A dermatitis of unknown etiology has occurred among the farmers working in paddyfields in some districts of Tokushima Prefecture, such as Anan, Kainan and Komatsujima.
The dermatitis occurs from March to May when rice-planting and weeding are on and is characterized by erythemato-papulo-vesicular eruptions accompanied with severe itching. The chief symptoms are observed on the parts exposed to water, especially on forearms and lower legs. The results of the epidemiologicaland clinical observations indicated that the dermatitis was due to the invasion of cercariae of an avian schistosome.
The investigation for snail intermediate hosts was carried out in the paddy fields where the dermatitis occurred.
Cercariae of apharyngeal furcocercous type were detected from the fresh water snails (Austropeplea ollula) which were collected most abundantly from the paddy fields during the season of occurence of the dermatitis.
The cercaria wasidentified as species belonging to the genus Trichobilharzia and was regarded as the same species as so far described in Saitama Prefecture by Suzuki et al (1973).
An experimental infection with the cercaria was performed. A few drops of watercontaining cercariae was placed on the fore-arm of. a voluntor. The cercariae invaded into the skin and produced a dermatitis quite similar to that prevailing in the endemic areas.
Therefore, it was concluded that theetiological agent was the cercaria of a species of an avian schistosome.