• Parasites, Hosts and Diseases
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• v.28 no.3
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• pp.155-160
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• 1990

The tribocytic organ and tegument of Fibricola seeulensis were examined histochemically for the detection of carbohydrates, mucosubstances, amyloid, collagen and alkaline phosphatase. The surface, secretes, gland cells of the tribocytic organ, and the tegument of the worms were positive to periodic acid Schig (PAS) and PAS with diastase stain but negative to other stains. It was inferred that the tribocytic organ and tegument of F. seoulensis comprise neutral mucopolysaccharides, which may take a protective role against host enzymes. The surface and secretes of the tribocytic organ, and the tegument of the worms were also Positive to double bridge PAP for alkaline phosphatase. This fact suggests that they may play a role as both self protective and host tissue Iytic functions.

• Parasites, Hosts and Diseases
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• v.23 no.1
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• pp.72-78
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• 1985

A total of 220 tadpoles was captured in 6 areas and total 117 frogs, Rana nigromacuzata, were collected in 11 areas in Korea. They were examined for their infection status by the metacercariae of Fibricola seoulensis by peptic digestion technique and by histological observation with hematoBylineosin staining. This study was carried out from August, 1983 to September, 1984. Followings are the results. 1. The tadpoles of R. nigromaculata were positive for the metacercariae from 3.3% to 100% 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. 2. The metacercariae from 16 tadpoles were counted by the body portion. A great majority of the metacercariae was collected from abdominal cavity, 98.3% of 484 counted larvae. And 6(1.2%) larvae were from proximal tail and 2(0.4%) from trunk. 3. 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 inaammatory cells. 4. The metacercarial infection rates of frogs ranged from 0% to 100% 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 nuke is prevalent almost nationwidely in rice paddies in Korea.

• Parasites, Hosts and Diseases
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• v.27 no.4
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• pp.231-248
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• 1989

The growth and development of the metacercariae of F. seoulensis cultivated in vitro or on the chick chorioallantois were assessed by comparison with the optimum process of maturation in albino rats and new born chickens. The process of maturation was divided for convenience into six stages: Stage 1 ; cell multiplication, Stage 2; body shaping, Stage 3; separation of genital anlagen, Stage :1 organogeny, Stage 5; gametogony, and Stage 6: oviposition. In Hank's and Tyrode's .solutions, the metacercariae were alive up to 200 days or more at $4^{\circ}C$ without any development. The in vivo maturation process in rats or chicks was as follows: stage 1 from 6 hours; stage 2 from 24 hours; stage 3 from 48 to 72 hours; stage 4 from 3 to 4 days; stage 5 from 4 to 5 days; and stage 6 from 5 to 8 days. Despite unsuccessful infection of the metacercariae to 12 day old chicks, fully mature worms of stage 5 or 6 were recovered from new born chicks (1 to 2 days old), The metacercariae of F. seoulensis grown in vitro were up to stage 3 and no further maturation was observed. Of various media employed, the medium NCTC 109 (Gibco) or NCTC 135(Gibco) supplemented with 20% egg yolk or 20% whole egg macerate or 0.5% yeast was basically required for the earlier development of the fluke. It took 16.1 days(in average) to reach the stage 3 after cultivation. The metacercariae cultivated on the chorioallantoic membranes of 6∼13 day old chick embryo at 37∼38℃ showed their full development up to stage 5 or 6. However, the worms were in general remarkably retarded, compared with those grown in rats or chickens. In the experiments of worm transplant, although the transfer was failed from in vitro culture to in vivo of rats(Per os), the transplants from in vitro culture to the chorioallantois and from the choriollantois to in vivo of rat host were successful with or without development of the transferred worms. In the present study, it was observed that the metacercariae of F, seoulensis can be maintained in vitro media with poor development as well as fully matured in 1 to 2 day-old chicks or on the chorioallantois at a very low rate.

• Parasites, Hosts and Diseases
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• v.23 no.1
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• pp.41-46
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• 1985

The therapeutic effects 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 meta cercariae in number through intragastric tubes. One or four weeks la er the rats were treated with 1, 5, 10 or 20 mg/kg single dose of prazipuantel and sacrificed after 3 days or 10-120 minutes to search for the worms in their small intestine. The worm recovery rate at 3 days after the treatment was 10.7 % in 1 mg/kg dose group and o. 03~0.2% in 5, 10 and 20 mg/kg groups, 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 single dose. By observing the distribution pattern of worms in the small intestine after the treatment, dislodgement of the worms from the duodenum, their normal habitat, to the lower portions 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.

