Phylogenetic analysis of Mexican Babesia bovis isolates using msa and ssrRNA gene sequences.

Variable merozoite surface antigens of Babesia bovis are exposed glycoproteins having a role in erythrocyte invasion. Members of this gene family include msa-1 and msa-2 (msa-2c, msa-2a(1), msa-2a(2), and msa-2b). Small subunit ribosomal (ssr)RNA gene is subject to evolutive pressure and has been used in phylogenetic studies. To determine the phylogenetic relationship among B. bovis Mexican isolates using different genetic markers, PCR amplicons, corresponding to msa-1, msa-2c, msa-2b, and ssrRNA genes, were cloned and plasmids carrying the corresponding inserts were sequenced. Comparative analysis of nucleotide and deduced amino acid sequences revealed distinct degrees of variability and identity among the coding gene sequences obtained from 12 geographically different B. bovis isolates and a reference strain. Overall sequence identities of 47.7%, 72.3%, 87.7%, and 94% were determined for msa-1, msa-2b, msa-2c, and ssrRNA, respectively. A robust phylogenetic tree was obtained with msa-2b sequences. The phylogenetic analysis suggests that Mexican B. bovis isolates group in clades not concordant with the Mexican geography. However, the Mexican isolates group together in an American clade separated from the Australian clade. Sequence heterogeneity in msa-1, msa-2b, and msa-2c coding regions of Mexican B. bovis isolates present in different geographical regions can be a result of either differential evolutive pressure or cattle movement from commercial trade.