• Parasites, Hosts and Diseases
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• v.24 no.2
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• pp.121-136
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• 1986

Recently there have been some reports on human infections of Echinostoma hortense in Korea. It was found that a few species of freshwater fishes were playing the role of the second intermediate host of E. hortense. However, molluscan intermediate host has not been identified yet in Korea. The present study aimed to establish the life cycle of E. hortense in laboratory. Experimental studies such as egg production from the rat, development of the eggs in vitro, exposure of miracidia to freshwater snails, shedding pattern of cercariae from infected snails, morphology of cercariae, cercarial infection to the second intermediate host and infection of metacercariae to the definitive hosts were done. In addition, epidemiological surveys on the infection status in inhabitants and house rats, and on the natural infection of larval echinostomes in the snails and fishes were carried out along the South Hangang-river. The results obtained were as follows: 1. The eggs deposited from adults in physiological saline were cultivated at room temperature($20{\sim}24^{\circ}C$). The miracidia were firstly observed on 8 days after cultivation, and 85.5% of the eggs contained the mature miracidia on 11 days after cultivation. More than 90% formed the miracidia when cultivated at temperature $22{\sim}27^{\circ}C$. Hatching of the miracidia began on 12 days after cultivation and continued for a week. The size of the miracidia was $103.0{{\times}}51.4{\mu}m$ in average. The motility of the miracidia were active up to 8 hours after shedding, but they were all dead within 10 hours after shedding. 2. A freshwater snail, Radix auricularia coreana was cultivated in aquaria. A hatched $F_1$ snails from the egg masses were exposed to 20 miracidia respectively. Escape of cercariae started on 15 days after infecton. Radix auricularia coreana was experimentally identified as the first intermediate host of E. hortense in Korea. 3. Cercarial shedding started on $15{\sim}20$ days after infection by snail, continued for about 10 days (8.8 days in average). Infected snails were dead within 32 days after the miracidial infection. About 1,335 cercariae($328{\sim}1,994$) per snail were shed in its life, and 119 cercariae in average per snail per day were shed. The cercariae were motile for more than 24 hours, and then squirming at the bottom until death. The body and tail sizes of cercariae were $356{\times}186{\mu}m$ and $510{\times}68{\mu}m$ in average, respectively. The rediae parasitized in the snail hosts were found mainly around the pericardial regions, and their size was $1,575{\times}258{\mu}m$ in average. The numbers of developing cercariae in a mature redia were 14 in average ($7{\sim}20$ in range). The numbers of rediae in a snail were 102 in average on 15 days after miracidial infection and 221 in average on 28 days. 4. Three uninfected Misgurnus anguillicaudatus, less than 6.5cm long were used in for the cercarial infection. They were all exposed with 755 cercariae, and examined at 5-day intervals starting from 10 days after infection. All the fishes were infected with metacercariae of E. hortense and a total of 275 was found infected(36.4%). The metacercariae were fed to rats and the adult worms were obtained on 15 days after infection. 5. The infected rats began to deposit the eggs on 11 days after infection. The number of eggs deposited per day per worm (EPD/worm) was $400{\sim}500$ on 3 weeks after infection and was increased to $1,000{\sim}1,500$ on 4 to 17 weeks, then decreased to 800 on 21 weeks after infection. 6. A total of 745 stool specimens collected from 576 male and 169 female residents of 8 different villages along South Hangang basin was examined. Out of 745 specimens, the eggs of Echinostoma sp. were found in 2 cases (0.3%). Of 34 house rats one showed egg-positive (2.9%). 7. Total 971 Radix auricularia coreana collected from 7 sampling stations were examined for shedding of cercariae. Three snails (0.3%) shed the cercariae of E. hortense. A total of 119 out of 542 freshwater fishes (22.0%) had the metacercariae of E. hortense. The fishes parasitized with the metacercariae were 4 out of 14 examined species. The infection rates of 4 species were 34.1% (106 out of 311) in Misgurnus anguillicaudatus, 30.4% (7 out of 23) in Misgurnus mizolepis, 4.3% (2 out of 46) in Moroco oxycephalus and 22.2% (4 out of 18) in Odontobutis obscura interrupta. In summarizing the above results, the first intermediate host of E. hortense was found as Radix auricularia coreana in Korea. Also, it took about 46 days for the shortest completion of a life cycle of E. hortense in summer; that is, 10 days for miracidial development in eggs, 15 days for cercarial development in the snail, about 10 days for metacercarial development in the second intermediate hosts, and 11 days for the maturation as the adults in the definitive hosts. The natural infection rates of E. hortense in the intermediate hosts were relatively high but those in the definitive hosts were low in the middle areas of South Hangang basin.

