[1] Otaru Ekisaikai Hosp, Dept Med Gastroenterol, 1-4-1 Inaho, Otaru, Hokkaido 0470032, Japan
[2] Sapporo Kosei Gen Hosp, Dept Diagnost Pathol, N3W8-5 Chuo Ku, Sapporo, Hokkaido 0600033, Japan
[3] Nippon Med Sch, Dept Internal Med, Div Gastroenterol, Bunkyo Ku, 1-1-5 Sendagi, Tokyo 1138603, Japan
[4] Natl Inst Infect Dis, Dept Parasitol, Shinjuku Ku, 1-23-1 Toyama, Tokyo 1628640, Japan
[5] Hokkaido Univ, Grad Sch Environm Earth Sci, N10W5 Kita Ku, Sapporo, Hokkaido 0600810, Japan
[6] Obihiro Univ Agr & Vet Med, Natl Res Ctr Protozoan Dis, Nishi 2-13 Inada Cho, Obihiro, Hokkaido 0808555, Japan