Prevalence of Zoonotic Trematode Metacercariae in Freshwater Fish from Gangwon-do,Korea

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.     

In vitro excystment of the metacercaria of Maritrema arenaria (Digenea: Microphallidae)

Metacercarial cysts of Mantrema arenaria were subjected to a solution containing trypsin and bile salts at 41°C. This treatment induced intense metacercarial activity and after 15 min metacercariae burst through their cyst walls and emerged. Electron microscopy demonstrated that during the process of excystment the inner layer of the cyst wall changed from a compact to a loose fibrous state. Experiments showed that only cysts containing viable metacercariae underwent this change whereas cysts which had been forcibly vacated before treatment did not. This indicated that the structural change of the inner layer of the cyst wall could not be attributed to the excystment medium. Also there was much less acid phosphatase activity in and on the surface of newly excysted metacercariae compared with encapsulated specimens. It was concluded that the excystment medium induced physical activity in, and the release of enzymic material by, the metacercariae. Together these activities rendered the cyst wall soft and susceptible to rupture by physical pressure.     

The responses of Ligia oceanica (L.) (Crustacea: Isopoda) to infection by Maritrema linguilla Jäg. 1908 and Microphallus similis (Jäg. 1900) (Digenea: Microphallidae) and to abiotic implants

The initial and principal encapsulation response of Ligia oceanica to Araldite implants and to encysted metacercariae of Maritrema linguilla is hemolymph coagulation followed by limited hemocyte agglutination. Granules secreted by isolated granulocytes and semigranulocytes may catalyze coagulation. Isolated hyaline cells explode and make an insignificant contribution to the initial cyst wall. Later, hemocytes agglutinate and some granulocytes retain their granules which become melanized. Eventually, a wide multilayered hos capsule is formed. Unencysted metacercariae of M. linguilla transplanted from the pleopods into the dorsal hemocoel of another specimen of L. oceanica encyst and become encapsulated but are not damaged by encapsulation. Transplanted encysted metacercariae are also encapsulated and unharmed. Cercariae implanted directly into the dorsal hemocoel, however, fail to encyst, become encapsulated, die, and lyse within the capsule. Implanted cercariae and encysted metacercariae of Microphallus similis are also encapsulated and destroyed in the hemocoel of L. oceanica. The absence of host response to the naturally infecting unencysted parasite in the pleopod sinuses may be attributed to rhythmic movement, mucopolysaccharide secretions and to the retention of excreta within the excretory bladder. Once the excreta is released during cyst formation in the dorsal hemocoel, encapsulation occurs but this does not appear to harm the parasite. On the contrary, considerable growth occurs within the cyst which suggests that the parasite may absorb nutrients released from necrotic hemocytes.     

Histopathological changes in livers of mice infected with tetrathyridia of Mesocestoides corti and exposed to different environmental temperatures

Novak M. 1982. Histopathological changes in livers of mice infected with tetrathyridia of Mesocestoides corti and exposed to different environmental temperatures. International Journal for Parasitology12: 41–45. Observations on the histopathology of the liver of mice infected with Mesocestoides corti and kept for 20 days p.i. (post-infection) at low (5 ± 1°C), room (21 ± 1°C) or high (35 ± 1°C) temperature revealed that the degree of liver pathology was directly proportional to the intensity of liver infection, which in turn was the result of the temperature effect. The most severe pathological changes occured in the heavily infected organs of mice kept at low temperature, followed by less prominent changes in moderately infected livers of mice kept at room temperature and the smallest changes in lightly infected livers of mice kept at high temperature. The pathological changes in infected and uninfected livers of hosts exposed to different environmental temperatures are described and compared.     

Foodborne Trematode Metacercariae in Fish from Northern Vietnam and Their Adults Recovered from Experimental Hamsters

