Control of Ixodes ricinus and Dermacentor reticulatus tick infestations in rabbits vaccinated with the Q38 Subolesin/Akirin chimera

Design and evaluation of vaccines for the control of the etiological agent of East Coast fever

East Coast fever is a tick-borne theileriosis caused by Theileria parva, a protozoan parasite with the primary vector being the tick Rhipicephalus appendiculatus. This disease poses significant challenges in sub-Saharan Africa, leading to severe economic losses by causing the death of over one million livestock annually. Current control measures include vector control with acaricides and the "infection and treatment" method, which involves immunization with live sporozoites of the pathogen and treatment with long acting oxytetracycline. Despite their effectiveness, these methods face scalability and usability issues, necessitating the development of new prevention strategies, particularly in the field of vaccines for the effective and sustainable control of East Coast fever. In this primer focus, East Coast fever serves as a case study to highlight recent concepts and advancements in tick and tick-borne disease vaccine research. Vaccine design and evaluation processes are reviewed, encompassing the utilization of omics datasets and knowledge on vectors and pathogens, and exploring new design methods, such as quantum vaccinomics and messenger RNA (mRNA)-based vaccines. Key limitations and areas requiring further research are addressed, including insufficient understanding of host-pathogen molecular interactions, the impact of post-translational modifications, and vaccine efficacy variability across different trials. Additionally, new research objectives are proposed to address East Coast fever but with possible impact on other tick-borne diseases. It includes advancing knowledge on tick-pathogen-host molecular interactions, studying tick microbiota, developing novel design approaches, such as combining tick and pathogen epitopes in chimeric vaccines (exemplified by the q38-p67c case), and exploring new immunological enhancers and delivery platforms.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Function-guided selection of salivary antigens from Ornithodoros erraticus argasid ticks and assessment of their protective efficacy in rabbits

The identification of new protective antigens for the development of tick vaccines may be approached by selecting antigen candidates that have key biological functions. Bioactive proteins playing key functions for tick feeding and pathogen transmission are secreted into the host via tick saliva. Adult argasid ticks must resynthesise and replace these proteins after each feeding to be able to repeat new trophogonic cycles. Therefore, these proteins are considered interesting antigen targets for tick vaccine development. In this study, the salivary gland transcriptome and saliva proteome of Ornithodoros erraticus females were inspected to select and test new vaccine candidate antigens. For this, we focused on transcripts overexpressed after feeding that encoded secretory proteins predicted to be immunogenic and annotated with functions related to blood ingestion and modulation of the host defensive response. Completeness of the transcript sequence, as well as a high expression level and a high fold-change after feeding were also scored resulting in the selection of four candidates, an acid tail salivary protein (OeATSP), a multiple coagulation factor deficiency protein 2 homolog (OeMCFD2), a Cu/Zn-superoxide dismutase (OeSOD) and a sulfotransferase (OeSULT), which were later produced as recombinant proteins. Vaccination of rabbits with each individual recombinant antigen induced strong humoral responses that reduced blood feeding and female reproduction, providing, respectively, 46.8%, 45.7%, 54.3% and 31.9% protection against O. erraticus infestations and 0.7%, 3.9%, 3.1% and 8.7% cross-protection against infestations by the African tick, Ornithodoros moubata. The joint protective efficacy of these antigens was tested in a second vaccine trial reaching 58.3% protection against O. erraticus and 18.6% cross-protection against O. moubata. These results (i) provide four new protective salivary antigens from argasid ticks that might be included in multi-antigenic vaccines designed for the control of multiple tick species; (ii) reveal four functional protein families never tested before as a source of protective antigens in ticks; and (iii) show that multi-antigenic vaccines increase vaccine efficacy compared with individual antigens. Finally, our data add value to the salivary glands as a protective antigen source in argasids for the control of tick infestations.

