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It is uncertain when the head collar and collar spines of Isthmiophora hortensis (Digenea: Echinostomatidae), a zoonotic echinostome species in Far Eastern Asia, develop during its larval stages. In this study, the appearance of the head collar and collar spines was studied using light and scanning electron microscopy in cercariae and metacercariae experimentally obtained from freshwater snails (Lymnaea pervia) and tadpoles (Rana nigromaculata), respectively. The cercariae were shed from the snail on day 30 after exposure to laboratory-hatched miracidia. Metacercariae were obtained from the experimental tadpoles at 3, 6, 12, 15, 20, 24, 26, and 30 h after exposure to the cercariae. The head collar was already visible in the cercarial stage, although its degree of development was weak. However, collar spines did not appear in the cercarial stage and even in the early metacercarial stage less than 24 h postinfection in tadpoles. Collar spines became visible in the metacercariae when they grew older than 24 h. It was concluded that the head collar of I. hortensis developed early in the cercarial stage, but the development of collar spines did not occur until the worms became 24-h-old metacercariae in our experimental setting. Counting the number of collar spines was concluded as an unfeasible diagnostic method for I. hortensis cercariae when they are shed from the snail host.

Epigenetic writers including DNA and histone lysine methyltransferases (DNMT and HKMT, respectively) play an initiative role in the differentiation and development of eukaryotic organisms through the spatiotemporal regulation of functional gene expressions. However, the epigenetic mechanisms have long been suspected in helminth parasites lacking the major DNA methyltransferases DNMT1 and DNMT3a/3b. Very little information on the evolutionary status of the epigenetic tools and their role in regulating chromosomal genes is currently available in the parasitic trematodes. We previously suggested the probable role of a DNMT2-like protein (CsDNMT2) as a genuine epigenetic writer in a trematode parasite Clonorchis sinensis. Here, we analyzed the phylogeny of HKMT subfamily members in the liver fluke and other platyhelminth species. The platyhelminth genomes examined conserved genes for the most of SET domain-containing HKMT and Disruptor of Telomeric Silencing 1 subfamilies, while some genes were expanded specifically in certain platyhelminth genomes. Related to the high gene dosages for HKMT activities covering differential but somewhat overlapping substrate specificities, variously methylated histones were recognized throughout the tissues/organs of C. sinensis adults. The temporal expressions of genes involved in eggshell formation were gradually decreased to their lowest levels proportionally to aging, whereas those of some epigenetic tool genes were re-boosted in the later adult stages of the parasite. Furthermore, these expression levels were significantly affected by treatment with DNMT and HKMT inhibitors. Our data strongly suggest that methylated histones are potent epigenetic markers that modulate the spatiotemporal expressions of C. sinensis genes, especially those involved in sexual reproduction.

This article analyzed the infection characteristics of metacercariae of Metagonimus spp. (MsMc) in fish from 9 major water systems in Korea. A total of 19,568 fish in 87 species were examined over a period of 10 years (2011-2020). MsMc were detected in fish from all 44 survey areas in 9 water systems. Most of the surveyed sites showed very low and low infection levels (66.7%), while 33.3% of the areas, such as Tamjin-gang and Seomjin-gang, revealed moderate and high infection levels. High endemicity depends on the abundance of susceptible fish species, especially sweet smelt (Plecoglosus altivelis). The susceptibility index (SI) with MsMc in index fish, Zacco spp., was very low and low levels in 62.0%, moderate in 28.0%, and high in 10.0% regions. The SI was highest in the following order: Yeongam-cheon (283.8), Hoeng-cheon (192.3), Togyo-jeosuji (131.2), Deokcheon-gang (119.1), and Joyang-gang (106.3). The recent infection status of MsMc in P. altivelis was analyzed by the survey localities. In addition, except for P. altivelis, 9 fish species were highly infected with MsMc in some survey areas, including Zacco platypus, Z. koreanus, Z. temminckii, Opsariichthys uncirostris, Rhynchocypris oxycephalus, Carassius auratus, Acheilognathus rhombeus, Onchorhynchus masou, and Tribolodon hakonensis. In Korea, 74 fish species (15 families) are collectively listed as second intermediate hosts of Metagonimus spp. This review provides several novel characteristics of MsMc infection and clarifies the fish species of second intermediate host of Metagonimus spp. in this country.

The endemicity of zoonotic trematode metacercariae (ZTM) was investigated with total 871 freshwater fishes (19 species) from Deokcheon-gang (a branch stream of Gyeongho-gang) in Sancheong-gun, Gyeongsangnam-do, Korea for 3 years (2018-2020). All fishes were examined with the artificial digestion method. The metacercariae of Clonorchis sinensis (CsMc) were detected in 233 (36.3%) out of 642 fish in 11 positive fish species (PFS), and their infection intensity was 27 per fish infected (PFI). Especially, in index fish, Puntungia herzi, of CsMc infection, prevalence was 64.2% and infection intensity was 37 PFI. Metagonimus spp. metacercariae (MsMc) were found in 760 (87.5%) out of 869 fish in 18 PFS and their infection intensity was 228 PFI. In sweet smelt, Plecoglossus altivelis, the prevalence of MsMc was 97.6% and their infection intensity was 3,570 PFI. Centrocestus armatus metacercariae were detected in 209 (29.4%) out of 710 fish in 8 PFS and their infection intensity was 1,361 PFI. Echinostoma spp. metacercariae were found in 293 (42.6%) out of 688 fish in 15 PFS and their infection intensity was 5 PFI. Metacercariae of Clinostomum complanatum and Metorchis orientalis were also detected in 2.7% and 21.2% fish in 4 PFS and their infection intensities were 3.1 and 3.4 PFI respectively. By the present study, it was confirmed that some species of ZTM including CsMc and MsMc are more or less prevalent in fishes from Deokcheon-gang in Sancheong-gun, Gyeongsangnam-do, Korea.

The infection status of zoonotic trematode metacercariae (ZTM) was investigated in total 568 freshwater fishes (19 species) from the irrigation canal of Togyo-jeosuji (Reservoir) in Cheorwon-gun, Gangwon-do, the Republic of Korea for 3 years (2018-2020). All fishes were examined using the artificial digestion method. The metacercariae of Clonorchis sinensis (CsMc) were detected in 180 (43.8%) out of 411 fish of positive species, and their infection intensity was 38 per fish infected (PFI). Especially, in 2 fish species, i.e., Pseudorasbora parva and Puntungia herzi, the prevalence was 82.1% and 31.3%, and the infection intensity with CsMc was 88 and 290 PFI, respectively. Metagonimus spp. metacercariae (MsMc) were found in 403 (74.1%) out of 544 fish of positive species, and their infection intensity was 62 PFI. In the pale chub, Zacco platypus, the prevalence of MsMc was 98.6%, and their infection intensity was 144 PFI. Centrocestus armatus metacercariae were detected in 171 (38.9%) out of 440 fish of positive species, and their infection intensity was 1,844 PFI. Echinostoma spp. metacercariae were found in 94 (19.6%) out of 479 fish of positive species, and their infection intensity was 3 PFI. Metorchis orientalis metacercariae were detected in 43 (29.3%) out of 147 fish of positive species, and their infection intensity was 4 PFI. By the present study, it has been confirmed that some species of ZTM, including CsMc and MsMc, are prevalent in fishes from the irrigation canal of Togyo-jeosuji in Cheorwon-gun, Gangwon-do, Korea.

