An epidemiologic survey along the several sites of southern coastal areas of Korean peninsula was performed to know the infection status of Parvatrema spp. metacercariae in Tapes philippinarum. The clams were purchased from 13 coastal areas in Kyongsangnam-do and Chollanam-do, in September, 1990. Each of them was digested with pepsin-HCl solution and examined under a stereomicroscope for the recovery of metacercariae. A total of 232 (77.3%) out of 300 examined clams were proved to have 1 to 273 Parvatrema spp. metacercariae (54.7 in average). None of the clams from Samsan-myon Kosong-gun and Dolsan-up, Yochon-gun was infected with metacercariae. However, all of the clams from Yonghyun-myon, Sachon-gun, Dohwa-myon, Kohung-gun, Ahllyang-myon, Changhung-gun and Chiryang-myon, Kangjin-gun was infected with about 71, 31, 80 and 42 metacercariae respectively. Of the clams from Kohyun-myon, Namhae-gun, Doam-myon, Kangjin-gun and Kusan-myon, Uichang-gun examined, 97.5%, 95.0% and 90.0% were infected with about 117, 76 and 28 metacercariae. In other 4 surveyed areas, Seolchon-myon, Namhae-gun, Hwayang-myon, Yochon-gun, Byollyang-myon, Sungju-gun and Bukpyung-myon, Haenam-gun, 55.0%-80.0% of clams were positive, and their average intensity of infection ranged from 6 to 25 metacercariae. From these results, it was confirmed that Tapes philippinarum from southern coastal areas of Korea are highly infected with Parvatrema spp. metacercariae.
parasitology-helminth-trematoda ; Parvatrema ; metacercaria ; epidemiology ; Tapes philippinarum

Surface ultrastructure of Parvatrema timondavidi developmental stages was studied using a scanning electron microscope. The metacercariae were collected from the marine clam, Tapes philippinarum, and juvenile and worms adult were recovered at 1, 2, 3, and 7 days after experimental infection of mice. The metacercariae had a large oral sucker and characteristic lateral projections. Around the lip of the oral sucker many type I and type II sensory papillae were observed, and type III papillae were located symmetrically on the medial side of the lateral projection. Numerous type I papillae were grouped around the genital pore. The tegumental spines were distributed over the worm surface except the lip of the sucker and genital pore. The 1-day old worm had a well-developed ventral sucker, with 6 type II sensory papillae on its outer surface and another 6 type I papillae on the inner side, Two small type I papillae were seen on the anterior side of the ventral sucker. The genital pore was and 15 type I papillae were grouped around it. The 2-, 3-, and 7-day worms revealed that as they grew to be adults, the spine tips became multipointed, the genital pore formed a genital atrium, and the cytoplasmic process became well differentiated. In 2- and 3-day worms 10 type II papillae encircling the lip of the oral sucker, and additional 4 papilled at the dorsal side of 4 dorsal type II papillae were a characteristic feature. The distribution pattern of sensory papillae around the oral sucker and genital pore, and 2 type I papillae on the anterior side of the ventra sucker, was so peculiar in P. timondavidi, that they seem to be useful keys for taxonomic differentiation from other gymnophallids.
parasitology-helminth-trematoda ; Parvatrema timondavidi ; surface ultrastructure ; scanning EM, sensory papilla ; spine ; cytoplasmic process