Subtype analysis of Blastocystis sp. isolates from human and canine hosts in an urban community in the Philippines.

Blastocystis sp. is a common gut-dwelling protist of both humans and animals. A cross-sectional survey among humans and their dogs was conducted to determine the prevalence of Blastocystis infection and to characterize the subtype (ST) distribution in an urban community in the Philippines. Fecal specimens from 1,271 humans and 145 dogs were collected and inoculated in diphasic culture medium. Prevalence of Blastocystis by culture was 13.0% (95% CI = 11.2-15.0) and 14.5% (95% CI = 9.6-21.2) for humans and dogs, respectively. A total of 168 culture isolates were genotyped using polymerase chain reaction (PCR) with seven pairs of ST-specific sequence-tagged-site (STS) primers. In humans, the ST present in this study were ST1 with 22.6% (95% CI = 17.2-29.0), ST2 with 3.1% (95% CI = 1.3-6.7), ST3 with 41.4% (95% CI= 34.9-48.6), ST4 with 14.8% (95% CI = 10.5-20.6), ST5 with 4.1% (95% CI = 2.0-8.0), and unknown ST with 13.9% (95% CI = 9.6-19.4). In dogs, the ST present in this study were ST1 with 4.3% (95% CI = 0.0-29.0), ST2 with 8.7% (95% CI = 1.3-28.0), ST3 with 17.4% (95% CI = 6.4-37.7), ST4 with 13.0% (95% CI = 3.7-33.0), ST5 with 13.0% (95% CI = 3.7-33.0), and unknown ST with 47.8% (95% CI = 29.2-67.0). This is the first study that reported Blastocystis ST4 in human and canine hosts in the Philippines.