More than 1,500 clams of Corbicula fluminea, the most favorable food source of freshwater bivalves in Korea, were collected from 5 localities to examine cercarial and metacercarial infection with Echinostoma cinetorchis. Although 3 clams infected with suspicious E. cinetorchis metacercariae out of 200 specimens collected at Kangjin, Chollanam-do were detected, no cercarial and metacercarial infections with E. cinetorchis were observed in field-collected Corbicula specimens. In the susceptibility experiments with laboratory-reared clams, those infected with miracidia of E. cinetorchis did not release their cercariae up to 60 days after infection. To confirm the identity of second intermediate host of E. cinetorchis experimentally, a total of 30 clams were exposed to the cercariae from Segmentina hemisphaerula that had been infected with miracidia of E. cinetorchis. The clams were susceptible to cercariae of E. cinetorchis with an infection rate of 93.3%. Metacercariae from clams taken more than 7 days after cercarial exposure were fed to rats (S/D strain), and adult worms of E. cinetorchis, characterized by 37-38 collar spines on the head crown, were recovered from the ileocecal regions. This is the first report of C. fluminea as a possible second intermediate host of E. cinetorchis.

Three freshwater snail species of the family Lymnaeidae have been reported from Korea, Radix auricularia coreana, Austropeplea ollula and Fossaria truncatula. Out of 3 lymnaeid snail species, A. ollula was naturally infected with the Echinostoma cinetorchis cercariae (infection rate = 0.7%). In the experiments with the laboratory-bred snails, F. truncatula as well as A. ollula was also susceptible to the E. cinetorchis miracidia with infection rates of 25% and 40%, respectively. All of three lymnaeid snail species exposed to the E. cinetorchis cercariae were infected with the E. cinetorchis metacercariae. It is evident that A. ollula acts as the first molluscan intermediate host of E. cinetorchis in Korea, and F. truncatula may be a possible candidate for the first intermediate host of this intestinal fluke. Also, three lymnaeid snail species targeted were experimentally infected with E. cinetorchis metacercariae.

Toxoplasma-killing activities of mouse peritoneal macrophages activated by the extracts of Tetrahymena pyriformis (Korean and Chinese strains) were evaluated, and the active protein fractions from both strains were partially characterized by a method including chromatographies and SDS-PAGE. The first peak in Korean strain and the second peak in Chinese strain of T. pyriformis obtained by DEAE-Sephadex A-50 chromatography were most effective in the activation of macrophages to kill Toxoplasma gondii tachyzoites in vitro. Subsequent fractionations of obtained peak fractions were performed on a Sephadex G-200 gel. The first peaks fractionated from both strains of T. pyriformis had the highest toxoplasmacidal activities, and when subjected to the SDS-PAGE, one prominent band was visualized for each of the strains showing the same molecular weight of ca. 52.6 kDa. This active protein is suggested to be related to non-specific activation of mouse peritoneal macrophages.