A Babesia bovis gene syntenic to Theileria parva p67 is expressed in blood and tick stage parasites

Analysis of Stage-Specific Protein Expression during Babesia Bovis Development within Female Rhipicephalus Microplus

Arthropod-borne protozoan pathogens have a complex life cycle that includes asexual reproduction of haploid stages in mammalian hosts and the development of diploid stages in invertebrate hosts. The ability of pathogens to invade, survive, and replicate within distinct cell types is required to maintain their life cycle. In this study, we describe a comparative proteomic analysis of a cattle pathogen, Babesia bovis, during its development within the mammalian and tick hosts with the goal of identifying cell-surface proteins expressed by B. bovis kinetes as potential targets for the development of a transmission blocking vaccine. To determine parasite tick-stage-specific cell-surface proteins, CyDye labeling was performed with B. bovis blood stages from the bovine host and kinetes from the tick vector. Cell-surface kinete-stage-specific proteins were identified using 2D difference in gel electrophoresis and analyzed by mass spectrometry. Ten proteins were identified as kinete-stage-specific, with orthologs found in closely related Apicomplexan pathogens. Transcriptional analysis revealed two genes were highly expressed by kinetes as compared with blood stages. Immunofluorescence using antibodies against the two proteins confirmed kinete-stage-specific expression. The identified cell-surface kinete proteins are potential candidates for the development of a B. bovis transmission blocking vaccine.

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

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

A novel candidate vaccine for cytauxzoonosis inferred from comparative apicomplexan genomics

Cytauxzoonosis is an emerging infectious disease of domestic cats (Felis catus) caused by the apicomplexan protozoan parasite Cytauxzoon felis. The growing epidemic, with its high morbidity and mortality points to the need for a protective vaccine against cytauxzoonosis. Unfortunately, the causative agent has yet to be cultured continuously in vitro, rendering traditional vaccine development approaches beyond reach. Here we report the use of comparative genomics to computationally and experimentally interpret the C. felis genome to identify a novel candidate vaccine antigen for cytauxzoonosis. As a starting point we sequenced, assembled, and annotated the C. felis genome and the proteins it encodes. Whole genome alignment revealed considerable conserved synteny with other apicomplexans. In particular, alignments with the bovine parasite Theileria parva revealed that a C. felis gene, cf76, is syntenic to p67 (the leading vaccine candidate for bovine theileriosis), despite a lack of significant sequence similarity. Recombinant subdomains of cf76 were challenged with survivor-cat antiserum and found to be highly seroreactive. Comparison of eleven geographically diverse samples from the south-central and southeastern USA demonstrated 91-100% amino acid sequence identity across cf76, including a high level of conservation in an immunogenic 226 amino acid (24 kDa) carboxyl terminal domain. Using in situ hybridization, transcription of cf76 was documented in the schizogenous stage of parasite replication, the life stage that is believed to be the most important for development of a protective immune response. Collectively, these data point to identification of the first potential vaccine candidate antigen for cytauxzoonosis. Further, our bioinformatic approach emphasizes the use of comparative genomics as an accelerated path to developing vaccines against experimentally intractable pathogens.

Comparative genomic analysis and phylogenetic position of Theileria equi

Background

Transmission of arthropod-borne apicomplexan parasites that cause disease and result in death or persistent infection represents a major challenge to global human and animal health. First described in 1901 as Piroplasma equi, this re-emergent apicomplexan parasite was renamed Babesia equi and subsequently Theileria equi, reflecting an uncertain taxonomy. Understanding mechanisms by which apicomplexan parasites evade immune or chemotherapeutic elimination is required for development of effective vaccines or chemotherapeutics. The continued risk of transmission of T. equi from clinically silent, persistently infected equids impedes the goal of returning the U. S. to non-endemic status. Therefore comparative genomic analysis of T. equi was undertaken to: 1) identify genes contributing to immune evasion and persistence in equid hosts, 2) identify genes involved in PBMC infection biology and 3) define the phylogenetic position of T. equi relative to sequenced apicomplexan parasites.

Results

The known immunodominant proteins, EMA1, 2 and 3 were discovered to belong to a ten member gene family with a mean amino acid identity, in pairwise comparisons, of 39%. Importantly, the amino acid diversity of EMAs is distributed throughout the length of the proteins. Eight of the EMA genes were simultaneously transcribed. As the agents that cause bovine theileriosis infect and transform host cell PBMCs, we confirmed that T. equi infects equine PBMCs, however, there is no evidence of host cell transformation. Indeed, a number of genes identified as potential manipulators of the host cell phenotype are absent from the T. equi genome. Comparative genomic analysis of T. equi revealed the phylogenetic positioning relative to seven apicomplexan parasites using deduced amino acid sequences from 150 genes placed it as a sister taxon to Theileria spp.

Conclusions

The EMA family does not fit the paradigm for classical antigenic variation, and we propose a novel model describing the role of the EMA family in persistence. T. equi has lost the putative genes for host cell transformation, or the genes were acquired by T. parva and T. annulata after divergence from T. equi. Our analysis identified 50 genes that will be useful for definitive phylogenetic classification of T. equi and closely related organisms.

Tick-borne diseases in cattle: applications of proteomics to develop new generation vaccines

Tick-borne diseases (TBDs) affect 80% of the world's cattle population, hampering livestock production throughout the world. Livestock industry is important to rural populations not only as food supply, but also as a source of income. Tick control is usually achieved by using acaricides which are expensive, deleterious to the environment and can induce chemical resistance of vectors; the development of more effective and sustainable control methods is therefore required. Theileriosis, babesiosis, anaplasmosis and heartwater are the most important TBDs in cattle. Immunization strategies are currently available but with variable efficacy. To develop a new generation of vaccines which are more efficient, cheaper and safer, it is first necessary to better understand the mechanisms by which these parasites are transmitted, multiply and cause disease; this becomes especially difficult due to their complex life cycles, in vitro culture conditions and the lack of genetic tools to manipulate them. Proteomics and other complementary post-genomic tools such as transcriptomics and metabolomics in a systems biology context are becoming key tools to increase knowledge on the biology of infectious diseases. Herein, we present an overview of the so called "Omics" studies currently available on these tick-borne pathogens, giving emphasis to proteomics and how it may help to discover new vaccine candidates to control TBDs.