Morphological observations of Echinochasmus japonicus cercariae and the in vitro maintenance of its life cycle from cercariae to adults

Lethal effects of praziquantel and albendazole, on the cercariae of Echinochasmus sp. (Dietz, 1909) in-vitro

Echinochasmidae are considered one of the digenean intestinal parasites of carnivorous mammals and humans. Some larvicidal medications, such as praziquantel and albendazole, were employed to interrupt the life cycle of Echinochasmidae, which may cause harmful and serious effects on the domestic fish, ducks, and humans in our ecosystem. Cercariae of Echinochasmus sp. (gymnocephalus type) were harvested by exposing snails to strong artificial illumination. The emerging cercariae were exposed in vitro to different concentrations of praziquantel and albendazole at the same period of incubation 12 h. Using probit analysis in SPSS version 25, the lethal concentrations 50 and 95% were determined. They were 0.036 and 0.82 ppm, respectively, for praziquantel and 5.3 and 9.2 ppm, respectively, for albendazole. The ultrastructural changes using scanning electron microscope on the tegumental surface of the treated cercariae with the two drugs were compared to the untreated cercariae. The untreated cercariae have a pear-shaped body with a long tail. The oral sucker is armed with a spiny collar and decorated with ciliated and unciliated sensory papillae. The cardinal ventral sucker has a thick, muscular wall. The cercarial tail is decorated with parallel longitudinal tegumental processes and spherical, unciliated papillae. In comparisons, cercariae treated with both drugs lost all healthy morphological features, but in varying degrees and effects between the two drugs. Our findings suggest that the use of both drugs can be recommended during the design of control strategies to combat this type of intestinal parasite.

Epidemiology and Geographical Distribution of Human Trematode Infections

Digenetic trematodes infecting humans are more than 109 species that belong to 49 genera all over the world. According to their habitat in the definitive hosts, they are classified as 6 blood flukes (Schistosoma japonicum. S. mekongi, S. malayensis, S. mansoni, S. intercalatum, and S. haematobium), 15 liver flukes (Fasciola hepatica, F. gigantica, Clonorchis sinensis, Opisthorchis viverrini, O. felineus, Dicrocoelium dendriticum, D. hospes, Metorchis bilis, M. conjunctus, M. orientalis, Amphimerus sp., A. noverca, A. pseudofelineus, Pseudamphistomum truncatum, and P. aethiopicum), nine lung flukes (Paragonimus westermani, P. heterotremus, P. skrjabini, P. skrjabini miyazakii, P. kellicotti, P. mexicanus, P. africanus, P. uterobilateralis, and P. gondwanensis), 30 heterophyid intestinal flukes (Metagonimus yokogawai, M. takahashii, M. miyatai, M. suifunensis, M. katsuradai, M. pusillus, M. minutus, Heterophyes heterophyes, H. nocens, H. dispar, Haplorchis taichui, H. pumilio, H. yokogawai, H. vanissinus, Centrocestus formosanus, C. armatus, C. cuspidatus, C. kurokawai, Procerovum calderoni, P. varium, Pygidiopsis genata, P. summa, Stictodora fuscata, S. lari, Stellantchasmus falcatus, Heterophyopsis continua, Acanthotrema felis, Apophallus donicus, Ascocotyle longa, and Cryptocotyle lingua), 24 echinostome intestinal flukes (Echinostoma revolutum, E. cinetorchis, E. mekongi, E. paraensei, E. ilocanum, E. lindoense, E. macrorchis, E. angustitestis, E. aegyptica, Isthmiophora hortensis, I. melis, Echinochasmus japonicus, E. perfoliatus, E. lilliputanus, E. caninus, E. jiufoensis, E. fujianensis, Artyfechinostomum malayanum, A. sufrartyfex, A. oraoni, Acanthoparyphium tyosenense, Echinoparymphium recurvatum, Himasthla muehlensi, and Hypoderaeum conoideum), 23 miscellaneous intestinal flukes (Brachylaima cribbi, Caprimolgorchis molenkampi, Phaneropsolus bonnei, P. spinicirrus, Cotylurus japonicus, Fasciolopsis buski, Gastrodiscoides hominis, Fischoederius elongatus, Watsonius watsoni, Gymnophalloides seoi, Gynaecotyla squatarolae, Microphallus brevicaeca, Isoparorchis hypselobagri, Nanophyetus salmincola, N. schikobalowi, Neodiplostomum seoulense, Fibricola cratera, Plagiorchis muris, P. vespertilionis, P. harinasutai, P. javensis, P. philippinensis, and Prohemistomum vivax), one throat fluke (Clinostomum complanatum), and one pancreatic fluke (Eurytrema pancreaticum). The mode of transmission to humans includes contact with cercariae contaminated in water (schistosomes) or ingestion of raw or improperly cooked food, including fish (liver flukes, heterophyid flukes, echinostomes, and throat flukes), snails (echinostomes, brachylaimids, and gymnophallid flukes), amphibia, reptiles (neodiplostomes), aquatic vegetables (fasciolids and amphistomes), and insect larvae or adults (lecithodendriids, plagiorchiids, and pancreatic flukes). Praziquantel has been proven to be highly effective against almost all kinds of trematode infections except Fasciola spp. Epidemiological surveys and detection of human infections are required for a better understanding of the prevalence, intensity of infection, and geographical distribution of each trematode species.

