Knowledge of output of Trichobilharzia brevis cercariae from the snail host, Austropeplea ollula is important in the design of control measures of paddy field dermatitis because the level of human infection will be related to the number of freed cercariae which emerged from infected snails and the duration of the cercarial shedding period.
To determine the number of cercariae emerging from a snail following exposure to a single miracidium, each of 33 snails was exposed for a 10-hour period to a miracidium of T. brevis. Thirteen of the exposed snails ultimately shed cercariae, which were counted at least once daily, usually at 10 a.m.
The snails began to release cercariae from 24 to 35 days after exposure at temperatures ranging from 22 to 24°C. The average output per snail per day of snails examined varied from 68. 4 to 312. 3: the greatest daily output of a single snail was 911.
The total output of a single snail varied from 3, 593 to 31, 091: the average for all 13 examined was 14, 159, with the cercarial shedding period ranging from 28 to 188 days.

1) The molluscicidal effect of 10 agricultural chemicals which are commonly usedby farmers in Saitama Prefecture was tested experimentally against A. ollula in the laboratory. The snails were made to contact with chemical solution for 48 hrs. at 23-25°C, then transferred to new containers with fresh water. The death rate was observed after 1 more hr.
LC₅₀ value of Saturn emulsion (Benthiocarb 50%), Saturn-S granule (Benthiocarb 7%, Simetryne 1.5%), MO emulsion (CNP 20%), NIP emulsion (NIP 25%), Sumithion emulsion (MEP 50%), Baysid emulsion (MPP 50%), Disiston granule (Ethylthiometon 5%), Bassa emulsion (BPMC 50%), Kitasin-Pemulsion (IBP 4%), and Lime nitrogen granule (CaNCN 21%) were 13.0, 92.5, 24.8, more than 50, 16.5, 13.5, more than 500, more than 50, more than 50 and 360 ppm. respectively, all figures were far larger than the doses in practical use for each chemicals. So it can not be expected that these chemicals would be effective against the snail in the ordinally practice.
2) Themolluscicidal effect of Lime nitrogen granule was also investigated with the snail in the paddy field where this fertilizer had been applied at an ordinally dose that is 2 Kg per are., 5 days prier to the test. The snails were introduced into the paddy and the mortality rate was observed 1, 2 and 3days after the introduction. The mortality rates of the snails at each day were 7.5%, 11.0% and 12.9% respectively. In the untreated field these figures were 7.0%, 14.9% and 4.4%.
It was concluded that Lime nitrogen granule was not effective against the snail at the ordinally dose for the use for fertilizer.

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 unknowns etiology has occurred among the farmers working in paddy fields in some districts of Kagoshima Prefecture, such as Ibusuki, Hiyoshi, Oura, Makizono and Minami-tane.
In order to acertain the cause of the disease, the epidemiological investigations have been made since1975.
The dermatitis occurrs from March to July 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 research for snail intermediate hosts was carried out in the paddy fields where the dermatitis originated.
As a result, two species of apharyngeal furcocercous cercariae were obtained from the fresh water snails, Polypylis hemisphaerula and Austropeplea ollula. The cercaria from P. hemisphaerula resembled to that of Gigantobilharzia sturniae in shape and size, and the other one from A. ollula was identified as species belonging to the genus Trichobilharzia and was regarded the same species as described in Saitama Prefecture by the authors.
An experimental infection with the cercaria belonging to the genus Trichobilharzia was performed. A few drops of water containing10cercariae were placed on the forearm. The cercariae invaded into the skin and produced a dermatitis quite similar to that prevailing in the endemic areas.
Therefore, it was concluded that the etiological agent were the cercariae of two different avian schistosomes, namely, G. sturniae and Trichobilharzia sp.

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.

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.

Surveys on the snail intermediate hosts were undertaken in the paddy fields in Yatomi-cho, Aichi Prefecture, once a year over a 5-year period (1983-1987).
And the cercariae of two different avian schistosomes were detected from snails in paddy fields.
The cercariae from Polyplis haemisphaerula were identified as species beloning to the genus Gigantobilharzia and the cercariae from austropeplea ollula as species belonging to the genus Trichobilharzia.
It was concluded that the paddy field dermatitis occurring in Yatomi-cho was proved to be caused by the invasion of these cercariae.