• Parasites, Hosts and Diseases
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• v.31 no.4
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• pp.353-362
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• 1993

The present study was carried out to investigate the localization and isozyme patterns of acid phosphatase and alkaline phosphatase in metacercariae and in adults of F. seoulensis by enzyme-histochemistry method and electrophoresis. Acidphosphatase showed a strong activity at pH 5 in the intestinal caecum of adults, but showed no reactions in the nonsubstrate control and in the inhibitor-treated control. Alkaline phosphatase showed a strong activity at pH 8 in the intestinal caecum and the tribocytic organ of adults, and in the intestinal caecum and in the genital anlagen of metacercariae. In non-denature PAGE, ten bands of protein fraction from the extracts of metacercariae and twenty-two bands from adults were detected. In denature PAGE, two protein bands having molecular weights of 192 kDa and 123 kDa were detected in the metacercariae, but absent from adult stage. In adults, protein fractions of 27.5 kDa, 24.5 kDa, 21.4 kDa, 18 kDa, 16 kDa and 15 kDa were detected. In non-denature PAGE, isozymes of acid phosphatase showed the most strong activity at pH 5, whereas no activity was shown at pH 2 and pH 7. One isozyme 85 kDa, 73 kDa and 62 kDa) in adults.

• Parasites, Hosts and Diseases
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• v.26 no.2
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• pp.117-120
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• 1988

The egg laying capacity of Fibritola 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 1st 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.

• Parasites, Hosts and Diseases
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• v.24 no.2
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• pp.115-120
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• 1986

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 summarized as follows. 1. From $4{\sim}5$ days after incubation in distilled water at $28^{\circ}C$ or at $11{\sim}26^{\circ}C$, the eyespots began to appear and the rates of eggs with eyespots were over 90% in $28^{\circ}C$ on the 7th or 8th day. However, eyespots did not appear in $5{\sim}15^{\circ}C$ or $4^{\circ}C$ by the 18th day. 2. The mature eggs began to hatch at the 8th day, and hatching rate 2 weeks after incubation was over 90% at $28^{\circ}C$, but it was below 5% at $11{\sim}26^{\circ}C$, and 0% at $5{\sim}15^{\circ}C$ and at $4^{\circ}C$. 3. Aeration did not influence the appearance of eyes pots nor hatching. 4. In salines under 0.6%, the rates of eyespots appearance were over 90% on the 7th day. The rate was 55.0% in 0.9% at 20 days, and 0% in 1.2%. 5. 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. 6. The eggs incubated in the dark hatched in 12.5% on the 10th day, but hatching rate of mature 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 $28^{\circ}C$, and the miracidia began to hatch at $8{\sim}9$ 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% concentration maturation and hatching were not influenced, but as salinity increased hatching was inhibited more than maturation was.

• Parasites, Hosts and Diseases
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• v.24 no.2
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• pp.109-114
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• 1986

In order to observe the growth and development of Fibricola seoulensis metacercariae, the tadpoles of Rana nigromaculata were experimentally infected with the cercariae. The meta cercariae 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. 1. All of the tadpoles exposed to the cercariae were observed to harbour the larvae in their abdominal cavity. 2. The young metacercariae of 2 days after infection were $121.1{\mu}m$ long and $63.3{\mu}m$ wide. They grew linearly for the first 14 days to be $262.0{\mu}m$ long and $166.4{\mu}m$ wide. Thereafter, no more growth recognized until 65 days. 3. The larvae of 2 days old were similar with cercarial body and had 2 suckers, a pharynx, 2 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. 4. The metacercariae younger than 10 days could not infect the mice. Only the metacercariae older than 14 days had infectivity. The recovery rates 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 indispensable 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.

• Parasites, Hosts and Diseases
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• v.23 no.1
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• pp.47-58
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• 1985

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 praziquantcl 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 parenchymal 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 teguments. These results show that the change in worm body is not confined to the tegument but extends to deeper parenchymal 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.

• Parasites, Hosts and Diseases
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• v.23 no.1
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• pp.58-72
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• 1985

A histopathological study was carried out on the duodenum of mice and rats experimentally infected by F. seoulensis. Each mouse was infected with 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 eosin, and PAS stained for the rats of 1 week group. The pathological findings are summarized as below. 1. There were no differences in mucosal findings between the mice and the rats, and between the location of duodenum, 1 and 5 em distal to the pylorus. 2. Each worm embraced a villus exclusively with its foliate fore body 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. 3. 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 trans:nural inflammation was encountered.