Status of Helminthic Infections in Residents around River Basins in the Republic of Korea for 10 Years (2011-2020).

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.

Clonorchis sinensis excretory-secretory products increase malignant characteristics of cholangiocarcinoma cells in three-dimensional co-culture with biliary ductal plates.

Clonorchis sinensis is a carcinogenic human liver fluke, prolonged infection which provokes chronic inflammation, epithelial hyperplasia, periductal fibrosis, and even cholangiocarcinoma (CCA). These effects are driven by direct physical damage caused by the worms, as well as chemical irritation from their excretory-secretory products (ESPs) in the bile duct and surrounding liver tissues. We investigated the C. sinensis ESP-mediated malignant features of CCA cells (HuCCT1) in a three-dimensional microfluidic culture model that mimics an in vitro tumor microenvironment. This system consisted of a type I collagen extracellular matrix, applied ESPs, GFP-labeled HuCCT1 cells and quiescent biliary ductal plates formed by normal cholangiocytes (H69 cells). HuCCT1 cells were attracted by a gradient of ESPs in a concentration-dependent manner and migrated in the direction of the ESPs. Meanwhile, single cell invasion by HuCCT1 cells increased independently of the direction of the ESP gradient. ESP treatment resulted in elevated secretion of interleukin-6 (IL-6) and transforming growth factor-beta1 (TGF-ß1) by H69 cells and a cadherin switch (decrease in E-cadherin/increase in N-cadherin expression) in HuCCT1 cells, indicating an increase in epithelial-mesenchymal transition-like changes by HuCCT1 cells. Our findings suggest that C. sinensis ESPs promote the progression of CCA in a tumor microenvironment via the interaction between normal cholangiocytes and CCA cells. These observations broaden our understanding of the progression of CCA caused by liver fluke infection and suggest a new approach for the development of chemotherapeutic for this infectious cancer.

High Endemicity with Clonorchis sinensis Metacercariae in Fish from Yongjeon-cheon (Stream) in Cheongsong-gun, Gyeongsangbuk-do, Korea.

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.

Endemicity of Zoonotic Trematode Metacercariae in Fish from Deokcheon-gang (River) in Sancheong-gun, Gyeongsangnam-do, Republic of Korea.

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.

Prevalence and Infection Intensity of Zoonotic Trematode Metacercariae in Fish from Soyang-cheon (Stream), in Wanju-gun, Jeollabuk-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.

Survey of Zoonotic Trematode Metacercariae in Fish from Irrigation Canal of Togyo-jeosuji (Reservoir) in Cheorwon-gun, Gangwon-do, Republic of 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.

Risk Factors of Clonorchis sinensis Human Infections in Endemic Areas, Haman-Gun, Republic of Korea: A Case-Control Study.

Clonorchis sinensis is the most common fish-borne intestinal parasite in Korea. The aim of the present investigation was to survey the status of C. sinensis infection and analyze associated risk factors in residents of Haman-gun, Gyeongsangnam-do. A total of 5,114 residents from 10 administrative towns/villages voluntarily agreed to participate in the study, which comprised fecal examination, a questionnaire survey for risk factors, ultrasonography, and enzymelinked immunosorbent assay for cancer biomarker detection in the blood. We detected C. sinensis eggs in 5.3% of the subjects. By region, Gunbuk-myeon had the highest number of residents with C. sinensis eggs. The infection rate and intensity were higher in male than in female residents. Based on the risk factor questionnaire, infection was highly associated with drinking, a history of C. sinensis infection, and the practice of eating of raw freshwater fish. Extension of the bile duct, infection intensity, and cancer biomarker detection significantly correlated with the presence of eggs in the study population. In conclusion, the development of feasible, long-term control policies and strategies for the elimination of C. sinensis in Korea is still required.

Infection Status with Clonorchis sinensis Metacercariae in Fish from Yangcheon (Stream) in Sancheong-gun, Gyeongsangnam-do, Korea.