We surveyed on the infection status of zoonotic trematode metacercariae (ZTM) in freshwater fishes from Soyang-cheon (a branch stream of Mangyeong-gang) in Wanju-gun, Jeollabuk-do, the Republic of Korea. A total of 927 fishes were individually examined with the artificial digestion method during 2013-2015 (462 fish in 15 spp.) and 2018-2019 (465 fish in 25 spp.). Clonorchis sinensis metacercariae were detected in 207 (31.4%) out of 659 fishes in 14 positive fish species (PFS), and their mean intensity was 114 per fish infected (PFI). Metagonimus spp. metacercariae were found in 302 (37.4%) out of 808 fishes in 21 PFS, and their mean intensity was 12 PFI. Centrocestus armatus metacercariae were detected in 222 (59.0%) out of 376 fishes in 12 PFS, and their mean intensity was 383 PFI. Echinostoma spp. metacercariae were found in 139 (22.1%) out of 628 fishes in 10 PFS, and their mean intensity was 7 PFI. Clinostomum complanatum metacercariae were detected in 14 (6.5%) out of 214 fishes in 4 PFS, and their mean intensity was 2.4 PFI. Metorchis orientalis metacercariae were detected in 36 (13.5%) out of 267 fishes in 5 PFS, and their mean intensity was 4.3 PFI. Conclusively, the prevalence and infection intensity of ZTM is generally not so high in fishes from Soyang-cheon. However, those of C. sinensis metacercariae are more or less higher in 2 fish species, Pungtungia herzi and Sarcocheilichthys variegatus wakiyae.

The infection status of zoonotic trematode metacercariae (ZTM) was surveyed in freshwater fishes from the water systems of Geum-gang (River) in the Republic of Korea (Korea). A total of 1,161 freshwater fishes from 6 local sites of Geum-gang were examined with the artificial digestion method for 4 years (2012-2015). Clonorchis sinensis metacercariae were detected in 122 (37.2%) out of 328 fishes in the positive fish species from 4 surveyed areas, and their mean intensity was 43 per fish infected. Metagonimus spp. metacercariae were found in 432 (51.7%) out of 835 fishes in the positive fish species from all 6 surveyed areas, and their mean intensity was 30 per fish infected. Centrocestus armatus metacercariae were detected in 285 (75.0%) out of 380 fishes in the positive fish species from 6 surveyed areas, and their mean intensity was 2,100 per fish infected. Echinostoma spp. metacercariae were found in 56 (19.7%) out of 284 fishes in the positive fish species from 5 surveyed areas, and their mean intensity was 10 per fish infected. Clinostomum complanatum metacercariae were detected in 98 (57.3%) out of 171 fishes in the positive fish species from only 2 surveyed areas, and their mean intensity was 11 per fish infected. Conclusively, the endemicity of ZTM is not so high in fishes from water systems of Geum-gang in Korea although it is more or less different by fish species, surveyed areas and ZTM species.

A survey was performed to investigate the infection status of zoonotic helminth larvae in fish from a local market of North Dagon District in Yangon City, Myanmar. A total of 486 fish in 13 species were collected 8 times from December 2015 to December 2019. All fish were transported under ice to a laboratory in Korea and examined for helminth larvae using artificial digestion method. Larval gnathostomes and metacercariae of more than 8 zoonotic trematode species, i.e., Opisthorchis viverrini, Haplorchis taichui, H. pumilio, H. yokogawai, Centrocestus spp., Stellantchasmus falcatus, Pygidiopsis cambodiensis, and Procerovum sp., were detected. Larval gnathostomes were found in 58 (16.0%) out of 362 fish of 6 species, with mean intensity of 2.8 per fish infected. Metacercariae of O. viverrini were detected in 10 (2.9%) out of 349 fish of 5 species, with mean intensity of 16.9 per fish infected. Metacercarial prevalences of 4 intestinal flukes, H. taichui, H. pumilio, H. yokogawai, and Centrocestus spp., were 16.8%, 26.0%, 12.5%, and 15.0% in the positive fish species, respectively, and mean metacercarial intensity was 63.3, 26.8, 86.2, and 8.7 per fish infected. Metacercariae of S. falcatus and P. cambodiensis were detected only from the mullet, Chelon macrolepis. Metacercariae of Procerovum sp. were found in Channa striata and Anabas testudineus. Collectively, it was confirmed that the fish were infected with gnathostome larvae and metacercariae of O. viverrini and intestinal flukes in Yangon City, Myanmar.

Morphological and molecular characterization of clinostomid metacercariae (CMc) was performed with the specimens collected in fish from Korea and Myanmar. Total 6 batches of clinostomid specimens by the fish species and geographical localities, 5 Korean and 1 Myanmar isolates, were analyzed with morphological (light microscopy and SEM) and molecular methods (the cytochrome c oxidase 1 gene and internal transcribed spacer 1/5.8S rRNA sequence). There were some morphological variations among CMc specimens from Korea. However, some morphometrics, i.e., the size of worm body and each organ, ratio of body length to body width, and morphology of cecal lumens, were considerably different between the specimens from Korea and Myanmar. The surface ultrastructures were somewhat different between the specimens from Korea and Myanmar. The CO1 sequences of 5 Korean specimens ranging 728-736 bp showed 99.6-100% identity with Clinostomum complanatum (GenBank no. KM923964). They also showed 99.9-100% identity with C. complanatum (FJ609420) in the ITS1 sequences ranging 692-698 bp. Meanwhile, the ITS1 sequences of Myanmar specimen showed 99.9% identity with Euclinostomum heterostomum (KY312847). Five sequences from Korean specimens clustered with the C. complanatum genes, but not clustered with Myanmar specimens. Conclusively, it was confirmed that CMc from Korea were morphologically and molecularly identical with C. complanatum and those from Myanmar were E. heterostomum.

A small survey was performed to investigate the recent infection status of Clonorchis sinensis and other zoonotic trematode metacercariae in freshwater fish from a local market of Yen Bai city, Yen Bai province, northern Vietnam. A total of 118 fish in 7 species were examined by the artificial digestion method on March 2016. The metacercariae of 4 species of zoonotic trematodes, i.e., C. sinensis, Haplorchis pumilio, Haplorchis taichui, and Centrocestus formosanus, were detected. The metacercariae of C. sinensis were found in 62 (69.7%) out of 89 fish (5 species), and their intensity of infection was very high, 81.2 per fish infected. Prevalences of 3 intestinal flukes, H. pumilio, H. taichui and C. formosanus, were 75.0%, 47.6%, and 31.7% in positive fish species, respectively, with the metacercarial intensities of 15.5, 10.3, and 2.2 per fish infected. From the above results, it has been confirmed that various species of freshwater fish continue to play the role of the infection source of C. sinensis and other zoonotic trematodes in Yen Bai city, Yen Bai province, northern Vietnam. It is of particular note that the prevalence and intensity of C. sinensis metacercariae are much higher than those reported in previous studies in fish in northern Vietnam.

Gymnophallid metacercariae found in the Manila clam Ruditapes philippinarum ('Banjirak' in Korean) from Gochang-gun, Jeollabuk-do, Korea were morphologically and molecularly confirmed to be Parvatrema duboisi (Dollfus, 1923) Bartoli, 1974. The metacercariae were morphologically characterized by having a large oral sucker, small ventral sucker, genital pore some distance anterior to the ventral sucker, no ventral pit, and 1 compact or slightly lobed vitellarium, which were all compatible with P. duboisi. Some of the metacercariae were experimentally fed to mice, and adult flukes were recovered at day 7 post-infection. The morphology of the adult flukes was basically the same as that of the metacercariae except for the presence of uterine eggs; the uterus was filled with up to 40 eggs. The nucleotide sequences (1,193 bp) from ITS regions (ITS1, 5.8S rDNA, and ITS2) of the metacercariae showed 99.7% identity with P. duboisi and 75.7% identity with Gymnophalloides seoi deposited in GenBank. These results confirmed the presence of P. duboisi metacercariae in the Manila clam R. philippinarum in an estuary region of Gochang-gun, Korea.

