The egg laying capacity of Fibricola seoulensis was observed in mice and rats. In mice, the mean number of eggs produced by an adult worm a day was 116 at the first week after infection, 123 at the 2nd week and 42 at the 3rd week. Thereafter, the capacity of about 20 eggs/worm/day was maintained up to one year period. In rats, it generally produced more eggs; 49 at 1 week, 250 at 2 weeks, 216 at 4 weeks, 327 at 6 months and 11 at one year after infection. It survived longer than a year in mice and rats.
parasitology-helminth-trematoda ; Fibricola seoulensis ; egg

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

The therapeutic effect of praziquantel on Fibricola seoulensis infection were studied by experimental infection of albino rats with the metacercariae obtained from the snakes. Total 51 albino rats were infected each with 500 or 1,000 metacercariae in number through intragastric tubes. One or four weeks later the rats were treated with 1, 5, 10 or 20 mg/kg sigle dose of praziquantel and sacrificed after 3 days or 10-120 minutes to search for the worms in their small intestine. The worms recovery rate at 3 days after the treatment was 10.7% in 1 mg/kg does group and 0.03-0.2% in 5, 10 and 20 mg/kg group, while that of untreated control was 51.3%. The minimum effective dose to treat F. seoulensis infection in the rats is considered to be 5 mg/kg in sigle dose. By observing the distribution pattern of worms in the small intestine after the treatment, dislodgment of the worms froms the duodenum, thier normal habitat, to the lower portion was recognizable within as early as 10 minutes. The majority of worms was found to have descended to the ileo-caecal portion after 60-120 minutes.
parasitology-helminth-trematoda ; Fibricola seoulensis ; chemotherapy-praziquantel

A histopathological study was carried out on the duodenum of mice and rats experimentally infected by F. seoulensis. Each mouse was infected wit 500 metacercariae and killed after 1, 2, 3 days, 1 and 2 weeks from infection. Each rat was given 1,000 metacercariae and was examined after 1, 2, and 4 weeks from infection. The duodenal tissue sections of mice and rats were stained with hematoxylin and eosin, and PAS stained for the rats of 1 week group. The pathological findings are summarized as below. There were no differences in mucosal findings between the mice and the rats, adn between the location of duodenum, 1 and 5 cm distal to the pylorus. Each worm embraced a villus exclusively with its foliate forebody which was inserted into the intervillous spaces. The fluke pinched villous epithelia using its oral and ventral suckers. The tribocytic organ destroyed the villous epithelia deeply up to the stroma after 3 days from infection. Apparent villous changes were observed in the mice after 3 days from infection. Villous changes were shortening, widening, blunting or fusion. The villous stroma showed edema, microscopic hemorrhage, capillary congestion, dilatation of lymphatics and inflammatory cell infiltration. The cells were lymphocytes, plasma cells, eosinophils and giant cells. Rarely submucosal and transmural inflammation was encountered.
parasitology-helminth-trematoda ; Fibricola seoulensis ; histology ; pathology ; intestine ; rat

An experimental study was performed to observe the in vivo effects of praziquantel on the light and scanning electron microscopic morphology of Fibricola seoulensis. The metacercariae were obtained from the snakes and 1,000 in each number was orally given to total 15 albino rats; 5 controls and 10 treatment group. Seven days later the 10 rats were treated with 10 mg/kg praziquantel and sacrificed 1-24 hours later to search for the worms from their small intestines. The major light microscopic changes in the drug-exposed worms were early contraction followed by relaxation of especially their forebody, vacuolization of the tegument and subtegumental parechymal layers, and narrowing of the intestinal lumens. The scanning electron microscopic findings were characterized by formation of numerous blebs followed by rupture and subsequent destruction of their whole tegument. These results show that the change in worm body is not confined to the tegument but extends to deeper parechymal portions and also occurs in their intestines. It is suggested that the drug uptake by the worms should be either through their tegument or through the digestive tract.
parasitology-helminth-trematoda ; Fibricola seoulensis ; chemotherapy-praziquantel ; electron microscopy

