Abstract

Bovine babesiosis caused by Babesia bovis is a tick-borne hemoparasitic disease of global impact, and improved control is needed. In B. bovis, spherical body protein 2 (SBP-2) truncated copies 7, 9 and 11 (sbp2t7, sbp2t9 and sbp2t11) gene transcripts were recently reported to be significantly upregulated in two geographically distinct attenuated B. bovis strains. In the present work, additional virulent and attenuated B. bovis strain pairs were compared in order to corroborate this finding. Sequences of the sbp2t7, sbp2t9 and sbp2t11 genes were not fully conserved among geographically distinct B. bovis strains, and varied between 70.6–93.3% sequence identity in all three genes. Comparisons among transcript levels of the three sbp2t genes of distinct virulent-attenuated B. bovis strain pairs confirmed that upregulation of the sbp2t11 gene was exclusively associated with an attenuated phenotype in the studied strain pairs. This rejects sbp2t7 and sbp2t9 as reliable attenuation markers. In addition, SBP2t11 protein was found to be significantly overexpressed in Texas attenuated B. bovis in comparison to the Texas virulent strain. Finally, sbp2t11 was differentially expressed in blood stages of the parasite but undetectable in Texas strain kinetes. Sbp2t11 is a strong candidate as a reliable attenuation marker for B. bovis, based on its consistent pattern of upregulation in four distinct attenuated strains when compared to their virulent parental strains. Sbp2t11 may only have functional roles associated with erythrocyte infection. Identification of attenuation markers will lead to future research focused on the production of novel and safer subunit and genetically defined vaccines against B. bovis.

Highlights

  • Bovine babesiosis caused by Babesia bovis is a tick-borne hemoparasitic disease of global impact, and improved control is needed

  • Sbp2t9 was significantly upregulated in Tvir strain but was not different in transcript levels in Expression of the SBP2t11 protein We previously reported protein expression of SBP2t11 in the Tx B. bovis strain by conducting western blot analysis using an affinity-purified polyclonal anti-SBP2t11 antibody where we demonstrated both the expression of SBP2t11 and its cleavage from the 30 kDa full-length protein to a predominant C-terminal 17 kDa protein, determined by the recognition of a PEXEL-like motif (PLM) [13]

  • In this study, we hypothesized that sbp2 truncated gene members 7, 9 and 11 were attenuation markers for B. bovis

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Summary

Introduction

Bovine babesiosis caused by Babesia bovis is a tick-borne hemoparasitic disease of global impact, and improved control is needed. The only effective strategy to alleviate economic losses and acute clinical pathologies is the use of live, attenuated vaccines These live vaccines are produced from virulent parasites that undergo a series of quick passages in splenectomized calves [2]. Members of a Babesia-specific gene family, spherical body proteins (SBPs), were shown to be transcriptionally upregulated exclusively in the attenuated derivatives. Why these transcripts were upregulated in attenuated B. bovis remains unknown, but it is reasonable to hypothesize they may directly or indirectly be involved in the attenuation of virulence

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