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

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

Universal Tick Vaccines: Candidates and Remaining Challenges

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

Co-Immunization Efficacy of Recombinant Antigens against Rhipicephalus microplus and Hyalomma anatolicum Tick Infestations

The immunoprophylactic management of ticks is the most effective option to control tick infestations and counter spread the acaricide resistance problem worldwide. Several researchers reported an inconsistent efficacy of the single antigen-based immunization of hosts against different tick species. In the present study, to develop a multi-target immunization protocol, proteins from Rhipicephalus microplus BM86 and Hyalomma anatolicum subolesin (SUB) and tropomyosin (TPM) were targeted to evaluate the cross-protective potential. The sequence identities of the BM86, SUB, and TPM coding genes amongst Indian tick isolates of targeted species were 95.6–99.8%, 98.7–99.6%, and 98.9–99.9%, respectively, while at the predicted amino acid level, the identities were 93.2 to 99.5, 97.6 to 99.4, and 98.2 to 99.3%. The targeted genes were expressed in the eukaryotic expression system, pKLAC2-Kluyveromyces lactis, and 100 µg each of purified recombinant protein (Bm86-89 kDa, SUB-21 kDa, and TPM-36 kDa) mixed with adjuvant was injected individually through the intramuscular route at different sites of the body on days 0, 30, and 60 to immunize cross-bred cattle. Post-immunization, a statistically significant (p < 0.001) antibody response (IgG, IgG1, and IgG2) in comparison to the control, starting from 15 to 140 days, against each antigen was recorded. Following multi-antigen immunization, the animals were challenged twice with the larvae of R. microplus and H. anatolicum and theadults of H. anatolicum, and a significant vaccine efficacy of 87.2% and 86.2% against H. anatolicum larvae and adults, respectively, and 86.7% against R. microplus was obtained. The current study provides significant support to develop a multi-antigen vaccine against cattle tick species.

Tick Vaccines and Concealed versus Exposed Antigens

Anti-tick vaccines development mainly depends on the identification of suitable antigens, which ideally should have different features. These should be key molecules in tick biology, encoded by a single gene, expressed across life stages and tick tissues, capable of inducing B and T cells to promote an immunological response without allergenic, hemolytic, and toxic effects; and should not be homologous to the mammalian host. The discussion regarding this subject and the usefulness of “exposed” and “concealed” antigens was effectively explored in the publication by Nuttall et al. (2006). The present commentary intends to debate the relevance of such study in the field of tick immunological control.

The Correlation between Subolesin-Reactive Epitopes and Vaccine Efficacy

Vaccination is an environmentally-friendly alternative for tick control. The tick antigen Subolesin (SUB) has shown protection in vaccines for the control of multiple tick species in cattle. Additionally, recent approaches in quantum vaccinomics have predicted SUB-protective epitopes and the peptide sequences involved in protein−protein interactions in this tick antigen. Therefore, the identification of B-cell−reactive epitopes by epitope mapping using a SUB peptide array could be essential as a novel strategy for vaccine development. Subolesin can be used as a model to evaluate the effectiveness of these approaches for the identification of protective epitopes related to vaccine protection and efficacy. In this study, the mapping of B-cell linear epitopes of SUB from three different tick species common in Uganda (Rhipicephalus appendiculatus, R. decoloratus, and Amblyomma variegatum) was conducted using serum samples from two cattle breeds immunized with SUB-based vaccines. The results showed that in cattle immunized with SUB from R. appendiculatus (SUBra) all the reactive peptides (Z-score > 2) recognized by IgG were also significant (Z-ratio > 1.96) when compared to the control group. Additionally, some of the reactive peptides recognized by IgG from the control group were also recognized in SUB cocktail−immunized groups. As a significant result, cattle groups that showed the highest vaccine efficacy were Bos indicus immunized with a SUB cocktail (92%), and crossbred cattle were immunized with SUBra (90%) against R. appendiculatus ticks; the IgG from these groups recognized overlapping epitopes from the peptide SPTGLSPGLSPVRDQPLFTFRQVGLICERMMKERESQIRDEYDHVLSAKLAEQYDTFVKFTYDQKRFEGATPSYLS (Z-ratio > 1.96), which partially corresponded to a Q38 peptide and the SUB protein interaction domain. These identified epitopes could be related to the protection and efficacy of the SUB-based vaccines, and new chimeras containing these protective epitopes could be designed using this new approach.

