Expression analysis of heat shock protein 20 and rhoptry-associated protein 1a in sexual stages and kinetes of Babesia bigemina

Spherical Body Protein 4 from Babesia bigemina: A Novel Gene That Contains Conserved B-Cell Epitopes and Induces Cross-Reactive Neutralizing Antibodies in Babesia ovata

Bovine babesiosis is a tick-transmitted disease caused by intraerythrocytic protozoan parasites of the genus Babesia. Its main causative agents in the Americas are Babesia bigemina and Babesia bovis, while Babesia ovata affects cattle in Asia. All Babesia species secrete proteins stored in organelles of the apical complex, which are involved in all steps of the invasion process of vertebrate host cells. Unlike other apicomplexans, which have dense granules, babesia parasites instead have large, round intracellular organelles called spherical bodies. Evidence suggests that proteins from these organelles are released during the process of invading red blood cells, where spherical body proteins (SBPs) play an important role in cytoskeleton reorganization. In this study, we characterized the gene that encodes SBP4 in B. bigemina. This gene is transcribed and expressed in the erythrocytic stages of B. bigemina. The sbp4 gene consists of 834 nucleotides without introns that encode a protein of 277 amino acids. In silico analysis predicted a signal peptide that is cleaved at residue 20, producing a 28.88-kDa protein. The presence of a signal peptide and the absence of transmembrane domains suggest that this protein is secreted. Importantly, when cattle were immunized with recombinant B. bigemina SBP4, antibodies identified B. bigemina and B. ovata merozoites according to confocal microscopy observations and were able to neutralize parasite multiplication in vitro for both species. Four peptides with predicted B-cell epitopes were identified to be conserved in 17 different isolates from six countries. Compared with the pre-immunization sera, antibodies against these conserved peptides reduced parasite invasion in vitro by 57%, 44%, 42%, and 38% for peptides 1, 2, 3, and 4, respectively (p < 0.05). Moreover, sera from cattle infected with B. bigemina cattle contained antibodies that recognized the individual peptides. All these results support the concept of spb4 as a new gene in B. bigemina that should be considered a candidate for a vaccine to control bovine babesiosis.

Borrelia burgdorferi infection modifies protein content in saliva of Ixodes scapularis nymphs

BACKGROUND

Lyme disease (LD) caused by Borrelia burgdorferi is the most prevalent tick-borne disease. There is evidence that vaccines based on tick proteins that promote tick transmission of B. burgdorferi could prevent LD. As Ixodes scapularis nymph tick bites are responsible for most LD cases, this study sought to identify nymph tick saliva proteins associated with B. burgdorferi transmission using LC-MS/MS. Tick saliva was collected using a non-invasive method of stimulating ticks (uninfected and infected: unfed, and every 12 h during feeding through 72 h, and fully-fed) to salivate into 2% pilocarpine-PBS for protein identification using LC-MS/MS.

RESULTS

We identified a combined 747 tick saliva proteins of uninfected and B. burgdorferi infected ticks that were classified into 25 functional categories: housekeeping-like (48%), unknown function (18%), protease inhibitors (9%), immune-related (6%), proteases (8%), extracellular matrix (7%), and small categories that account for <5% each. Notably, B. burgdorferi infected ticks secreted high number of saliva proteins (n=645) than uninfected ticks (n=376). Counter-intuitively, antimicrobial peptides, which function to block bacterial infection at tick feeding site were suppressed 23-85 folds in B. burgdorferi infected ticks. Similar to glycolysis enzymes being enhanced in mammalian cells exposed to B. burgdorferi : eight of the 10-glycolysis pathway enzymes were secreted at high abundance by B. burgdorferi infected ticks. Of significance, rabbits exposed to B. burgdorferi infected ticks acquired potent immunity that caused 40-60% mortality of B. burgdorferi infected ticks during the second infestation compared to 15-28% for the uninfected. This might be explained by ELISA data that show that high expression levels of immunogenic proteins in B. burgdorferi infected ticks.

CONCLUSION

Data here suggest that B. burgdorferi infection modified protein content in tick saliva to promote its survival at the tick feeding site. For instance, enzymes; copper/zinc superoxide dismutase that led to production of H2O2 that is toxic to B. burgdorferi were suppressed, while, catalase and thioredoxin that neutralize H2O2, and pyruvate kinase which yields pyruvate that protects Bb from H2O2 killing were enhanced. We conclude data here is an important resource for discovery of effective antigens for a vaccine to prevent LD.

Stimulation and quantification of Babesia divergens gametocytogenesis

BACKGROUND

Babesia divergens is the most common blood parasite in Europe causing babesiosis, a tick-borne malaria-like disease. Despite an increasing focus on B. divergens, especially regarding veterinary and human medicine, the sexual development of Babesia is poorly understood. Development of Babesia sexual stages in the host blood (gametocytes) plays a decisive role in parasite acquisition by the tick vector. However, the exact mechanism of gametocytogenesis is still unexplained.

METHODS

Babesia divergens gametocytes are characterized by expression of bdccp1, bdccp2 and bdccp3 genes. Using previously described sequences of bdccp1, bdccp2 and bdccp3, we have established a quantitative real-time PCR (qRT-PCR) assay for detection and assessment of the efficiency of B. divergens gametocytes production in bovine blood. We analysed fluctuations in expression of bdccp genes during cultivation in vitro, as well as in cultures treated with different drugs and stimuli.

RESULTS

We demonstrated that all B. divergens clonal lines tested, originally derived from naturally infected cows, exhibited sexual stages. Furthermore, sexual commitment was stimulated during continuous growth of the cultures, by addition of specific stress-inducing drugs or by alternating cultivation conditions. Expression of bdccp genes was greatly reduced or even lost after long-term cultivation, suggesting possible problems in the artificial infections of ticks in feeding assays in vitro.

CONCLUSIONS

Our research provides insight into sexual development of B. divergens and may facilitate the development of transmission models in vitro, enabling a more detailed understanding of Babesia-tick interactions.

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.

Validation of BdCCp2 as a marker for Babesia divergens sexual stages in ticks

Babesiosis is a tick-transmitted disease of mammalian hosts, caused by the intraerythrocytic protozoan parasites of the genus Babesia. Transmission of Babesia parasites from the vertebrate host to the tick is mediated by sexual stages, the gametocytes which are the only intraerythrocytic stages that survive and develop inside the vector. Very few data are available concerning these parasite stages and some markers are needed in order to refine our knowledge of Babesia life cycle inside the tick and to permit the monitoring of parasite transmission from vertebrate to vector. We previously identified some potential markers of the Babesia divergens gametocytes using an in silico post-genomic approach based on sequence identity between the available genomes of Plasmodium and Babesia spp. Here, one of the identified proteins, BdCCp2, was validated as a marker of sexual stages of B. divergens, in infected ticks challenged with antisera directed against recombinant BdCCp2 protein. The BdCCp2 protein was detected by Western blot in some infected ticks, as a discrete band of approximately 171 kDa, while no signal was detected in the laboratory-reared non-infected tick. BdCCp2 was also detected, by immunohistochemical analyses, in piriform or ovoid bodies, measuring 2.5-4.5 μm in diameter, in the gut of partially engorged ticks that were experimentally infected. This molecular marker can then be used in the future to characterize and analyze the biology of B. divergens gametocytes.

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.