• Parasites, Hosts and Diseases
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• v.58 no.1
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• pp.27-35
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• 2020

This study aimed to investigate metacercarial infections in the wrestling halfbeak, Dermogenys pusilla, collected from Bangkok metropolitan region of Thailand. A total of 4,501 fish from 78 study sites were commonly examined with muscle compression and digestion methods (only head part of fish) during September 2017 to July 2018. The overall prevalence of metacercarial infection was 86.1% (3,876/4,501 individuals), and the mean intensity was 48.9 metacercariae per fish infected. Four species, i.e., Posthodiplostomum sp., Stellantchasmus falcatus, Cyathocotylidae fam. sp., and Centrocestus formosanus, of digenetic trematode metacercariae (DTM) were detected. The prevalences were 65.8%, 52.0%, 2.1%, and 1.2%, respectively and their mean intensities were 23.1, 51.6, 1.4, and 3.2 per fish infected, respectively. The seasonal prevalences were 81.0% in winter, 87.8% in summer and 87.4% in rainy, and the mean intensities were 38.9, 46.6, and 55.2 metacercariae per fish infected, respectively. Conclusively, it was confirmed that the wrestling halfbeak play the role of second intermediate hosts of 4 species of digenetic trematodes including S. falcatus and Posthodiplostomum sp. in Bangkok metropolitan region. And then the metacercariae of C. formosanus and Cyathocotylidae fam. sp. are to be first found in the wrestling halfbeak by this study.

• Parasites, Hosts and Diseases
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• v.32 no.3
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• pp.157-162
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• 1994

A highly endemic focus of human infection with Heterophves nocens (Heterophyidae) was discovered from a small coastal village of Shinan-gun, Chollanam-do, for the first time in Korea. Fecal examinations by cellophane thick smear and formalin- ether sedimentation techniques revealed 42.9% heterophyid egg Positive rate out of 98 inhabitants examined. It was difficult to confirm the species of heterophylds only by eggs. In order to collect the adult flukes, the egg Positive cases were treated with 10 mg/kg single dose of praziquantel and purged with magnesium sulfate, and the adult worms were collected from the diarrheic stools. From each of 18 cooperative patients 1 to 1,124 (total 4,730) H. nocens worms were recovered, together with a few to large numbers of heterophyids (Pvginiopsis summa, Stictonora juscatunl and for gymnophallids (Gvmopholloides stool) . It is speculated that H. nocen might be widely distributed along the southwestern coastal areas where the brackish water fish such as the mullets or gobies are popularly eaten raw.

• Parasites, Hosts and Diseases
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• v.57 no.3
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• pp.257-264
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• 2019

We tried a series of morphological and molecular approaches to identify a new species of Stellantchasmus (Digenea: Heterophyidae) originating from the wrestling half-beaked fish, Dermogenys pusillus of Thailand. Adult worm samples of the new species were recovered from hamsters experimentally infected with the metacercariae from D. pusillus in Thailand. Two isolates (Thai and Korean) of Stellantchasmus falcatus were used as comparative control groups. Worm samples of 3 Stellantchasmus groups were morphologically observed and molecularly analyzed with the mitochondrial cytochrome c oxidase 1 gene. The morphological characteristics of S. dermogenysi n. sp. are similar to S. falcatus originating from brackish water fish, but minor difference was noted including the absence of the prepharynx, position of the ovary near the ceca end, smaller body size, and shorter esophageal length. A phylogenetic tree derived from neighbor-joining and maximum-likelihood methods suggests that S. dermogenysi n. sp. is separated from S. falcatus supported by high bootstrap values. The relative divergences persist between these host-specific trematodes, which we suggest should be recognized as 2 distinct species. Comparisons of S. dermogenysi n. sp. with S. falcatus isolated from mullets in Thailand and Korea indicate a genetic divergence of mitochondrial DNA of 19.4% and 21.7%, respectively. By the present study, a new species, Stellantchasmus dermogenysi n. sp. (Digenea: Heterophyidae), is proposed in Thailand based on molecular evidences, in addition to minor morphological differences between S. falcatus and the new species.