Oral vaccine formulation combining tick Subolesin with heat inactivated mycobacteria provides control of cross-species cattle tick infestations

Tick vaccines are necessary as part of a One Health approach for the control of tick infestations and tick-borne diseases. Subolesin (SUB, also known as 4D8) is a tick protective antigen that has shown efficacy in vaccine formulations for the control of ectoparasite infestations and pathogen infection/transmission. A recent proof-of-concept study reported oral vaccination combining Rhipicephalus microplus SUB with heat inactivated Mycobacterium bovis (IV) as an immunostimulant for the control of cattle tick infestations. Based on the efficacy of Rhipicephalus decoloratus SUB for the control of multiple cattle tick species in Uganda, herein we design a controlled pen trial using an oral formulation combining R. decoloratus SUB with IV for the control of R. decoloratus and Rhipicephalus appendiculatus cattle tick infestations. Vaccine efficacy (E) of SUB + IV on tick life cycle was compared with IV and SUB alone and with PBS as control. The IgG antibody titers against SUB and M. bovis P22 and the serum levels of selected protein immune biomarkers (IL-1beta, TNF-alpha, C3) were determined and analyzed as possible correlates of protection. Oral immunization with IV and SUB alone and in SUB + IV combination were effective for the control of tick infestations (E = 71-96% for R. decoloratus and 87-99% for R. appendiculatus) with highest E (higher than 95%) for SUB + IV. The results demonstrated that oral immunization with the SUB + IV formulation resulted in effective control of cattle tick infestations through the activation of multiple immune mechanisms. These results support the application of oral vaccine formulations with SUB + IV for the control of cattle infestations with Rhipicephalus species towards improving animal health.

Ticks and antibodies: May parasite density and tick evasion influence the outcomes following immunization protocols?

Ticks are a major concern to human health and livestock worldwide, being responsible for economic losses that go beyond billions of US dollars per year. This scenario instigates the development of vaccines against these ectoparasites, emphasized by the fact that the main method of controlling ticks still relies on the use of acaricides, what increases costs and may affect the environment as well as human and animal health. The first commercial vaccines against ectoparasites were produced against the tick Rhipicephalus microplus and their efficacy were based on antibodies. Many additional attempts have been conducted to produce protective immune responses against ticks by immunization with specific antigens and the antibody response has usually been the main target of evaluation. But some controversy still populates the roles possibly performed by humoral responses in tick-mammalian host relationships. This review focuses on the analysis of specific aspects concerning antibodies and ticks, especially the influence of parasite density and evasion/modulation. The immunization trials already described against R. microplus were also compiled and analyzed based on the characteristics of the molecules tested, protocols of immunization and tick challenge. Within these issues, it is discussed if or when antibody levels can be directly correlated with the development of tick resistance, and whether anti-tick protective immune responses generated by infestations may become ineffective under a different tick density. Also, higher titers of antibodies can be correlated with protection or susceptibility to tick infestations, what may be altered following continuous or repeated infestations and differ greatly comparing hosts with distinct genetic backgrounds. Regarding evasion, ticks present a sophisticated mechanism for dealing with antibodies, including Immunoglobulin Binding Proteins (IGBPs), that capture, transport and inject them back into the host, while keeping their properties within the parasite. The comparison of immunization protocols shows a total of 22 molecules already tested in cattle vaccination trials against R. microplus, with the predominance of concealed and dual antigens as well as marked differences in tick challenge schemes. The presence of an antibody evasion apparatus and variable levels of tick resistance when facing different densities of parasites are concerns that should be considered when testing vaccine candidates. Ultimately, more refinement may be necessary to effectively design a cocktail vaccine with tick molecules, which may be needed to be altered and combined in non-competing immune contexts to be universally secure and protective.

Additional evidence on the efficacy of different Akirin vaccines assessed on Anopheles arabiensis (Diptera: Culicidae)

Background

Anopheles arabiensis is an opportunistic malaria vector that rests and feeds outdoors, circumventing current indoor vector control methods. Furthermore, this vector will readily feed on both animals and humans. Targeting this vector while feeding on animals can provide an additional intervention for the current vector control activities. Previous results have displayed the efficacy of using Subolesin/Akirin ortholog vaccines for the control of multiple ectoparasite infestations. This made Akirin a potential antigen for vaccine development against An. arabiensis.

Methods

The efficacy of three antigens, namely recombinant Akirin from An. arabiensis, recombinant Akirin from Aedes albopictus, and recombinant Q38 (Akirin/Subolesin chimera) were evaluated as novel interventions for An. arabiensis vector control. Immunisation trials were conducted based on the concept that mosquitoes feeding on vaccinated balb/c mice would ingest antibodies specific to the target antigen. The antibodies would interact with the target antigen in the arthropod vector, subsequently disrupting its function.

Results

All three antigens successfully reduced An. arabiensis survival and reproductive capacities, with a vaccine efficacy of 68–73%.

