• Journal of fish pathology
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• v.25 no.2
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• pp.85-93
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• 2012

Many metacercariae in the musculature of southern top mouthed minnow (Pseudorasbora parva) cultured at a farm in Chonbuk Province. The excysted metacercariae looked yellowish white and were $4.02{\pm}1.80$ mm (1.66-5.81) in length and $1.27{\pm}0.27$ mm (1.01-1.64) in width for acetocarmin-stained specimens. The oral sucker measuring $0.18{\pm}0.05$ mm (0.11-0.24) in length and $0.23{\pm}0.07$ mm (0.15-0.33) in width, was located at the anterior end of the body. The ventral sucker situated at the fourth third of the body were measured $0.47{\pm}0.08$ mm (0.35-0.53) in length and $0.55{\pm}0.09$ mm (0.43-0.63) in width. The tongue-shaped metacercariae were identified as Clinostomum complanatum on the basis of morphological characteristics. The metacercaria was also confirmed to be C. complanatum using PCR reaction with C. complanatum-specific primer sets, Trem 18S F and Ccom670 R. No histopathological changes in the infected fish were observed except necrosis and exfoliation of epidermis in the skin and atrophy of muscle fibers.

• Parasites, Hosts and Diseases
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• v.45 no.2 s.142
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• pp.115-120
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• 2007

Parvatrema chaii n. sp. (Digenea: Gymnophallidae) is described using the worms recovered from experimentally infected mice in Korea. The metacercariae were collected from surf-clams, Mactra veneriformis, from a tidal flat in Sochon-gun, Chungchongnam-do. The metacercariae were elliptical ($0.262{\times}0.132 mm$), and the genital pore had an anterior arch of 16-17 sensory papillae in scanning electron microscopic view, Adult worms were ovoid to foliate (0.275-0.303 by 0.140-0.150 mm), and their characteristic features included the presence of lateral lips, short esophagus, genital pore located some distance anterior to the ventral sucker, club-shaped seminal vesicle, a compact to slightly lobed vitellarium, elliptical eggs (0.018-0.020 by 0.010-0.013 mm), and absence of the ventral pit. This gymnophallid is classified as a member of the genus Parvatrema because of the location of the wide genital pore some distance from the ventral sucker, and the absence of the ventral pit. It differs from previously reported Parvatrema species, including the type species, P. borinquenae. In particular, the morphologies of the vitellarium and the genital pore with an anterior arch of 16-17 sensory papillae are unique features. Therefore, we propose it as a new species, Parvatrema chaii n. sp. (Digenea: Gymnophallidae).

• Parasites, Hosts and Diseases
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• v.53 no.2
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• pp.201-207
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• 2015

This study aimed to investigate the infection status, worm development, and phylogenetic characteristics of the intestinal trematode, Stellantchasmus falcatus. The metacercariae of S. falcatus were detected only in the half-beak (Dermogenus pusillus) out of the 4 fish species examined. Their prevalence was 90.0%, and the intensity of infection was 919 metacercariae on average. Worms were recovered from 33 (97.1%) of 34 chicks that were experimentally infected with 200 S. falcatus metacercariae each, and the average recovery rate was 43.0%. The body size and inner organs of S. falcatus quickly increased in the experimental chicks over days 1-2 post-infection (PI). In addition, ITS2 sequence data of this parasite were analyzed to examine the phylogenetic relationships with other trematodes using the UPGMA method. The results indicated that the ITS2 sequence data recorded from trematodes in the family Heterophyidae appeared to be monophyletic. This study concluded that D. pusillus serves as a compatible second intermediate host of S. falcatus in Thailand and that S. falcatus can develop rapidly in the experimental chicks. Data collected from this study can help to close the gap in knowledge regarding the epidemiology, biology, and phylogenetic characteristics of S. falcatus in Thailand.

• Parasites, Hosts and Diseases
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• v.59 no.1
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• pp.97-101
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• 2021

The infection status with Clonorchis sinensis metacercariae (CsMc) was examined in freshwater fishes from Yongjeon-cheon (a branch of Nakdong-gang) located in Cheongsong-gun, Gyeongsangbuk-do, the Republic of Korea (Korea). A total of 750 fishes in 19 species were examined by the artificial digestion method for 2 years (2019 and 2020). CsMc were detected in 378 (51.4%) out of 735 fishes in 14 species (73.7%), and the infection intensity was 666 per fish infected. In 2019, CsMc were found in 172 (68.0%) out of 253 fishes in 10 species, and the infection intensity was 565 per fish infected. In 2020, CsMc were detected in 206 (62.2%) out of 331 fishes in 10 species, and the infection intensity was 751 per fish infected. The other zoonotic trematode, ie. Metagonimus spp., Centrocestus armatus, Echinostoma spp. and Clinostomum complanatum, metacercariae were also detected in fishes from the survey streams, but their endemicities were relatively low. Conclusively, it was first confirmed that CsMc are highly endemic in fishes from Yongjeon-cheon in Cheongsong-gun, Gyeongsangbuk-do, Korea.

