Life history of Echinoparyphium recurvatum (Trematoda: Echinostomatidae) in Korea.

The present study was performed to observe characteristics of the life history of Echinoparyphium recurvatum under both natural and laboratory conditions in Korea. A batch of Radix auricularia coreana was collected from Sunamchon, one of the stream of West Naktonggang (River), in Kangso-gu, Pusan during August and September 1992. Out of 106 snails examined by crushing, 52 (49.0%) were infected with larval E. recurvatum, i.e. rediae, cercariae and metacercariae. Cercariae naturally shed from snails encysted in the snails of same species and loaches, but not in mud-snails. Adult worms were detected from chicks and ducks experimentally infected with metacercariae, but not from rats and mice. The average recovery rate of adults from chicks was 13.1%. Rediae were sac-like, 2.437 x 0.317 mm in average size, with a muscular pharynx and a brownish cecum which reached the anterior half of the body. Cercariae consisted of a spindle-shaped body (0.262 x 0.129 mm in average) and a rod-like tail (0.528 x 0.056 mm in average). In the cercarial body, 45 collar spines were observed on the head crown, and double rows of excretory ducts with fine granules were laterally arranged between the pharynx and the ventral sucker. Metacercariae were spherical, 0.144 x 0.142 mm in average size, with thick hyaline outer and thin elastic inner walls, and many excretory granules. Adults were slender and more attenuated in the anterior end, 2.760 x 0.550 mm in average size, and had 45 collar spines including four end group spines on both ventral corners. From the above results, it was confirmed that R. auricularia coreana plays a pivotal role in the life cycle of E. recurvatum as the first and/or second intermediate hosts in Korea.