• Parasites, Hosts and Diseases
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• v.60 no.3
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• pp.187-193
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• 2022

The positive rate of Clonorchis sinensis is the highest among intestinal parasites in the Republic of Korea (Korea). More than 1.2 million people were at risk of C. sinensis infection in Korea in 2012. An intensive control program is being implemented for residents of the 5 major river basins to reduce helminthic infections, including C. sinensis infection. This study evaluated the continuous intensive control program for parasitic diseases including clonorchiasis in areas near the 5 major river basins in Korea over the past 10 years (2011-2020). A total of 335,020 fecal samples (one sample per resident) prepared by the modified sedimentation technic were microscopically examined. Those who expelled helminth eggs were treated with anthelmintics through local health centers and re-examined 3 months later. The overall positive rate of helminths egg was 7.1%. The annual positive rates were dramatically decreased from 14.4% (2011) to 5.9% (2020). The egg positive rate was highest in C. sinensis (5.3%), followed by heterophyid flukes (1.5%) and Trichuris trichiura (0.2%). The prevalence of C. sinensis was significantly higher in males (7.6%) than in females (3.7%), and the highest in the 50-59 years (7.0%) age group. Our results are beneficial to establish prevention and control policies against helminthiases including clonorchiasis in endemic areas in this country.

• Parasites, Hosts and Diseases
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• v.61 no.2
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• pp.163-171
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• 2023

The present study aimed to determine the infection status of trematode metacercariae and adults in cyprinoid fish from the Khun Thale Swamp in Surat Thani, Southern Thailand, with epidemiologic and faunistic viewpoints. In 2020, 577 fish in 15 species were collected in the summer (February-April) and rainy (September-November) seasons. Fish were individually examined for trematode metacercariae in the whole body and adults in the gastrointestinal tract using a stereomicroscope. Three species of digenetic trematode metacercariae, i.e., Haplorchis taichui, Haplorchoides mehrai, and Centrocestus formosanus, were detected in the muscle, fin, and/or scale of fish. Two species of adult flukes, including Rohdella siamensis and Helostomatis cyprinorum, were collected in the intestines. The prevalence of overall trematode infections was 32.4% (187/577 fish), which was higher in the rainy season (41.4%; 118/285) than in the summer season (23.6%; 69/292). The metacercariae of H. taichui and H. mehrai were detected in 7 fish species each, and those of C. formosanus were found only in Rasbora toneri. The aspidogastrean trematode R. siamensis (adult) was detected in Babonymus gonionotus. A digenean species, H. cyprinorum (adult), was found in Labiobarbus siamensis and Osteochilus vittatus. The present study has first confirmed that the metacercariae of heterophyid flukes, including H. taichui, H. mehrai, and C. formosanus, and adults of R. siamensis (Aspidogastrea) and H. cyprinorum (Digenea) are infected in some species of the cyprinoid fish from the Khun Thale Swamp in Surat Thani, Thailand.

• Parasites, Hosts and Diseases
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• v.22 no.2
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• pp.171-180
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• 1984

