Molecular characterization of Theileria equi in horses from the state of Rio de Janeiro, Brazil.

Theileria equi is one of the etiologic agents of the equine piroplasmosis. This infectious disease is transmitted by ticks and is a worldwide problem in the international horse movement. The 18S rRNA gene of T. equi is often used for genotyping and phylogenetic purpose. This study aimed to analyze the degree of the heterogeneity of the 18S rRNA gene of T. equi in horses from the state of Rio de Janeiro, Brazil. The complete T. equi 18S rRNA sequences were obtained from twenty naturally infected horses. The PCR amplicons were cloned and sequenced. The phylogenetic analyses were performed using a set of T. equi 18S rRNA sequences and other related organisms available in ARB-Silva database. There were twelve distinct T. equi 18S rRNA gene sequences circulating in horses in the state of Rio de Janeiro, Brazil. Monophyletic clades with 2% evolutionary divergence between clades and high bootstrap value were the support to divide T. equi sequences in three distinct clades. The sequences from this study grouped into clades I (70%, n=14/20) and II (30%, n=6/20). All of the T. equi sequences grouped within a node other than the theileriids. This study reported a clear division of two distinct genotypes of T. equi 18S rRNA sequences in state of Rio de Janeiro, Brazil, and it demonstrates that distinct isolates of T. equi can coexist in the same geographic region.