Conclusions

These results were the first to show that hosts vaccinated with recombinant Akirin vaccines could develop a protective response against this outdoor malaria transmission vector, thus providing a step towards the development of a novel intervention for An. arabiensis vector control.

Graphic Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04711-8.

Tick Importin-α Is Implicated in the Interactome and Regulome of the Cofactor Subolesin

Ticks and tick-borne diseases (TBDs) represent a burden for human and animal health worldwide. Currently, vaccines constitute the safest and most effective approach to control ticks and TBDs. Subolesin (SUB) has been identified as a vaccine antigen for the control of tick infestations and pathogen infection and transmission. The characterization of the molecular function of SUB and the identification of tick proteins interacting with SUB may provide the basis for the discovery of novel antigens and for the rational design of novel anti-tick vaccines. In the present study, we used the yeast two-hybrid system (Y2H) as an unbiased approach to identify tick SUB-interacting proteins in an Ixodes ricinus cDNA library, and studied the possible role of SUB as a chromatin remodeler through direct interaction with histones. The Y2H screening identified Importin-α as a potential SUB-interacting protein, which was confirmed in vitro in a protein pull-down assay. The sub gene expression levels in tick midgut and fat body were significantly higher in unfed than fed female ticks, however, the importin-α expression levels did not vary between unfed and fed ticks but tended to be higher in the ovary when compared to those in other organs. The effect of importin-α RNAi was characterized in I. ricinus under artificial feeding conditions. Both sub and importin-α gene knockdown was observed in all tick tissues and, while tick weight was significantly lower in sub RNAi-treated ticks than in controls, importin-α RNAi did not affect tick feeding or oviposition, suggesting that SUB is able to exert its function in the absence of Importin-α. Furthermore, SUB was shown to physically interact with histone 4, which was corroborated by protein pull-down and western blot analysis. These results confirm that by interacting with numerous tick proteins, SUB is a key cofactor of the tick interactome and regulome. Further studies are needed to elucidate the nature of the SUB-Importin-α interaction and the biological processes and functional implications that this interaction may have.

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

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

Subolesin vaccination inhibits blood feeding and reproduction of Haemaphysalis longicornis in rabbits

Background

Ticks can transmit numerous tick-borne pathogens and cause a huge economic loss to the livestock industry. Tick vaccines can contribute to the prevention of tick-borne diseases by inhibiting tick infestation or reproduction. Subolesin is an antigenic molecule proven to be a potential tick vaccine against different tick species and even some tick-borne pathogens. However, its effectivity has not been verified in Haemaphysalis longicornis, which is a widely distributed tick species, especially in East Asian countries. Therefore, the purpose of this study was to evaluate the effectivity of subolesin vaccination against H. longicornis in a rabbit model.

Methods

Haemaphysalis longicornis (Okayama strain, female, adult, parthenogenetic strain) and Japanese white rabbits were used as the model tick and animal, respectively. The whole open reading frame of H. longicornis subolesin (HlSu) was identified and expressed as a recombinant protein using E. coli. The expression was verified using sodium dodecyl sulfate polyacrylamide gel electrophoresis, and the immunogenicity of rHlSu against anti-H. longicornis rabbit serum was confirmed using Western blotting. After vaccination of rHlSu in rabbits, experimental infestation of H. longicornis was performed. Variables related to blood-feeding periods, pre-oviposition periods, body weight at engorgement, egg mass, egg mass to body weight ratio, and egg-hatching periods were measured to evaluate the effectiveness of subolesin vaccination.

Results

The whole open reading frame of HlSu was 540 bp, and it was expressed as a recombinant protein. Vaccination with rHlSu stimulated an immune response in rabbits. In the rHlSu-vaccinated group, body weight at engorgement, egg mass, and egg mass to body weight ratio were statistically significantly lower than those in the control group. Besides, egg-hatching periods were extended significantly. Blood-feeding periods and pre-oviposition periods were not different between the two groups. In total, the calculated vaccine efficacy was 37.4%.

Conclusions

Vaccination of rabbits with rHlSu significantly affected the blood-feeding and reproduction in H. longicornis. Combined with findings from previous studies, our findings suggest subolesin has the potential to be used as a universal tick vaccine.

