In order to observe the growth and development of Fibricola seoulensis metacercariae, the tadpoles of Rana nigromagulata were experimentally infected with the cercariae. The metacercariae of various developmental stages were recovered from the tadpoles after 2 to 65 days of infection. They were prepared for morphological observation, and were given orally to mice to observe their infectivity. The following results were obtained. All of the tadpoles exposed to the cercariae were observed to harbour the larvae in their abdominal cavity. The young metacercariae of 2 days after infection were 121.1 micrometer long and 63.3 micrometer wide. They grow linearly for the first 14 days to be 262.0 micrometer long and 166.4 micrometer wide. Thereafter, no more growth recognized until 65 days. The larvae of 2 days old were similar with cercarial body and had 2 suckers, a pharynx, two ceca and a primordium of germ cells but no tribocytic organ. On the 8th day, they had tribocytic organ, and their morphology resembled that of mature metacercariae. The metacercariae younger than 10 days could not infect the mice. Only the metacercariae older than 14 days had infectivity. The recovery rate increased by the age of metacercariae from 19.0% in 14 days old to 70.0% in 40 days old. Above findings indicate that the tadpole is indispensible for metacercarial development and it needs at least 2 weeks for maturation. The tadpole is a pivotal host in the life cycle of F. seoulensis for connection between the snail and the frog.
parasitology-helminth-trematoda ; Fibricola seoulensis ; metacercaria ; development

Metacercariae were found from 6 samples among 4,382 Parlemon nipponensis which were caught at Podu, Kohung, Korea. The metacercaria was inclined as a larval stage of Paragonimus westermani by following reason: Semisulcospira libertina was the only one species which lives in Podu area. No other metacercaria except Paragonimus westermani were found from the craw or cray fish which were caught in the endemic aera. Metacercariae, ovary, testes and cuticular spines resmbled the characteristics of Paragonimus westermani, which have been described by previous workers.
parasitology ; helminth ; trematoda ; Paragonimus westermani ; metacercaria ; epidemiology

The distribution and the infestation rates of metacercariae in fishes from the Kum-Ho river were observed from June 1965 to August l967. The results obtained are as follows: The Fourteen kinds of metacercariae; Exorchis oviformis, Metorchis orientalis, Cyathocotyle species, Metacercaria hasegawai, Clonorchis sinensis, Metagonimus species, Pseudexorchis major, Echinochasmus species, Centrocestus species, Prosorhpynchus species, and four kinds of unidentified species, A, B, C and D were detected from 12 kinds of fishes. Clonorchis sinensis, Metagonimus species, Echinochasmus species, and Centrocestus species of the detected 14 kinds of flukes were noted to be parasited in man; Metorchis orientalis and Cyathocotyle species in avian species; and Exorchis ovifomis and Pseudexorchis major in wels, but the definite host of the other 6 kinds of flukes were not identified. Exorchis oviformis was found in 64.5 percent, of all kinds of fishes, Cyathocotyle species in 36.8 percent of 7 kinds of fishes, Metacercaria hasegawai in 36.3 percent of 8 kinds, Clonorchis sinensis in 95.0 percent of 6 kinds and Metagonimus species in 47.9 percent of 10 kinds. Concerning the infested rates of metacercaria and the length of fishes, Exorchis oviformis and Clonorchis sinensis showed increased rate by the length of fishes but the rest of fishes showed no relationship between them. The infested degree of metacercaria of Clonorchis sinensis was highest in Pseudorasbora parva with 34.3 parasites per cubic cm of flesh, of Exorchis oviformis in Carassius carassius with 7.3, of Cyathocotyle species in Acheilognathus with 6.0, and of Metacercaria hasegawai in Pseudogobio esocinus with 5.7 but Prosorhpynchus etc. were very few in all kinds of fishes. The infested rates of metacercaria in the four kinds of fishes, Pseudorasbora parva, Pungtungia herzi, Pseudogobio esocinus and Gnathopogon coreanus seemed not to be influenced by season, Spring and Autumn. In the infested rates of metacercariae by parts of fishes, Exorchis oviformis was chiefly infested in scales and fins; Metorchis orientalis, Cyathocotyle species, Clonorchis sinensis, Pseudexorchis major, Centrocestus species and Prosorhpynchus ecinatus were chiefly infested in muscle; Metacercaria hasegawai in muscle and fins; Metagonimus species chiefly in scales; and Echinochasmus chiefly in gills.
parasitology-helminth-trematoda- Exorchis oviformis-Metorchis orientalis-Cyathocotyle species-Metacercaria hasegawai-Clonorchis ; epidemiology ; metacercaria