The infection status with Clonorchis sinensis metacercariae (CsMc) was examined in freshwater fishes from Yangcheon (a branch of Gyeongho-gang), which is located in Sancheong-gun, Gyeongsangnam-do, the Republic of Korea. Total 2,201 fishes in 26 species were examined by the artificial digestion method through 7 years. CsMc were detected in 1,171 (53.2%) fishes in 21 spp. (80.8%) and their density was 85 per fish infected. Total 532 (99.6%) out of 534 Pungtungia herzi (index fish) examined were infected with 147 CsMc per fish infected. Metacercarial densities in this fish were highest in 2015 (179 CsMc), followed by 2012 (168), 2013 (152), 2016 (145), 2014 (114), and 2017 (89) respectively. In the gobioninid fish group, i.e., P. herzi, Sarcocheilichthys spp., Squalidus spp., Pseudogobio esocinus, Hemibarbus longirostris, and Hemibarbus labeo, 841 (92.7%) fishes were infected with 117 CsMc per fish infected. Total 250 (54.7%) acheilognathinid fish (bitterlings), Acheilognathus spp. and Acanthorhodeus spp. were infected with 5.8 CsMc. In the rasborinid fish (chubs) group, i.e., Zacco platypus, Zacco temminckii, and Zacco koreanus, 77 (13.7%) out of 563 fish examined were infected with 2.4 CsMc in average. The susceptibility indices of CsMc were 49.09 in the overall positive fish group, 104.15 in the gobioninid group, 3.17 in the acheilognathinid group and 0.35 in the rasborinid fish group respectively. Only 1 CsMc was detected in 3 fish species, Coreoperca herzi, Channa argus, and Lepomis macrochirus, respectively. Conclusively, it was confirmed that CsMc are moderately prevalent in fishes from Yangcheon in Sancheon-gun, Gyeongsangnam-do, Korea.

Venom allergen-like protein 28 in Clonorchis sinensis: four epitopes on its surface and the potential role of Cys124 for its conformational stability.

Venom allergen-like (VAL) proteins are important to host-parasite interactions. We previously demonstrated that a Clonorchis sinensis VAL (CsVAL) protein-derived synthetic peptide suppresses allergic and inflammatory responses. However, little is known regarding the physicochemical and antigenic properties of CsVAL proteins. Here, we identified a novel 194 amino acid VAL protein, named C. sinensis VAL 28 (CsVAL28), and characterized its functional motifs and structural details as a new member of the CAP superfamily. Unlike members of the Schistosoma mansoni VAL (SmVAL) family, CsVAL28 has a single CAP1 motif and six highly conserved disulfide bond-forming cysteines. Tertiary models of wild-type CsVAL28 and mutants were built using SmVAL4 as template via homology modeling. Normal mode analysis predicted that disulfide bond breaking by mutation of cysteine 124 to serine would greatly affect protein mobility. Four major immunoreactive linear epitopes were identified in the surface-exposed region or its vicinity via epitope mapping, using sera from clonorchiasis patients and healthy controls. Our findings provide in-depth knowledge on the structure-function properties of VAL proteins and may help determine highly antigenic regions for developing new diagnostic approaches.

Infection Status of Isthmiophora hortensis Metacercariae in Dark Sleepers, Odontobutis Species, from Some Water Systems of the Republic of Korea.

Present study was performed to survey on infection status of Isthmiophora hortensis (formerly Echinostoma hortense) metacercariae (IhMc) in dark sleepers, Odontobutis spp., from some water systems of the Republic of Korea. A total of 237 Odontobutis spp. was collected in the water systems of 5 rivers, i.e., Mangyeong-gang (gang means river), Geum-gang, Tamjin-gang, Seomjin-gang, and Nakdong-gang. They were all examined with artificial digestion method for 5 years (2013-2017). A total of 137 (57.8%) Odontobutis spp. were infected with 14.8 IhMc in average. The prevalence was the highest in Nakdong-gang areas (62.9%) and followed by in Mangyeong-gang (57.1%), Geum-gang (56.3%), Tamjin-gang (54.8%), and Seomjin-gang (53.9%) areas. Metacercarial densities were 28.1 (Geum-gang), 13.9 (Mangyeong-gang), 13.3 (Nakdong-gang), 13.1 (Tamjin-gang), and 2.3 (Seomjin-gang) per infected fish. Especially, in case of Yugucheon (cheon means stream), a branch of Geum-gang, IhMc were detected in all fish (100%) examined and their density was about 48 per fish. By the present study, it was confirmed that the infection status of IhMc is more or less different by the surveyed areas and the dark sleepers, Odontobutis spp., are suitable fish hosts of I. hortensis.

Infection Status with Metagonimus spp. Metacercariae in Fishes from Seomjin-gang and Tamjin-gang in Republic of Korea.