General overview of the current status of human foodborne trematodiasis

Foodborne trematodes (FBT) of public health significance include liver flukes (Clonorchis sinensis, Opisthorchis viverrini, O. felineus, Fasciola hepatica and F. gigantica), lung flukes (Paragonimus westermani and several other Paragonimus spp.) and intestinal flukes, which include heterophyids (Metagonimus yokogawai, Heterophyes nocens and Haplorchis taichui), echinostomes (Echinostoma revolutum, Isthmiophora hortensis, Echinochasmus japonicus and Artyfechinostomum malayanum) and miscellaneous species, including Fasciolopsis buski and Gymnophalloides seoi. These trematode infections are distributed worldwide but occur most commonly in Asia. The global burden of FBT diseases has been estimated at about 80 million, however, this seems to be a considerable underestimate. Their life cycle involves a molluscan first intermediate host, and a second intermediate host, including freshwater fish, crustaceans, aquatic vegetables and freshwater or brackish water gastropods and bivalves. The mode of human infection is the consumption of the second intermediate host under raw or improperly cooked conditions. The major pathogenesis of C. sinensis and Opisthorchis spp. infection includes inflammation of the bile duct which leads to cholangitis and cholecystitis, and in a substantial number of patients, serious complications, such as liver cirrhosis and cholangiocarcinoma, may develop. In lung fluke infections, cough, bloody sputum and bronchiectasis are the most common clinical manifestations. However, lung flukes often migrate to extrapulmonary sites, including the brain, spinal cord, skin, subcutaneous tissues and abdominal organs. Intestinal flukes can induce inflammation in the intestinal mucosa, and they may at times undergo extraintestinal migration, in particular, in immunocompromised patients. In order to control FBT infections, eating foods after proper cooking is strongly recommended.

Prevalence of fish-borne zoonotic trematode infection in Jilin Province, China

Fish-borne zoonotic trematodes (FZTs) are the most serious food-borne parasites in Asia and have become a burden to public health and a new challenge in food safety. In Jilin Province, China, the prevalence of FZTs in intermediate and definitive hosts has not been extensively explored. In the present study, we investigated the prevalence of FZTs in Jilin Province, China. From July to November 2020, a total of 132 freshwater snails (the first intermediate host of FZTs), 4122 wild freshwater fishes (the second intermediate host of FZTs) and 143 fecal samples from canines, ducks and swine (the definitive host of FZTs) were collected from the Yitong River basin of Jilin Province. FZT species were identified by morphological observation combined with internal transcribed spacer (ITS) sequence analysis. The prevalence of FZTs was then calculated. The results showed that the prevailing species of FZTs in Jilin Province, China, were Clonorchis sinensis, Metorchis orientalis and Echinochasmus japonicus. The total prevalence of FZTs was 29.74% (1226/4122) in fish, the total infection rates were 2.27% (3/132) in snails, 75.00% (21/28) in canines and 37.18% (29/78) in ducks. The coinfection rates of the two trematodes were 13.39% (552/4122) in fish, 35.71% (10/28) in canines and 7.69% (6/78) in ducks. The coinfection rate of the three flukes was 2.60% (107/4122) in fish. Nine of the 12 fish species examined were infected with FZT metacercariae.

• C.

sinensis, M. orientalis and E. japonicus were reported in Jilin province of China.

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The prevalence of FZTs in freshwater fish were 29.74% (1226/4122).

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Four fish species were identified as new second intermediate hosts of E. japonicus.

