Paddy field dermatitis was raging among inhabitants in an area nearthe mouth of the Kiso River around 1968. Kumada et al.(1970) attributed the occurrence of the skin disease to the cercariae of an avian species of schistosomiasis parasite whose intermediate host is Austropeplea ollula.
The prevalence of this parasitic disease has subsided for a while, but in recent years it has been ascertained that the number of patients afflicted with the cercariae is on the rise.
In this report, we will try to probe into the actual status of the occurrence of paddy field dermatitis in the area in recent years.
A questionnaire survey was conducted on a total of 876 households in 24 sections of the infected area during the three-year period from 1976 to 1978. Questionnaires were recovered from 785 households (89.6%) and 3, 786 persons, who are engaged in farm work. Effective replies were obtained from 570 households (65.1%).
The results of our survey revealed that the number of persons suffered from paddy field dermatitis during the period was 157 (disease rate: 4.15%), of which surprisingly as high as 72.6 percent had not visited hospitals and clinics.
By age, nine 'persons (1.9%) among the respondents in their 20's said they have contracted the skin disease, while among those in their 40's as many as 59 persons (4.8%) said they have been attacked by the parasite.
A significant difference in the infection rate was found between male (4.86%) and female (3.38%).
Our survey also found that the skin disease more often than not breaks out between the middle of April and the last third of June, particularly between the last third of May and the middle of June, when weeding work is conducted.
It was also observed that the symptomes of the dermatitis persist longer as the number of infections increases.
Another significant difference in the infection rate was found between farmers who raise a second crop and those who do not. Fifty-three of the 192 winter crop raisers contracted the disease (27.6%), while 18 out of the 325 farmers who do not raise any winter crop were attacked by the parasite (5.5%).
In the survey, we confirmed that a larger number of intermediate host snails lurk in the paddy fields that are used during winter months than in those fields used only for rice cultivation.
Relationships between second crop raising and the number of Austropeplea ollula between the visit of wild birds carrying the parasite and the incidence of the disease will be reported later, along with the result of surveys of overwintering of the disease-transmitting snails.