In order to provide some clues for differential diagnosis of trematode infections in fecal examination, the comparative morphology of eggs of 5 kinds of heterophyid flukes (Metagonimus yokogawai, Heterophyes heterophyes nocens, Heterophyopsis continua, Stellantchasmus falcatus and Pygidiopsis summa) and Clonorchis sinensis was studied. The eggs were obtained from distal portion of uteri of worms which were recovered from men after treatment. The characteristic shape and appearance of each kind of eggs were observed in detail under light microscope, and their length and width measured and compared one another. The results are as follows: 1. Eggs of C. sinensis are elongated ovoidal in shape with attenuated anterior end, 25.3~33. 2 (28. 3 in average) ${\mu}m$ long and 14.2~17.4(5.9) ${\mu}m$ wide with length/width ratio of 1.60~2.00 (1.78). They differ from all heterophyid eggs in that they have prominent wrinkling (muskmelon pattern) at their shell surface. 2. P. summa eggs are ovoid to pyriform in shape and characterized by the smallest size of all kinds examined, 19.8~22.9 (21.6) ${\mu}m$ long and 11.1~13.4 (12.1) ${\mu}m$ wide and the ratio 1.63~1.99 (1.78). 3. Eggs of S. falcatus are elongated ovoidal and most slender form, 25.3~29.2 (27.2) ${\mu}m$ long and 11.1~13.4 (12.5) ${\mu}m$ wide with the ratio of 2.00~2.57 (2.17). 4. Eggs of M. yokogawai are ellipsoid to elliptical in shape with round both ends, 26.9~31.6 (28.5) ${\mu}m$ long and 14.2~18.2 (16.8)${\mu}m$ wide with the ratio of 1.48~2.11 (1.70). 5. H. continua eggs are oval in shape, sometimes similar to M. yokogawai or H. h. nocen$ eggs, however, the relative breadth is broadest among all kinds, with maximum width at posterior half portion. They are 23.7~27.7 (25.0) ${\mu}m$ long, 15.8~18.9 (16.4) ${\mu}m$ wide with the ratio of 1. 33~1.75 (1.53). 6. Eggs of H. h. nocens are ellipsoid to ovoid in shape but sometimes more slender than M. yokogawai and have slightly pointed both ends. They are 23.7~29.2 (25.7) p.m long, 14.2~15.8 (15.4) ${\mu}m$ wide, and the ratio 1.50~2.06 (1.67). From the results, it is concluded that eggs, of 5 kinds of heterophyids and C. sinensis can be morphologically differentiated one another, however, careful observation and measurement on sufficient number of eggs are needed.

• Parasites, Hosts and Diseases
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• v.45 no.1 s.141
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• pp.39-44
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• 2007

A new endemic focus of Gymnophalloides seoi infection has been discovered on Aphae Island(Shinan-gun, Jeollanam-do), Republic of Korea. This area, which is referred to as Bokyong-ri, is a small seashore village located in the northern portion of the island. Fecal samples were collected from a total of 57 residents and examined by the Kato-Katz and formalin-ether sedimentation techniques. Helminth eggs were detected in 37 samples(64.9%); 33 samples were positive for G. seoi eggs(57.9%), 4 for Pygidiopsis summa(7.0%), 13 for other heterophyids(22.8%), 1 for Clonorchis sinensis(1.7%), and 1 for Trichuris trichiura(1.7%). Women(70.4%) revealed higher rates of G. seoi infection than did men(46.7%), and individuals older than 50 years of age also evidenced higher rates of G. seoi infection than in other age groups(P<0.05). In worm collection from 13 G. seoi egg positive cases, G. seoi (total 86,558 specimens), Heterophyes nocens(278), Stictodora sp.(10), Heterophyopsis continua(3), P. summa(3), and unidentified flukes(42) were collected. Oysters, the source of G. seoi infection, were collected from an area proximal to the village and 50 were examined for metacercariae; 47(94%) were found infected and the observed metacercarial density was $9.5{\pm}8.9$ per oyster. The results of this study indicate that Bokyong-ri is a new endemic area of G. seoi infection, with high rates of infection in humans and oysters.

• Parasites, Hosts and Diseases
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• v.45 no.3
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• pp.205-211
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• 2007