The prevalence of foodborne trematode (FBT) metacercariae was investigated in fish from 2 localities of northern Vietnam in 2004-2005. Freshwater fish (9 species) were collected from local markets in Hanoi City (n=76) and Nam Dinh Province (n=79), and were examined for FBT metacercariae using the artificial digestion technique. Adult flukes were obtained from hamsters experimentally infected with the metacercariae at day 8 post-infection. Three (Haplorchis pumilio, Centrocestus formosanus, and Procerovum varium) and 6 (Haplorchis taichui, H. pumilio, C. formosanus, P. varium, Stellantchasmus falcatus, and Heterophyopsis continua) species of FBT metacercariae were detected in the 2 regions, respectively. Overall, among the positive fish species, H. pumilio metacercariae were detected in 104 (80.0%) of 130 fish examined (metacercarial density per infected fish; 64.2). C. formosanus metacercariae were found in 37 (40.2%) of 92 fish (metacercarial density; 14.7). P. varium metacercariae were detected in 19 (63.3%) of 30 fish (Anabas testudineus and Mugil cephalus) (metacercarial density; 247.7). S. falcatus metacercariae were found in all 10 M. cephalus examined (metacercarial density; 84.4). H. continua metacercariae (2 in number) were detected in 1 fish of Coilia lindmani. Morphologic characteristics of the FBT metacercariae and their experimentally obtained adults were described. The results have demonstrated that various FBT species are prevalent in northen parts of Vietnam.     

Infection Status of Zoonotic Trematode Metacercariae in Fishes from Vientiane Municipality and Champasak Province in Lao PDR

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.     

Prevalence and Intensity of Opisthorchis viverrini Metacercarial Infection in Fish from Phnom Penh,Takeo, and Kandal Provinces,Cambodia

The prevalence and intensity of Opisthorchis viverrini metacercariae (OvMc) were investigated in fish from 3 southern administrative regions along the Mekong River in Cambodia, i.e., Phnom Penh, Takeo, and Kandal Provinces from 2017 to 2020. A total of 295 freshwater fish (24 species) were transported to our laboratory with ice and examined using the artificial digestion method. In Phnom Penh, among 4 fish species positive for OvMc, 9 (23.7%) of 38 specimens examined were infected, and their intensity of infection averaged 4.3 metacercariae per infected fish. In Takeo Province, among 10 fish species positive for OvMc, 24 (38.1%) out of 63 fish examined were infected, and their intensity of infection was av. 14.4 metacercariae per infected fish. In particular, all of 3 Osteochilus schlegelii fish examined were infected, and their infection intensity was high, 34.7 metacercariae per fish. In Kandal Province, among 6 fish species positive for OvMc, 46 (90.2%) out of 51 specimens examined were infected, and their infection intensity was 24.0 metacercaraie per infected fish. All fish of Systomus orphoides (n=17), Barbonymus altus (n=14), and Rasbora aurotaenia (n=2) were infected, and their intensity of infection averaged 37.7, 21.6, and 18.5 metacercariae per fish, respectively. Metacercariae of Haplochis yokogawai, Haplorchis taichui, and Centrocestus formosanus were detected in fish from Takeo and Kandal Provinces. From these results, it has been confirmed that a variety of fish species from Phnom Penh, Takeo, and Kandal Provinces are commonly infected with OvMc, and preventive measures to avoid human O. viverrini infection should be performed in Cambodia.     

Fishborne Trematode Metacercariae in Luang Prabang,Khammouane, and Saravane Province,Lao PDR

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.     

Melophagus ovinus (Pupipara: Hippoboscidae): Confirmation of the nonpathogenicity of Trypanosoma melophagium for sheep keds

Data are presented to show that Trypanosoma melophagium is not pathogenic to the sheep ked, Melophagus ovinus. During each normal cycle of the ked population on sheep, death of variable numbers of keds occurs that cannot be attributed to host resistance. Pathological signs include abdominal swelling, reddening of the hemolymph, cessation of peristalsis, and desquamation of the epithelium of the posterior midgut. These pathological developments are attributed to hypoxia in the gut wall resulting from occlusion of abdominal spiracles with debris. They occur alike in keds infected with T. melophagium and in keds that have been made flagellate free experimentally.     

On the viability of Fasciola gigantica metacercariae ingested by Lymnaea auricularia

The effect of ingestion by Lymnaea auricularia on the viability and infectivity of Fasciola gigantica metacercariae was studied. The cyst wall was unaffected by the snail's digestive processes. Two rabbits, each infected with 50 ingested metacercariae, died at 83 and 87 days post-infection. Eight and 10 immature flukes were recovered from the livers, indicating that the metacercariae had remained infective after passing through the intestine of the snail.     

