Life-cycle of Euparyphium albuferensis n. sp. (Trematoda: Echinostomatidae) from rats in Spain

The morphology of the different life-history stages and life-cycle of Euparyphium albuferensis are described and drawn. The freshwater snail Gyraulus chinensis (Gastropoda: Planorbidae) serves as the natural and experimental first intermediate host. This and other freshwater snails, such as Lymnaea truncatula, L. peregra, L. palustris and Physa acuta, serve as second intermediate hosts. Adult worms, possessing 45 collar spines, were obtained naturally from Rattus norvegicus and R. rattus, and experimentally from albino rats, mice and golden hamsters. Chickens, ducks and pigeons were not suitable experimental definitive hosts. E. albuferensis differs from the most closely related species, E. murinum Tubangui, 1931, in its larger body, suckers and oesophageal measurements, in the distribution of vitelline follicles and in the morphology of the collar spines.     

The life-cycle of Echinostoma friedi n. sp. (Trematoda: Echinostomatidae) in Spain and a discussion on the relationships within the `revolutum' group based on cercarial chaetotaxy

The morphology of the different stages and life-cycle of Echinostoma friedi n. sp. are described and figured. The freshwater snail Lymnaea peregra (Gastropoda: Lymnaeidae) serves as the natural and experimental first intermediate host and L. corvus and Gyraulus chinensis (Gastropoda: Planorbidae) as experimental first intermediate hosts. These, and Physella acuta (Gastropoda: Physidae), also serve as second intermediate hosts. Adult worms, possessing 37 collar spines, were obtained from naturally infected Rattus norvegicus and experimentally from albino rats, golden hamsters and chickens. Mice were not suitable experimental definitive hosts. E. friedi differs from the most closely related species in the `revolutum' group mainly in terms of several morphological and biological features of the life-cycle stages and in its cercarial chaetotaxy. The chaetotaxy patterns of the species of the `revolutum' group are analyzed and the results show that a taxonomic comparison of these species may be carried out on the basis of the number of sensilla in the clusters CIII V₁, CIII V₂ (or CIII V₁ + CIII V₂), CIV DL and UV_b. These clusters appear adequate to establish taxonomic relationships between different species within the `revolutum' group.     

Echinostoma caproni: Differential tegumental responses to growth in compatible and less compatible hosts

The topography of the tegument of Echinostoma caproni adults collected from high (mice) and low (rats) compatible hosts was compared by SEM. In the oral (OS) and the ventral sucker (VS) areas, a worm age-host species interaction was found with regard to the density of spines. There was a decrease in the density of spines in the adults collected from mice, whereas an increase occurred in the OS area in worms from rats over time. The tegumentary spines in adults from mice became larger and blunter. Some spines from the VS area in adults from mice at 4 wpi were multipointed. The spines of adults from rats were sharper, not covered by the tegument and no multipointed spines were observed. We detected a greater level of actin gene expression in the adults collected from rats. These facts suggest that the low compatible host induces an increased turnover of tegumentary spines.     

Life-cycle ofEchinochasmus macrocaudatus n. sp. (Trematoda: Echinostomatidae)

The life-cycle ofEchinochasmus macrocaudatus n. sp., from mother-sporocyst to adult, was studied under natural and experimental conditions. The aquatic snailsPyrgophorus coronatus (Prosobranchia: Hydrobiidae) from cenotes (sinkholes) of the Yucatan Peninsula, Mexico, served as the first intermediate host of this parasite, liberating cercariae possessing an extremely large tail (zygocercous cercaria). Metacercariae of the fluke were encysted on the gills of the characid fishAstyanax fasciatus (natural infection); the poeciliidsXiphophorus variatus andPoecilia velifera were suitable experimental hosts. Feeding experiments withE. macrocaudatus metacercariae resulted in finding adult trematodes, possessing 22 collar spines (with 2 angle spines on each side), in the intestine of chicks and ducks.E. macrocaudatus differs from the most closely related species,E. schwartzi Price, 1931, by its larger oral sucker (138–170×118–176 m) and by the position of the acetabulum which is situated at two-fifths of the body length.     

