The epidemiology of schistosome dermatitis (“Koganbyo”) in Japan

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Abstract
A “paddy itch” in the valley area adjacent to Lake Shinji, Shimane Prefecture, Japan, was discovered to be a schistosome dermatitis, the first reported in Japan. The disease is known locally as “koganbyo” or “lakeside disease,” and is of public health concern. The aetiological agent is the cercaria of a bird schistosome, Gigantobilharzia sturniae n. sp. by Tanabe. The intermediate snail host is Polypylis hemisphaerula Benson, and the definitive hosts include the large starling, Spodiopsar cineraceus (Temminck); the sparrow, Passer montanus saturatus Stejneger; and the wagtail, Motacilla (motacilla) grandis Sharpe. The snail intermediate host occurs in irrigation ditches and rice paddies, commonly in seepage water between ridges prepared for winter crops. The environment of the snails in the paddies is drastically changed in the preparation of the soil for rice; many snails are buried in the mud, but escape during cultivation. “Koganbyo” is moderate until the middle of July, by which time the preparation of the paddies, the transplanting and cultivation have been completed. During the time of the first weeding from mid-July to mid-August the disease reaches the peak of severity. The incidence of infection in the snail was 5·5 per cent. in June, 1949, and 5 per cent. in June, 1950. During July, 1949, the incidence was only 1·4 per cent., yet the peak of “koganbyo” begins in July and extends into August. Intermediate and definitive hosts are widespread in Japan. Infected birds and snails have been found in areas other than Shimane Prefecture. The term “koganbyo” is proposed as the general term to be applied to schistosome dermatitis in Japan.

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