[Studies on Echinostoma spp. in the Chungju Reservoir and upper streams of the Namhan River].

The present study was performed to know the epidemiological status of echinostomiasis in the Chungju Reservoir and upper streams of Namhan River, together with an experimental study on the life history of Echinostoma hortense. The stool specimens of 169 inhabitants and 473 junior high school students from 5 different villages revealed 3 (0.5%) echinostomatid egg positive cases. E. hortense adult worms were recovered from one patient after a treatment and purgation. For the other two patients, it was presumed that one had E. hortense and another E. cinetorchis infection, based on the morphology of eggs. Five kinds of freshwater snails (168 Radix auricularia coreana, 534 Physa acuta, 144 Hippeutis cantori, 56 Cipangopaludina chinensis malleata and 125 Semisulcospira nodifila globus) examined for the cercariae of echinostomes showed negative results. Ten kinds of freshwater fishes examined for E. hortense metacercariae revealed positive rates as Misgurnus anguillicaudatus 40.5%, Odontobutis obscura interrupta 20.3%, Moroco oxycephalus 3.9%, and Coreoperca kawamebari 2.0%. In the experimental study, the metacercariae of E. hortense were infected to rats, eggs were collected from adult worms and cultivated, and miracidia were obtained. The miracidia were artificially infected to freshwater snails (R. auricularia), and cercarial shedding was studied. It was revealed that, when the snails were kept at a low temperature (24 degrees C), only 523 cercariae (on average) were produced during 24 hrs, while they were at a high temperature (30 degrees C), as many as 9,990 cercariae (on average) were shed during the same time. The experimental infection of E. hortense cercariae to freshwater fishes was successful in O. obscura interrupta 52.0%, M. anguillicaudatus 30.3%, C. kawamebari 27.0%, Cobitis lutheri 15.0%, M. oxycephalus 7.3%, Pseudogobio esocinus 4.3%, Squalidus coreanus 2.0%, Zacco platypus 1.3%, and Pungtungia herzi 1.3%. However, infection was not successful to snails, C. chinensis. It has been proved that the Chungju Reservoir and upper streams of Namhan river are endemic areas of echinostomiasis, especially of E. hortense, and snails such as R. auricularia coreana and fishes such as O. obscura interrupta, M. anguillicaudatus, and others are taking the role of first and second intermediate hosts, respectively.