Control of tick infestations in wild roe deer (Capreolus capreolus) vaccinated with the Q38 Subolesin/Akirin chimera

Ticks (Acari: Ixodidae) are considered to be the most important vectors of disease-causing pathogens in domestic and wild animals, and emerging and re-emerging tick-borne diseases (TBD) exert an enormous impact on them. Wild ungulates are hosts for a wide variety of tick species and tick-borne pathogens that affect human and animal health. Consequently, the control of tick infestations and tick-borne pathogen prevalence is essential in some regions. Acaricides and animal management or culling have been used for the control of tick infestations and TBD, but tick vaccines constitute the best alternative to reduce the impact of acaricides on tick resistance and the environment. Previous results of controlled vaccination trials have shown that the Q38 Subolesin/Akirin chimera containing conserved protective epitopes could be a candidate universal antigen to control multiple tick species infestations. Thus, vaccination trials are necessary to validate these results under field conditions. In this study, we characterized the effect of Q38 vaccine on a wild population of European roe deer (Capreolus capreolus) in the Andalusian roe deer Reference Station (Junta de Andalucía, Cádiz, Spain). In this location, roe deer suffer especially severe parasitic conditions in some periods and commercial pesticides and ixodicides that are authorized to control ticks without specificity are frequently applied in the field, posing a threat to the environment. Animals vaccinated over a three-year period showed an antibody response to the vaccine antigen and a reduction in tick infestations by multiple species including Hyalomma marginatum, H. lusitanicum, Rhipicephalus bursa and Ixodes ricinus previously identified in roe deer, when compared to untreated controls. These results suggest the efficacy of Q38 for the control of tick infestations in wildlife.

Vaccination with Recombinant Subolesin Antigens Provides Cross-Tick Species Protection in Bos indicus and Crossbred Cattle in Uganda

Cattle tick infestations and transmitted pathogens affect animal health, production and welfare with an impact on cattle industry in tropical and subtropical countries. Anti-tick vaccines constitute an effective and sustainable alternative to the traditional methods for the control of tick infestations. Subolesin (SUB)-based vaccines have shown efficacy for the control of multiple tick species, but several factors affect the development of new and more effective vaccines for the control of tick infestations. To address this challenge, herein we used a regional and host/tick species driven approach for vaccine design and implementation. The objective of the study was to develop SUB-based vaccines for the control of the most important tick species (Rhipicephalus appendiculatus, R. decoloratus and Amblyomma variegatum) affecting production of common cattle breeds (Bos indicus and B. indicus x B. taurus crossbred) in Uganda. In this way, we addressed the development of anti-tick vaccines as an intervention to prevent the economic losses caused by ticks and tick-borne diseases in the cattle industry in Uganda. The results showed the possibility of using SUB antigens for the control of multiple tick species in B. indicus and crossbred cattle and suggested the use of R. appendiculatus SUB to continue research on vaccine design and formulation for the control of cattle ticks in Uganda. Future directions would include quantum vaccinology approaches based on the characterization of the SUB protective epitopes, modeling of the vaccine E under Ugandan ecological and epidemiological conditions and optimization of vaccine formulation including the possibility of oral administration.

A Novel Combined Scientific and Artistic Approach for the Advanced Characterization of Interactomes: The Akirin/Subolesin Model

The main objective of this study was to propose a novel methodology to approach challenges in molecular biology. Akirin/Subolesin (AKR/SUB) are vaccine protective antigens and are a model for the study of the interactome due to its conserved function in the regulation of different biological processes such as immunity and development throughout the metazoan. Herein, three visual artists and a music professor collaborated with scientists for the functional characterization of the AKR2 interactome in the regulation of the NF-κB pathway in human placenta cells. The results served as a methodological proof-of-concept to advance this research area. The results showed new perspectives on unexplored characteristics of AKR2 with functional implications. These results included protein dimerization, the physical interactions with different proteins simultaneously to regulate various biological processes defined by cell type-specific AKR–protein interactions, and how these interactions positively or negatively regulate the nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway in a biological context-dependent manner. These results suggested that AKR2-interacting proteins might constitute suitable secondary transcription factors for cell- and stimulus-specific regulation of NF-κB. Musical perspective supported AKR/SUB evolutionary conservation in different species and provided new mechanistic insights into the AKR2 interactome. The combined scientific and artistic perspectives resulted in a multidisciplinary approach, advancing our knowledge on AKR/SUB interactome, and provided new insights into the function of AKR2–protein interactions in the regulation of the NF-κB pathway. Additionally, herein we proposed an algorithm for quantum vaccinomics by focusing on the model proteins AKR/SUB.

