A Newly Discovered Habitat of Oncomelania Snails in the Obitsu River Basin of the Central Boso Peninsula, Japan
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[Jpn. J. Parasitol., Vol. 34, No. 5, 419-421, October, 1985] Research Note A Newly Discovered Habitat of Oncomelania Snails in the Obitsu River Basin of the Central Boso Peninsula, Japan Somei KOJIMA, Munetoshi NIIMURA, Masashi KOBAYASHI, Hidekazu HATA, Tamotsu KANAZAWA, Yasuhide ORIDO and Ken TOKITA (Received for publication ; June 25, 1985) Key words : schistosomiasis japonica, Oncomelania snails, new habitat The Tone River basin of Chiba, Ibaragi one after the other. All of the patients were and Saitama Prefectures has been known as found to be living or to have been living at one of the former endemic areas of schistosom least for some years in Kisarazu district. It iasis in Japan (Yokogawa, 1970). As far was disclosed by an interview with four patients as Chiba Prefecture is concerned, reports on at the Kimitsu Central Hospital that they the occurrence of patients or detection of had worked in rice fields along both sides of Oncomelania hupensis nosophora snails have the Obitsu River, the source of irrigation been limited in areas of the Tone River basin water. such as Abiko, Kashiwa, Sakura and Shimo- The Obitsu River issues from mountainous fusa. areas of the Central Boso Peninsula and it It was in 1970 that an outbreak of schisto irrigates areas of about 200 km2 of the north somiasis japonica was found among dairy ern part of Kimitsu district and Kisarazu cattle pastured on riverbeds of the Tone River City. It should be noted that the River has running along Narita City and its neigh no relation with the Tone River (Fig. 1). bouring towns (Nakano, 1970 ; Yokogawa et This communication is to describe the fact al., 1971). Human infections were also demon that we have found a new habitat of Onco strated in those areas by mass-examinations melania snails in rice fields and irrigation carried out with immunological methods as ditches in the west side of the Obitsu River well as parasitological ones (Yokogawa et al., at Ushibukuro and Takayanagi areas (Figs. 1973). There was no report on the occur 2 and 3). The snails were quite similar in rence of the disease in any place of Chiba size and shape to those obtained from Yama- Prefecture other than the areas mentioned nashi Prefecture (Fig. 4). More than 2,519 above. snails were found along one of the ditches Quite recently, however, information on with 30 cm in width within a distance of 525 detection of schistosome eggs from autopsy cm from the edge. Among 3,685 snails col or biopsy materials was brought to one of lected on 7 th and 13 th June 1985 in total, the authors (S.K.) from the National Chiba 1,055 were crushed and examined for the Hospital (Drs. H. Takazawa and H. Musha) presence of cercariae of Schistosoma japon- and from the Kimitsu Central Hospital (Drs. icum. However, none of them were found to H. Koen and H. Mori) independently but be infected. It is necessary to know as to whether new Department of Parasitology, Chiba University, cases of schistosomiasis exist in these areas, School of Medicine, Chiba 280, Japan. and whether reservoir animals are found with (105) 420 ROOT 16 Fig. 1 Map of Chiba Prefecture showing no relation between the Tone River and the Obitsu River. A : The Obitsu River, B : The Yoro River, C : Fig. 2 Sites where Oncomelania snails were The Tone River. 1 : Kisarazu City, 2 : Ichihara found (HHO and not found (!*.V.l) in the west City, 3 : Chiba City, 4 : Choshi City, 5 : Shimo- side of the Obitsu River. fusa-machi, 6 : Narita City, 7 : Abiko-machi, 8 : ~X 1 : Iwane Junior High School, ~X. 2 : Takaya Kashiwa City. nagi Primary School, a: Obitsu-gawa Bridge, b : Nakasato-ohashi Bridge. infenction of S. japonicum. It is also impor tant to know a precise distribution of the snails for prevention of the disease. Epidemiologi- cal surveys are now under way from these points of view in collaboration with the gov ernment office of Chiba Prefecture. Clinical or pathological reports on patients mentioned above will be made separately from the res pective hospitals. Thus, this is the first report on a new habitat of Oncomelania snails dis covered in areas other than the previously M »4 known endemic areas of shistosomiasis in Japan. The authors wish to thank Drs. H. Takazawa and H. Musha of the National Chiba Hospital, Fig. 3 Rice fields and irrigation ditches in front Drs. Y. Kanda, H. Mori and H. Koen of the of Takayanagi Primary School. Kimitsu Central Hospital, for their kind demon Fig. 4 Comparison of Oncomelania snails found stration of their cases, and Professor Emeritus M. in the Obitsu River basin with those obtained from Yamanashi Prefecture. Yokogawa for his valuable advice. Supported by Left: Snails collected in Yamanashi Prefecture. grants from the Ministry of Health and Welfare Right: Snails collected in the Obitsu River basin. and from the US-Japan Cooperative Medical Sci- (106) 421 ences Program. 3) Yokogawa, M., Sano, M., Kojima, S., Araki, K., Ogawa, K., Yamada, T., Shimotokube, References A., Iijima, T., Higuchi, K. and Hayasaka, S. (1971) : An outbreak of Schistosoma infec 1) Nakano, M. (1970) : An occurrence of schist - tion among dairy-cows in the Tone River osomiasis-like disease in cows. A peculiar basin in Chiba Prefecture (I). Jpn. J. Para- disease of the rectal wall of cows pastured in sitol., 20, 507-511. (in Japanese). a river bed. Kachiku Shinryo, 86, 23-29. (in 4) Yokogawa, M., Sano, M., Kojima, S., Araki, Japanese). K., Tokita, K., Nagai, K., Maruyama, M. 2) Yokogawa, M. (1970): Schistosomiasis in and Aizawa, T. (1973) : Epidemiological sur Japan. In Recent Advances in Researches on vey for schistosomiasis among the inhabitants Filariasis and Schistosomiasis in Japan, ed. in Tone River basin, Chiba Prefecture and by Manabu Sasa, University of Tokyo Press, snail control by burning. Jpn. J. ParasitoL, Tokyo, 231-255. 22, 116-125. (in Japanese). a *- fc - t<D&z&% tc 5, (107).