The infection status of digenetic trematode metacercariae (DTM) was investigated in fishes from coastal lakes in Gangwon-do, the Republic of Korea (Korea). All fishes collected in 5 lakes were examined with the artificial digestion method. More than 10 species, i.e., Metagonimus spp., Pygidiopsis summa, Centrocestus armatus, Metorchis orientalis, M. taiwanensis, Clinostomum complanatum, Echinostoma spp., Stictodora spp., Diplostomum sp. and Diplostomid No. 1. by Morita (1960), of DTM were detected in fishes from 5 coastal lakes in Gangwon-do. Metagonimus spp. metacercariae were found in 52 (41.3%) out of 126 sea rundace, Tribolodon hakonensis, from 5 lakes, and their density was 14.6 per fish infected. P. summa metacercariae were detected in 48 (84.2%) out of 57 mullets from 5 lakes, and their density was 316 per fish infected. C. armatus metacercariae were detected in 7 (14.6%) T. hakonensis and 3 (15.0%) Tridentiger brevispinis from Hyang-ho, and 5 (19.2%) Acanthogobius flavimanus from Gyeongpo-ho. Stictodora spp. metacercariae were found in 4 fish species, i.e., Tridentiger obscurus, Tridentiger trigonocephalus, Chelon haematocheilus, and Acanthogobius lactipes, from Gyeongpo-ho. Total 15 C. complanatum metacercariae were detected in 2 (9.1%) crucian carp, Carassius auratus, from Songji-ho. M. taiwanensis metacercariae were found in T. hakonensis from Hyang-ho and Gyeongpo-ho and in Pseudorasbora parva from Gyeongpo-ho. Total 11 M. orientalis metacercariae were detected in 3 (6.3%) T. hakonensis from Hyang-ho. From the above results, it was confirmed that various species of DTM are infected in fishes from coastal lakes in Gangwon-do, Korea.

The infection status of digenetic trematode metacercariae (DTM) was investigated in fishes from 2 representative visiting sites of migratory birds in Gyeongsangnam-do, the Republic of Korea (Korea). A totaly 220 freshwater fishes (7 species) were collected from Junam-jeosuji (reservoir), and 127 fishes (7 species) were also collected from Woopo-neup (swamp) in June and October 2017. As the control group, total 312 fish (22 spp.) from Yangcheon in Sancheong-gun, Gyeongsangnam-do were also collected in June and October 2017. All fishes collected in 3 sites were examined with the artificial digestion method. In the fishes from Junam-jeosuji, more than 4 species, i.e., Clonorchis sinensis, Echinostoma spp., Diplostomum spp. and Cyathocotyle orientalis, of DTM were detected and their endemicy was very low, 0.70. More than 6 species, i.e., C. sinensis, Echinostoma spp., Metorchis orientalis, Clinostomum complanatum, Diplostomum spp. and C. orientalis, of DTM were found in the fishes from Woopo-neup, and their endemicy was low, 5.16. In the fishes from Yangcheon, more than 8 species, i.e., C. sinensis, Metagonimus spp., Centrocestus armatus, C. complanatum, C. orientalis, M. orientalis, Echinostoma spp., and Diplostomum spp., of DTM were detected, and their endemicity was relatively high, 95.48. The percentages of avian trematode metacercariae (ATM) were 99.6% and 94.7% in fishes from Junam-jeosuji and Woopo-neup whereas it was 74.1% in the control site, Yangcheon. The above findings suggested that migratory birds partly affect in endemicity of DTM in the fish in the 2 visiting sites in Gyeongsangnam-do, Korea.

A stray female cat of unknown age, presenting bright red watery diarrhea, was submitted to the Animal and Plant Quarantine Agency for diagnosis. In the small intestines extracted from the necropsied cat, numerous white oval-shaped organisms were firmly embedded in the mucosa and there was thickening of intestinal wall. Histopathological analysis revealed severe necrotizing enteritis, together with atrophied intestinal villi, exfoliated enterocytes, and parasitic worms. Recovered worms were identified as Pharyngostomum cordatum by morphological observation and genetic analysis. Although P. cordatum is known to occur widely in Korea, this is the first clinical description of an infection by P. cordatum causing severe feline enteritis.

We described here the morphological characteristics for the species identification and fish hosts of Isoparorchis sp. (Digenea: Isoparorchiidae) in the Republic of Korea (Korea). Total 1,371 freshwater fishes collected in Yangcheon (Stream) in Sancheong-gun, Gyeongsangnam-do were examined by the artificial digestion methods to survey the infection status of digenetic trematode metacercariae for 4 years (2013-2016). Adult and larval worms of Isoparorchis sp. were detected in 38 (8.4%) out of 451 fish in 4 species, i.e., Pungtungia herzi, Acheilognathus koreensis, Squalidus japonicus coreanus and Odontobutis platycephala, examined. The infection density was 1.1 worm per fish infected. They were mainly found in the subcutaneous tissues and abdominal cavities. Nodules with worms in the subcutaneous tissues were revealed as the blue ink-colored bulges. Adults leaf-like, 21.6×9.84 mm in average size. The ratio of body length to body width was 2.20: 1. Oral sucker subterminal, 1.03×1.22 mm. Pharynx muscular, 0.55×0.54 mm. Esophagus very short. Ceca convoluted, terminated near the posterior end. Ventral sucker anterior 1/3.75, 1.99×2.10 mm. The ratio of ventral sucker to oral sucker was 1.74: 1. Testes round to elliptical, both sides of ventral sucker, 1.43×1.33 mm. Vitellaria highly dendritic, posterior 1/3 level. Eggs operculated, embryonated, 52×32 μm in size. By the present study, 4 fish species aforementioned are to be listed as the fish hosts of Isoparorchis sp. in Korea and additionally the morphological characteristics are to be described for the species identification.

To investigate the infection status of zoonotic trematode metacercariae in yellowfin goby, Acanthogobius flavimanus, from coastal areas of the Republic of Korea (Korea), we examined total 344 gobies from 21 localities with an artificial digestion method from 2013 to 2017. The metacercariae of Stictodora lari were most frequently detected in 45.3% goby from 7 localities, i.e., Taean-gun (Chungcheongnam-do), Gochang-gun (Jeollabuk-do), Muan-gun, Shinan-gun, Haenam-gun (Jeollanam-do), Hadong-gun and Goseong-gun (Gyeongsangnam-do). Their infection rates were 90.0%, 66.7%, 46.7%, 8.0%, 3.3%, 26.7%, and 86.7% and intensities were 1,090, 6.2, 1.6 1.0, 2.0, 2.0, and 7.2 metacercariae per fish infected respectively. Heterophyopsis continua metacercariae were found in 38.2% goby from 6 localities, i.e., Gochang-gun, Muan-gun, Shinan-gun, Gangjin-gun, Boseong-gun (Jeollanam-do) and Goseong-gun, and their intensities were relatively low, 1-21 metacercariae. Stictodora fuscata metacercariae were detected in 61.3% goby from 4 localities, i.e., Taean-gun, Gochang-gun, Hadong-gun and Goseong-gun. Their infection rates were 90.0%, 53.3%, 5.9%, and 73.3% and intensities were 1,081, 3.1, 3.0, and 10.2 metacercariae per fish infected respectively. Heterophyes nocens metacercariae were found in 55.0% goby from Muan-gun and Shinan-gun. Total 3 metacercariae of Isthmiophora hortensis were detected in 2 (8.0%) gobies from Shinan-gun. Total 15 metacercariae of Centrocestus armatus were detected in 5 gobies (33.3%) from Gyeongpo-ho (ho means lake) in Gangneung-si, Gangwon-do. The present study suggests that yellowfin goby, A. flavimanus, acts as the infection sources of zoonotic intestinal flukes in western and southern coastal areas than in eastern coastal areas of Korea.