Migration, site selection, and development of Ornithodiplostomum sp. metacercariae (Digenea: Strigeoidea) in fathead minnows (Pimephales promelas)

The metacercarial stage of trematodes is typically considered an encysted, developmentally quiescent, resting stage. Yet the metacercariae of some species of strigeoid trematode undergo extravagant development within specific tissues of their second intermediate host. Our understanding of patterns of migration, site selection and development of these types of metacercariae is known for only a few species. In this study, we characterize the invasion and development of Ornithodiplostomum sp. metacercariae in their second intermediate host, the fathead minnow, Pimephales promelas. Diplostomules completed their migration into the abdominal cavity between 15 min and 48 h p.i. Most diplostomules migrated along muscular and connective tissue then penetrated the peritoneal lining of the abdominal cavity en route to the liver or pancreas. Alternatively, some diplostomules migrated within the host’s circulatory system, including the heart and arteries of the hepatic portal system. Metacercarial development in the liver and pancreas involved distinct growth, encystment and consolidation phases. Metacercarial volume increased 15-fold between 48 h and 4 weeks p.i., presumably due to absorptive and/or ingestive feeding activities within host tissues. By 2 weeks p.i., metacercariae were enveloped within a cyst wall and they were found loosely attached to the surfaces of internal tissues or unattached within the body cavity. These results emphasize the complex nature of metacercarial migration and growth and demonstrate that their growth and encystment phases occur within different habitats within their intermediate hosts.     

Histochemical and ultrastructural studies on the metacercarial cyst of Echinostoma revolutum (Trematoda).

Histochemical and ultrastructural studies were made on the metacercarial cyst of Echinostoma revolutum obtained from the kidney of experimentally infected Physa and Lymnaea snails. Ultrastructural studies revealed three cyst walls, an outer, middle and inner. The outer wall was more electron-dense than the middle, and contained coarser granules than those found in the middle layer. The inner wall was lamellated and contained membranous whorls. Collagenous fibers presumably of host origin surrounded the outer cyst wall. The outer and middle cyst walls stained identically with all histochemical procedures used. These walls contained acid mucopolysaccharides and glycoprotein, whereas the inner cyst wall contained glycoprotein. All cyst walls stained positively with a variety of protein stains.     

弗氏柠檬酸杆菌对河蟹致病性的研究

首次报道了弗氏柠檬酸杆菌对河蟹的病原性、并导致其病理变化,药物对该菌的敏感试验及生产中药物治疗效果.从垂死的病蟹肝胰脏中分离得到可疑病菌,经人工感染试验证实此菌导致健康蟹发病死亡.该菌可导致河蟹的肝胰腺、鳃等发生病理变化,最终引起败血症而死亡.通过16种药物对该菌的敏感试验,筛选出有效药物,应用于生产中取得了较好疗效.       

A Novel Fungal Hyperparasite of Puccinia striiformis f. sp. tritici,the Causal Agent of Wheat Stripe Rust

Puccinia striiformis f. sp. tritici (Pst), the causal fungus of wheat stripe rust, was previously reported to be infected by Lecanicillium lecanii, Microdochium nivale and Typhula idahoensis. Here, we report a novel hyperparasite on Pst. This hyperparasitic fungus was identified as Cladosporium cladosporioides (Fresen.) GA de Vries based on morphological characteristics observed by light and scanning electron microscopy together with molecular data. The hyperparasite reduced the production and viability of urediniospores and, therefore, could potentially be used for biological control of wheat stripe rust.     

Fasciola hepatica: Simple,large-scale, in vitro excystment of metacercariae and subsequent isolation of juvenile liver flukes

A simple method has been developed for the in vitro excystment of metacercariae of Fasciola hepatica, and for the isolation of large numbers of juvenile liver flukes free from intact metacercariae and from cyst-wall material. In this method, the outer cyst wall was removed by gently grinding the metacercariae between small glass plates. The metacercariae were activated by incubation for 1 hr under $\text{60\%}\text{CO}{}_2\text{40\%}\text{N}{}_2$ and excysted by the addition of 10% sterilized sheep bile or an equivalent amount of taurocholic acid. Excystment was accomplished in an experimental apparatus allowing the newly excysted juveniles to escape from the bile-containing excystment medium into a medium with low bile content. The yield of isolated liver flukes was 60–80%; their protein content was about 125 ng. Both bile and taurocholic acid, though necessary for excystment, were detrimental to the survival of the juvenile liver flukes. The presence of bile in the host intestine may be a stimulus for juveniles to leave the gut and enter the abdominal cavity.     

