Echinostoma macrorchis (Digenea: Echinostomatidae): Metacercariae in Cipangopaludina chinensis malleata Snails and Adults from Experimental Rats in Korea

A survey was performed to know the infection status of echinostome metacercariae in Cipangopaludina chinensis malleata snails from Korea. Total 75 snails collected in 5 localities, i.e., Imsil-gun, Jeollabuk-do, Hwasun-gun and Shinan-gun (Aphae and Jido), Jeollanam-do, and Jinju-si, Gyeongsangnam-do, were examined for metacercariae by the artificial digestion method. Infection rates of metacercariae were 80.0%, 66.7%, 100%, 60.0%, and 73.3%, and their densities were 39, 32, 183, 19, and 30 per snail infected, respectively. The metacercariae were round, 105-118×105-118 μm in size, with a thin cyst wall, collar spines on the head collar, and excretory granules in 2 canals of excretory tube. Adult flukes were elongated, ventrally curved, and 5,167×939 μm in average size. Head collar distinct, bearing 45 collar spines with 5 end groups on each side. Oral sucker subterminal, pharynx well developed, and esophagus somewhat short. Cirrus sac well developed, with a saccular seminal vesicle, and ventral sucker very large. Ovary elliptical and on the median line of the body. Testes tandem and slightly lobed. Eggs operculated, elliptical, and 90-103×55-60 μm in size. By scanning electron microscopy, the head collar was prominent with 45 collar spines resembling horns of younger stags. Scale-like tegumental spines were densely distributed on the body surface between the head collar and ventral sucker. Conclusively, it has been first confirmed that the life cycle of E. macrorchis is indigenously maintained in Korea, and C. chinensis malleata snails are popularly infected with the metacercariae of this echinostome.