A survey was performed to investigate the infection status of zoonotic trematode (ZT) metacercariae in fish from a local market in Yangon City, Myanmar. A total of 264 fish (12 species) were collected through 4 times from December 2013 to June 2015. All collected fish were transferred to our laboratory on ice and examined by the artificial digestion method. More than 7 species of ZT metacercariae, i.e., Haplorchis taichui, H. pumilio, H. yokogawai, Centrocestus spp., Stellantchasmus falcatus, Pygidiopsis cambodiensis, and Procerovum sp. were detected. Metacercariae of H. taichui were collected in 58 (42.3%) out of 137 fish (5 species), and their average density was 42.9 per fish infected. Metacercariae of H. pumilio were detected in 96 (49.0%) out of 196 fish (9 species), and their average density was 23.6 per fish infected. H. yokogawai metacercariae were found in 40 (50.0%) out of 80 fish (5 species), and Centrocestus spp. metacercariae in 91 (50.8%) out of 179 fish (8 species), and their densities were 306 and 25.8 per fish infected, respectively. Metacercariae of S. falcatus and P. cambodiensis were detected only in mullets, Chelon macrolepis. A total of 280 Procerovum sp. metacercariae were found in 6 out of 12 climbing perch, Anabas testudineus. Morphological characteristics of adult flukes recovered from experimental animals were described. It has been first confirmed that fish from Yangon, Myanmar are commonly infected with various species of ZT metacercariae.

A survey was performed to know the recent infection status of digenetic trematode metacercariae in clams and oysters from 4 sites in western coastal regions of the Republic of Korea (=Korea). Four species of clams (Mactra veneriformis, Ruditapes philippinarum, Cyclina sinensis, and Saxidomus purpuratus) were collected from Taean-gun, Chungcheongnam-do (Province), Buan-gun (County) and Gochang-gun, Jeollabuk-do, and oysters, Crassostrea gigas, from Shinan-gun, Jeollanam-do were transferred to our laboratory on ice and examined by the artificial digestion method. The metacercariae of Himasthla alincia were detected in 3 species of clams, M. veneriformis, R. philippinarum, and C. sinensis from the 3 surveyed areas. The positive rate and the mean density per clam infected were 98.9% (30.8 metacercariae) in M. veneriformis, 60.0% (5.0) in R. philippinarum, and 96.0% (28.4) in C. sinensis. The positive rate (mean density) of Acanthoparyphium tyosenense metacercariae in M. veneriformis was 50.0% (2.1) from Taean-gun and 70.0% (2.8) from Gochang-gun. The metacercariae of Parvatrema spp. were detected in M. veneriformis and R. philippinarum from Taean-gun and Gochang-gun; the positive rate (mean density) was 63.3% (4,123) and 50.0% (19) in M. veneriformis, and 6.7% (126) and 100% (238) in R. philippinarum from the 2 regions, respectively. The metacercariae of Gymnophalloides seoi were detected in all 30 oysters from Shinan-gun, and their average density per oyster was 646. From the above results, it has been confirmed that more than 3 species of metacercariae are prevalent in clams from the western coastal regions, and G. seoi metacercariae are still prevalent in oysters from Shinan-gun, Jeollanam-do, Korea.

The metacercariae of Artyfechinostomum malayanum (Leiper, 1911) Mendheim, 1943 were discovered in Pila sp. snails purchased from a market in Phnom Penh, Cambodia. They were isolated from the snails using the artificial digestion technique and were orally fed to 2 hamsters, 1 rat, and 2 mice to obtain the adult flukes. The metacercariae were round, 145-165 μm in diameter, having a cyst wall of 6-10 μm in thickness, a head collar and collar spines, and characteristic features of excretory granules. Adult flukes were recovered in the small intestines of the animals at days 14 and 32 post infection and were morphologically observed using a light microscope and a scanning electron microscope. They were plump or elongated, ventrally curved, 6.0-8.1 × 1.6-2.0 mm in size, and characterized by the head collar bearing 43 collar spines, including 5 end group ones on each side, a long cirrus sac extending beyond the posterior margin of the ventral sucker, a submedian ovary, and 2 deeply lobed testes. Eggs in uteri were operculate, ovoid to ellipsoid, and 120-135 × 68-75 μm in size. In scanning electron microscopy, the head collar was prominent with collar spines looking like horns. Scale-like tegumental spines were densely distributed on the ventral surface between the head collar and ventral sucker. Sensory papillae were distributed mainly on the tegument around suckers. By this study, it has been first confirmed that the life cycle of A. malayanum exists in Cambodia.

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.

The infection status of freshwater fish with digenetic trematode metacercariae was examined in water systems of Hantangang and Imjingang (River), the Republic of Korea. A total of 877 (594 from Hantangang and 283 from Imjingang) fishes were examined by the artificial digestion methods. Clonorchis sinensis metacercariae were detected in 7 (1.2%) fishes (in 3 spp.) from Hantangang in Cheorwon-gun, Gangwon-do, and 40 (14.1%) fishes (in 7 spp.) from Munsancheon in Paju-si, Gyeonggi-do. The average densities were 1.9 and 35.6 per fish infected, respectively. Metagonimus spp. metacercariae were detected in 312 (52.5%) and 113 (39.9%) fishes from Hantangang and Imjingang, and their average densities were 47.5 and 9.6 per fish infected, respectively. Centrocestus armatus metacercariae were found in 161 (27.1%) and 70 (24.7%) fishes from Hantangang and Imjingang, and their average number per fish infected was 694 and 82, respectively. Echinostoma spp. metacercariae were detected in 50 (8.4%) and 94 (33.2%) fishes from Hantangang and Imjingang, and their average densities were 9.6 and 23.1 per fish infected, respectively. The infection status of fishes with metacercariae of Stephanoprora spp., Diplostomum spp., Clinostomum complanatum, Metorchis orientalis, and Metorchis taiwanensis were analyzed by surveyed regions. Conclusively, it was confirmed that C. sinensis metacercariae were quite commonly detected in fishes from Munsancheon but rarely from other localities, whereas the metacercariae of other digenetic trematodes were relatively prevalent in fishes from water systems of Hantangang and Imjingang in Korea.

The present study was performed to survey the infection status of zoonotic intestinal trematode (ZIT) in stray cats from 5 major riverside areas in the Republic of Korea. Total 400 stray cats were captured with live-traps in riverside areas of Seomjingang ('gang' means river) (203 cats) from June to October 2010, and of Yeongsangang (41), Nakdonggang (57), Geumgang (38), and Hangang (61 cats) from June to October 2011, respectively. Small intestines resected from cats were opened with a pair of scissors in a beaker with 0.85% saline and examined with naked eyes and under a stereomicroscope. More than 16 ZIT species were detected in 188 (92.6%) cats from Seomjingang areas, and the number of worms recovered was 111 per cat infected. In cats from riverside areas of Yeongsangang, Nakdonggang, Geumgang, and Hangang, more than 9, 8, 3, and 5 ZIT species were recovered, and the worm burdens were 13, 42, 11, and 56 specimens per infected cat, respectively. As the members of family Heterophyidae, more than 10 species, i.e., Metagonimus spp., Pygidiopsis summa, Heterophyes nocens, Stellantchasmus falcatus, Heterophyopsis continua, Acanthotrema felis, Centrocestus armatus, Procerovum varium, Cryptocotyle concava, and Stictodora lari, were recovered. More than 5 species of echinostomes, i.e., Echinostoma hortense, Echinochasmus japonicus, Echinochasmus sp., Echinoparyphium sp., and unidentified larval echinostomes, were collected. Plagiorchis spp. were detected in cats from areas of Seomjin-gang and Yeongsangang. From the above results, it has been confirmed that stray cats in 5 major riverside areas of Korea are highly infected with various species of ZITs.

