Studies were conducted to determine the ecology of the snail, Parafossarulus manchouricus, the seasonal variation of the snail population, and the infestation rates of these snails with the cercariae of digenetic trematodes, in the snail habitat of river Kumho, in Dongchon of Taegu city, in Kyungpook Province, Korea, from 1975 to 1979. The earliest time the snails were found was early in April every year. At that time the water temperature ranged from 13 to 14 degrees C. The population density of snails ranged from 2 to 8 per square meter. The highest population density of snails was encountered in late June and the water temperature was between 24 and 26 degrees C. The snails disappeared in early and mid-November, when the water temperature dropped to 10-13 degrees C. The average snail population in June was 115.9 per square meter in 1975 but in 1976 dropped abruptly to 30.5 and remained at approximately the same level in 1977. It then decreased at considerably lower rates, with the average of 18.7 in 1978 and 14.5 in 1979. The snails collected in the habitat were examined for the presence of cercariae of digenetic trematodes. Of these, four species, Clonorchis sinensis, Cyathocotyle orientalis, Exorchis oviformis, and Loxogenes liberum were found. The most frequently liberated cercaria was L. liberum 43.3 per cent, followed by E. oviformis 6.2 per cent and C. orientalis 1.5 per cent. The least frequently liberated was C. sinensis 0.1 per cent. In the monthly liberation rates for larval trematodes, the higher rates were observed in June, July and August every year, and the cercarial rates for Clonorchis sinensis, Cyathocotyle orientails and Exorchis oviformis demonstrate a fairly consistently fluctuating downward trend over the five-year period, except for Loxogenes liberum. Summarizing the results, this study indicated that the population density of snails in the habitat and the infection of the snail with the cercariae of digenetic trematodes has decreased over the five-year period from 1975 to 1979.
parasitology-helminth-trematoda ; Clonorchis sinensis ; Parafossarulus manchouricus ; Cyathocotyle orientalis ; Exorchis oviformis ; Loxogenes liberum ; epidemiology ; cercaria

The Jinyang Lake is dammed up Nam River, and surrounded by Jinju city and four counties; Jinyang, Sanchong, Hadong, and Sachon in Kyongsang-Nam-Do, Korea. The area around this man-made lake have been known as an endemic focus of clonorchiasis in Korea. The present study was first aimed to know the distribution of freshwater mollusks including medically important snails, and larval trematodes shed from Parafossarulus manchouricus and Semisulcospira libertina. In addtion to above studies, water analyses in each snail habitat were carried out in order to figure out a part of their environmental factors. This malaco-ecological survey was done at the six areas around upper, middle and lower parts of the lake for 4 months, August-November, 1983. Total nine species of freshwater mollusks were collected throughout the study: 4 species of gastropods; Semisulcospira libertina, Cipangopaludina chinensis, Parafossarulus manchouricus and Radix auricularia, and 5 species of bivalves; Unio douglasiae, Anodonta woodiana, Lamprotula gottschei, Corbicula fluminea and Limnoperma lucustris. Out of nine species of freshwater mollusks, three species of gastropods; S. libertina, P. manchouricus and R. auricularia were medically important in terms of the transmission of digenetic trematodes to humans. P. manchouricus and R. auricularia were mainly collected from the shallow ponds and the irrigation channels with the muddy basin, but S. libertina and the bivalves were only collected from the stream of Nam river where the gravels and rocks were dominant. The levels of dissolved oxygen(D.O.) and biochemical oxygen demand (B.O.D.(5)) of the water specimens sampled from the study areas ranged from 6.0 to 9.6 ppm and from 0.4 to 1.6 ppm respectively. As a result, it is considered that water system around the Jinyang Lake might be relatively clean without any heavy pollution of aquatic microorganisms and organic materials during the period of this study. On the other hand, eight metalic constituents from the water samples were also assayed, and all metalic ions detected were remarkably low below the legal criteria. However, calcium ion in the water samples from the habitats of P. manchouricus was considerably higher than others. Infection rates of digenetic trematodes in the snails were 6.9 percent in P. manchouricus and 4.8 poercent in S. libertina, respectively. P. manchouricus snails harboring with the cercariae of Clonorchis sinensis were only 0.14 percent among the snails examined and other trematode cercariae except cercaria of C. sinensis were; furcocercus cercariae, cercaria of Loxogenes liberum type I and II. S. libertina snails parasitized with the cercariae of Metagonimus yokogawai were 1.5 percent out of the snails examined and no cercaria of Paragonimus westermani was found in S. libertina snails in the present study. Digenetic trematode cercariae other then M. yokogawai in S. libertina snails were: Cercaria yoshidae (B type), Cercaria cristata, Cercaria innominatum, Cercaria of Centrocestus formosanus and Cercaria nipponensis.
parasitology-helminth-trematoda ; Clonorchis sinensis ; Loxogenes liberum ; Metagonimus yokogawai ; Centrocestus formosanus ; Cercaria cristata ; Cercaria innominatum ; Cercaria nipponensis ; epidemiology ; Parafossarulus manchouricus ; Semisulcospira libertina ; Radix auricularia