Search, find, and penetrate: ultrastructural data of furcocercariae of Cardiocephaloides longicollis (Digenea, Strigeidae) explain their transmission and infection strategy into fish hosts

The present study provides an overview of the structures linked to fish host finding, recognition, and invasion of one of the most commonly occurring morphotypes among trematodes, furcocercariae. For this, we use free-swimming cercariae of the strigeid Cardiocephaloides longicollis (Rudolphi 1819) Dubois, 1982. Their elongated cercarial body and bifurcated tail are covered by a tegument with an irregular surface, showing numerous folds arranged in different directions and a typical syncytial organization. Both the body and the bifurcated tail are covered with short spines, rose-thorn shaped, as well as four types of sensory papillae, distinguished by the presence or absence of a cilium, its length, and their position on the cercarial body. These papillae are especially important for free-living stages that rely on external stimuli to locate and adhere to the host. A specialized anterior organ is located at the anterior part of the cercariae and is encircled by a triangle-shaped group of enlarged pre-oral spines followed by a transverse row of enlarged post-oral spines that, together with the sensory papillae, allow active finding, recognition, and penetration into fish. The ventral sucker, covered with inner-oriented spines, sensory papillae, and cilia, helps during this process. The cercariae of C. longicollis possess three types of gland cells (a head gland and two types of penetration glands), each containing different types of secretory granules that play a role in host invasion. The protonephridial excretory system consists of an excretory bladder, a system of collecting tubules, flame cells, and two excretory pores in the middle of each furcae, which serve to control osmoregulation in their marine environment, as well as to eliminate metabolic waste. Together with the four types of sensory endings, the central ganglion forms the nervous system. Our results add novel information on the ultrastructure of strigeid furcocercariae, being essential to interpret these data in relation of their functional role to better understand the transmission and penetration strategies that cercariae display to infect their fish hosts.

Foodborne intestinal flukes: A brief review of epidemiology and geographical distribution

Foodborne intestinal flukes are highly diverse consisting of at least 74 species with a diverse global distribution. Taxonomically they include 28 species of heterophyids, 23 species of echinostomes, and 23 species of miscellaneous groups (amphistomes, brachylaimids, cyathocotylids, diplostomes, fasciolids, gymnophallids, isoparorchiids, lecithodendriid-like group, microphallids, nanophyetids, plagiorchiids, and strigeids). The important heterophyid species (15 species) include Metagonimus yokogawai, M. takahashii, M. miyatai, Heterophyes heterophyes, H. nocens, Haplorchis taichui, H. pumilio, H. yokogawai, Heterophyopsis continua, Centrocestus formosanus, Pygidiopsis genata, P. summa, Stellantchasmus falcatus, Stictodora fuscata, and S. lari. The echinostome species of public health significance (15 species) include Echinostoma revolutum, E. cinetorchis, E. lindoense, E. ilocanum, Isthmiophora hortensis, Echinochasmus japonicus, E. perfoliatus, E. liliputanus, E. fujianensis, E. caninus, Acanthoparyphium tyosenense, Artyfechinostomum malayanum, A. sufrartyfex, A. oraoni, and Hypoderaeum conoideum. Among the other zoonotic intestinal flukes, Gastrodiscoides hominis, Brachylaima cribbi, Neodiplostomum seoulense, Fasciolopsis buski, Gymnophalloides seoi, Caprimolgorchis molenkampi, Phaneropsolus bonnei, Microphallus brevicaeca, Nanophyetus salmincola, and N. schikhobalowi (10 species) have drawn considerable medical attention causing quite a fair number of human infection cases. The principal mode of human infections include ingestion of raw or improperly cooked fish (heterophyids and echinostomes), snails including oysters (echinostomes and G. seoi), amphibians and reptiles (N. seoulense), aquatic vegetables (amphistomes and F. buski), and insect larvae or adults (C. molenkampi and P. bonnei). Epidemiological characteristics such as the prevalence, geographical distribution, and clinical and public health significance are poorly known in many of these species. Praziquantel has been proved to be highly effective against most species of intestinal fluke infections. Surveys and detection of human infection cases are urgently required for better understanding of the global status and public health significance of each species.