The infection status of mullets Mugil cephalus (n = 139) and gobies (n = 35) Acanthogobius fIavimanus with metacercariae of Heterophyes nocens and Pygidiopsis summa was examined in 11 western, southern, and eastern coastal areas of the Republic of Korea, using a digestion technique. Heterophyid metacercariae were highly prevalent in mullets from western and southern coastal areas; Shinan-gun (100% for H. nocens and 100% for P. summa), Muan-gun (93% and 100%), Buan-gun (42% and 75%), Seocheon-gun (73% and 53%), Ganghwa-gun (47% and 100%), Sacheon-shi (47% and 77%), and Gangjin-gun (50% and 70%, respectively). Only 1 (10%) of 10 mullets from an eastern coastal area, i.e., Donghae-shi, was positive for P. summa metacercariae. Metacercarial densities were the highest in the trunk of mullets for H. nocens and the gill for P. summa. Gobies from Muan-gun were positive for H. nocens (40%) and P. summa metacercariae (40%), and gobies from Seocheon-gun revealed H. nocens metacercariae (20%). The metacercarial density was remarkably higher in mullets than in gobies. The results revealed that H. nocens and P. summa metacercariae are prevalent in mullets and gobies from coastal areas of the Republic of Korea, and the prevalence and intensity of infection vary according to geographical locality.

• Parasites, Hosts and Diseases
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• v.53 no.4
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• pp.447-453
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• 2015

The infection status of fishborne zoonotic trematode (FZT) metacercariae was investigated in fishes from 2 localities of Lao PDR. Total 157 freshwater fishes (17 species) were collected in local markets of Vientiane Municipality and Champasak Province in December 2010 and July 2011, and each fish was examined by the artificial digestion method. Total 6 species of FZT metacercariae, i.e., Opisthorchis viverrini, Haplorchis taichui, Haplorchis yokogawai, Haplorchis pumilio, Centrocestus formosanus, and Procerovum varium, were detected in fishes from Vientiane Municipality. The metacercariae of O. viverrini were detected in 50 (49.5%) out of 101 fishes (6 species), and their average number was 154 per fish infected. The remaining 5 species of heterophyid metacercariae were detected in 36.8%, 65.8%, 9.4%, 23.9%, and 5.1% fishes examined, and their average densities were 12, 1,038, 4, 15, and 13 per infected fish, respectively. In fishes from Champasak Province, 3 species of FZT metacercariae, i.e., O. viverrini, H. taichui, and H. yokogawai, were detected. Only 2 O. viverrini metacercariae were found in only 1 Barbonymus schwanefeldi. The metacercariae of H. taichui and H. yokogawai were detected in 60.0% and 50.0% of fishes examined, and their average densities were 47 and 28 per fish infected. By the present study, it has been confirmed that several species of FZT metacercariae are prevalent in fishes from Vientiane Municipality, with P. varium being a new member of FZT in Lao PDR. In comparison, FZT metacercariae are less prevalent in fishes from Champasak Province.

• Parasites, Hosts and Diseases
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• v.51 no.3
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• pp.305-311
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• 2013

In this study, we found that Haplorchis taichui, a heterophyid intestinal fluke, is highly prevalent, with heavy worm loads, among riparian people in Saravane and Champasak province, Lao PDR. Fecal specimens were collected from 1,460 people (717 men and 743 women) in 12 riparian (Mekong river) districts and were examined by the Kato-Katz fecal smear technique. The overall helminth egg positive rate was 78.8% and 66.4% in Saravane and Champasak province, respectively. The positive rate for small trematode eggs (STE), which included H. taichui and other heterophyids, Opisthorchis viverrini, and lecithodendriids, was 69.9% and 46.3% in Saravane and Champasak province, respectively. To obtain adult flukes, 30 STE-positive people were treated with 40 mg/kg praziquantel and then purged. Whole diarrheic stools were collected 4-5 times for each person and searched for fluke specimens using a stereomicroscope. Mixed infections with various species of trematodes (H. taichui, Haplorchis pumilio, O. viverrini, Prosthodendrium molenkampi, Centrocestus formosanus, and Echinochasmus japonicus) and a species of cestode (Taenia saginata) were found. However, the worm load was exceptionally high for H. taichui compared with other trematode species, with an average of 21,565 and 12,079 specimens per infected person in Saravane and Champasak province, respectively, followed by H. pumilio (41.9 and 22.5, respectively) and O. viverrini (9.4 and 1.5, respectively). These results show that diverse species of intestinal and liver flukes are prevalent among riparian people in Saravane and Champasak province, Lao PDR, with H. taichui being the exceptionally dominant species.