To grasp the infection status of Metagonimus spp. metacercariae (MsMc), the freshwater fishes were surveyed from Seomjin-gang (river) and Tamjin-gang in the Republic of Korea. Total 1,604 fishes from 7 local sites of Seomjin-gang and 1,649 fishes from 2 sites of Tamjin-gang were examined for 6 years (2012-2017) by the artificial digestion method. MsMc were detected in fishes from 7 sites, i.e., Osucheon in Imsil-gun (36.3% fish in 6 spp.), Seomjin-gang in Sunchanggun (49.8% in 18 spp.), Songdaecheon in Namwon-si (64.5% in 8 spp.), Seomjin-gang in Gokseong-gun (72.4% in 14 spp.) and in Gurye-gun (78.8% in 17 spp.), Hoengcheon (75.9% in 11 spp.) and Namsancheon (58.9% in 7 spp.) in Hadong-gun. Their average densities were 4.2, 86.8, 39.9, 43.1, 246.5, 173.6 and 67.5 per fish infected respectively. Prevalence with MsMc in rasborinid fish from Seomjin-gang was 89.2% and their intensity was 73.6 per fish infected. Endemicities of MsMc in rasborinid fish from Seomjin-gang were significantly higher in fishes from the lower reaches (prevalence: 98.7%; density: 137) rather than in fishes from the middle (93.5%; 38) and upper (72.4%; 13) reaches. MsMc were also detected in 56.1% and 66.4% fishes from 2 surveyed areas, i.e., the middle reaches in Jangheung-gun and the lower reaches in Gangjin-gun, of Tamjin-gang, and their densities were 147 and 121 per fish infected. In susceptible fishes from Tamjin-gang, the prevalence was 84.1% and density was 227 per fish infected. By the present study, it was confirmed that MsMc is highly prevalent in the fishes from Seomjin-gang and Tamjin-gang in Korea.

Prevention and Control Strategies for Parasitic Infections in the Korea Centers for Disease Control and Prevention.

Korea is successfully controlled intestinal parasitic infections owing to economic development and high health consciousness. The Division of Vectors and Parasitic Diseases (formerly the Division of Malaria and Parasitology) is in the Center for Laboratory Control of Infectious Diseases of the Korea Centers for Disease Control and Prevention. It has been the governmental agency responsible for controlling and leading scientific research on parasitic diseases. The Division of Vectors and Parasitic Diseases has conducted and funded basic research and disseminated the research results to various medical fields, ultimately promoting public health in Korea. Among the noteworthy achievements of this division are the national surveillance of healthcare-associated parasitic infections, prevention and control for parasitic infections, and the elimination of lymphatic filariasis from Korea. On a broader scale, the division's research programs and academic supports were influential in preventing and treating infectious parasitic diseases through public policies and laws. In this review, we summarize the past and present role of the Division of Vectors and Parasitic Diseases in preventing and treating infectious parasitic diseases in Korea.

Prevalence and Intensity of Clonorchis sinensis Metacercariae in Freshwater Fish from Wicheon Stream in Gunwi-gun, Gyeongsangbuk-do, Korea.

The infection status of Clonorchis sinensis metacercariae (CsMc) was examined in freshwater fish from a highly prevalent site, Wicheon (a branch of Nakdong-gang), which is located in Gunwi-gun, Gyeongsangbuk-do, the Republic of Korea. Total 1,162 fish in 32 species were examined by the artificial digestion method through 6 years. CsMc were detected in 720 (67.5%) out of 1,067 fish (26 spp.) and their density was 610 per fish infected. In the susceptible gobioninid fish group, i.e., Pungtungia herzi, Squalidus gracilis majimae, Squalidus japonicus coreanus, Sarcocheilichthys variegatus wakiyae and Pseudorasbora parva, all of 323 fish were infected with an average of 1,310 CsMc. Total 23 (95.8%) gobioninid fish, i.e., Pseudogobio esocinus, Abbottina springeri, Hemibarbus longirostris, Microphysogobio koreensis, and Microphysogobio jeoni, were infected with 127 CsMc in average. In the acheilognathinid fish (bitterlings) group, the prevalence was 77.0%, and the density was 50 CsMc per fish infected. In the rasborinid fish (chubs) group, i.e., Zacco platypus, Zacco temminckii, Zacco koreanus, and Opsariichthys uncirostris amurensis, 147 (36.5%) out of 403 fish examined were infected with 15 CsMc in average. The susceptibility indices of CsMc were 412 in the overall positive fish group, 1,310 in the gobioninid group-1, 122 in the gobioninid group-2, 38.5 in the acheilognathinid group, and 5.5 in the rasborinid fish group. Conclusively, it was confirmed that CsMc are highly prevalent in fish from Wicheon, and their infection tendency varied according to the subfamily groups in Cyprinidae fish hosts.

Infections with Zoonotic Trematode Metacercariae in Yellowfin Goby, Acanthogobius flavimanus, from Coastal Areas of Republic of Korea.

