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

The metacercariae of Metagonimus yokogawai were isolated from the sweetfish Plecoglossus altivelis, clollected at Hwagae, South Kyongsang Do, one of the newly known endemic foci of metagonimiasis in Korea. The body structure of metacercaria of M.yokogawai was described and the measurements of the excysted metacercaria were also made. In order to know the distribution of metacercariae within the host, the rate of infection and the intensity of infection, a total of 10 sweet fishes was examined and it was found all infected, from which a total of 38,511 metacercariae was isolated. The number of metacercariae in a fish varied from 219 to 14,427. The average number of metacercaria per fish was 3,851. The distribution of metacercariae in the four divided parts of fish was observed in the following order; number of metacercaria in the muscles; 2,417 (62.8%), in the subcutaneous tissues; 1,126.9 (29.3%), and on the scale; 291.9(7.7%). The development of the metacercaria of M. yokogawai in the mouse host was experimentally traced every day for 10 days after infection . In an earlier period of infection, the growth rate of the genital primordia was distinctly high, particularly in the testes. The seminal receptable and seminal vesicle became clearly recognized in measurable size at 4 days after infection. The vitelline follicles and their ducts were also first visible in the living specimens at 6 days after infection. The oral sucker was larger in size than the ventral sucker in an early stage of the worms, however after 7 days after infection it reversed. The posterior part of body began to extend since two days after infection. Fully matured worms were able to collect only after 7 days after infection. At this stage, the body of worm became 0.7 mm long and 0.3 mm wide. The first positive appearance of eggs in the uterine tubule and in feces was on the 6th day and 10th day of infection, respectively. In an earlier stage of infection, the worms were found mostly in the upper portion of small intestine and the recovery rates of the worms were high, however according to the course of infection in later stage they were seen rather in the lower part of the intestine and the recovery rate also decreased.
parasitology-helminth-trematoda ; Metagonimus yokogawai ; development ; metacercaria ; Plecoglossus altivelis

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 Hongcheon river system flows down through the Hongcheon area of Kangwon-do, and reaches to the Cheongpyeong Dam in Kyonggi-do. Stool specimens from the inhabitants residing along the Hongcheon river basin were examined to detect infection rate of Metagonimus sp., and the intermediate hosts were collected to detect larval stages. The results obtained were as follows: Thirty-nine (33 males and 6 females) out of 529 (314 males and 215 females) inhabitants were infected with Metagonimus sp., showing a total positive rate of 7.4 per cent. In eight areas surveyed, the specimens from Kulji-ri of Bukbang-myon at the middle part of the river showed the highest positive rate of 26.9 per cent (14 positives out of 52) (males; 38.2per cent). The specimens from Mogog-ri of Seo-myon at the downstream of the river showed a positive rate of 10.4 per cent (13 positives out of 125) (males;12.6 per cent). The positive rates in other regions were less than 10 per cent. The density of the first intermediate host, Semisulcospira sp., was the highest in Kulji-ri of Bukbang-myon (10-20 snails per m(2)), and the infection rate of Metagonimus cercariae in the snails was 10.7 per cent(13 positives out of 121 snails). The infection rate of Metagonimus metacercariae in Zacco platypus, the fresh water fish favorably eaten raw by the inhabitants, was 68.2 per cent (30 positives out of 44 fishes), and most metacercariae were detected under the scales (89.9 per cent). Adult flukes were obtained from the small intestine of a rat, 15 days after infection with the metacercariae obtained from Z. platypus. These adult flukes were identified to be the same srecies as those obtained from human hosts. By this survey, new endemic areas of Metagonimus infection were discovered along the Hongcheon river basin and the main source of infection was the fresh water fish, Z. platypus.
parasitology-helminth-termatoda ; Metagonimus sp. ; epidemiology ; metacercaria ; Zacco platypus

The fresh water snail, Hippeutis(Helicorbis) cantori, caught from the rice paddies in Namyangju-gun, Gyeonggi-do, was found to be a new second intermediate host of E. cinetorchis in Korea. The metacercariae were found from 89(76.7 %) out of 116 snails examined and the average metacercarial burden was 4.7 per infected snails. Some developmental characteristics of E. cinetorchis were observed after experimental infection of the metacercariae to rats and mice.
parasitology-helminth-termatoda ; Echinostoma cinetorchis ; Hippeutis cantori ; metacercaria ; epidemiology ; development

A group of metacercariae encysted in the flesh of Mugil sp. were identified to be Stellantchasmus falcatus by the morphology of adult worms obtained experimentally. It is confirmed that mullets serve as a second intermediate host of this heterophyid fluke in Korea.
parasitology-helminth-trematoda ; Stellantchamus falcatus ; metacercaria ; Mugil sp. ; intermediate host

The worm development and egg laying pattern of Echinostoma hortense(Trematoda: Echinostomatidae) were studied in albino rats and the brief clinical course was observed in human volunteers. A total of 21 rats were infected with 20-69 metecercariae each and two humans were with 7 and 27 metacercariae, which were collected from loaches. For recovery of worms, the rats were sacrificed at irregular intervals from the 6th to 150th day after infection and the human volunteers were treated with praziquantel and purged with magnesium salt on the 26-27th day. The stools of the rats and humans were examined for the eggs. The results were as follows: The worm recovery rate from the rats was not affected by the increase of infection time but varied individually; 9.1-50.0% (31.1% in average). From humans, 14.3% and 37.0% (32.4% in average) of challenged were recovered. In the rats, it was revealed that the worms rapidly grew for the first 14 days to become 7.59 mm in average length and 1.17 mm in average width but the growth became much slower thereafer until the 150th day; 7.95 mm in length on the 21th day, 9.04 mm on the 28th day, 10.21 mm on the 49th day and 12.62 mm on the 150th day. During the early stage of infection, the growth of genital organs(male or female) was expressed as sigmoid curves whereas non-genital organs(such as suckers) was simply as straight lines. The prepatent period of this fluke was 10-12 days in the rats and 16-17 days in men. After the start of oviposition, the egg production by the worms remarkably increased, reached maximum on the 32-33th day, followed by decrease thereafter. The maximum value of E.P.G./worm was 390. The major subjective symptoms in human volunteers were abdominal pain and diarrhea during the early stage of infection. The results show that human is as susceptible as the rats to E. hortense infection and the amount of egg production in the rats is greatly affected by the age of worms.
parasitology-helminth-trematoda ; Echinostoma hortense ; rat ; biology ; metacercaria