The prevalence of C. sinensis infection along the Nam river, Korea, was 38.7% of 5,291 people examined. Prevalence rates varied from 42% at the upper stream to 34% at the middle stream and 40% at the down stream region. Rates were highest (53.4-54.3%) in the 30-59 years of age group. The positive rates in primary school chidren, school students, teachers and local officers, and other inhabitants were 16.5%, 22.6%, 46.2% and 49.6% respectively. 53.6% of cases were light infected, i.e. less than 4,000/EPG. The cercarial expulsion rate of 5,005 Parafossarulus sp. was 0.34%. Snails naturally infected with C. sinensis expelled about 788 cercariae/day. Ten of 18 species of freshwater fish examined had C. sinensis metacercariae. To prevent clonorchiasis in the endemic areas, the effective health education system is suggested as a control measure. [retyped from English summary]
parasitology-helminth-trmatoda ; Clonorchis sinensis ; clonorchiasis ; epidemiology ; Pseudorasbora parva ; Parafossarulus sp. ; Loxogenes liberum ; Cyathocotyle orientalis ; Notocotylus attenuatus ; Zacco platypus ; Hemibarbus sp. ; Gnathopogon sp. ; Ischikauia steenackeri ; Pseudogobio esocinus

An investigation on the trematodes of Korean amphibians was carried out during the period from April to September of 1976. A total of 883 amphibians of 6 species were examined. These frogs, toads and salamanders were collected in the areas of the Han river side. And also these amphibians comprised 775 Rana nigromaculata, 53 Rana rugosa, 21 Hyla arborea japonica, 2 Bufo bufo gargarizans, 2 Gallula tornieri and 30 Hynobius leechi. Out of the results of this work, 7 species of trematodes belonging to 2 orders were found as follows: Monogenea: Diplorchis ranae Ozaki, 1931. Digenea: Diplodiscus japonicus (Yamaguti , 1936), Gorgodera japonica Yamaguti, 1936, Haematoloechus sibiricus japonicus(Yamaguti, 1936) , Mesocoelium brevicaecum Ochi, 1929, Loxogenes liberum Seno,1980, Pleurogenoides japonicus (Yamaguti, 1936).
parasitology-helminth-trematoda ; monogenea ; digenea ; epidemiology ; frog ; Rana nigromaculata ; Rana rugosa ; Hyla arborea japonica ; Bufo bufo gargarizans ; Gallula tornieri ; Hynobius leechi ; Diplorchis ranae ; Diplodiscus japonicus ; Gorgodera japonica ; Haematoloechus sibiricus japonicus ; Mesocoelium brevicaecum ; Loxogenes liberum ; Pleurogenoides japonicus