• Journal of IKEEE
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• v.11 no.4
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• pp.331-339
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• 2007

The problem of architecting a reliable transport system across an overlay network using split TCP connections as the transport primitive is mainly considered. The considered overlay network uses the application-level switch in each intermediate host. We first argue that natural designs based on store-and-forward principles that are maintained by split TCP connections of hop-by-hop approaches. These approaches in overlay networks do not concern end-to-end TCP semantics. Then, a new transport protocol-Overlay Transport Protocol (OTP)-that manages the end-to-end connection and is responsible for the congestion/flow control between source host and destination host is proposed. The proposed network model for the congestion and flow control mechanisms uses a new window size-Ownd-and a new timer in the source host and destination host. We validate our analytical findings and evaluate the performance of our OTP using a prototype implementation via simulation.

• Bulletin of the Korean Chemical Society
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• v.10 no.6
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• pp.572-577
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• 1989

Using the low valent titanium induced carbonyl-carbonyl coupling reaction, it was attempted to synthesize sterically hindered 17-membered cyclic chiral host 2. The semifinal dialdehyde 12 was obtained through 11 step reactions beginning from p-tert-butylphenol and dibenzofuran. When dialdehyde 12 was treated with $TiCl_3-Zn/Cu,$ only intermolecularly coupled dimer 14 was obtained instead of intramolecularly coupled cyclic alkene 2. The mechanistic consideration leading to 14 was discussed and the cation binding properties of dimer 14 and dicarboxylic intermediate 13 was reported, which implies the significance of the principle of preorganization of host's binding sites prior to complexation.

• Parasites, Hosts and Diseases
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• v.21 no.1
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• pp.11-18
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• 1983

As a part of observation on the suitability as a second intermediate host of Clonorchis sinensis, various infection experiments were tried to Cyprinus carpio nodus. The results obtained were summarized as follows: 1. The cercariae which attempted to contact with Cyprinus carpio nodus in the water were observed under the stereomicroscope. After contact, cercariae began to separate its tails from the bodies at 4 minutes increasingly, and then the numbers ranged to 80% at 13 minutes after the encounter. But very few cercariae could actually invade into the epidermis of the fish. 2. When Cyprinus carpio nudes were exposed to a number of cercariae in the beaker, only a few cercariae could invade through the epidermis. Most of the invaded cercariae were killed before forming the cyst. Also rare encysted cercariae were found to be dead within 48 hours. 3. Cyprinus carpio nudes were reared with Parafossarulus manchouricus shedding numerous cercariae in the indoor aquarium. When observed after 12 days, to determine the susceptibility, no metacercaria was found infected. 4. Cyprinus carpio nudum were reared with Parafossarulus manchouricus shedding numerous cercariae in Kimhae lake for 2 months in summer of 1982, in order to check the natural infection. No metacercaria of Clonorchis sinensis was found from the fish. 5. In the cases of control fish, Pseudoraibora larva, numerous cercariae were inspected on the course of invasion through epidermis of the fish under the stereomicroscope. And many metacercariae were also found from the Ssh whenever they were kept in beaker, indoor aquarium, or the lake for natural infection. The results suggested that Cyprinus carpio kudus might not be proper intermediate host of Clonorchis sinensis.