Epidemiology of Trematode Infections: An Update

Digenetic trematodes infecting humans are more than 91 species which belong to 46 genera all over the world. According to their habitat in definitive hosts, they are classified as blood flukes (Schistosoma japonicum. S. mekongi, S. mansoni, S. haematobium, and S. intercalatum), liver flukes (Clonorchis sinensis, Opisthorchis viverrini, O. felineus, Metorchis conjunctus, M. bilis, M. orientalis, Fasciola hepatica, F. gigantica, Dicrocoelium dendriticum, and D. hospes), lung flukes (Paragonimus westermani, P. heterotremus, P. skrjabini, P. miyazakii, P. kellicoti, P. mexicanus, P. africanus, and P. uterobilateralis), throat fluke (Clinostomum complanatum), pancreatic fluke (Eurytrema pancreaticum), and intestinal flukes (Metagonimus yokogawai, M. miyatai, M. takahashii, Heterophyes nocens, H. heterophyes, Haplorchis taichui, H. pumilio, H. yokogawai, Centrocestus formosanus, Echinostoma revolutum, E. ilocanum, Isthmiophora hortensis, Echinochasmus japonicus, E. lilliputanus, Artyfechinostomum malayanum, A. sufrartyfex, A. oraoni, Fasciolopsis buski, Gymnophalloides seoi, Neodiplostomum seoulense, Caprimolgorchis molenkampi, Phaneropsolus bonnei, and Plagiorchis muris). The mode of transmission to humans includes contact with cercariae contaminated in water (schistosomes) and ingestion of raw or improperly cooked fish (liver and throat flukes, heterophyids, and echinostomes), snails (echinostomes and gymnophallids), amphibia, reptiles (neodiplostomes), aquatic vegetables (amphistomes), or insect larvae or adults (plagiorchiids, lecithodendriids, and pancreatic fluke). Praziquantel has been proved to be highly effective against most species of trematode infections except fascioliasis. Epidemiological surveys and detection of human infections are required for better understanding of the geographical distribution and endemicity of each trematode species.

Echinochasmus swabiensis n. sp. (Digenea: Echinostomatidae) from Black Kite (Milvus Migrans Migrans) in Swabi District, Pakistan

A new species of the genus Echinochasmushas been described from the small intestine of the black kite (Milvus m. migrans) collected from Swabi, Khyber Pakhtunkhwa, Pakistan and identified as E. swabiensis n. sp. The new species is different from its congeners in its body size; it has 22 collar spines which includes two corner spines on one side, four on the other side and eight marginal plus ventral spines on each side. There aretegumental-scale like spines interspersed on the anterior margin of the ventral sucker with a smaller, terminal oral sucker. The pharynx is nearly twice as large as the oral sucker, while the ventral sucker is nearly six times as large as the oral sucker. The suckers’ width ratio is 1 : 4.7 to 1 : 5.6. The vitelline follicles are compact and denser at the lateral sides masking the caeca. This species has been added to the record of trematodes circulating among avian species, especially in the study area.

Malformations of the gill filaments of the ruffe Gymnocephalus cernuus (L.) (Pisces) caused by echinostomatid metacercariae

In parasite surveys of fishes from Lake Balaton and its tributaries in Hungary, infections with metacercariae of a species of the digenean genus Echinochasmus (Trematoda: Echinostomatidae) were found in seven species of fish. In ruffe, Gymnocephalus cernuus, malformations of the gill filaments apparently caused by these infections were observed. These malformations were in the form of bifurcations of the filaments at about their mid-length. At the point where the filaments bifurcate, an Echinochasmus metacercaria was always embedded in the cartilaginous ray of the gill filament. All specimens of the ruffe were found to be infected by these metacercariae, and each ruffe specimen was infected by 30-300 metacercariae. Such a bifurcation was found in all of the ruffe specimens, but, apart from these gill malformations, the metacercariae produced only local changes in the cartilage. In the other six infected fish species, only local signs were observed in the cartilage. Experimental infections of chicks with metacercariae resulted in the finding of the sexual adult (marita) of an unidentified species of Echinochasmus. ITS sequences of the adult and metacercaria corresponded with each other, and also with a cercaria isolated from a gravel snail (Lithoglyphus naticoides), with a 99.5-100% similarity.

Reprint of "An overview of freshwater snails in Asia with main focus on Vietnam"

Freshwater snails have received much attention for their role as intermediate hosts for trematodes causing disease in people and animals such as schistosomiasis and various food-borne trematodes. While effective medical treatment exists for some of these diseases there is need for preventive measures to reduce transmission, e.g. control of intermediate hosts because transmission patterns are often complicated due to presence of reservoir final hosts. In order to implement control measures against the intermediate host snails with minimal impact on the freshwater ecosystems and their biodiversity, a profound knowledge on transmission patterns of the trematodes is required and this is partly related to distribution, habitat preferences, and seasonal variation in density of the intermediate host species. Identification of snail species can be problematic on the basis of morphological and anatomical characters alone as some species show morphological plasticity and similarly morphological differentiation of cercariae found in snails may be difficult and this could lead to biased perceptions of intermediate host spectra and transmission patterns. In this paper, we give an overview of the snail families and their medical and veterinary importance in Asia but with main focus on Vietnam.

