Identification of a putative methyltransferase gene of Babesia bigemina as a novel molecular biomarker uniquely expressed in parasite tick stages.

Authors: BOHALIGA, GAMILA - Washington State University; Johnson, Wendell; Taus, Naomi; HUSSEIN, HALA - Washington State University; Ueti, Massaro

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2018
Publication Date: 8/24/2018
Citation: Bohaliga, G.A., Johnson, W.C., Taus, N.S., Hussein, H.E., Ueti, M.W. 2018. Identification of a putative methyltransferase gene of Babesia bigemina as a novel molecular biomarker uniquely expressed in parasite tick stages. Parasites & Vectors. 11(1):480. https://doi.org/10.1186/s13071-018-3052-9.
DOI: https://doi.org/10.1186/s13071-018-3052-9

Interpretive Summary: Bovine babesiosis is a tick transmitted disease that is distributed worldwide. The pathogens Babesia bigemina and B. bovis are the main causative agents of babesiosis which has a negative economic impact on the cattle industry due to the cost of cattle treatment, morbidity and mortality. Cattle infected with B. bigemina develop high fever, anemia and hemoglobinuria. Bovine babesiosis remains without effective methods to study specific parasite stages due to the lack of consistent approaches to induce and rear Babesia stage specific parasites. In malaria, caused by parasites related to Babesia, in vitro approaches have been used to test efficacy of drugs or vaccines to block parasite transmission. In this study we developed a new method of inducing B. bigemina sexual stages in vitro. Using this method, we identified a gene containing a methyltransferase domain that is transcribed exclusively by B. bigemina tick stages. This induction method will allow in vitro evaluation of drugs or vaccines targeting sexual stage genes or proteins and subsequent interference with transmission.

Technical Abstract: Bovine babesiosis is a tick transmitted disease that is distributed worldwide and caused by apicomplexan pathogens of the genus Babesia including B. bigemina, B. bovis and B. divergens. These tick-borne pathogens have a complex life cycle with infection of vertebrate and invertebrate hosts for transmission. In the tick midgut, extracellular Babesia parasites transform into gametes that fuse to form zygotes. Therefore, intervention at the extracellular Babesia tick stages could prevent tick infection and subsequent parasite transmission. In this study, we used bioinformatic analysis to identify B. bigemina homologs of Plasmodium falciparum gamete specific genes. Our in silico analysis identified 11 common genes that share an amino acid sequence identity ranging from 18 to 58%. These proteins contained conserved domains, one of which was a methyltransferase domain. We analyzed transcription of the identified genes using total RNA extracted from B. bigemina infected calf blood, and adult female tick midguts, hemolymph and ovaries. All genes examined were transcribed by B. bigemina blood and tick stages except BBBOND_0204030. This gene contains a methyltransferase domain that has been previously shown to be important in gametogenesis. BBBOND_0204030 was transcribed exclusively by B. bigemina tick stages and transcription was detectable in infected engorged females immediately after ticks dropped off the infected animal. Additionally, we report a new method to induce B. bigemina sexual stages in vitro using Tris 2_carboxyethyl phosphine. This method did not require secondary induction triggers such as temperature reduction or addition of xanthurenic acid. To confirm that this gene is transcribed by early tick stages of B. bigemina, we demonstrated upregulation of BBOND_0204030 by in vitro induced sexual stages using reverse transcription PCR. Our findings improve the understanding of the B. bigemina life cycle at the molecular level, and identify a parasite stage specific gene as a potential target for drug intervention of bovine babesiosis.