A scanning electron microscopic study was performed to observe the tegumental surface of adult Fibricola seoulensis. The adult worms were collected from the small intestine of mice 5 days to 3 weeks after experimental infection with the metacercariae. The metacercariae were obtained from the viscera of the snakes, Natrix tigrina lateralis, by artificial digestion technique. The results were as follows: The tegument of anterior body was covered with cobblestone-like cytoplasmic processes and that of posterior body showed finger-like processes. The posterior body had 4-5 large transverse wrinklings which formed many discontinued shallow rugae. The entire surface of anterior body was regularly arranged with the spines of which tips diverged into 3 to 4 points. They were densely packed in anterior mid-median portion of dorsal surface where appeared a few spines indented upto 5 points. Farther laterally and posteriorly from this portion, the pointed spines were more sparse and became single tipped and extended to anterior one-third of posterior body. The posterior surface of oral sucker was armed with 50-60 spines having 2-3 tips and ventral sucker also covered with such spines. On anteriormost dorsal surface arranged 60-70 spade-shaped spines. The tribocytic organ was armed with many stout recurved pile-like spines arranged radially. There were 3 types of sensory papillae. The ciliated knob-like (Type I) papillae were almost bilaterally symmetrical in ventral and dorsal surfaces of anterior body, and abundant especially around bases of oral and ventral suckers, tribocytic organ, and in lateral margins of anterior body. About 24 non-ciliated round swellings (Type II) were observed around each lip of oral and ventral suckers. The plate-1ike elevated papilla without cilium (Type III) was found to distribute only in posterior body. These 3 types of papillae seem to be tangoreceptive and/or rheoreceptive in function when their morphology and distributions are considered.
parasitology-helminth-trematoda ; Fibricola seoulensis ; electron microscopy ; tegument ; mouse

This study was carried out to observe the growth and development of Fibricola seoulensis in experimentally infected rats and mice. The metacercariae were obtained from naturally infected Natrix tigrina lateralis which were collected in Hoengseong Gun, Gangweon Do, in August 1982. The results were summarized as follows. Growth and development of worm were not different between the rat and mouse. Body growth was attained within a week in both hosts. The testes differentiated first on the 2nd day after infection, and then ovary on the 3rd day, vitelline follicles on the 4th day, vitelline reservoir on the 5th day. A few eggs appeared in uterus on the 5th day and in feces on the 6th day. The body length grew almost linearly for the first 7 days after infection. The growth of posterior body was more remarkable, and the ratio of posterior body length to that of anterior body increased to 1.099 until 4 weeks after infection. The worms of 4weeks age in rats measured 1.10-1.92 mm long and 0.511 - 0.696 mm wide. The morphological characteristics of adult worms were identical to the original description of F. seoulensis, though dimensions varied in wider range. The worms were recovered from the rats 12.5% on the day after infecion, and the rate ranged 21.0-59.0% up to 6th day. One week after infection, the rates were 42.6%, 60.9% and 43.9% respectively by the metacercarial group of 200, 1,000 and 2,000 and the rates decreased to 16.2%, 29.1% and 3.1% respectively by the group on the 4th week after infection. Most of the worms were recovered from duodenum, and a part of worms were found in jejunum or ileum in heavily infected rats. The worms of 23.5-63.5% were recovered from mice from 3 to 10 days after infection. A great majority of them was found in duodenum, too.
parasitology-helminth-trematoda ; Fibricola seoulensis ; development ; biology ; rat

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

A total of 220 tadpoles was captured in 6 areas and total 117 frogs, Rana nigromaculata, were collected in 11 areas in Korea. They were examined for their infecion status by the metacercariae of Fibricola seoulensis by peptic digestion technique and by histological observation with hematoxylin-eosin staining. This study was carried out from August 1983 to September 1984. Followings are the results. The tadpoles of R. nigromaculata were positive for the metacercariae from 3.3 percent to 100 percent by area. The number of metacercariae per infected tadpole ranged from 1 to 584, and the mean number per tadpole ranged from 7.6 to 221 by area. The metacercariae from 16 tadpoles were counted by the body portion. A great majority of the metacercariae was collected from abdominal cavity, 98.3 percent of 484 counted larvae. And 6(1.2 percent) larvae were from proximal tail and 2(0.4 percent) from trunk. Histological sections of tadpoles showed many metacercariae in abdominal cavity but none in other parts. The larvae were free in the spaces among intestinal loops or around primitive liver. A few larvae were in duct-like tissues near trunk wall. There was little infiltration of inflammatory cells. The metacercarial infection rates of frogs ranged from 0 percent to 100 percent by area. The larval burden was 1 to 470 by infected frogs, and mean number ranged from 1 to 175.6 by area. By above results, it is suggested that the cercariae of F. seoulensis may infect R. nigromaculata already in the stage of tadpole. Almost all of the metacercariae were concentrated in abdominal cavity of tadpoles. According to the infection status of frogs, this fluke is prevalent almost nation-widely in rice paddies in Korea.
parasitology-helminth-trematoda ; Fibricola seoulensis ; epidemiology ; metacercaria ; frog ; tadpole ; Rana nigromaculata

Ten soldiers of the Korean Army were found to have F. seoulensis ova in their faeces. These men were treated with praziquantel and the worms passed after purging were successfully collected in one case: 59 F. seoulensis, 68 Metagonimus and 2 Stellantchasmus falcatus were collected. 2 men were also infected with Clonorchis sinensis. All the cases of fibricoliasis had eaten raw or undercooked snake meat or frogs during survival training. All were egg-negative 2-6 months after treatment.
parasitology-helminth-trematoda ; Fibricola seoulensis ; Stellantchasmus falcatus ; Metagonimus ; case report ; praziquantel ; Clonorchis sinensis