Brugian Filariasis in Japan

A tiny islet named Hachijo-Koshima was known as the only one focus of brugian filariasis in Japan. It is located about 300 km south to Tokyo in the Pacific Ocean. It had been rather hard to access due to the lack of the regular transportation system. The island was visited for the first time after the last World War II by the medical doctors for the investigation of the nature of a debilitating disease annoying much the inhabitants for long years there. They were Dr. Manabu Sasa, Associate Professor of Medical Zoology, Institute of Infectious Diseases, University of Tokyo and Dr. Rokuro Kano, Senior Assistant in the same department at that time. During their short stay of two days, July 3 to 4, 1948 they took blood thick smear samples from 17 school children and 22 adults at night from 9 to 12 pm. Microfilariae were detected in 3 cases of school children and 4 cases of adults. Thus the disease named as “Baku” by the natives was reconfirmed to be a filariasis. However, at that time the microfilariae were not carefully observed and they were granted to be of Wuchereria bancrofti, as it had been the only one species of filaria known prevailing widely through Japan. Two years later in May, 1950, Sasa and Kano revisited the island accompanied with two new members; Shigeo Hayashi, M.D., a junior assistant and Koji Sato, V.D., a research fellow. During the 3 weeks’ stay in the island they made night blood smear examinations, investigated the clinical manifestations and also carried out selective chemotherapy to the detected microfilaria carriers with diethylcarbamazine citrate (Supatonin ). The mosquito fauna of the island was also carefully investigated. The blood smears were brought back to the laboratory in the institute for a more detailed morphological examination. The microfilariae from the carriers in Hachijo-Koshima were all identified as of Brugia malayi (Brug, 1927). The detail of the survey was reported by Hayashi S, Sasa M, Kano R, and Sato K. (1951) [1]. This was the first record of brugian filariasis in Japan. 2 Identification of microfilaria