This study was carried out to reveal the effect of temperature, salinity and aeration on maturation and hatching of Fibricola seoulensis eggs. The eggs were incubated and were observed daily for the appearance of eyespots and hatching. The results were summerized as follows: From 4-5 days after incubation in distilled water at 28C or at 11-26C, the eyespots began to appear and the rate of eggs with eyespots were over 90% in 28C on the 7th or 8th day. However, eyespots did not appear in 5-15C or 4C by the 18th day. The mature eggs began to hatch at the 8th day, and hatching rate 2 weeks after incubation was over 90% at 28C, but it was below 5% at 11-26C, and 0% at 5-15C and 4C. Aeration did not influence the appearance of eyespots nor hatching. In saline under 0.6%, the rates of eyespots were over 90% on the 7th day. The rate was 55.0% in 0.9% at 20 days, and 0% in 1.2%. The hatching rates in salines below 0.3% concentration were over 90% by 14 days of incubation. However, the rate decreased to 44% in 0.6% saline and to 0% over 0.9% salinity. The eggs incubated in the dark hatched in 12.5% on the 10th day, but hatching rate of maturation eggs increased to 85.7% within 2 hours after exposure to light. Above results demonstrated that the best temperature for maturation and hatching of F. seoulensis eggs was 28C, and the miracidia began to hatch at 8-9 days after incubation. In the field hatching and invasion into snails of the miracidia may occur from May to September in Korea. In salines under 0.3 percent concentration maturation and hatching were not influenced, but as salinity increased hatching was inhibited more than maturation was.
parasitology-helminth-trematoda ; Fibricola seoulensis ; metacercaria ; development ; egg ; saline

An epidemiological investigation was conducted on Metagonimus yokogawai infection in Hadong Gun (County), Gyeongsang Nam Do, Korea, and following findings were obtained. Overall prevalence rate of Metagonimus yokogawai infection was 29.1 percent from a total of 1,163 inhabitants examined. By area of river and stream, Seomjin-gang R.: 9.5 percent (out of 95 inhabitants examined) in Jeondo Ri in the lower river, 19.9 percent (156) at Dugog Ri near Hadong town, and 90.8 percent (65) in Tab Ri of Hwagae Myeon where Hwagae-cheon Stream joins; Hwagae-Cheon Stream: 42.2 percent (45) in Yonggang Ri of the middle stream and 27.5 percent (72) in Daeseong Ri of the upper stream; Hoengcheon-gang R.: 54.7 percent (161) in Gojeol Ri of the lower river, 40.6 percent (128) in Hoengcheon Ri of the middle stream, and 5.4 percent (93) in Jungi Ri of the upper stream, and 43.8 percent (89) in Uge Ri located along a tributary of the Hoengcheon-gang R. and 4.0 percent (101) in Jangam Ri which is located about 4 km away from the river; Deogcheon-gang R.: 18.5 percent (54) in Munam Ri; Gwangog-cheon Stream: 2.8 percent (107) in Gwangog Ri. The difference in prevalence rate of the infection by area was correlated with the opportunity and amount of raw eating of sweetfish by the inhabitants in the respective areas. By age and sex, the overall prevalence rate increased from young age group and reached a peak at 20-29 age group and then the rate decreased gradually. In high endemic areas, however, a peak level of the rate lasted up to 40-49 age group in male. On the other hand, in low endemic areas, the rate was significantly lower in female, though moderate level of the infection was seen in male. The overall prevalence rate was higher in male than in female and the difference was greater in middle age groups. The most significant mode of infection by the inhabitants was the raw eating of sweetfish which commonly harbour metacercariae of M. yokogawai during summer through autumn. Besides, it was noted that the infection can be acquired through contamination with the metacercariae on food of various side-dish and kitchen utensils as well as on hands of a cook when such fish are prepared or handled. The inhabitants usually begin to acquire infection from early June of a year when fishing of sweetfish opens and acquire infection more frequently in July and August when fish are caught more productively and favored for raw consumption by inhabitants. From September, sweetfish are no more favored for raw consumption and accordingly are dried and cooked in this season. The infection in the sweetfish Plecoglossus altivelis as the second intermediate host was first observed from May with low level of infection and the intensity of infection in a fish rapidly increased until reaching a peak in October when sweetfish season normally ends. The first intermediate host snail of M. yokogawai in this area was Semisulcospira coreana (Martens) which is widely distributed in the streams and rivers in this locality.
parasitology-helminth-trematoda ; Metagonimus yokogawai ; metacercaria ; Plecoglossus altivelis ; epidemiology

There are a number of eating-houses in the basin of river Ahnseong that sell rawsweetfish, Plecoglossus altivelis, to local residents and visitors. These facts called attention to the possibility of wide spread of metagonimiasis in that area. In an attempt to determine whether the metacercaria of Metagonimus yokogawai does present in the sweetfish caught in the river Ahnseong, a total of 77 fish were examined in the period from April to September 1978. All the fish were infected with the encysted larvae. The average number of larvae persweetfish was 1,815, of which the metacercaria rate for the fluke in the flesh was 56.9 per cent and in the scale, 30.5 per cent. These results indicate that all the sweetfish in the river Ahnseong harbour the metacercaria of Metagonimus yokogawai.
parasitology-helminth-trematoda ; Metagonimus yokogawai ; metacercaria ; Plecoglossus altivelis ; epidemiology