洞庭湖外睾吸虫新种及其生活史

本文报告洞庭湖区鲶鱼肠道寄生的洞庭湖外睾吸虫Exorchis dongtinghuensis sp.nov(新种)及其全程生活史,其第一中间宿主为湖北钉螺Oncomelania hupensis;第二中间宿主为鲤鱼、鲫鱼和金鱼;终宿主为鲶鱼Parasilurus asotus。作者对各期宿主作了人工感染试验和现场自然感染调查。对其发育过程作了观察比较。     

Phaneropsolus spinicirrus n. sp. (Digenea: Lecithodendriidae), a human parasite in Thailand

Phaneropsolus spinicirrus n. sp., collected in a postpraziquantel treatment stool of a 44-yr-old woman from Kalasin Province in northeastern Thailand, is described. It is the second species of the genus Phaneropsolus Looss, 1899, found to parasitize a human host. It differs from the first species, Phaneropsolus bonnei Lie, 1951, in the presence of a short spinose cirrus and the structure and distribution of tegumental spines. The new species is most similar to Phaneropsolus perodictici Goodman and Panesar, 1986, isolated from the potto, Perodicticus potto, in Uganda because digeneans of both species have numerous spines on the cirrus. However, the new species differs from P. perodictici in having more conspicuous spines, the genital pore at the posterior border of the oral sucker or lateral to the pharynx, a body and internal organs of larger size, conical spines on the tegument, an ovoid to bilobed ovary and a large V-shaped excretory bladder. Phaneropsolus spinicirrus is distinguishable from other previously reported Phaneropsolus by possessing a spinose cirrus.     

Cipangopaludina chinensis malleata (Gastropoda: Viviparidae): a new second molluscan intermediate host of a human intestinal fluke Echinostoma cinetorchis (Trematoda: Echinostomatidae) in Korea

Two species of the viviparid snails have been reported in Korea, e.g., Cipangopaludina chinensis malleata and Cipangopaludina japonica. Cipangopaludina chinensis malleata collected at 3 of 12 localities were found to be infected with metacercariae of Echinostoma cinetorchis, one of the snail-borne human intestinal trematodes in Korea. Metacercariae from these snails were fed to rats (S/D strain), and adult worms of E. cinetorchis, characterized by 37-38 collar spines on the head crown, were recovered from the ileocecal regions. However, no C. japonica collected from 2 localities harbored the metacercariae. In experiments with laboratory-bred viviparid snails, all viviparids were not susceptible to miracidia of E. cinetorchis. To confirm the identity of second intermediate hosts of E. cinetorchis experimentally, 2 species of viviparid snails were exposed to the cercariae from Segmentina hemisphaerula that had been infected with miracidia of E. cinetorchis. Both species of snails were susceptible to cercariae of E. cinetorchis. This is the first report of Cipangopaludina spp. serving as the second intermediate host of E. cinetorchis and as a potential source of human infection.     

Echinostoma macrorchis in Lao PDR: Metacercariae in Cipangopaludina Snails and Adults from Experimentally Infected Animals

The echinostome metacercariae encysted in Cipangopaludina sp. snails that were purchased from a market in Vientiane Municipality, Lao PDR, were identified as Echinostoma macrorchis (Digenea: Echinostomatidae) through recovery of adult flukes after experimental infection to rats and a cat. The metacercariae were round, 113-128 (121)×113-125 (120) µm, having a thick cyst wall, a head collar armed with collar spines, and excretory granules. The adult flukes recovered from the rats and cat at day 14 and 30 post-infection, respectively, were elongated, ventrally curved, and 3.9-6.3×0.7-1.1 mm in size. The head collar was distinct, bearing 43-45 collar spines with 5 angle spines on each side. Two testes were large (as the name implies), tandem, and slightly constricted at the middle, with irregular margins. Eggs were operculated, ovoid to elliptical, and 88-95×56-60 µm. In scanning electron microscopy, the head collar was prominent, with 43-45 collar spines. Scale-like tegumental spines were densely distributed on the ventral surface between the oral and ventral suckers. Sensory papillae were distributed mainly on the tegument around the 2 suckers. It is confirmed that E. macrorchis is distributed in Lao PDR using Cipangopaludina sp. snails as the second intermediate host.     