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.

Infections with Centrocestus armatus Metacercariae in Fishes from Water Systems of Major Rivers in Republic of Korea.

The infection status of Centrocestus armatus metacercariae (CaMc) was broadly surveyed in freshwater fishes from major river systems in the Republic of Korea (Korea) during 2008-2017. A total of 14,977 fishes was caught and examined by the artificial digestion method. CaMc were detected in 3,818 (97.1%) (2,114 Z. platypus: 96.1% and 1,704 Z. temminckii: 98.4%) out of 3,932 Zacco spp. examined and their density was 1,867 (2,109 in Z. platypus and 1,567 in Z. temminckii) per fish infected. The prevalences with CaMc were high, 93.7-100%, in Zacco spp. from all surveyed areas. However, their densities were more or less different by the surveyed areas and fish species. They were most high in Nakdong-gang in Gyeongsangnam-do (4,201 in average), and followed by Geum-gang (2,343), Nakdong-gang in Gyeongsangbuk-do (1,623), Han-gang (1,564), Tamjin-gang and Yeongsan-gang (1,540), streams in the east coast (1,028), Seomjin-gang (488) and Mangyeong-gang (170). In another species of rasborinid fish, Opsariichthys uncirostris amurensis, CaMc were detected in 222 (74.8%) out of 297 ones examined and their density was 278 (1-4,480) per fish infected. CaMc were also detected in total 41 fish species except for the rasborinid fish, Z. platypus, Z. temminckii and O. uncirostris amurensis. Conclusively, it was confirmed that among the 3 species of rasborinid fish, Z. platypus and Z. temminckii are highly prevalent and O. uncirostris amurensis is moderately prevalent with CaMc. Additionally, we could know that variety of fish species act as the second intermediate hosts of C. armatus in Korea.

Infection Status with Clonorchis sinensis Metacercariae in Fish from Tamjin-gang (River) in Jeollanam-do, Republic of Korea.

The present study was performed to investigate the infection status with Clonorchis sinensis metacercariae (CsMc) in fishes from 2 sites, the middle and lower reaches, of Tamjin-gang (River) in Jeollanam-do, the Republic of Korea. Total 1,132 fishes in 22 species were collected from the middle reaches in Jangheung-gun for 4 years (2014-2017) and 517 fishes in 17 species were also collected from the lower reaches in Gangjin-gun in 2014 and 2017. They were all individually examined with the artificial digestion method in our laboratory. CsMc were detected in 322 (28.5%) out of 1,132 fishes from Jangheung-gun, and in 161 (31.1%) out of 517 fishes from Gangjin-gun, and their densities were 51 and 57 per fish infected each. In the fish species with CsMc, positive rates were 61.5% in Jangheung-gun and 62.7% in Gangjin-gun. A total of 222 Pungtungia herzi were examined and they were all infected with CsMc. The average intensity was 103 CsMc in the index fish, P. herzi (95 in Jangheung-gun and 121 in Gangjin-gun). In P. herzi bimonthly examined in 2017, the intensity was commonly most higher in March in 2 surveyed sites, however the significant seasonal endemicity was not showed. Conclusively, it was confirmed that CsMc is more or less prevalent in fishes from Tamjin-gang and their endemicity is higher in fish from the lower reaches in Gangjin-gun than the middle reaches in Jangheung-gun in Jeollanam-do, Korea.

Molecular and Structural Characterization of the Tegumental 20.6-kDa Protein in Clonorchis sinensis as a Potential Druggable Target.

The tegument, representing the membrane-bound outer surface of platyhelminth parasites, plays an important role for the regulation of the host immune response and parasite survival. A comprehensive understanding of tegumental proteins can provide drug candidates for use against helminth-associated diseases, such as clonorchiasis caused by the liver fluke Clonorchis sinensis. However, little is known regarding the physicochemical properties of C. sinensis teguments. In this study, a novel 20.6-kDa tegumental protein of the C. sinensis adult worm (CsTegu20.6) was identified and characterized by molecular and in silico methods. The complete coding sequence of 525 bp was derived from cDNA clones and encodes a protein of 175 amino acids. Homology search using BLASTX showed CsTegu20.6 identity ranging from 29% to 39% with previously-known tegumental proteins in C. sinensis. Domain analysis indicated the presence of a calcium-binding EF-hand domain containing a basic helix-loop-helix structure and a dynein light chain domain exhibiting a ferredoxin fold. We used a modified method to obtain the accurate tertiary structure of the CsTegu20.6 protein because of the unavailability of appropriate templates. The CsTegu20.6 protein sequence was split into two domains based on the disordered region, and then, the structure of each domain was modeled using I-TASSER. A final full-length structure was obtained by combining two structures and refining the whole structure. A refined CsTegu20.6 structure was used to identify a potential CsTegu20.6 inhibitor based on protein structure-compound interaction analysis. The recombinant proteins were expressed in Escherichia coli and purified by nickel-nitrilotriacetic acid affinity chromatography. In C. sinensis, CsTegu20.6 mRNAs were abundant in adult and metacercariae, but not in the egg. Immunohistochemistry revealed that CsTegu20.6 localized to the surface of the tegument in the adult fluke. Collectively, our results contribute to a better understanding of the structural and functional characteristics of CsTegu20.6 and homologs of flukes. One compound is proposed as a putative inhibitor of CsTegu20.6 to facilitate further studies for anthelmintics.