A trematode metacercaria encysted in the nerves of the dungeness crab, Cancer magister

Of 188 Dungeness crabs, Cancer magister, 8 contained unidentified trematode metacercariae encysted in various components of the nervous system, including the thoracic ganglion, brain, lamina ganglionaris of the eyestalk, and major nerves arising from the thoracic ganglion. A single cyst was present in the available tissue sections of 7 of the crabs and no behavioral abnormalities were exhibited. One crab with multiple cysts in major nerves near the thoracic ganglion was markedly ataxic. The cysts and included worms distorted, compacted, and destroyed nervous tissue, and occupied most of the nerves where present. Host response was minimal, but some cysts invoked massive hemocytic accumulations near the infection site. Infections probably seriously affect nerve impulse transmission and accounts for the lethargic behavior of the crab with multiple cysts in major nerves. The present report is the first record of digenetic trematode infections in the Dungeness crab and the apparent restriction of the worm to nervous tissue is unusual if not unique in the Digenea. Because of the absence of grossly recognizable lesions and the small samples excised at necropsy, both the incidence and intensity of infection in Dungeness crab populations are almost certainly higher than indicted by our data.     

Studies on metacercarial excystment in Himasthla leptosoma (Trematoda: Echinostomatidae) and newly emerged metacercariae

Metacercarial cysts of Himasthla leptosoma were subjected to a solution containing bile salts, trypsin and l cysteine at 41°C. The treatment induced intense metacercarial activity and after 20 min metacercariae burst through the cyst walls and emerged. Electron microscopy demonstrated that organisms burst through a small area of cyst wall which was devoid of a layer of lamellae present elsewhere towards the innermost surface. The appearance of ruptured cyst walls indicated that they had been softened by the excystment medium. Newly emerged metacercariae possessed a reniform collar of 29 cephalic spines and these were sometimes withdrawn into pits, presumably by action of a muscle complex in the head region. Sensory papillae were distributed in a bilaterally symmetrical arrangement around the anterior sucker and none were visible on the surface of the ventral sucker. Tegumental spines were found only from a point some distance behind the head collar to the region of the ventral sucker. The most anterior spines were simple and peg-like and they quickly merged posteriorly into more complex palmate forms.     

Paragonimus paishuihoensis Metacercariae in Freshwater Crabs,Potamon lipkei,in Vientiane Province,Lao PDR

Among Paragonimus species, P. paishuihoensis is one of the most mysterious and poorly understood species. Metacercariae are characterized by having a unique dendritically branched excretory bladder. However, the morphology of the adult worm remains unknown. To date, metacercariae of this species have been reported only in China and Thailand. In this study, we first found P. paishuihoensis metacercariae in freshwater crabs, Potamon lipkei, in Hinheub District, Vientiane, Lao PDR, with a prevalence of 77.7% and the average intensity of 10.3 (range 1-28) metacercariae per crab. The molecular data based on ITS2 and CO1 markers indicated that P. paishuihoensis from Laos and Thailand were almost completely identical and were close to members of the Paragonimus bangkokensis/Paragonimus harinasutai complex. Attempts to infect experimental animals (cats, dogs, and rats) with P. paishuihoensis were unsuccessful, suggesting that these animals might be unsuitable definitive hosts for the species. Further studies are necessary to elucidate the taxonomic status and life cycle of P. paishuihoensis.     

Infection Status of Freshwater Crabs and Crayfish with Metacercariae of Paragonimus westermani in Korea

The present study investigated the infection status of Paragonimus westermani metacercariae in freshwater crabs (n = 363) and crayfish (n = 31) from October 2007 to October 2008 using the crush method. All of the freshwater crabs, Eriocheir japonicus, were negative for P. westermani metacercariae while 10 (32.3%) of the 31 examined crayfish were positive. The 10 positive crayfish were caught in Haenam, Jeollanam-do, and there were 8-59 (mean 28.4) metacrcariae per infected crayfish. These results suggest that P. westermani metacerariae are still transmitted by crayfish enzootically in southern Korea, and that freshwater crabs may transmit metacercariae only on rare occasions.     

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.