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

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Reduction in Oviposition of Poultry Red Mite (Dermanyssus gallinae) in Hens Vaccinated with Recombinant Akirin

The poultry red mite (PRM), Dermanyssus gallinae, is a hematophagous ectoparasite of birds with worldwide distribution that causes economic losses in the egg-production sector of the poultry industry. Traditional control methods, mainly based on acaricides, have been only partially successful, and new vaccine-based interventions are required for the control of PRM. Vaccination with insect Akirin (AKR) and its homolog in ticks, Subolesin (SUB), have shown protective efficacy for the control of ectoparasite infestations and pathogen infection/transmission. The aim of this study was the identification of the akr gene from D. gallinae (Deg-akr), the production of the recombinant Deg-AKR protein, and evaluation of its efficacy as a vaccine candidate for the control of PRM. The anti-Deg-AKR serum IgY antibodies in hen sera and egg yolk were higher in vaccinated than control animals throughout the experiment. The results demonstrated the efficacy of the vaccination with Deg-AKR for the control of PRM by reducing mite oviposition by 42% following feeding on vaccinated hens. A negative correlation between the levels of serum anti-Deg-AKR IgY and mite oviposition was obtained. These results support Deg-AKR as a candidate protective antigen for the control of PRM population growth.

Why New Vaccines for the Control of Ectoparasite Vectors Have Not Been Registered and Commercialized?

The prevention and control of vector-borne diseases is a priority for improving global health. Despite recent advances in the characterization of ectoparasite-host-pathogen molecular interactions, vaccines are not available for most ectoparasites and vector-borne diseases that cause millions of deaths yearly. In this paper, in response to the question of why new vaccines for the control of ectoparasite vectors have not been registered and commercialized, and to contribute developing new effective vaccines against ectoparasite vectors, we propose challenges and approaches to be addressed.

A Vaccinomics Approach for the Identification of Tick Protective Antigens for the Control of Ixodes ricinus and Dermacentor reticulatus Infestations in Companion Animals

Ticks and tick-borne pathogens affect health and welfare of companion animals worldwide, and some human tick-borne diseases are associated with exposure to domestic animals. Vaccines are the most environmentally friendly alternative to acaracides for the control of tick infestations, and to reduce the risk for tick-borne diseases affecting human and animal health. However, vaccines have not been developed or successfully implemented for most vector-borne diseases. The main limitation for the development of effective vaccines is the identification of protective antigens. To address this limitation, in this study we used an experimental approach combining vaccinomics based on transcriptomics and proteomics data with vaccination trials for the identification of tick protective antigens. The study was focused on Ixodes ricinus and Dermacentor reticulatus that infest humans, companion animals and other domestic and wild animals, and transmit disease-causing pathogens. Tick larvae and adult salivary glands were selected for analysis to target tick organs and developmental stages playing a key role during tick life cycle and pathogen infection and transmission. Two I. ricinus (heme lipoprotein and uncharacterized secreted protein) and five D. reticulatus (glypican-like protein, secreted protein involved in homophilic cell adhesion, sulfate/anion exchanger, signal peptidase complex subunit 3, and uncharacterized secreted protein) proteins were identified as the most effective protective antigens based on the criteria of vaccine E > 80%. The putative function of selected protective antigens, which are involved in different biological processes, resulted in vaccines affecting multiple tick developmental stages. These results suggested that the combination of some of these antigens might be considered to increase vaccine efficacy through antigen synergy for the control of tick infestations and potentially affecting pathogen infection and transmission. These antigens were proposed for commercial vaccine development for the control of tick infestations in companion animals, and potentially in other hosts for these tick species.

Function-guided selection of midgut antigens from Ornithodoros erraticus ticks and an evaluation of their protective efficacy in rabbits