• Parasites, Hosts and Diseases
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• v.46 no.2
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• pp.101-104
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• 2008

Metacercariae of Acanthoparyphium marilae Yamaguti, 1934 (Digenea: Echinostomatidae) were discovered in an intertidal clam, Mactra veneriformis, in a southwestern coastal area of the Republic of Korea. A total of 128 metacercariae were detected from 10 clams examined. They were round, 320 m in average diameter, with 23 collar spines. They were fed experimentally to chicks, and 10 days later adult flukes were obtained. The adults were morphologically characterized by the head collar with a single row of 23 dorsally uninterrupted spines, without special end group spines, a round ventral sucker, 2 round and tandem testes, and vitellaria extending at lateral fields from the posterior extremity not beyond the middle level of the posterior testis. The most characteristic feature of this species was the limited distribution of vitellaria, which differs from Acanthoparyphium tyosenense Yamaguti, 1939, the metacercariae of which are encysted in the same mollusk species. This is the first report in which the metacercariae of this species were detected, and the intertidal bivalve, M. veneriformis, has been identified as a second intermediate host for A. marilae.

• Korean Journal of Veterinary Research
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• v.33 no.3
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• pp.455-460
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• 1993

In the present study, the effects of 4 agricultural chemicals commonly used in this conuntry were experimentally assessed on Lymnaea viridis the intermediate host of Fasciola hepatica, which in non-target organism of these chemicals. The major habitat of the snail is rice paddies in Korea and many agricultural chemicals are used for weed, fungi or insect control in rice paddies and there is a general concern that certain levels of these chemicals could reach the aquatic ecosystem and possible alter the snail life. Agricultural chemicals used in this study included two herbicides, an insecticide and a fungicide. The tenth generation of laboratory reared snails were selected and exposed to the varying concentrations(0-100 ppm) of these chemicals. As concentrations and time of exposure increase, the per cent mortality increases(p<0.01). $LC_{50}$(lethal concentration for 50% mortality) values of these chemicals on snail after 96-hour exposure were variable; iprobenfos showed the highest acute toxicity(12.6 ppm), while carbofuran showed the lowest acute toxicity(74.5ppm). Sublethal concentrations of chemicals after 96-hour exposure were also variable ; bentazone showed the highest chronic toxicity(0.81ppm), while carbofuran showed the lowest chronic toxicity(5.04 ppm).

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.66.2-66.2
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• 2016

Red quasars have been suspected to be an intermediate population between merger-driven star-forming galaxies and normal quasars. In this scenario, red quasars are expected to have dusty red color coming from the dust extinction by dust and gas in their host galaxy. However, several studies have proposed different explanation of the red color of red quasars, which are i) a moderate viewing angle between type 1 and 2 quasars, ii) an unusual covering factor of dust torus, and iii) an anomalous synchrotron emission with a peak at NIR wavelength. In this study, we investigate the factor leading to the red color of red quasars by using the line luminosity ratios of the hydrogen Balmer to Paschen series of 11 red quasars. We find the Pb/Hb luminosity ratios of the red quasars are significantly higher than those of normal quasars. Moreover, we compare the Pb/Hb luminosity ratios of the red quasars to the theoretically expected line luminosity ratios computed from the CLOUDY code. We find the line luminosity ratios of the red quasars cannot be explained by the theoretical line luminosity ratios with any physical conditions. We conclude that red color of red quasars comes from dust extinction by their host galaxy. This result is consistent with the picture that red quasars are an intermediate population between the merger-driven star-forming galaxies and normal quasars.

