Blastocystis spp. Subtype Distribution from Human and Animals at the Thai-Myanmar Border: The Public Health Implication

• Published in: International journal of infectious diseases 2022-03, Vol.116, p.S80-S80
• Main Authors: Pawestri, A.R., Padungsombat, J., Deesitthivech, O., Nakayama, E., Shioda, T., Moonsom, S.
• Format: Article
• Language: English
• ISSN: 1201-9712; 1878-3511
• DOI: 10.1016/j.ijid.2021.12.190

Blastocystis spp. is a cosmopolitan intestinal protozoa, infecting 30 - 60% population in the developing countries worldwide. Although often asymptomatic, chronic Blastocystis spp. infection is associated with irritable bowel syndrome. The parasite displays 17 genetically diverse subtypes (STs), exhibiting a wide host-range including human, ungulates, avian, and non-human primates. In areas where human and animal live closely together, this potentially results in zoonotic infection by Blastocystis spp. This study aims to identify Blastocystis spp. subtype distribution in human and domestic animals in an endemic area for intestinal parasitic infections at the Thai-Myanmar border. Human and animal stool samples collected from six subdistricts of Tak province, Thailand, were microscopically screened for the presence of Blastocystis spp. The Blastocystis-positive samples were subjected to 18s small-subunit rRNA-based PCR amplification of the Blastocystis spp. and chain-termination sequencing. Neighbour-joining analysis was performed on the sequences for evolutional study and phylogenetic tree construction using previously published strains as reference. Forty-four samples were positive by microscopy for Blastocystis spp. and 27 samples were successfully cultured. Eight isolates from human and three from domestic animals (goats and buffalo) were PCR amplified. Multiple alignment of the DNA sequences with the subtype reference sequences and phylogenetic analysis of the 18s small-subunit rRNAs revealed ST3, a human specific subtype, as the most prevalent (6/11). Other subtypes were ST1 (1/11), ST2 (1/11), and ST13 (1/11). Two samples yielded dubious results, although one sequence from buffalo sample showed high similarity to ST15, previously reported in camels and gibbons. Two sequences of the human samples identified as ST1 (specific in human and ungulates) and ST2 (specific to human and avian) showed close resemblance to those of pigs and ducks, indicating possible zoonotic transmission risks. We provided information on the Blastocystis spp. subtypes circulating in an endemic area at the Thai-Myanmar border. The high sequence identity of Blastocystis isolates between human and domestic animal samples warrants the possible zoonotic transmission of this parasite. Our results suggest the proper policy implementation regarding water-supply and animal waste-management to prevent the parasite transmission to human.