Blastocystis subtypes detected in long-tailed macaques in Thailand-Further evidence of cryptic host specificity.

Blastocystis is an enteric parasitic protist with a widespread distribution in a variety of human and non-human hosts and supposedly a source of zoonotic transmission. This study aimed to determine the frequency and distribution of Blastocystis subtypes in free-ranging Macaca fascicularis (long-tailed macaques, LTMs) in Thailand. A total of 628 faecal samples were collected from free-ranging LTMs inhabiting fourteen tourist attraction sites in Thailand. Fresh faecal samples were individually cultured in Jones' medium, and Blastocystis-positive samples were subtyped using nuclear small subunit ribosomal DNA (SSU rDNA) sequencing. Two hundred and sixty-three (41.87%) samples were positive by culture, and 197 and 154 were successfully SSU rDNA-amplified and sequenced, respectively. Three subtypes (ST1, ST2, and ST3) comprising 19 alleles were observed. ST3 was the most common subtype detected (36.55%), followed by ST2 and ST1 (24.37% and 17.26%, respectively). Some subtype alleles not previously observed were identified. A couple of strains appeared similar to those found in humans as evidenced by SSU rDNA allelic profiles, while further evidence of cryptic host specificity emerged. This study provides the first data on Blastocystis subtypes in non-human primates in Thailand and confirms the trend observed in other Old-World countries with regard to the colonization rate and subtype distribution.