The infection status of zoonotic trematode metacercariae was investigated in a total of 2,293 freshwater fish collected from 11 rivers or streams in 9 administrative regions of Gangwon-do, Korea for 5 years (2009-2013). All fish were collected by netting methods and examined using the artificial digestion methods. Clonorchis sinensis metacercariae were detected in 4 fish species, i.e., Pungtungia herzi, Squalidus japonicus coreanus, Acheilognathus rhombeus, and Ladislabia taczanowskii, from only Hantangang in Cheorwon-gun. Metagonimus spp. metacercariae were found in 1,154 (50.3%) fish and their average number per infected fish was 55.8. Among the positive fish species, especially Tribolodon hakonensis from Namdaecheon in Yangyang-gun and Plecoglossus altivelis from Osipcheon in Samcheok-si were most heavily infected. Centrocestus armatus metacercariae were detected in 611 (26.7%) fish and the average metacercarial burden per infected fish was 1,032. Two chub species, Zacco platypus and Zacco temminckii were highly and heavily infected with C. armatus metacercariae in almost all regions surveyed. Echinostoma spp. metacercariae were also found in 24 fish from a few localities, but their numbers per fish infected were very low. From the above results, it is confirmed that the metacercariae of intestinal flukes, especially Metagonimus spp. and C. armatus, were heavily infected, while C. sinensis metacercariae were rarely found in fish from Gangwon-do, Korea.

This study confirmed the prevalence of the intestinal fluke Haplorchis taichui (Trematoda: Heterophyidae) among people and fish in Luang Prabang Province, Lao PDR. Fecal specimens were collected from 559 riparian people (229 males and 330 females), residing in 4 Districts (Luang Prabang, Xieng Ngeun, Pak Ou, and Nam Bak) and were examined by the Kato-Katz fecal smear technique. The overall helminth egg positive rate was 64.9%. The positive rate for small trematode eggs (STE), which may include H. taichui and other heterophyids, Opisthorchis viverrini, and lecithodendriids, was 15.2%. For recovery of adult helminths, 10 STE-positive people were treated with 40mg/kg praziquantel and 15mg/kg pyrantel pamoate, and then purged. Mixed infections with 3 Haplorchis species (H. taichui, H. pumilio, and H. yokogawai), a species of cestode (Taenia saginata), and several species of nematodes including Enterobius vermicularis and hookworms were found. The worm load for trematodes was exclusively high for H. taichui with an average of 7691 specimens per infected person, followed by H. yokogawai (8.3 specimens) and H. pumilio (4.1 specimens). Out of 207 freshwater fish (17 species) purchased in a market in Luang Prabang District, 138 (67%) harboured H. taichui metacercariae (metacercarial burden per fish; 520). Lower prevalence of fish and lower metacercarial density were observed for H. yokogawai (52% and 50 per fish, respectively) and H. pumilio (18% and 3 per fish, respectively). STE found in the surveyed population of Luang Prabang Province were verified to be those of intestinal fukes, particularly H. taichui., (Copyright © 2014 Elsevier B.V. All rights reserved.)

A survey was performed to investigate the infection status of freshwater fish with zoonotic trematode metacercariae in Phnom Penh and Pursat Province, Cambodia. All collected fish with ice were transferred to our laboratory and examined using the artificial digestion method. In fish from Phnom Penh, 2 kinds of metacercariae (Opisthorchis viverrini and Haplorchis yokogawai) were detected. O. viverrini metacercariae were positive in 37 (50.0%) of 74 fish in 11 species (average no. metacercariae/fish, 18.6). H. yokogawai metacercariae were detected in 23 (57.5%) of 40 fish in 5 species (average no. metacercariae/fish, 21.0). In fish from Pursat Province, 5 kinds of metacercariae (O. viverrini, H. yokogawai, Haplorchis pumilio, Centrocestus formosanus, and Procerovum sp.) were detected; O. viverrini metacercariae (n=3) in 2 fish species (Henicorhynchus lineatus and Puntioplites falcifer), H. yokogawai metacercariae (n=51) in 1 species (P. falcifer), H. pumilio metacercariae (n=476) in 2 species (H. lineatus and Pristolepis fasciata), C. formosanus metacercariae (n=1) in 1 species (H. lineatus), and Procerovum sp. metacercariae (n=63) in 1 species (Anabas testudineus). From the above results, it has been confirmed that various freshwater fish play the role of a second intermediate host for zoonotic trematodes (O. viverrini, H. yokogawai, H. pumilio, C. formosanus, and Procerovum sp.) in Cambodia.

In 2005, we reported the infection status of 438 stray cats with various species of intestinal helminths, including nematodes (4 species), trematodes (23 species), and cestodes (5 species) in the Republic of Korea. However, morphologic details of each helminth species have not been provided. In the present study, we intended to describe morphologic details of 13 trematode species which were either new fauna of cats (10 species) or new fauna of not only cats but also all animal hosts (3 species). The worms were fixed in 10% neutral buffered formalin under a cover slip pressure, stained with Semichon's acetocarmine, and then observed using a light microscope equipped with a micrometer. The 13 subjected species included members of the Heterophyidae (Stellantchasmus falcatus, Stictodora fuscata, Stictodora lari, Centrocestus armatus, Procerovum varium, and Cryptocotyle concava), Echinostomatidae (Echinostoma hortense, Echinostoma revolutum, Echinochasmus japonicus, and Stephanoprora sp.), Diplostomidae (Neodiplostomum seoulense), Plagiorchiidae (Plagiorchis muris), and Dicrocoeliidae (Eurytrema pancreaticum). By the present study, Cryptocotyle sp. and Neodiplostomum sp. recored in our previous study were identified as C. concava and N. seoulense, respectively. Three species, P. varium, C. concava, and Stephanoprora sp., are new trematode fauna in Korea.

Fishborne trematode (FBT) metacercariae were investigated in fish from 3 Provinces of Lao PDR. Total 242 freshwater fish of 40 species were collected in local markets of Luang Prabang (59 fish of 16 species), Khammouane (81 fish of 19 species), and Saravane (97 fish of 14 species), and each of them was examined by artificial digestion method. Four species of metacercariae (Opisthorchis viverrini, Haplorchis taichui, Haplorchis yokogawai, and Centrocestus formosanus) were detected. O. viverrini was detected in 35 fish (14.5%), and their density was 252 per infected fish (Luang Prabang, 88 metacercariae in 5 fish; Khammouane, 187 in 6 fish; Saravane, 303 in 24 fish). H. taichui was found in 102 fish (42.1%), and their density was 485 per infected fish (Luang Prabang, 260 metacercariae in 38 fish; Khammouane, 1,084 in 23 fish; Saravane, 359 in 41 fish). H. yokogawai was detected in 92 fish (38.0%), and their density was 222 per infected fish (Luang Prabang, 362 metacercariae in 17 fish; Khammouane, 126 in 20 fish; Saravane, 214 in 55 fish). Metacercariae of C. formosanus were found in 8 fish (3.3%), and their density was 3 per infected fish. In the present study, it has been confirmed that FBT metacercariae, in particular, H. taichui, H. yokogawai, and O. viverrini, are highly prevalent in fish from Luang Prabang, Khammouane, and Saravane Province, Lao PDR.

