Genotyping Giardia intestinalis by Using DNA Extracted from Long-Term Preserved Human Specimens Stained with Chlorazol Black E

Giardia intestinalis is a parasitic protozoan that causes diarrhea and abdominal pain in humans. Studies of the Giardia genotypes are thought to be important for understanding their infection routes and prevalence. However, few have reported pathogen genotyping in human giardiasis cases in Japan. In this study, we genotyped G. intestinalis by using DNA extracted from chlorazol black E-stained fecal smears from patients. The triosephosphate isomerase gene was amplified from 21 (91.3%) of 23 human fecal samples. Twelve (52.2%) of pathogens detected were of the genotype A, and 9 (39.1%) of the genotype B. A restriction fragment length polymorphism analysis showed that all genotype A found in the present study were of the genotype AI, which were presumed to be zoonotic. The source of Giardia infections was unclear in the present study. However, patients' histories of international travel appeared not to be associated with the Giardia genotypes. Thus, most cases were thought to be acquired sporadically and domestically.