• Parasites, Hosts and Diseases
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• v.59 no.1
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• pp.47-53
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• 2021

Echinostoma mekongi was reported as a new species in 2020 based on specimens collected from humans in Kratie and Takeo Province, Cambodia. In the present study, its metacercarial stage has been discovered in Filopaludina martensi cambodjensis snails purchased from a local market nearby the Tonle Sap Lake, Pursat Province, Cambodia. The metacercariae were fed orally to an experimental hamster, and adult flukes were recovered at day 20 post-infection. They were morphologically examined using light and scanning electron microscopes and molecularly analyzed by sequencing of their mitochondrial cox1 and nad1 genes. A total of 115 metacercariae (1-8 per snail) were detected in 60 (60.0%) out of 100 Filopaludina snails examined. The metacercariae were round, 174 ㎛ in average diameter (163-190 ㎛ in range), having a thin cyst wall, a head collar armed with 37 collar spines, and characteristic excretory granules. The adult flukes were elongated, ventrally curved, 7.3 (6.4-8.2)×1.4 (1.1-1.7) mm in size, and equipped with 37 collar spines on the head collar (dorsal spines in 2 alternating rows), being consistent with E. mekongi. In phylogenetic analyses, the adult flukes showed 99.0-100% homology based on cox1 sequences and 98.9-99.7% homology based on nad1 sequences with E. mekongi. The results evidenced that F. martensi cambodjensis snails act as the second intermediate host of E. mekongi, and hamsters can be used as a suitable experimental definitive host. As local people favor to eat undercooked snails, these snails seem to be an important source of human infection with E. mekongi in Cambodia.

• Parasites, Hosts and Diseases
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• v.60 no.2
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• pp.79-96
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• 2022

The infection nature of Clonorchis sinensis metacercariae (CsMc) in freshwater fish hosts is closely related to the transmission of human clonorchiasis. This article reviewed the infection characteristics of CsMc in freshwater fish in the Republic of Korea (Korea). The status of CsMc infection was examined in a total of 17,792 cyprinid fish of 49 species in 9 water systems, which included Hantan-/Imjin-gang, Han-gang, Geum-gang, Mangyeong-gang, Yeongsan-gang, Tamjin-gang, Seomjin-gang, Nakdong-gang, and streams in the east coastal areas from 2010 to 2020. The infection status of CsMc was examined according to cyprinid fish species and water systems, after which analyzed by endemicity and susceptibility index. The high endemicity was shown in the cyprinid fish from 3 regions (6.1%) in the upper reaches of Nakdong-gang, such as Banbyeon-cheon (stream), Yongjeon-cheon, and Wi-cheon. The moderate levels were observed in fishes from 8 regions (16.3%), and low endemicity was shown in fishes from 20 regions (40.8%). No CsMc were detected in fish from 18 regions (36.7%). The susceptibility of CsMc in index fish, Puntungia herzi, was found to be a reliable index without examination of other fish species. CsMc infection rates were closely related to subfamily groups in the cyprinid fish hosts in a highly endemic area. In Korea, a total of 58 fish species in 10 families has been listed as the second intermediate hosts for C. sinensis. This review provides several novel features of CsMc infection and clarifies the species of second intermediate freshwater fish host in Korea.

• Parasites, Hosts and Diseases
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• v.24 no.2
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• pp.137-144
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• 1986

The author has studied the $\beta$-glucuronidase activity in several tissues such as liver, stomach and small intestine of the male and female rabbits infected with different doses of metacercariae of Clonorchis sinensis. The metacercariae of Clonorchis sinensis were isolated from Pseudorasbora parva caught in Kim Hae by digestion technic. The experimental animals were sacrificed in the period of 1, 7, 14, 21, 28 and 35th days following the infection. The results obtained were summarized as follows. 1. In the groups infected with 100 metacercariae, $\beta$-glucuronidase activity was slightly increased during the entire periods than control rabbits. It was the highest in the first day with 1.535 and $1.421m{\mu}/g$, 14th days with 2.521 and $2.200m{\mu}/g$, and then lowered by the time, gradually. 2. In the groups infected with 500 metacercariae, $\beta$-glucuronidase activity was highly increased on the first day with 1.535 and $1.856m{\mu}/g$ than that 100 metacercariae groups according to each organs. It was the highest on the 7th day and 14th day. 3. In the groups infected with 1,000 metacercariae, $\beta$-glucuronidase activity was remarkably increased in the first and 14th days according to each organs, and then lowered gradually day by day. 4. $\beta$-glucuronidase activity of all organs was more increased than that of normal organs and the highest activity in the liver with $2.521m{\mu}/g$, intestine(1.612) and stomach (1.581) respectively. 5. $\beta$-glucuronidase activity of rabbits was higher in the female than in the male. On the basis of these results, it was suggested that $\beta$-glucuronidase activity was affected by the duration of infection and by the number of Clonorchis sinensis, according to the organs and sex of the rabbits.