The source of human infection with intestinal flukes was surveyed in estuarine fishes, including the dotted gizzard shad, common sea bass, common blackish goby, redlip mullet, black sea bream, and oyster collected from Muan-gun, Jeollanam-do, Korea during August and September 2007. Collected fishes and oysters were artificially digested in pepsin-HCl solution and examined under a stereomicroscope. In 36 shads (Konosirus punctatus) and 20 basses (Lateolabrax japonicus) examined, Heterophyopsis continua metacercariae were found in 58.3% and 100%, and their average numbers were 12.0 and 6.3 per infected fish, respectively. In 34 gobies (Acanthogobius flavimanus) examined, metacercariae of H. continua were detected in 79.4%, Stictodora lari in 97.1%, and Acanthotrema felis in 92.1%, and their average numbers were 45.8, 189.3, and 235.3 per infected fish, respectively. In 37 redlip mullets (Chelon haematocheilus), Heterophyes nocens metacercariae were found in 56.8%, Pygidiopsis summa in 94.6%, and Stictodora fuscata in 45.9%, and the average metacercarial densities were 17.4, 31.3, and 35.1 per infected fish, respectively. In 30 black sea breams (Acanthopagrus schlegeli) and 45 oysters (Crassostrea gigas) examined, no metacercariae were detected. From the above results, it has been confirmed that the dotted gizzard shad, common sea bass, common blackish goby, and redlip mullet from Muan-gun, Jeollanam-do, Korea are infected with the metacercariae of heterophyid flukes.

Adults of Maritrema obstipum (Digenea: Microphallidae) were found in the intestines of 4 species of migratory birds, including the sanderling (Crocethia alba), Kentish plover (Charadrius alexandrines), Mongolian plover (Charadrius mongolus), and red-necked stint (Calidris ruficollis), collected from Yubu Island, Chungcheongnam-do, Korea. The worms of were 451 × 265 µm in size, and were easily identifiable as Maritrema species by the presence of the cirrus sac, and the ring-like distribution of the vitellaria. More specifically, the ejaculatory duct curved posteromedially, and the 2 parts of vitelline follicles were found to be distinct at the posterior end. The eggs were brown-colored, and 19.8 × 12.3 µm in size. All these findings implicated M. obstipum as the pertinent species of the worms. Beside these, adult worms of Gynaecotyla squatarolae, Parvatrema duboisi, and Acanthoparyphium sp. were also discovered. This is the first report establishing migratory birds as the natural definitive hosts for M. obstipum.

Maritrema spp. (Digenea: Microphallidae) are parasites of birds, but have not been found in the Republic of Korea. In this study, metacercariae of Maritrema sp. were discovered in the Asian shore crab, Hemigrapsus sanguineus, caught in the mud-flats of Jebu-do, Hwasung-gun, Gyeonggi-do, and the adult flukes were confirmed by experimental infection into mice. Based on the symmetric ribbon-like vitellarium, adult flukes of Maritrema sp. were identified, but did not belong to previously described species in terms of the following morphologic characteristics: ceca reaching to the lateral wall at the anterior border of the ovary; ventral sucker larger than oral sucker; a prominent metraterm; and vitellarium forming a complete ring. Hence, we named this microphallid M. jebuensis n. sp. after the island where the second intermediate hosts were collected. From this study, it has been shown that Maritrema sp. is distributed in Korea and transmitted by the Asian shore crab, H. sanguineus.

Adult worms of Parvatrema spp. (Digenea: Gymnophallidae) were found in the intestines of 2 species of migratory birds, i.e., a great knot, Calidris tenuirostris, and 2 Mongolian plovers, Charadrius mongolus, in the coastal area of Gunsan-si, Jeollabuk-do in October 2009. The recovered Parvatrema worms were 79 in total number and composed of 2 species. The worms from a great knot were 289 µm in length with the oral and ventral sucker ratio of 2 : 1. They had a single vitellarium, and their intrauterine eggs were 25.0 x 17.5 µm in size. These findings were compatible with P. duboisi (Dollfus, 1923) Bartoli, 1974 (syn. P. timondavidi Bartoli, 1963). The worms recovered from the Mongolian plovers were smaller in length than P. duboisi and had 2 vitellaria. The oral and ventral sucker ratio was 2.5:1, and the eggs were 17.5 x 8.8 µm in size. These worms were assigned to be P. homoeotecnum James, 1964. This is the first report on the natural final hosts of Parvatrema spp. in Korea.

Infection status of intestinal flukes was investigated in residents of Muan-gun, Jeollanam-do, the Republic of Korea. Total 1,257 fecal samples of residents were examined by formalin-ether sedimentation technique and Kato-Katz thick smear method. Helminth eggs were detected from 95 (7.6%) residents, and eggs of heterophyid flukes and Clonorchis sinensis were found from 62 (4.9%) and 40 (3.2%) cases, respectively. The larger heterophyid eggs, somewhat dark-brown in color and 37.7 x 21.5 microm in average size, and found in 32 (2.6%) out of 62 egg positive cases of heterophyid flukes. To confirm the adult flukes, we performed worm recovery from 12 cases after praziquantel treatment and purgation with MgSO(4). A total of 1,281 adult flukes, assigned to 7 species, were recovered from 9 cooperative cases. Heterophyes nocens (total 981 specimens) was collected from 9 cases, Stictodora fuscata (80) from 7, Gymnophalloides seoi (75) from 5, Pygidiopsis summa (140) from 3, Stellantchasmus falcatus (3) from 2, and Stictodora lari and Acanthotrema felis (each 1 worm) from 1 case each. The intrauterine eggs of S. fuscata collected from the recovered worm were identical with the larger heterophyid eggs detected in the stool examination. By the present study, it was confirmed that A. felis is a new intestinal fluke infecting humans, and residents in Muan-gun, Jeollanam-do are infected with variable species of intestinal trematodes.

The prevalence of fish-borne trematodes (FBT), including Clonorchis sinensis, is still high in riverside areas of the Republic of Korea. The author reviewed the detection and identification methods, differential keys, fish intermediate hosts, and morphological characteristics of FBT metacercariae. FBT metacercariae found in freshwater fish are classified mainly into 4 families, i.e., Opisthorchiidae, Heterophyidae, Echinostomatidae, and Clinostomidae. The metacercariae of C. sinensis, found in 40 species of freshwater fish, are elliptical and 0.15-0.17 x 0.13-0.15 mm in size, have nearly equal sized oral and ventral suckers, brownish pigment granules, and an O-shaped excretory bladder. Their general morphologies are similar to those of Metorchis orientalis (except in the thickness of the cyst wall). Metagonimus spp. (M. yokogawai, M. takahashii, and M. miyatai) metacercariae are subglobular or disc-shaped, and 0.14-0.16 mm in diameter. They have yellow-brownish pigment granules, a ventral sucker deflectively located from median, and a V-shaped excretory bladder. The metacercariae and fish intermediate hosts of Centrocestus armatus, Clinostomum complanatum, and 3 echinostomatid flukes (Echinostoma hortense, E. cinetorchis, and Echinochasmus japonicus) were summarized. FBT metacercariae detected in brackish water fish are mainly members of the Heterophyidae. The morphological characters, identification keys, and fish intermediate hosts of 7 species (Heterophyes nocens, Heterophyopsis continua, Pygidiopsis summa, Stellantchasmus falcatus, Stictodora fuscata, Stictodora lari, and Acanthotrema felis) were also reviewed. The contents treated in this study will provide assistance at the laboratory bench level to those working on recovery of metacercariae from fish hosts and identifying them.

Fishborne trematode (FBT) metacercariae were investigated in yellowfin goby, Acanthogobius flavimanus, collected from Shinan-gun and Muan-gun, Jeollanam-do (province), Korea. All collected fishes were examined using the artificial digestion method. In all of 15 gobies from Aphae-myeon in Shinan-gun, metacercariae of Stictodora spp. (334 metacercariae/fish), Heterophyes nocens (153/fish), and Heterophyopsis continua (20/fish) were detected. In 2 of 14 gobies from Jido-myeon in Shinan-gun, 8 Echinostoma hortense metacercariae in total were detected. In 15 gobies from Haeje-myeon in Muan-gun, the metacercariae of H. continua were found in 100%, Stictodora spp. in 86.7%, and H. nocens in 6.7% of fish examined. The average numbers of metacercariae per infected fish were 23.3 (H. continua), 416.0 (Stictodora spp.), and 2.0 (H. nocens), respectively. The metacercariae of E. hortense found in gobies were elliptical, with 150 x 138 microm in average size, and had 27 collar spines on the head crown. The above results suggest that yellowfin gobies from 2 localities may be the potential infection sources of FBT. Moreover, it is proved for the first time that the yellowfin goby, A. flavimanus, acts as a second intermediate host for E. hortense.

