Infection Status with Digenetic Trematode Metacercariae in Fishes from Coastal Lakes in Gangwon-do, Republic of 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.

Pygidiopsis summa (Digenea: Heterophyidae): Status of Metacercarial Infection in Mullets from Coastal Areas in the Republic of Korea

To know the infection status of zoonotic trematode metacercariae in brackish water fish, we surveyed mullets collected from 18 coastal areas in the Republic of Korea. The metacercariae of Pygidiopsis summa were detected in 236 (68.2%) out of 346 mullets examined. They were found in mullets from 15 areas except for those from Boseong-gun (Jeollanam-do), Pohang-si, and Uljin-gun (Gyeongsangbuk-do). Especially in mullets from Taean-gun (Chungcheongnam-do) and Geoje-si (Gyeongsangnam-do), their prevalences were 100% and 95.5%, and the average metacercarial density was more than 1,000 per fish. They were also detected in mullets from 3 coastal lakes, Gyeongpoho, Songjiho, and Hwajinpoho, in Gangwon-do, and their average densities were 419, 147, and 672 per infected fish, respectively. The metacercariae of 5 other heterophyid species, including Heterophyes nocens, Heterophyopsis continua, Metagonimus sp., Stictodora fuscata, and Stictodora lari, were found in the mullets examined. The metacercariae of H. nocens were detected in 66.7, 100, 28.6, 81.6, 3.9, 61.5, and 27.3% of mullets from Muan-gun, Shinan-gun, Haenam-gun, Gangjin-gun, and Boseong-gun (Jeollanam-do), Hadong-gun, and Geoje-si (Gyeongsangnam-do), and their metacercarial intensities were 64, 84, 119, 99, 1, 24, and 24 per fish infected, respectively. From the above results, it has been confirmed that P. summa metacercariae are heavily infected in mullets from coastal areas of Korea. It is suggested that residents who frequently consume raw mullet dish can be easily infected with heterophyid flukes.

Zoonotic Intestinal Trematodes in Stray Cats (Felis catus) from Riverside Areas of the Republic of 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.

Mucosal Immune Responses of Mice Experimentally Infected with Pygidiopsis summa (Trematoda: Heterophyidae)

Mucosal immune responses against Pygidiopsis summa (Trematoda: Heterophyidae) infection were studied in ICR mice. Experimental groups consisted of group 1 (uninfected controls), group 2 (infection with 200 metacercariae), and group 3 (immunosuppression with Depo-Medrol and infection with 200 metacercariae). Worms were recovered in the small intestine at days 1, 3, 5, and 7 post-infection (PI). Intestinal intraepithelial lymphocytes (IEL), mast cells, and goblet cells were counted in intestinal tissue sections stained with Giemsa, astra-blue, and periodic acid-Schiff, respectively. Mucosal IgA levels were measured by ELISA. Expulsion of P. summa from the mouse intestine began to occur from days 3-5 PI which sustained until day 7 PI. The worm expulsion was positively correlated with proliferation of IEL, mast cells, goblet cells, and increase of IgA, although in the case of mast cells significant increase was seen only at day 7 PI. Immunosuppression suppressed all these immune effectors and inhibited worm reduction in the intestine until day 7 PI. The results suggested that various immune effectors which include IEL, goblet cells, mast cells, and IgA play roles in regulating the intestinal mucosal immunity of ICR mice against P. summa infection.

Infection Status of Estuarine Fish and Oysters with Intestinal Fluke Metacercariae in Muan-gun, Jeollanam-do, Korea

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.

Intestinal Helminth Infections in Feral Cats and a Raccoon Dog on Aphaedo Island, Shinan-gun, with a Special Note on Gymnophalloides seoi Infection in Cats

Four feral cats and a raccoon dog purchased from a local collector on Aphaedo Island, Shinan-gun, where human Gymnophalloides seoi infections are known to be prevalent, were examined for their intestinal helminth parasites. From 2 of 4 cats, a total of 310 adult G. seoi specimens were recovered. Other helminths detected in cats included Heterophyes nocens (1,527 specimens), Pygidiopsis summa (131), Stictodora fuscata (4), Acanthotrema felis (2), Spirometra erinacei (15), toxocarids (4), and a hookworm (1). A raccoon dog was found to be infected with a species of echinostome (55), hookworms (7), toxocarids (3), P. summa (3), and S. erinacei (1). No G. seoi was found in the raccoon dog. The results indicate that feral cats and raccoon dogs on Aphaedo are natural definitive hosts for intestinal trematodes and cestodes, including G. seoi, H. nocens, and S. erinacei. It has been first confirmed that cats, a mammalian species other than humans, play the role of a natural definitive host for G. seoi on Aphaedo Island.