• Parasites, Hosts and Diseases
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• v.25 no.1
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• pp.69-82
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• 1987

The prevalences of the cuke belonging to genus Metagonimus hove been reported along the upper stream of inhabitants by several workers since 1980, however the taxonomical problems of the fluke was not yet settled. The larval flukes; cercaria and metacercaria as well as their intermediate hosts, and adult were studied in order to identify the Mepagonimus in the areas. The results obtained are summarized as follows: 1. The snails, Semisulcospira globus were collected (rom the three different localities along the upper stream of the River. The cercariae were found from 125(7.2%) out of 1,730 snails by natural emerging method, and were identified into 5 species including Metagenimus sp. (3.7%), Pseudexorchis major(1.4%), Cercaria nipponensis (0.9%), Cercaria incerpa(0.6%), and Cercaria yoshidae(0.6%). Cercariae of Metagonimus species had four to dye oral spines on its anterior of the first line. 2. The cercariae of Metagonimus were experimentally exposed to goldfish. nfection rate was 22.9% out of 105 goldfish, and the encysted metacercariae were found in fins(86.7%) and on scales (13.7%) of the fishes, but not in their muscle, head or visceral organs. 3. Seven species of ask were caught in the Daecheong Reservoir and the upper stream. Infestations with metacercaria of Metagonimus were found 100% in Opsariichtys widens and the parasitized numbers of the metacercariae were observed from 250 to 2,400 per fish. In the upper stream, Zacco termmincki, Z. platypus and Pseudogobio esocinus were infected 100% with the metacercaria, on the other hand, the fishes caught in the reservoir showed the lower infestation rates, and a few metacercariae found in the fishes Carassius carassius and Cyprinus carpio in the reservoir and the stream. The majority of metacercariae was detected only on the scales of fishes. 4. In order to know the infectivity and the distribution patterns in the intestine of hosts, rats and dogs were infected with the metacercariae obtained from O. bidens and Z. platypus. In addition the metacercariae obtained from Z. temmincki, P. esocinus and goldfish were given to the rats. The recovery rates of the worms in the small intestine of dogs were higher (63.3~65.8%) than those of the rats (3.5~31.6%). The flukes were found mostly in the middle and the lower part of small intestine of the rats and the dogs, but no worm was collected in the upper part of the intestine of rats. 5. The sixte of adult flukes varied by the hosts. In the adult cukes, oral sucker was smaller than ventral sucker, and the right and left testes were located diagonally, the uterine tubules circled around the upper left testis. The average egg sixte was $29.1{\times}1.7{\mu\textrm{m}}$. According to the above results, the cukes belonging to genus Metagonimus distributed along the Geum River was concluded to be identical with Miyata type of M. yokogawai as that Saito had proposed.

• Parasites, Hosts and Diseases
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• v.33 no.4
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• pp.297-304
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• 1995

To evaluate the feasibility of irradiation as a control measure for metagonimiasis, the metacercariae of Metagonimus yokogcwni were irradiated with gamma ray, either after isolation from the sweetfish (Plecoglossus cltivelis) or in situ of the fish, and their survival and development in rats were observed at 7 days post-infection. The radiation dose varied from 5 to 100 Gy for the metacercaria-irradiation group and from 5 to 500 Gy for fish-irradiation group. The results showed that the worm recovery rate from the irradiation groups decreased as the radiation dose was increased. Higher doses of radiation were required for the fish-irradiation group to obtain the same results as the metacercaria-irradiation group. The LD50 of the metacercaria-irradiation group was 4.5 Gy, whereas that of the fish-irradiation group 6.2 Gy A few number of worms which survived until 7 days in rats were severely retarded especially in the growth of their reproductive organs, j.e., complete or partial failure in the development of testes and formation of uterine eggs . The present study revealed that irradiation of sweetfish by 200 Gy is effective to control infectivity as well as development of M. vokogawai metacercariae in rats.

• Parasites, Hosts and Diseases
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• v.33 no.4
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• pp.289-296
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• 1995

The surface ultrastructure of metacercariae and adults of Gymnophallokles seoi, the only known gymnophallid infecting humans, was observed by scanning electron microscopy. Metacercariae were ovoid or pyriform in shape and slightly concave ventrally. The oral sucker had two sizes of type I papillae, small and large, encircling its lip. Type I papillae were arranged in a row on both side oi the body. The ventral pit had several type I papillae on its inner surface. The ventral sucker was covered with cobble-stone like cytoplasmic processes and had 6 type I papillae on its lip. The surface of the body was covered with the tegumental spines except for the ventromedian area between the two suckers. The spines at anterior body were digitated into 3-5 points, and their size decreased at posterior one third or the body. Adult worms were rhomboid or ellipsoid in shape and covered with tegumental spines except for the ventromedian area. The shape and distribution of the tegumental spines and sensory papillae were similar to those of metacercariae. However, sensory papillae arranged in a row on the ventral surface of metacercariae were not observed in adults. The ventral pit became larger and more prominent as the fluke grew. It is suggested that the ventral pit function as an additional adhesive organ to the host tissue.