An endemic dermatitis of unknown etiology has occurred among farmers working in paddy fields in the eastern area of Saitama Pref. In view of the results of the epidemiological and clinical observations, it was anticipated that the dermatitis might be caused by a bird schistosome (Ozu et al., 1972).
Thus, the research for snail intermediate hosts was carried out in the paddy fields as well as in the laboratory. Snails from the fields were placed in containers in which they could be checked for the shedding of cercariae. As a result, a species of furcocercous cercaria was obtained from Austropeplea (Lymnaea) ollula. The cercaria was identified as species belonging to the genus Trichobilharzia on the basis of the flame cell pattern, the behaviour, the responses to light and the detailed morphology of living and preserved specimens.
In order to determine the dermatitis-producing properties of the cercaria, an experimental infection with the cercaria into the human skin was performed.The cercaria invaded into the human skin and produced a dermatitis quite similar to that prevailing in the endemic area.
On the basis of the results from this study, the paddy field dermatitis occurring in the eastern area of Saitama Pref.was proved to be caused by the invasion of the cercaria belonging to the genus Trichobilharzia into the human skin.It was also proved that A.ollula served as the snail host of the cercaria.

A dermatitis of unknown etiology has occurred among farmers working in Chichibu City, in north-west of Saitama Prefecture from 1970 to 1972.
The dermatitis exhibited clinical, manifestations quite similar to a already known bird schistosome.dermatitis being characterized by erythemato-papulo-vesicular eruptions accompanied with severe itching on the parts exposed to the water, especially legs and arms.
Survey on the snail intermediate hosts were undertaken in the paddy fields and a species of furcocercous cercaria was found from Polypylis hemisphaerula.The incidence of the snails infected with the cercariae was 3.2%.The cercaria resembled to that of Gigantobilharzia struniae in size and shape.
The cercaria invaded into the human skin within 30 minutes after being put on a part of the surface of skin and caused a pinpoint-sized red maculae and tingling itching.
From these results, the paddy field dermatitis occurring in Chichibu City was proved to be caused by the invasion of the cercaria into the human skin, which differed from that served as causative organism of the dermatitis occurring in the eastern area of Saitama Prefecture.

A dermatitis of unknown etiology has occurred among farmers working in paddy fields in the eastern area of Saitama Prefecture (Ozu et al., 1972). And it was proved to be caused by the invasion of a bird schistosome cercaria shed from Austropeplea ollula (Suzuki et al., 1973).
In an attempt to dertermine the final host of this schistosome, a survey on the wild birds was undertaken in the endemic area. But, no natural infection was found in 8 Corvus corone, 7 Sturnus cineraceous, 5 Egretta garzetta, 4 Nycticorax nycticorax, 8Anas platyrhynchos, 7 A. crecca and 170 A. poecilorhyncha.
Experimental infections with the cercariae were performed using domestic ducklings and canaries, and a bird schistosome egg could be found in feces of the domestic ducklings 20 days after the infection. The egg was crescent-shaped and the miracidium was clearly seen within.
Based on the results of the experimental infections, the most probable final host of this schistosome in Saitama Prefecture was supposed to be the anatid birds.