Prevalence of Zoonotic Metacercariae in Two Species of Grouper, Epinephelus coioides and Epinephelus bleekeri, and Flathead Mullet, Mugil cephalus, in Vietnam

Fishborne zoonotic metacercariae have not been reported from brackish water and marine fish from Vietnam waters although these parasites are common in the country's freshwater fish. Both wild-caught and cultured grouper (Epinephelus coioides and Epinephelus bleekeri), and mullet (Mugil cephalus) from brackish and marine waters locate in Khanh Hoa province in central coastal Vietnam were examined, and found positive for zoonotic trematode metacercariae. From grouper, Heterophyopsis continua and Procerovum varium were recovered. The prevalence of H. continua ranged from 2.0 to 6.0% and that for P. varium ranged from 11.6 to 15.8%. Mullet were infected with Pygidiopsis summa and H. continua both of these species are new records for Vietnam. The prevalence of P. summa in mullet was generally high, ranging from 17.6 to 75.5%, and was significantly higher than the prevalence of H. continua (2.5 to 32.4%). There were no significant differences in the prevalence of metacercariae between grouper from natural or cultured habitats, indicating that the highest risk of infection occurs in the wild-caught state prior to their placement in culture. Further, there was no difference in metacercarial prevalence between the 2 species of grouper. Infected wild-caught seed were only observed from January to October. Monthly variation in prevalence suggests seasonal variation in mullet infections occurs in this region with the highest transmission taking place from October to December. Basic investigations on the ecology and epidemiology of these intestinal flukes need to be carried out to determine their significance as a public health problem and the aspects of their biology that may be vulnerable to control interventions.

A new endemic focus of Gymnophalloides seoi infection on Aphae Island, Shinan-gun, Jeollanam-do

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

A survey of Heterophyes nocens and Pygidiopsis summa metacercariae in mullets and gobies along the coastal areas of the Republic of Korea

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

Heterophyid metacercarial infections in brackish water fishes from Jinju-man (Bay), Kyongsangnam-do, Korea

Heterophyid metacercarial infections in brackish water fishes, i.e., perch, shad, mullet, redlip mullet, and goby, of Jinju-man (Bay), Kyongsangnam-do, Korea, were investigated using a digestion technique. Among 45 perch (Lateolabrax japonicus), the metacercariae of Heterophyopsis continua were found in 55.6% (18.5 metacercariae per fish), Stictodora spp. in 28.9% (3.6), and Metagonimus takahashii in 6.7% (17.0). The metacercariae of H. continua were detected in 23 (65.7%) of 35 shad (Konosirus punctatus). Among 15 mullet (Mugil cephalus), the metacercariae of Pygidiopsis summa were found in 100% (105.9 metacercariae per fish), Heterophyes nocens in 40.0% (8.5), H. continua in 13.3%, and Stictodora spp. in 6.7%. Among 12 redlip mullet (Chelon haematocheilus), the metacercariae of P. summa were detected in 91.7% (1,299 metacercariae per fish), H. nocens in 16.7%, and Stictodora spp. in 16.7%. Among 35 gobies (Acanthogobius flavimanus), the metacercariae of Stictodora spp. were found in 82.9% (44.5 metacercariae per fish), and H. continua in 25.7% (2.8). The adult flukes recovered from a cat experimentally infected with metacercariae from perches were compatible with M. takahashii. The results confirm that the estuarine fish in Jinju-man (Bay) are heavily infected with heterophyid metacercariae. Furthermore, it was found for the first time that the perch acts as a second intermediate host for M. takahashii.

Surface ultrastructure of Pygidiopsis summa (Digenea: Heterophyidae) adult flukes

A scanning electron microscopic study was performed on the surface ultrastructure of Pygidiopsis summa (Digenea: Heterophyidae) adults. Metacercariae were collected from gills and muscles of mullets (Mugil cephalus) caught in a known endemic area, and adult flukes were harvested from dogs after 8 weeks of experimental infection. The worm was calabash form with its posterior part broader than the anterior part. Tegumental spines were densely distributed over the body surface, except on the suckers and genital apparatus, and around the excretory pore. Well differentiated spines were observed on the anterior half of the body, with 14-16 tips ventrally, and 19-20 tips dorsally. On the oral sucker, three pairs of type I sensory papillae (uni-ciliated knob-like swellings) and one pair of type II sensory papillae (aciliated round-swellings) were observed on the anterior and posterior parts of the lip, respectively. On the lip of the ventral sucker, one pair of type II sensory papillae was distributed only on its posterior part. Sperms were seen emerging from or entering into the genital apparatus. The results showed that the surface ultrastructure of P. summa was unique among the heterophyid trematodes, especially in digitation of tegumental spines and in distribution of sensory papillae on oral and ventral suckers.