The identification of candidate protective antigens for the development of tick vaccines may be approached by selecting antigen candidates that play key biological functions. Tick midgut proteins that play essential functions in tick survival and disease transmission are upregulated in response to blood feeding and digestion. In this study, Ornithodoros erraticus midgut transcriptomic and proteomic data upon feeding were inspected to select functionally relevant antigens to be assessed as vaccine candidate antigens. For this, we primarily focused on proteins with relevant biological functions in key physiological processes for ticks and tick-host-pathogen interactions. Later, we used additional criteria based on overexpression after feeding, predicted antigenicity and cellular localisation, resulting in the selection of four theoretical candidates, two aquaporins (OeAQP, OeAQP1), one ABC transporter (OeABC) and one selenoprotein T (OeSEL). Rabbit vaccination with synthetic immunogenic peptides designed from the extracellular antigenic regions of the selected candidates induced humoral responses that reduced tick feeding and reproduction performance. Both AQPs and OeSEL demonstrated significant protection efficacy against the homologous species O. erraticus, but lower non-significant cross-species protection against Ornithodoros moubata. Conversely, OeABC showed no protection against the homologous species O. erraticus, but significant cross-species protection against O. moubata. These results are the first demonstration of the protective potential of argasid aquaporins, suggesting that they might be included in vaccines for the control of multiple tick species. Additionally, these results also unveiled two novel protective antigens from argasid ticks, OeABC and OeSEL, belonging to functional protein families that have never been explored as a source of vaccine candidates and are deserving of further studies. Finally, our data add value to the midgut as a protective candidate antigen source in argasids for the control of tick infestations.

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

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

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

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

Inward rectifier potassium (Kir) channels mediate salivary gland function and blood feeding in the lone star tick, Amblyomma americanum

Background

Tick feeding causes extreme morbidity and mortality to humans through transmission of pathogens and causes severe economic losses to the agricultural industry by reducing livestock yield. Salivary gland secretions are essential for tick feeding and thus, reducing or preventing saliva secretions into the vertebrate host is likely to reduce feeding and hinder pathogen life cycles. Unfortunately, the membrane physiology of tick salivary glands is underexplored and this gap in knowledge limits the development of novel therapeutics for inducing cessation of tick feeding.

Methodology

We studied the influence of inward rectifier potassium (Kir) channel subtypes to the functional capacity of the isolated tick salivary gland through the use of a modified Ramsay assay. The secreted saliva was subsequently used for quantification of the elemental composition of the secreted saliva after the glands were exposed to K⁺ channel modulators as a measure of osmoregulatory capacity. Lastly, changes to blood feeding behavior and mortality were measured with the use of a membrane feeding system.

Principal findings

In this study, we characterized the fundamental role of Kir channel subtypes in tick salivary gland function and provide evidence that pharmacological inhibition of these ion channels reduces the secretory activity of the Amblyomma americanum salivary gland. The reduced secretory capacity of the salivary gland was directly correlated with a dramatic reduction of blood ingestion during feeding. Further, exposure to small-molecule modulators of Kir channel subtypes induced mortality to ticks that is likely resultant from an altered osmoregulatory capacity.

Conclusions

Our data contribute to understanding of tick salivary gland function and could guide future campaigns aiming to develop chemical or reverse vaccinology technologies to reduce the worldwide burden of tick feeding and tick-vectored pathogens.

Tick feeding results in negative health and economic consequences worldwide and there has been continued interest in the development of products with novel mechanisms of action for control of tick populations. Kir channels have been shown to be a significant ion conductance pathway in arthropods and are critical for proper functioning of multiple biological processes. Previous work on insect Kir channels has focused on their physiological roles in renal system of mosquitoes and the data suggest that these channels represent a viable pathway to induce renal failure that leads to mortality. Based on the functional and cellular similarities of arthropod salivary glands and Malpighian tubules, we hypothesized that Kir channels constitute a critical conductance pathway within arthropod salivary glands and inhibition of this pathway will preclude feeding. Data presented in this study show that pharmacological modulators of Kir channels elicited a significant reduction in the fluid and ion secretory activity of tick salivary glands that resulted in reduced feeding, altered osmoregulation, and lead to mortality. These data could guide the future development of novel acaricides, RNAi, or genetically modified ticks to mitigate health and economic damages resulting from their feeding. Further, these data indicate a conserved function of Kir channels within multiple tissues of taxonomically diverse organisms, such as ticks and humans.

Functional Evolution of Subolesin/Akirin

The Subolesin/Akirin constitutes a good model for the study of functional evolution because these proteins have been conserved throughout the metazoan and play a role in the regulation of different biological processes. Here, we investigated the evolutionary history of Subolesin/Akirin with recent results on their structure, protein-protein interactions and function in different species to provide insights into the functional evolution of these regulatory proteins, and their potential as vaccine antigens for the control of ectoparasite infestations and pathogen infection. The results suggest that Subolesin/Akirin evolved conserving not only its sequence and structure, but also its function and role in cell interactome and regulome in response to pathogen infection and other biological processes. This functional conservation provides a platform for further characterization of the function of these regulatory proteins, and how their evolution can meet species-specific demands. Furthermore, the conserved functional evolution of Subolesin/Akirin correlates with the protective capacity shown by these proteins in vaccine formulations for the control of different arthropod and pathogen species. These results encourage further research to characterize the structure and function of these proteins, and to develop new vaccine formulations by combining Subolesin/Akirin with interacting proteins for the control of multiple ectoparasite infestations and pathogen infection.