The metacercariae of Echinostoma cinetorchis (Trematoda: Echinostomatidae) were found infected in the loaches (Misgurnus anguillicaudatus) purchased from two local markets in Korea. Identification of the metacercariae was done after obtaining adult worms from experimentally infected albino rats. Brief course of worm development in rats was also observed up to 28th post-infection day. The results are as follows: The metacercariae of E. cinetorchis were detected from 5 (10.9 percent) out of 46 loaches examined and the average metacercarial burden per infected loach was 34.4. They were always found from the posterior abdominal wall. The worm recovery rate from 8 rats was 24.6 percent in average. It was observed that the rate decreased according to age of infection; from 40.7 percent after 6 days to 15.0 percent after 28 days. The adult worms were morphologically characterized by the presence of head crown with dorsally uninterrupted collar spines, 37-38 in number, and the tendency of migration or disappearance of testes. So that they were identified as Echinostoma cinetorchis Ando et Ozaki, 1923. The development of worm was very rapid during 6-10 days after infection and became much slower thereafter. During the rapid worm growth the development of genital organs was more prominent than that of non-genital organs. From the results it is concluded that the loach is involved in the life cycle of E. cinetorchis in this country and may take a role for infection source to animals and man. It is also confirmed that migration or loss of testes is the distinct specific character of this echinostomatid fluke.
parasitology-helminth-trematoda ; Echinostoma cinetorchis ; metacercaria ; mouse ; development

This study was carried out to outline the geographical distribution of the sweetfish which were infected by the metacercariae of Metagonimus yokogawai from August to October in 1979. The infection status was examined both by the muscle compression method and by digestion technique. The result was summarized as follows: A total of 197 sweetfish, Plecoglossus altivelis was collected, 125 fish from 5 streams along the East Coast and 72 fish from 4 streams along the South Coast. Total 125(63.5 percent) fish were infected by the metacercariae of M. yokogawai. The rate and intensity of infection in the south coastal areas were much higher than those in the east coastal areas; the rate was 42.4 percent in the East and 100 percent in the South, mean number of metacercariae per fish was 721 in the East and 14,308 in the South, and mean number of metacercariae per gram of flesh was 43 in the East compare with 904 in the South. The sweetfish infected by the metacercaria of M. yokogawai were newly observed in 5 foci, i.e., Yeongogcheon in Myeongju Gun and Namdaecheon in Gangneung Si, Gangweon Do and Wangpicheon in Uljin Gun, Gyeongsangbug Do in the East, and a branch of Namgang in Euiryeong Gun and Sinhyeoncheon in Geoje Gun, Gyeongsangnam Do in the South. The rate of metacercarial infection was 4.1 percent in Yeongogcheon and 100 percent in others. The number of metacercariae in a fish ranged from 9 to 45,018 and the number of metacercariae per gram of flesh was the lowest in Gangneung Namdaecheon as 19 and the highest in Geoje Sinhyeoncheon as 1,237. Summarizing these findings with previous records, M. yokogawai might be prevalent in the streams along the East Coast southern from Myeongju Gun, Gangweon Do and along the South Coast in Korea.
parasitology-helminth-trematoda ; Metagonimus yokogawai ; sweetfish-Plecoglossus altivelis-epidemiology ; metacercaria

The echinostomatid metacercariae encysted in the gill of the fresh water fish, Pseudorasbora parva were identified through obtaining adult worms after experimental infection to mice. In addition, a brief course of worm development and maturation was observed in this experimental host. The results were as follows: The echinostomatid metacercariae were elliptical, golden yellow, 0.073-0.078 mm long and 0.054-0.065 mm wide. Their head portions were characterized by the presence of a head crown armed with collar spines of total 24 in number and interrupted at the mid-dorsal side of the oral sucker. The average rate of worm recovery from 12 mice (on the 1-21th postinfection days) was 19.4 percent and the rate revealed no decrease in accordance with the increase of infection duration. The worms were collected chiefly from the lower part of the small intestine. After the infection, their sexual maturation was attained in 5 days and their growth in size nearly completed in 7 days. The early growth curve of genital organs was S shape while that of nongenital organs was C form. In 5 day old worms, l or 2 eggs were found from their uteri and the stools of mice revealed echinostomatid eggs from the 5-6th postinfection day. The 7 day old adult worms were ovoid in shape, 0.54-0.69 mm long and 0.29-0.34 mm wide, and characterized by a well developed head crown with 24 collar spines and vitelline follicles distributed from the acetabular level down to the posterior end of body. Based on these characters they were identified to be Echinochasmus japonicus Tanabe, 1926. From these results, it is verified that P. parva is one of the second intermediate hosts of E. japonicus in Korea.
parasitology-helminth-trematoda ; Echinochasmus japonicus ; metacercaria ; Pseudorasbora parva

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