A survey was performed to investigate the infection status of fishborne trematode (FBT) metacercariae in freshwater fish from Guangxi Zhuang Autonomous Region, China. A total of 307 freshwater fish of 31 species were collected from 5 administrative regions of Guangxi Zhuang Autonomous Region. They were examined by artificial digestion method from July 2003 to August 2004. No metacercariae were detected in fish from Fusui-xian. In fish from Mashan-xian and a market in Nanning, 3 species of metacercariae, Haplorchis taichui, Haplorchis pumilio, and Centrocestus formosanus, were mainly detected. Metacercariae (8 in number) of Clonorchis sinensis were found in 1 Chanodichthys dabryi purchased from a market in Nanning. In fish from Yangshuo, Metagonimus yokogawai metacercariae were detected from all 18 fish species examined. Total 13 C. sinensis metacercariae were found in 3 out of 10 Hemibarbus maculatus from Yangshuo. All 7 Zacco platypus from Yangshuo were infected with 8-112 Echinochasmus perfoliatus metacercariae. In fish from Binyang-xian, H. pumilo metacercariae were mainly detected in all 5 fish species examined, and only 1 metacercaria of C. sinensis was found in a Hemiculter leucisculus. From the above results, it was confirmed that some species of freshwater fish play a role of second intermediate hosts for FBT in Guangxi Zhuang Autonomous Region, China. In particular, 4 species of intestinal flukes, M. yokogawai, H. taichui, H. pumilio, and C. formosanus, were prevalent in fish hosts, whereas C. sinensis metacercariae were detected only in 3 fish species.

Microphallus species occur primarily as intestinal parasites of birds and mammals, and metacercariae of a new species belonging to this genus have been discovered from the crab, Macrophthalmus dilatatus, in the Republic of Korea. The metacercaria of this fluke was round with 2 thick walls, and the excysted one had mature genital organs. The adult flukes recovered from experimentally infected chicks had numerous intrauterine eggs, well-developed pars prostatica, widely bifurcating ceca, and prominent uterine bulge. After observing internal structures, it was concluded that this species is different from any other known Microphallus spp. Based on the morphology of metacercariae and adult flukes, we describe this specimen as a new species, Microphallus koreana n. sp.

Holostephanus metorchis (Digenea: Cyathocotylidae) is a parasite of birds, transmitted by freshwater fishes. H. metorchis adults were recovered from chicks experimentally infected with metacercariae collected from freshwater fishes, Pseudorasbora parva. The metacercariae were oval, surrounded with thick fibrous capsules. In adult flukes, the holdfast organ occupied the ventral concavity, and the anterior testis did not reach the level of the ventral sucker. Based on these morphological characteristics, these flukes were identified as H. metorchis.

The prevalence of liver and intestinal fluke infections was surveyed on residents of Savannakhet Province, Laos. Fecal specimens were collected from a total of 981 residents in 4 Mekong riverside villages and examined by the Kato-Katz thick smear technique. The results revealed that the overall helminth egg positive rate was 84.2%, and the positive rate for small trematode eggs, including Opisthorchis viverrini, heterophyids, or lecithodendriids, was 67.1%. To obtain adult flukes, 38 small trematode egg positive cases were treated with a 20-30 mg/kg single dose of praziquantel and purged. Diarrheic stools were then collected from 29 people and searched for helminth parasites using stereomicroscopes. Mixed infections with O. viverrini and 6 kinds of intestinal flukes were found, namely, Haplorchis taichui, Haplorchis pumilio, Haplorchis yokogawai, Prosthodendrium molenkampi, Phaneropsolus bonnei, and echinostomes. The total number of flukes collected was 7,693 specimens (av. no. per treated person; 265.3). The most common species was O. viverrini, followed by H. taichui, P. molenkampi, echinostomes, H. pumilio, P. bonnei, and H. yokogawai. The results indicate that foodborne liver and intestinal fluke infections are prevalent among residents of Savannakhet Province, Laos.

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 x 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).

The cercaria morphology of Echinochasmus japonicus was investigated using light and scanning electron microscopy. Cercariae, liberated from naturally infected snails (Parafossarulus manchouricus), had ovoid bodies and diminutive tails. The cercaria tegument was covered with minute spines. Four type II sensory papillae were observed on the dorsal side of the oral sucker, and type I papillae were distributed on the dorsal tegument surfaces. When cercariae were kept in the same bath as the freshwater fish, Pseudorasbora parva, which were free from trematode infections, parasites encysted only in the gills of fishes at day 4 postinfection (PI). The outermost metacercaria wall was fully formed in host tissues at day 7 PI. Adult worms were recovered from the intestines of rats, chicks, and ducks 28 days after experimental exposure to metacercariae. The head crown of the adult was armed with 24 collar spines, which were interrupted dorsal to the oral sucker, and the species was identified as E. japonicus.

A survey was performed in order to determine the infection status of the metacercariae of heterophyid fluke in two goby species, Boleophthalmus pectinirostris and Scartelaos sp., collected from Gangjin-gun, and Shinangun, Sooncheon-shi, Jeollanam-do, Republic of Korea. A total of three metacercariae of Heterophyopsis continua was found in only one B. pectinirostris (10.0%) from Gangjin-gun. Heterophyes nocens metacercariae were detected in 24 B. pectinirostris (96.0%) and 14 Scartelaos sp. (63.6%) from Shinan-gun. Heterophyopsis continua metacercariae were found in 11 B. pectinirostris (44.0%) and 21 Scartelaos sp. (95.5%) from Shinan-gun. Stictodora fuscata metacercariae were detected in 18 B. pectinirostris (72.0%) from Shinan-gun. No metacercariae were detected in 20 B. pectinirostris from Sooncheon-shi. From the above results, this study is the first to prove that B. pectinirostris and Scartelaos sp. serve as the second intermediate hosts of some heterophyid flukes in Korea.

The present study was performed to investigate the infection status with helminth in a group of feral cats in Korea. More than 29 helminth species including adults or eggs were detected in visceral and fecal samples of the examined cats. Among these were a host of nematodes, including toxocarids, Ancylostoma sp. and the larva of Anisakis simplex; trematodes, including Clonorchis sinensis, Paragonimus westermani, Eurytrema pancreaticum, Pharyngostomum cordatum, Metagonimus spp., Heterophyes nocens, Pygidiopsis summa, Heterophyopsis continua, Stictodora fuscata, Stictodora lari, Acanthotrema felis, Stellantchasmus falcatus, Centrocestus armatus, Procerovum varium, Cryptocotyle sp., Echinostoma revolutum, Echinostoma hortense, Echinochasmus japonicus, Stephanoprora sp., Plagiorchis muris, Neodiplostomum sp. and diplostomulum. We also detected a variety of cestodes, including Spirometra erinacei, Taenia taeniaeformis and unidentified species of tapeworm. We also found examples of the acanthocephalan, Bolbosoma sp. In our assessment of the stools, we detected at least 12 species of helminth eggs. These findings confirmed that feral cats in Korea are infected with a variety of helminth parasite species. Furthermore, among the helminths detected, E. pancreaticum, S. fuscata, S. lari, A. felis, S. falcatus, C. armatus, P. varium, Cryptocotyle sp., E. revolutum, E. japonicus, Stephanoprora sp., P. muris, Neodiplostomum sp. and Bolbosoma sp. represent helminth fauna which have not been reported previously in feral cats in the Republic of Korea.

