Marinela Contreras

Tick vaccines: current status and future directions

Ticks and tick-borne diseases are a growing problem affecting human and animal health worldwide. Traditional control methods, based primarily on chemical acaricides, have proven not to be sustainable because of the selection of acaricide-resistant ticks. Tick vaccines appear to be a promising and effective alternative for control of tick infestations and pathogen transmission. The purpose of this review is to summarize previous tick vaccine development and performance and formulate critical issues and recommendations for future directions for the development of improved and effective tick vaccines. The development of effective screening platforms and algorithms using omics approaches focused on relevant biological processes will allow the discovery of new tick-protective antigens. Future vaccines will likely combine tick antigens with different protective mechanisms alone or pathogen-derived antigens. The application of tick vaccines as a part of integrated control strategies will ultimately result in the control of tick-borne diseases.

Identification and Characterization of Anaplasma phagocytophilum Proteins Involved in Infection of the Tick Vector, Ixodes scapularis

Anaplasma phagocytophilum is an emerging zoonotic pathogen transmitted by Ixodes scapularis that causes human granulocytic anaplasmosis. Here, a high throughput quantitative proteomics approach was used to characterize A. phagocytophilum proteome during rickettsial multiplication and identify proteins involved in infection of the tick vector, I. scapularis. The first step in this research was focused on tick cells infected with A. phagocytophilum and sampled at two time points containing 10–15% and 65–71% infected cells, respectively to identify key bacterial proteins over-represented in high percentage infected cells. The second step was focused on adult female tick guts and salivary glands infected with A. phagocytophilum to compare in vitro results with those occurring during bacterial infection in vivo. The results showed differences in the proteome of A. phagocytophilum in infected ticks with higher impact on protein synthesis and processing than on bacterial replication in tick salivary glands. These results correlated well with the developmental cycle of A. phagocytophilum, in which cells convert from an intracellular reticulated, replicative form to the nondividing infectious dense-core form. The analysis of A. phagocytophilum differentially represented proteins identified stress response (GroEL, HSP70) and surface (MSP4) proteins that were over-represented in high percentage infected tick cells and salivary glands when compared to low percentage infected cells and guts, respectively. The results demonstrated that MSP4, GroEL and HSP70 interact and bind to tick cells, thus playing a role in rickettsia-tick interactions. The most important finding of these studies is the increase in the level of certain bacterial stress response and surface proteins in A. phagocytophilum-infected tick cells and salivary glands with functional implication in tick-pathogen interactions. These results gave a new dimension to the role of these stress response and surface proteins during A. phagocytophilum infection in ticks. Characterization of Anaplasma proteome contributes information on host-pathogen interactions and provides targets for development of novel control strategies for pathogen infection and transmission.

Comparative Genomics of Field Isolates of Mycobacterium bovis and M. caprae Provides Evidence for Possible Correlates with Bacterial Viability and Virulence

Mycobacteria of the Mycobacterium tuberculosis complex (MTBC) greatly affect humans and animals worldwide. The life cycle of mycobacteria is complex and the mechanisms resulting in pathogen infection and survival in host cells are not fully understood. Recently, comparative genomics analyses have provided new insights into the evolution and adaptation of the MTBC to survive inside the host. However, most of this information has been obtained using M. tuberculosis but not other members of the MTBC such as M. bovis and M. caprae. In this study, the genome of three M. bovis (MB1, MB3, MB4) and one M. caprae (MB2) field isolates with different lesion score, prevalence and host distribution phenotypes were sequenced. Genome sequence information was used for whole-genome and protein-targeted comparative genomics analysis with the aim of finding correlates with phenotypic variation with potential implications for tuberculosis (TB) disease risk assessment and control. At the whole-genome level the results of the first comparative genomics study of field isolates of M. bovis including M. caprae showed that as previously reported for M. tuberculosis, sequential chromosomal nucleotide substitutions were the main driver of the M. bovis genome evolution. The phylogenetic analysis provided a strong support for the M. bovis/M. caprae clade, but supported M. caprae as a separate species. The comparison of the MB1 and MB4 isolates revealed differences in genome sequence, including gene families that are important for bacterial infection and transmission, thus highlighting differences with functional implications between isolates otherwise classified with the same spoligotype. Strategic protein-targeted analysis using the ESX or type VII secretion system, proteins linking stress response with lipid metabolism, host T cell epitopes of mycobacteria, antigens and peptidoglycan assembly protein identified new genetic markers and candidate vaccine antigens that warrant further study to develop tools to evaluate risks for TB disease caused by M. bovis/M.caprae and for TB control in humans and animals.

Targeting a global health problem: Vaccine design and challenges for the control of tick-borne diseases

It has been over twenty years since the first vaccines for the control of tick infestations became commercially available. These vaccines proved their efficacy and the potential of this approach for the control of tick-borne diseases (TBDs), which represent a growing burden for human and animal health worldwide. In all these years, research in this area has produced new tick-derived and pathogen-derived candidate protective antigens. However, the potential of vaccines for the control of TBDs has been underestimated due to major challenges to reduce tick infestations, pathogen infection, multiplication and transmission, tick attachment and feeding time and/or host pathogen infection. Nevertheless, vaccines constitute the most safe and effective intervention for the control of TBDs in humans, domestic and wild animals.