An overview of freshwater snails in Asia with main focus on Vietnam

Freshwater snails have received much attention for their role as intermediate hosts for trematodes causing disease in people and animals such as schistosomiasis and various food-borne trematodes. While effective medical treatment exists for some of these diseases there is need for preventive measures to reduce transmission, e.g. control of intermediate hosts because transmission patterns are often complicated due to presence of reservoir final hosts. In order to implement control measures against the intermediate host snails with minimal impact on the freshwater ecosystems and their biodiversity, a profound knowledge on transmission patterns of the trematodes is required and this is partly related to distribution, habitat preferences, and seasonal variation in density of the intermediate host species. Identification of snail species can be problematic on the basis of morphological and anatomical characters alone as some species show morphological plasticity and similarly morphological differentiation of cercariae found in snails may be difficult and this could lead to biased perceptions of intermediate host spectra and transmission patterns. In this paper, we give an overview of the snail families and their medical and veterinary importance in Asia but with main focus on Vietnam.

Foodborne intestinal flukes in Southeast Asia

In Southeast Asia, a total of 59 species of foodborne intestinal flukes have been known to occur in humans. The largest group is the family Heterophyidae, which constitutes 22 species belonging to 9 genera (Centrocestus, Haplorchis, Heterophyes, Heterophyopsis, Metagonimus, Procerovum, Pygidiopsis, Stellantchasmus, and Stictodora). The next is the family Echinostomatidae, which includes 20 species in 8 genera (Artyfechinostomum, Acanthoparyphium, Echinochasmus, Echinoparyphium, Echinostoma, Episthmium, Euparyphium, and Hypoderaeum). The family Plagiorchiidae follows the next containing 5 species in 1 genus (Plagiorchis). The family Lecithodendriidae includes 3 species in 2 genera (Phaneropsolus and Prosthodendrium). In 9 other families, 1 species in 1 genus each is involved; Cathaemaciidae (Cathaemacia), Fasciolidae (Fasciolopsis), Gastrodiscidae (Gastrodiscoides), Gymnophallidae (Gymnophalloides), Microphallidae (Spelotrema), Neodiplostomidae (Neodiplostomum), Paramphistomatidae (Fischoederius), Psilostomidae (Psilorchis), and Strigeidae (Cotylurus). Various types of foods are sources of human infections. They include freshwater fish, brackish water fish, fresh water snails, brackish water snails (including the oyster), amphibians, terrestrial snakes, aquatic insects, and aquatic plants. The reservoir hosts include various species of mammals or birds.The host-parasite relationships have been studied in Metagonimus yokogawai, Echinostoma hortense, Fasciolopsis buski, Neodiplostomum seoulense, and Gymnophalloides seoi; however, the pathogenicity of each parasite species and host mucosal defense mechanisms are yet poorly understood. Clinical aspects of each parasite infection need more clarification. Differential diagnosis by fecal examination is difficult because of morphological similarity of eggs. Praziquantel is effective for most intestinal fluke infections. Continued efforts to understand epidemiological significance of intestinal fluke infections, with detection of further human cases, are required.

Human waterborne trematode and protozoan infections

Waterborne trematode and protozoan infections inflict considerable morbidity on healthy, i.e., immunocompetent people, and may cause life-threatening diseases among immunocompromised and immunosuppressed populations. These infections are common, easily transmissible, and maintain a worldwide distribution, although waterborne trematode infections remain predominantly confined to the developing countries. Waterborne transmission of trematodes is enhanced by cultural practices of eating raw or inadequately cooked food, socio-economical factors, and wide zoonotic and sylvatic reservoirs of these helminths. Waterborne protozoan infections remain common in both developed and developing countries (although better statistics exist for developed countries), and their transmission is facilitated via contacts with recreational and surface waters, or via consumption of contaminated drinking water. The transmissive stages of human protozoan parasites are small, shed in large numbers in feces of infected people or animals, resistant to environmental stressors while in the environment, and few are (e.g., Cryptosporidium oocysts) able to resist standard disinfection applied to drinking water.