A culture-adapted strain of Babesia bovis has reduced subpopulation complexity and is unable to complete its natural life cycle in ticks

Authors: ALZAN, HEBA - Washington State University; BASTOS, REGINALDO - Washington State University; LAUGHERY, JACOB - Washington State University; Scoles, Glen; Ueti, Massaro; Johnson, Wendell; Suarez, Carlos

Submitted to: Frontiers in Cellular and Infection Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/21/2022
Publication Date: 2/10/2022
Citation: Alzan, H.F., Bastos, R.G., Laughery, J.M., Scoles, G.A., Ueti, M.W., Johnson, W.C., Suarez, C.E. 2022. A culture-adapted strain of Babesia bovis has reduced subpopulation complexity and is unable to complete its natural life cycle in ticks. Frontiers in Cellular and Infection Microbiology. 12. Article 827347. https://doi.org/10.3389/fcimb.2022.827347.
DOI: https://doi.org/10.3389/fcimb.2022.827347

Interpretive Summary: Bovine babesiosis caused by Babesia bovis is a costly tick-borne disease widely spread in tropical and semi-tropical countries worldwide. The disease can be controlled by using attenuated live vaccines that can be produced by passage of a virulent strain in splenectomized calves. However, this procedure is cumbersome and costly, and this vaccines may have the risk of transmission. Hereby, we describe phenotypic and genotypic differences among B. bovis parasites maintained in in vitro cultures for more than12 years (LTCP), with its short term cultured parental strain (STCP). The STCP are distinct in morphology and in their speed of growth in in vitro cultures when compared to STCP. In contrast to STCP, the LTCP appear to be attenuated in virulence, have reduced genetic content, lack the ability to transition to sexual forms, and cannot be transmited to recipient calves by transmission competent ticks. It is possible that these differences among the LTCP and the STCP are due to the selection of a culture-adapted subpopulation from the original strain, the result of epigenetic changes, or a combination of events. LTCP are candidate components of non-transmissible vaccines against B. bovis.

Technical Abstract: Babesia bovis field strains are composed of several distinct geno-phenotypically subpopulations. This feature, together with possible epigenetic modifications, may facilitate adaptation to changes in environmental conditions. In this study we compare geno-phenotypical features among long-term (more than 12 years) (LTCP) and short-term cultured B. bovis parasites (STCP) derived from the B. bovis T3Bo strain. LTCPs intraerythrocytic forms are smaller in size than STCPs, and have faster in vitro growth rate. In contrast to its parental strain, the LTCP lack expression of the sexual stage specific 6cysA and 6cysB proteins, are unable to develop sexual forms upon in vitro sexual stage induction. Consistently, in contrast to its parental strain LTCPs are not transmissible by competent R. microplus ticks in in vivo B. bovis transmission feeding experiments performed in cattle, and have reduced virulence. Similar with previous comparisons among attenuated and virulent B. bovis strains, the LTCP line has decreased genomic diversity compared to the STCP line. Thus, LTCP may contribute to our understanding of the adaptive mechanisms used by the parasites in response to environmental changes, protective immunity, virulence, and transmission by ticks. In addition LTCPs may be consideredas as a candidate non-tick transmissible vaccine against bovine babesiosis.