Diversity of Blastocystis subtypes in horses in Colombia and identification of two new subtypes

Authors: BAEK, SOHYEONG - US Department Of Agriculture (USDA); Maloney, Jenny; Molokin, Aleksey; George, Nadja; CORTES VECINO, JESÚS - National University Of Colombia; Santin-Duran, Monica

Submitted to: Microorganisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/17/2022
Publication Date: 8/24/2022
Citation: Baek, S., Maloney, J.G., Molokin, A., George, N.S., Cortes Vecino, J.A., Santin, M. 2022. Diversity of Blastocystis subtypes in horses in Colombia and identification of two new subtypes. Microorganisms. 10:1693. https://doi.org/10.3390/microorganisms10091693.
DOI: https://doi.org/10.3390/microorganisms10091693

Interpretive Summary: Blastocystis is one of the most common intestinal parasites of humans. It is also common in many other mammalian and avian species making zoonotic transmission a concern. Data on the prevalence and subtypes of Blastocystis in horses is limited. Therefore, we have conducted the most comprehensive study of Blastocystis in horses ever performed through PCR and sequencing of fecal samples from 185 horses from four regions of Colombia. Blastocystis was observed to be quite common in horses in this study with 43.8% of horses being positive overall, and positive horses were observed in all sampled regions. Horses were also host to a wide variety of Blastocystis subtypes. There were 10 previously described subtypes (ST1, ST3-ST6, ST10, ST14, ST25, ST26) observed among horses, and two new subtypes, named ST33 and ST34, were described for the first time. Horse samples frequently contained mixed subtype infections which were present in 55.6% of Blastocystis-positives horses. Horses were also frequently infected with potentially zoonotic subtypes and one or more of the potentially zoonotic subtypes ST1, ST3-ST6, ST10, or ST14, were identified in 88.9% of Blastocystis-positive horses. This study demonstrates that horses can be host to a variety of Blastocystis subtypes, including many potentially zoonotic subtypes, indicating that horses may contribute to the transmission of Blastocystis to humans. This information will be useful to other scientists, veterinarians, and public health agencies to better understand transmission, zoonotic potential, and public health importance of Blastocystis.

Technical Abstract: Blastocystis is a common intestinal protist in humans and animals worldwide. Wild and domestic animals are thought to be reservoirs of Blastocystis subtypes which also infect humans. There are limited studies on 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 twelve Blastocystis subtypes, ten known subtypes (ST1, ST3-ST6, ST10, ST14, ST25, ST26) and two novel subtypes (ST33 and ST34). Validity of novel subtypes was confirmed via phylogenetic and pairwise distance analyses of full-length SSU rRNA gene sequences. Mixed subtype infections were common (55.6% of Blastocystis-positives 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 harbour potentially zoonotic subtypes and could contribute to the transmission of Blastocystis to humans.