICA

Emerging and re-emerging tick-borne diseases threaten public health and the wellbeing of domestic animals and wildlife globally. The adoption of an evolutionary ecology framework aimed to diminish the impact of tick-borne diseases needs to be part of strategies to protect human and animal populations. We present a review of current knowledge on the adaptation of ticks to their environment, and the impact that global change could have on their geographic distribution in North America. Environmental pressures will affect tick population genetics by selecting genotypes able to withstand new and changing environments and by altering the connectivity and isolation of several tick populations. Research in these areas is particularly lacking in the southern United States and most of Mexico with knowledge gaps on the ecology of these diseases, including a void in the identity of reservoir hosts for several tick-borne pathogens. Additionally, the way in which anthropogenic changes to landscapes may influence tick-borne disease ecology remains to be fully understood. Enhanced knowledge in these areas is needed in order to implement effective and sustainable integrated tick management strategies. We propose to refocus ecology studies with emphasis on metacommunity-based approaches to enable a holistic perspective addressing whole pathogen and host assemblages. Network analyses could be used to develop mechanistic models involving multihost-pathogen communities. An increase in our understanding of the ecology of tick-borne diseases across their geographic distribution will aid in the design of effective area-wide tick control strategies aimed to diminish the burden of pathogens transmitted by ticks.

A model to assess the efficacy of vaccines for control of liver fluke infection

Fasciola hepatica, common liver fluke, infects cattle and sheep causing disease and production losses costing approximately $3 billion annually. Current control relies on drugs designed to kill the parasite. However, resistance is evident worldwide and widespread in some areas. Work towards a vaccine has identified several antigens of F. hepatica that show partial efficacy in terms of reducing worm burden and egg output. A critical question is what level of efficacy is required for such a vaccine to be useful? We have created the first mathematical model to assess the effectiveness of liver fluke vaccines under simulated field conditions. The model describes development of fluke within a group of animals and includes heterogeneity in host susceptibility, seasonal exposure to metacercariae and seasonal changes in temperature affecting metacercarial survival. Our analysis suggests that the potential vaccine candidates could reduce total fluke burden and egg output by up to 43% and 99%, respectively, on average under field conditions. It also suggests that for a vaccine to be effective, it must protect at least 90% of animals for the whole season. In conclusion, novel, partial, vaccines could contribute substantially towards fasciolosis control, reducing usage of anthelmintics and thus delaying the spread of anthelmintic resistance.

Cattle tick vaccine researchers join forces in CATVAC

A meeting sponsored by the Bill & Melinda Gates Foundation was held at the Avanti Hotel, Mohammedia, Morocco, July 14–15, 2015. The meeting resulted in the formation of the Cattle Tick Vaccine Consortium (CATVAC).

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.

Rhipicephalus (Boophilus) microplus aquaporin as an effective vaccine antigen to protect against cattle tick infestations

Background

Vaccination as a control method against the cattle tick, Rhipicephalus (Boophilus) microplus has been practiced since the introduction of two products in the mid-1990s. There is a need for a vaccine that could provide effective control of R. microplus in a more consistent fashion than existing products. During our transcriptome studies of R. microplus, several gene coding regions were discovered to encode proteins with significant amino acid similarity to aquaporins.

Methods

A cDNA encoding an aquaporin from the cattle tick, Rhipicephalus microplus, was isolated from transcriptomic studies conducted on gut tissues dissected from fully engorged adult female R. microplus.

Results

Bioinformatic analysis indicates this aquaporin, designated RmAQP1, shows greatest amino acid similarity to the human aquaporin 7 family. Members of this family of water-conducting channels can also facilitate the transport of glycerol in addition to water. The efficacy of this aquaporin as an antigen against the cattle tick was explored in cattle vaccine trials conducted in Brazil. A cDNA encoding a significant portion of RmAQP1 was expressed as a recombinant protein in Pichia pastoris, purified under native conditions using a polyhistidine C-terminus tag and nickel affinity chromatography, emulsified with Montanide adjuvant, and cattle vaccinated intramuscularly. The recombinant protein provided 75% and 68% efficacy in two cattle pen trials conducted in Campo Grande, Brazil on groups of 6 one year old Holstein calves.

Conclusion

The effectiveness of this vaccine in reducing the numbers of adult female ticks shows this aquaporin antigen holds promise as an active ingredient in cattle vaccines targeted against infestations of R. microplus.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-014-0475-9) contains supplementary material, which is available to authorized users.

Calculation of the efficacy of vaccines against tick infestations on cattle

Cattle ticks are responsible for great economic losses in cattle farming worldwide, and their main control method, chemicals, has been showing problems, whether resulting from the development of resistant strains of ticks or environmental contamination. Research studies directed toward developing vaccines against ticks are emerging. One way to evaluate those vaccines is to calculate the percentage of efficacy. The aim of this study was to analyze scientific publications archived in PubMed that used this method of assessment and discuss the main factors that may affect its calculation. Thus, 25 articles addressing this subject were selected. The percentage of efficacy was usually calculated in one of two ways, with one considering the reduced fertility of eggs and the other not. The latter method may underestimate the vaccine efficacy, and the most complete formula for calculating the efficacy reflects how much the vaccine actually affects the infestation. In our view, the use of the complete formula for calculating the percentage of efficacy is broader and more representative of the vaccine effect on the tick population.

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.