• The Korean Journal of Malacology
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• v.12 no.1
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• pp.47-51
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• 1996

Radix auricularia coreana, the intermediate host of Fasciola gigantica, is the most common pulmonate snail in Korea, This species is often found intermingled with Austropeplea ollula, the intermediate host of F. hepatica, in their natural habitats. In the present study. the life history of Radix auricularia coreana was examined under three different laboratory conditions. Egg-masses were taken from the field-collected adult R. auricularia coreana and incubated in the temperature ramges of 22-26$^{\circ}C$. The hatching began after 11 days from spawned eggs, and complete hatching took about 12 days. The hatching rate was about 88%. The juvenile snails were cultured at three different laboratory conditions. When the juvenile snails were cultured in the aquarium fed on lettuce leaves at 22-26$^{\circ}C$, the snails reached 20 mm in shell length at 86 days after hatching. The bottom of each aquarium was filled up with washed sand(1.5 cm) and decomposing ark shells were put on the sand. The aquarium was then filled with four litres of distilled water and continuously aerated. Most of snails (93%) survived until the experimenta period. The dggs are laid in 40 days after hatching; the averge number of eggs per egg-mass was 40.8.

• Parasites, Hosts and Diseases
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• v.53 no.5
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• pp.647-651
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• 2015

The aim of this study was to determine the presence and prevalence of larval stages of Dicrocoelium dendriticum and Brachylaima sp. in the first intermediate host, a species of land snail, Helix aspersa, in Turkey. A total of 211 snails were collected in April-May 2014 from pastures in Mersin District. Larval stages of D. dendriticum were identified under a light microscope. Hepatopancreas from naturally infected H. aspersa snails were examined histologically. The prevalence of larval stages of D. dendriticum and Brachylaima sp. in H. aspersa snails was found to be 2.4% and 1.9%, respectively, in Mersin, Turkey. Cercariae were not matured in sporocysts at the beginning of April; however, it was observed that cercariae matured and started to leave sporocysts by early-May. Thus, it was concluded that H. aspersa acts as an intermediate host to D. dendriticumin and Brachylaima sp. in Mersin, Turkey. A digenean trematode Brachylaima sp. was seen for the first time in Turkey.

• Korean Journal of Veterinary Research
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• v.13 no.2
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• pp.147-160
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• 1973

The present experiments proposed to pass judgement upon the suitability as the second intermediate host of Clonorchis sinensis, of three kinds of fresh-water fish by having them infected with the cercaria of Clonorchis sinensis and then observing the penetrating ability of the cercaria, and maturity, the process of degeneration and extinction, and infectivity of the metacercaria of Clonorchis sinensis. The following is a brief summary of the leading facts gained through the experiments; 1. P. parva was easily subject to invasion of the cercaria, A. signifer was much less subject to the invasion, and finally A. asmussi was hard to invade. And the infectivity of the cercariae was in proportion to their penetrating ability mentioned in the above. 2. The examination of the cercariae after having three kinds of fresh-water fish infected with them disclosed that 24 hours after the infection, all of the cercariae formed their cysts in muscle and the metacercariae kept growing, and that 7 days later the metacercariae were found folding their bodies twice, and that in 15 days the characteristic structure of the metacercariae was complete and they made a vigorous rotary movement intermittently. 3. Then the metacercariae came to a state of maturity and beyond this stage some metacercariae in P. parva started the process of degeneration and extinction in 133 days; some in A. asmussi, in 140 days; and A. signifer, in 70 days. As more days elapsed, their degeneration and extinction increased in number, and in 269 days all of them in A. signifer became dead while those in A. asmussi were all dead in 460 days. However almost all of them in P. parva survived even after 770 days. The results shown above revealed that P. parva was the most suitable as the second intermediate host among three kinds of fresh-water fish and that A. signifer and A. asmussi were not quite recommendable as the second intermediate host. The ability of the cercaria to invade fresh-water fish, and life span of the metacercaria within fresh-water fish vary outstandingly according to species of fresh-water fish. An explanation as to the mechanism must wait as the subject to be further pursued.