Intestinal Parasite Infections among Inhabitants in Yanbian Prefecture, Jilin Province, China.

To investigate the prevalence of intestinal parasite infections in Yanbian Prefecture, Jilin Province, China, epidemiological surveys were conducted on a collaboration basis between the Korean Centers for Disease Control and Prevention and the Yanbian Center for Disease Control and Prevention. A total of 8,396 (males 3,737 and females 4,659) stool samples were collected from 8 localities and examined with the formalin-ether sedimentation technique, and additionally examined with the cellotape anal swab to detect Enterobius vermicularis eggs. The overall rate of intestinal parasites was 1.57%. The prevalence of Ascaris lumbricoides was the highest (0.80%), followed by Entamoeba spp. (0.23%), heterophyid flukes (0.15%), Clonorchis sinensis (0.08%), Enterobius vermicularis (0.07%), hookworms (0.06%), Trichostrongylus spp. (0.06%), Giardia lamblia (0.04%), Paragonimus spp. (0.02%), Diphyllobothrium spp. (0.02%), Trichuris trichiura (0.02%). The prevalence by sex was similar, 1.58% (n=59) in males and 1.57% (n=73) in females. By the present study, it is partly revealed that the prevalences of intestinal parasite infections are relatively low among the inhabitants of Yanbian Prefecture, Jilin Province, China.

Prevalence of Clonorchis sinensis Infection among Residents along 5 Major Rivers in the Republic of Korea.

Clonorchis sinensis is currently the most important parasite affecting public health problems in the Republic of Korea. We investigated the prevalence of C. sinensis infection among residents living along 5 major rivers in Korea. A total of 42,562 individual stool samples were collected from 37 localities and examined using the formalin-ether sedimentation technique. Helminth eggs were detected in 4,052 (9.5%) residents and 3,586 (8.4%) were infected with C. sinensis. The egg positive rate of C. sinensis in Nakdong, Seomjin, Geum, Yeongsan, and Han River was 11.7%, 9.9%, 6.5%, 3.1%, and 1.0%, respectively. The overall prevalence of clonorchiasis by sex was 11.2% in males and 6.2% in females. The age-prevalence was the highest in the 50-59 years band. It has been reconfirmed that the endemicity of clonorchiasis is higher in southern areas of Korea, especially along Nakdong and Seomjin Rivers. A combination of continuous control programs with health education initiatives is urgently required in these highly endemic areas of clonorchiasis in Korea.

Expression and biochemical characterization of a type I methionine aminopeptidase of Plasmodium vivax.

Methionine aminopeptidases (MetAPs), ubiquitous enzymes that play an important role in nascent protein maturation, have been recognized as attractive targets for the development of drugs against pathogenic protozoa including Plasmodium spp. Here, we characterized partial biochemical properties of a type I MetAP of Plasmodium vivax (PvMetAP1). PvMetAP1 had the typical amino acid residues essential for metal binding and substrate binding sites, which are well conserved in the type I MetAP family enzymes. Recombinant PvMetAP1 showed activity in a broad range of neutral pHs, with optimum activity at pH 7.5. PvMetAP1 was stable under neutral and alkaline pHs, but was relatively unstable under acidic conditions. PvMetAP1 activity was highly increased in the presence of Mn(2+), and was effectively inhibited by a metal chelator, EDTA. Fumagillin and aminopeptidase inhibitors, amastatin and bestatin, also showed an inhibitory effect on PvMetAP1. The enzyme had a highly specific hydrolytic activity for N-terminal methionine. These results collectively suggest that PvMetAP1 belongs to the family of type I MetAPs and may play a pivotal role for the maintenance of P. vivax physiology by mediating protein maturation and processing of the parasite.