To determine the molecular phylogenic location of Plagiorchis muris, 28S D1 ribosomal DNA (rDNA) and mitochondrial cytochrome C oxidase subunit I (mtCOI) were sequenced and compared with other trematodes in the family Plagiorchiidae. The 28S D1 tree of P. muris was found to be closely related to those of P. elegans and other Plagiorchis species. And, the mtCOI tree also showed that P. muris is in a separate clade with genus Glypthelmins. These results support a phylogenic relationship between members of the Plagiorchiidae, as suggested by morphologic features.

The surface ultrastructure of Acanthotrema felis (Trematoda: Heterophyidae) adults, recovered from a kitten experimentally infected with the metacercariae, was observed using a scanning electron microscope. The worm was leaf-like, ventrally concave and covered with scale-like multi-pointed tegumental spines. The spines on the anterior surface were short but broad, and had 10-12 pointed tips. The cytoplasmic processes protruded around the spines, like pockets for the spines. The ventrogenital opening was crescent, or kidney-shaped, and had protuberances with minute spines on its surrounding tegument. The spines on the posterior surface were long, but narrow, with 6-8 pointed tips. The cytoplasmic processes on this tegument were ridge-like, and elevated along the row of the spines. The surface ultrastructure of A. felis is generally similar to that of other heterophyid flukes, but some features are characteristic, and may be of taxonomic and bio-ecological significance.

The metacercariae of Acanthotrema felis Sohn et al., 2003 (Digenea: Heterophyidae) were discovered in a species of the brackish water fish, Acanthogobius flavimanus, in the Republic of Korea. They were experimentally fed to kittens, and adult flukes were harvested 7 days later. The adults were morphologically characterized by the presence of a bipartite seminal vesicle, the ventral sucker associated with a ventrogenital sac enclosing 3 sclerites (2 long and pointed, and 1 short and thumb-like), and an unarmed gonotyl. The adult flukes were identified as A. felis Sohn et al., 2003, and the brackish water fish A. flavimanus has been verified as one of its second intermediate hosts.

Acanthotrema felis n. sp. (Digenea: Heterophyidae) is described from adult flukes recovered in the small intestine of stray cats caught in the southwestern part of the Republic of Korea. The worms were characterized by minute body size, the presence of a bipartite seminal vesicle, and a ventral sucker associated with a ventrogenital sac, which enclosed 3 sclerites (2 long and pointed, and I short and thumblike), and an unarmed gonotyl. They were assigned to Acanthotrema Travassos, 1928, which currently contains 4 species. The new species resembles A. acanthotrema, the type species, because both have 3 sclerites on the ventrogenital sac. However, all 3 sclerites in the new species are armed with minute spines on their base, whereas only 2 sclerites in A. acanthotrema have minute spines near their tips. Three species of Stictodora Looss, 1899, namely,Stictodora tridactyla Martin and Kuntz, 1955, S. cursitans Kinsella and Heard, 1974, and S. tanayensis Velasquez, 1973, are transferred to Acanthotrema, and the new species is distinguished from them particularly in terms of the number and shape of its sclerites. The generic diagnosis of Acanthotrema is emended.

Opisthorchis viverrini infection is an emerging disease in Cambodia, especially in central and southeastern areas. However, its status in northern areas bordering Lao PDR has been relatively unknown. The present study was performed to investigate the status of O. viverrini infection among people in Preah Vihear and Stung Treng provinces through fecal examination to detect eggs and recovery of adult flukes from some of the egg-positive cases. Fecal examinations were performed on a total of 1101 people from 10 villages in the 2 provinces using the Kato-Katz thick smear technique. For recovery of adult flukes and other helminth parasites 10 volunteers positive for eggs of Opisthorchis viverrini and/or minute intestinal flukes (Ov/MIF), in Kampong Sangkae village, Preah Vihear province, were administered a single oral dose of 40 mg/kg praziquantel plus 5–10 mg/kg of pyrantel pamoate and purged with 40–50 g magnesium salts. Adult trematodes, together with nematodes and cestodes expelled in diarrheic stools were collected under a stereomicroscope or with the naked eye. The proportion of egg-positive cases for overall liver and intestinal helminths was high but not notably different between the 2 provinces, 65.5% in Preah Vihear versus 64.7% in Stung Treng. The average proportion of Ov/MIF egg-positive cases was 59.8%. A total of 315 adult specimens of O. viverrini were recovered from the 10 volunteers (4–98 specimens per individual; mean, 32). A smaller number of Haplorchis taichui adults, an intestinal fluke, were found mixed-infected in 7 (103 specimens in total; 1–31 per individual; mean, 15) of the 10 volunteers. Adult specimens of hookworms, Enterobius vermicularis, Trichostrongylus sp., and a Taenia tapeworm strobila were recovered in some cases. Based on the results, it has been confirmed that the surveyed areas in Preah Vihear and Stung Treng provinces, Cambodia, are highly endemic areas of O. viverrini infection with a low-grade mixed infection with H. taichui. [ABSTRACT FROM AUTHOR]

Background: MF6p/host defense molecules (HDMs) are a broad family of small proteins secreted by helminth parasites. Although the physiological role of MF6p/HDMs in trematode parasites is not fully understood, their potential biological function in maintaining heme homeostasis and modulating host immune response has been proposed. Methods: A gene encoding the MF6p/HDM of Clonorchis sinensis (CsMF6p/HDM) was cloned. Recombinant CsMF6p/HDM (rCsMF6p/HDM) was expressed in Escherichia coli. The biochemical and immunological properties of rCsMF6/HDM were analyzed. CsMF6p/HDM induced pro-inflammatory response in RAW 264.7 cells was analyzed by cytokine array assay, reverse transcription polymerase chain reaction, and enzyme-linked immunosorbent assay. The structural feature of CsMF6p/HDM was analyzed by three-dimensional modeling and molecular docking simulations. Results: The CsMF6p/HDM shares a high level of amino acid sequence similarity with orthologs from other trematodes and is expressed in diverse developmental stages of the parasite. The rCsMF6p/HDM bound to bacteria-derived lipopolysaccharide (LPS), without effectively neutralizing LPS-induced inflammatory response in RAW 264.7 macrophage cells. Rather, the rCsMF6p/HDM induced pro-inflammatory immune response, which is characterized by the expression of TNF-α and IL-6, in RAW 264.7 cells. The rCsMF6p/HDM-induced pro-inflammatory immune response was regulated by JNK and p38 MAPKs, and was effectively down-regulated via inhibition of NF-κB. The structural analysis of CsMF6p/HDM and the docking simulation with LPS suggested insufficient capture of LPS by CsMF6p/HDM, which suggested that rCsMF6p/HDM could not effectively neutralize LPS-induced inflammatory response in RAW 264.7 cells. Conclusions: Although rCsMF6p/HDM binds to LPS, the binding affinity may not be sufficient to maintain a stable complex of rCsMF6p/HDM and LPS. Moreover, the rCsMF6p/HDM-induced pro-inflammatory response is characterized by the release of IL-6 and TNF-α in RAW 264.7 macrophage cells. The pro-inflammatory response induced by rCsMF6p/HDM is mediated via NF-κB-dependent MAPK signaling pathway. These results collectively suggest that CsMF6p/HDM mediates C. sinensis-induced inflammation cascades that eventually lead to hepatobiliary diseases. [ABSTRACT FROM AUTHOR]

We performed an epidemiologic survey of opisthorchiasis in Yangon, Myanmar. The fecal egg-positive rate of residents was 0.7%, and we recovered an adult fluke after chemotherapy and purging of an egg-positive resident. We detected Opisthorchis viverrini metacercariae in freshwater fish. We found the Yangon area to have low-grade endemicity of opisthorchiasis. [ABSTRACT FROM AUTHOR]