Recent Advances in Molecular Genetic Tools for Babesia

Establishment of a stable transfection and gene targeting system in Babesia divergens

Babesia divergens is an emerging tick-borne pathogen considered as the principal causative agent of bovine babesiosis in Europe with a notable zoonotic risk to human health. Despite its increasing impact, considerable gaps persist in our understanding of the molecular interactions between this parasite and its hosts. In this study, we address the current limitation of functional genomic tools in B. divergens and introduce a stable transfection system specific to this parasite. We define the parameters for a drug selection system hdhfr-WR99210 and evaluate different transfection protocols for highly efficient generation of transgenic parasites expressing GFP. We proved that plasmid delivery into bovine erythrocytes prior to their infection is the most optimal transfection approach for B. divergens, providing novel evidence of Babesia parasites' ability to spontaneously uptake external DNA from erythrocytes cytoplasm. Furthermore, we validated the bidirectional and symmetrical activity of ef-tgtp promoter, enabling simultaneous expression of external genes. Lastly, we generated a B. divergens knockout line by targeting a 6-cys-e gene locus. The observed dispensability of this gene in intraerythrocytic parasite development makes it a suitable recipient locus for further transgenic application. The platform for genetic manipulations presented herein serves as the initial step towards developing advanced functional genomic tools enabling the discovery of B. divergens molecules involved in host-vector-pathogen interactions.

A conserved protein of Babesia microti elicits partial protection against Babesia and Plasmodium infection

BACKGROUND

The protozoan parasite Babesia microti that causes the zoonotic disease babesiosis resides in the erythrocytes of its mammalian host during its life-cycle. No effective vaccines are currently available to prevent Babesia microti infections.

METHODS

We previously identified a highly seroactive antigen, named Bm8, as a B. microti conserved erythrocyte membrane-associated antigen, by high-throughput protein chip screening. Bioinformatic and phylogenetic analysis showed that this membrane-associated protein is conserved among apicomplexan hemoprotozoa, such as members of genera Babesia, Plasmodium and Theileria. We obtained the recombinant protein Bm8 (rBm8) by prokaryotic expression and purification.

RESULTS

Immunofluorescence assays confirmed that Bm8 and its Plasmodium homolog were principally localized in the cytoplasm of the parasite. rBm8 protein was specifically recognized by the sera of mice infected with B. microti or P. berghei. Also, mice immunized with Bm8 polypeptide had a decreased parasite burden after B. microti or P. berghei infection.

CONCLUSIONS

Passive immunization with Bm8 antisera could protect mice against B. microti or P. berghei infection to a certain extent. These results lead us to hypothesize that the B. microti conserved erythrocyte membrane-associated protein Bm8 could serve as a novel broad-spectrum parasite vaccine candidate since it elicits a protective immune response against Babesiosis and Plasmodium infection.

Degrade to survive: the intricate world of piroplasmid proteases

Piroplasmids of the genera Babesia, Theileria, and Cytauxzoon are tick-transmitted parasites with a high impact on animals and humans. They have complex life cycles in their definitive arthropod and intermediate vertebrate hosts involving numerous processes, including invasion of, and egress from, host cells, parasite growth, transformation, and migration. Like other parasitic protozoa, piroplasmids are equipped with different types of protease to fulfill many of such essential processes. Blockade of some key proteases, using inhibitors or antibodies, hinders piroplasmid growth, highlighting their potential usefulness in drug therapies and vaccine development. A better understanding of the functional significance of these enzymes will contribute to the development of improved control measures for the devastating animal and human diseases caused by these pathogens.

A Transfected Babesia bovis Parasite Line Expressing eGFP Is Able to Complete the Full Life Cycle of the Parasite in Mammalian and Tick Hosts

Bovine babesiosis is caused by apicomplexan pathogens of the genus Babesia, including B. bovis. This protozoan parasite has a complex life cycle involving dynamic changes to its transcriptome during the transition between the invertebrate and vertebrate hosts. Studying the role of genes upregulated by tick stage parasites has been hindered by the lack of appropriate tools to study parasite gene products in the invertebrate host. Herein, we present tfBbo5480, a transfected B. bovis cell line, constitutively expressing enhanced green fluorescent protein (eGFP) created by a whole gene replacement transfection strategy, that was capable of completing the parasite’s entire life cycle in both the vertebrate and invertebrate hosts. tfBbo5480 was demonstrated to respond to in vitro sexual stage induction and upon acquisition by the female tick vector, Rhipicephalus microplus, the tick specific kinete stage of tfBbo5480 was detected in tick hemolymph. Larvae from tfBbo5480 exposed R. microplus female ticks successfully transmitted the transfected parasite to a naïve calf. The development of the whole gene replacement strategy will permit a deeper understanding of the biology of parasite-host-vector triad interactions and facilitate the evaluation of upregulated genes during the parasite’s journey through the tick vector leading to new intervention strategies for the control of bovine babesiosis.