Metazoan Parasite Vaccines: Present Status and Future Prospects

Eukaryotic parasites and pathogens continue to cause some of the most detrimental and difficult to treat diseases (or disease states) in both humans and animals, while also continuously expanding into non-endemic countries. Combined with the ever growing number of reports on drug-resistance and the lack of effective treatment programs for many metazoan diseases, the impact that these organisms will have on quality of life remain a global challenge. Vaccination as an effective prophylactic treatment has been demonstrated for well over 200 years for bacterial and viral diseases. From the earliest variolation procedures to the cutting edge technologies employed today, many protective preparations have been successfully developed for use in both medical and veterinary applications. In spite of the successes of these applications in the discovery of subunit vaccines against prokaryotic pathogens, not many targets have been successfully developed into vaccines directed against metazoan parasites. With the current increase in -omics technologies and metadata for eukaryotic parasites, target discovery for vaccine development can be expedited. However, a good understanding of the host/vector/pathogen interface is needed to understand the underlying biological, biochemical and immunological components that will confer a protective response in the host animal. Therefore, systems biology is rapidly coming of age in the pursuit of effective parasite vaccines. Despite the difficulties, a number of approaches have been developed and applied to parasitic helminths and arthropods. This review will focus on key aspects of vaccine development that require attention in the battle against these metazoan parasites, as well as successes in the field of vaccine development for helminthiases and ectoparasites. Lastly, we propose future direction of applying successes in pursuit of next generation vaccines.

Arthropod-borne pathogens of dogs and cats: From pathways and times of transmission to disease control

Vector-borne pathogens have developed a close relationship with blood feeding arthropod ectoparasites (e.g., mosquitoes, ticks, phlebotomine sand flies, black flies, fleas, kissing bugs, lice) and exploited a huge variety of vector transmission routes. Therefore, the life cycles of these pathogens result in a long evolved balance with the respective arthropod biology, ecology and blood feeding habits, instrumentally to the infection of several animal species, including humans. Amongst the many parasite transmission modes, such as ingestion of the arthropod, with its faeces or secretions, blood feeding represents the main focus for this article, as it is a central event to the life of almost all arthropod vectors. The time frame in which pathogens are transmitted to any animal host is governed by a large number of biological variables related to the vector, the pathogen, the host and environmental factors. Scientific data available on transmission times for each pathogen are discussed relative to their impact for the success of vector-borne disease control strategies. Blocking pathogen transmission, and thus preventing the infection of dogs and cats, may be achievable by the use of chemical compounds if they are characterised by a fast onset of killing activity or repellence against arthropods. The fast speed of kill exerted by systemic isoxazoline, as well as the repellent effect of pyrethroids have renewed the interest of the scientific community and pharmaceutical companies towards reducing the burden of vector-borne diseases under field conditions. However, endosymbionts and vaccines targeting arthropods or pathogen antigens should be further investigated as alternative strategies towards the goal of achieving an effective integrated control of vector-borne diseases.

Control of infestations by Ixodes ricinus tick larvae in rabbits vaccinated with aquaporin recombinant antigens

BACKGROUND

Tick-borne diseases greatly impact human and animal health worldwide, and vaccines are an environmentally friendly alternative to acaricides for their control. Recent results have suggested that aquaporin (AQP) water channels have a key function during tick feeding and development, and constitute good candidate antigens for the control of tick infestations.

METHODS

Here we describe the effect of vaccination with the Ixodes ricinus AQP1 (IrAQP) and a tick AQP conserved region (CoAQP) on I. ricinus tick larval mortality, feeding and molting.

RESULTS

We demonstrated that vaccination with IrAQP and CoAQP had an efficacy of 32% and 80%, respectively on the control of I. ricinus larvae by considering the cumulative effect on reducing tick survival and molting.

CONCLUSIONS

The effect of the AQP vaccines on larval survival and molting is essential to reduce tick infestations, and extended previous results on the effect of R. microplus AQP1 on the control of cattle tick infestations. These results supports that AQP, and particularly CoAQP, might be a candidate protective antigen for the control of different tick species.