Kinpei YAGI
Hokkaido Institute of Public Health, North-19, West-12, Kita-ku, Sapporo 060, Japan.

Kazuya NAGASAWA
National Research Institute of Far Seas Fisheries, 5-7-1, Orito, Shimizu 424, Japan.

Hiroshi IHIKURA
Department of Pathology, Hokkaido University, School of Medicine, North-15, West-7, Kita-ku, Sapporo 060, Japan.

Akihira NAKAGAWA
Nakagawa Clinic, 4-2-18-20, Atsubetsu-cho, Atsubetu-ku, Sapporo 004, Japan.

Noriyuki SATO
Koichi KIKUCHI
Department of Pathology, Sapporo Medical University, South-1, West-17, Chuo-ku, Sapporo 060, Japan.

Hajime ISHIKURA
Division of Parasitic Diseases, Department of Pathology, Sapporo Medical University, South-1, West-17, Chuo-ku, Sapporo 060, Japan.