Anaplasma phagocytophilum MSP4 and HSP70 Proteins Are Involved in Interactions with Host Cells during Pathogen Infection

Anaplasma phagocytophilum transmembrane and surface proteins play a role during infection and multiplication in host neutrophils and tick vector cells. Recently, A. phagocytophilum Major surface protein 4 (MSP4) and Heat shock protein 70 (HSP70) were shown to be localized on the bacterial membrane, with a possible role during pathogen infection in ticks. In this study, we hypothesized that A. phagocytophilum MSP4 and HSP70 have similar functions in tick-pathogen and host-pathogen interactions. To address this hypothesis, herein we characterized the role of these bacterial proteins in interaction and infection of vertebrate host cells. The results showed that A. phagocytophilum MSP4 and HSP70 are involved in host-pathogen interactions, with a role for HSP70 during pathogen infection. The analysis of the potential protective capacity of MSP4 and MSP4-HSP70 antigens in immunized sheep showed that MSP4-HSP70 was only partially protective against pathogen infection. This limited protection may be associated with several factors, including the recognition of non-protective epitopes by IgG in immunized lambs. Nevertheless, these antigens may be combined with other candidate protective antigens for the development of vaccines for the control of human and animal granulocytic anaplasmosis. Focusing on the characterization of host protective immune mechanisms and protein-protein interactions at the host-pathogen interface may lead to the discovery and design of new effective protective antigens.

Prospects for vaccination against the ticks of pets and the potential impact on pathogen transmission

Diseases transmitted by arthropod vectors such as ticks greatly impact human and animal health. In particular, many diseases of dogs and cats are potentially transmissible to people by arthropod vectors and therefore their control is important for the eradication of vector-borne diseases (VBD). Vaccination is an environmentally friendly alternative for vector control that allows control of several VBD by targeting their common vector. Recent results have shown that it is possible to use vector protective antigens for the control of arthropod vector infestations and pathogen infection. However, as reviewed in this paper, very little progress has been made for the control of ectoparasite infestations and VBD in pets using vaccination with vector protective antigens. The growing interaction between pets and people underlines the importance of developing new interventions for the monitoring and control of VBD.

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

Diseases transmitted by ticks greatly impact human and animal health and their control is important for the eradication of tick-borne diseases. Vaccination is an environmentally friendly alternative for tick control. Recent results have suggested that Subolesin/Akirin (SUB/AKR) are good candidate antigens for the control of arthropod vector infestations. Here, we describe the effect of vaccination with the Q38 chimera containing SUB/AKR conserved protective epitopes on Ixodes ricinus and Dermacentor reticulatus tick larval mortality, feeding and molting. We demonstrated that Q38 vaccination had an efficacy of 99.9% and 46.4% on the control of I. ricinus and D. reticulatus larvae by considering the cumulative effect on reducing tick survival and molting. The effect of the Q38 vaccine on larval feeding and molting is essential to reduce tick infestations and supports that Q38 might be a candidate universal antigen for the control of multiple tick species that can infest the same host.

Vaccinomics approach to tick vaccine development

Ticks are blood-feeding arthropod ectoparasites that transmit disease-causing pathogens to humans and animals worldwide. Vaccines using tick antigens have proven to be cost-effective and environmental friendly for the control of vector infestations and pathogen infection and transmission. However, new strategies are needed to identify tick protective antigens for development of improved vaccines. These strategies will be greatly enhanced by vaccinomics approaches starting from the study of tick-host-pathogen molecular interactions and ending in the characterization and validation of vaccine formulations. The discovery of tick antigens that affect both tick infestations and pathogen infection/transmission could be used for vaccines targeting human and animal populations at risk and reservoir species to reduce host exposure to ticks while reducing the number of infected ticks and their vector capacity for pathogens that affect human and animal health. In this chapter, we describe methods of the vaccinomics platform using transcriptomics and proteomics for the identification of candidate protective antigens in Ixodes scapularis, the vector for human and animal granulocytic anaplasmosis, tick-borne encephalitis, and Lyme disease.

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.

Vaccinomics Approach to the Identification of Candidate Protective Antigens for the Control of Tick Vector Infestations and Anaplasma phagocytophilum Infection

Anaplasma phagocytophilum is an emerging tick-borne pathogen causing human granulocytic anaplasmosis (HGA), tick-borne fever (TBF) in small ruminants, and other forms of anaplasmosis in different domestic and wild animals. The main vectors of this pathogen are Ixodes tick species, particularly I. scapularis in the United States and I. ricinus in Europe. One of the main limitations for the development of effective vaccines for the prevention and control of A. phagocytophilum infection and transmission is the identification of effective tick protective antigens. The objective of this study was to apply a vaccinomics approach to I. scapularis-A. phagocytophilum interactions for the identification and characterization of candidate tick protective antigens for the control of vector infestations and A. phagocytophilum infection. The vaccinomics pipeline included the use of quantitative transcriptomics and proteomics data from uninfected and A. phagocytophilum-infected I. scapularis ticks for the selection of candidate protective antigens based on the variation in tick mRNA and protein levels in response to infection, their putative biological function, and the effect of antibodies against these proteins on tick cell apoptosis and pathogen infection. The characterization of selected candidate tick protective antigens included the identification and characterization of I. ricinus homologs, functional characterization by different methodologies including RNA interference, immunofluorescence, gene expression profiling, and artificial tick feeding on rabbit antibodies against the recombinant antigens to select the candidates for vaccination trials. The vaccinomics pipeline developed in this study resulted in the identification of two candidate tick protective antigens that could be selected for future vaccination trials. The results showed that I. scapularis lipocalin (ISCW005600) and lectin pathway inhibitor (AAY66632) and I. ricinus homologs constitute candidate protective antigens for the control of vector infestations and A. phagocytophilum infection. Both antigens are involved in the tick evasion of host defense response and pathogen infection and transmission, but targeting different immune response pathways. The vaccinomics pipeline proposed here could be used to continue the identification and characterization of candidate tick protective antigens for the development of effective vaccines for the prevention and control of HGA, TBF, and other forms of anaplasmosis caused by A. phagocytophilum.