Epidemiological survey and classification of genotypes of intestinal parasitic protozoa Blastocystis

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Although, pathogenic potential of an intestinal parasite, Blastocystis hominis, had been proposed on the basis of clinical symptom, the true nature of the parasite infection in humans is still controversial. Since B. hominis is known to be genetically polymorphic, it is generally assumed that the certain genotype of the parasite may contribute to its pathogenic potential. Based on these backgrounds, this project was performed on the survey of human Blastocystis infection and determined genotypes among Blastocystis populations. Since the prevalence of human Blastocystis infection in Japan was lower than other developing Asian countries, this project was performed in Thailand, China and Singapore. Finally, a total 47 isolates were obtained from 2 different epidemiological setting in Thailand. In China, 270 isolates were obtained from 4 different epidemiological setting. In Singapore, only 9 isolates were obtained from a major hospital in Singapore. When 270 isolates in China was screened by PCR with our developed sequenced tagged-site primers, all of the isolates except for an isolate were classified into the known genotypes. Since an isolate was negative with any STS primers, entire sequence of the small subunit rRNA gene was sequence and phylogenetically analyzed with the known genotypes. Interestingly, an human isolates was positioned in an additional new clade with other 2 isolates reported in GenBank.