Diversity of Blastocystis Subtypes in Horses in Colombia and Identification of Two New Subtypes

Abstract

Blastocystis is a common intestinal protist in humans and animals worldwide. Wild and domestic animals are thought to be reservoirs of Blastocystis subtypes that also infect humans. There are limited studies on the prevalence and subtype distribution of Blastocystis in horses. In this study, 185 fecal samples were collected from horses (1 month to 17 years of age) in four regions of Colombia (Sabana de Bogotá, Costa Atlántica, Llanos Orientales, and Bogotá D.C.). Blastocystis presence and subtypes were determined by PCR and next generation amplicon sequencing. Eighty-one (43.8%) horses were positive for Blastocystis, with positive horses in all four regions. Molecular characterization identified 12 Blastocystis subtypes, 10 known subtypes (ST1, ST3-ST6, ST10, ST14, ST25, ST26), and 2 novel subtypes (ST33 and ST34). The validity of the novel subtypes was confirmed via phylogenetic and pairwise distance analyses of the full-length SSU rRNA gene sequences. Mixed subtype infections were common (55.6% of Blastocystis-positive horses). ST10 was the most prevalent subtype, present in 82.8% of Blastocystis-positive horses. Potentially zoonotic subtypes were identified in 88.9% of the Blastocystis-positive horses. This constitutes the most comprehensive study of Blastocystis in horses. Our findings indicate that horses harbor potentially zoonotic subtypes and could contribute to the transmission of Blastocystis to humans.

Keywords: Blastocystis; Colombia; Illumina; MinION; NGS; epidemiology; horses; subtypes.

Figure 1

Phylogenetic relationships among Blastocystis full-length sequences generated in the present study (novel subtypes are new subtypes ST33 and ST34, which are denoted with black- and gray-filled circles, respectively) and representative reference sequences of all accepted subtypes. Proteromonas lacertae was used as outgroup taxon to root the tree. Analysis was conducted by a neighbor-joining method. Genetic distances were calculated using the Kimura two-parameter model. This analysis involved 74 nucleotide sequences, and there were a total of 1953 positions in the final dataset. Bootstrap values lower than 75% are not displayed.