Corbicula fluminea (Bivalvia: Corbiculidae): a possible second molluscan intermediate host of Echinostoma cinetorchis (Trematoda: Echinostomatidae) in Korea.

More than 1,500 clams of Corbicula fluminea, the most favorable food source of freshwater bivalves in Korea, were collected from 5 localities to examine cercarial and metacercarial infection with Echinostoma cinetorchis. Although 3 clams infected with suspicious E. cinetorchis metacercariae out of 200 specimens collected at Kangjin, Chollanam-do were detected, no cercarial and metacercarial infections with E. cinetorchis were observed in field-collected Corbicula specimens. In the susceptibility experiments with laboratory-reared clams, those infected with miracidia of E. cinetorchis did not release their cercariae up to 60 days after infection. To confirm the identity of second intermediate host of E. cinetorchis experimentally, a total of 30 clams were exposed to the cercariae from Segmentina hemisphaerula that had been infected with miracidia of E. cinetorchis. The clams were susceptible to cercariae of E. cinetorchis with an infection rate of 93.3%. Metacercariae from clams taken more than 7 days after cercarial exposure were fed to rats (S/D strain), and adult worms of E. cinetorchis, characterized by 37-38 collar spines on the head crown, were recovered from the ileocecal regions. This is the first report of C. fluminea as a possible second intermediate host of E. cinetorchis.     

Intermediate host availability masks the strength of experimentally-derived colonisation patterns in echinostome trematodes

A fundamental goal of parasite evolutionary ecology is to elucidate patterns of host use and determine the underlying mechanisms of parasite colonisation. In order to distinguish the relative contributions of host encounter rates and host compatibility to infection outcomes, we compared host use in both field and experimental laboratory settings. Two years of bi-weekly snail sampling at a freshwater pond demonstrated fluctuating availability among three potential second intermediate snail host species and suggested that two trematode species (Echinostoma revolutum and Echinoparyphium sp.) did not colonise the three potential snail host species, Lymnaea elodes, Physa gyrina and Helisoma trivolvis, differentially. However, a series of experimental infections demonstrated that both parasites colonised H. trivolvis more so than the other two host species. Thus, more echinostome parasites utilised snail hosts that cannot serve as their first intermediate host. In experimental infections, host size and vagility were not strong determinants of infection. By utilising field and laboratory approaches, we were able to compare the strength of host compatibility under controlled conditions with patterns of infection in nature. Based on the results from these studies, it appears that host encounter is the primary mechanism dictating infection outcomes in the field.     

Life-cycle,delimitation and redescription of Echinostoma revolutum (Froelich, 1802) (Trematoda: Echinostomatidae)

The life-cycle of Echinostoma revolutum (Froelich, 1802) Dietz, 1909 has been completed experimentally beginning with infected snails collected at the type-locality, near Erlangen, Germany. Based on the specimens obtained, each stage of the life-cycle has been redescribed. Important taxonomic features are discussed and hitherto unknown characteristics are described. Synonyms for E. revolutum are: Fasciola revoluta Froelich, 1802; Echinostoma paraulum Dietz, 1909; E. audyi Lie & Umathevy, 1965; and E. ivaniosi Mohandas, 1973. Adults and larvae described as E. revolutum in other works are found to be identical with Echinostoma echinatum (Zeder, 1803), E. trivolvis (Cort, 1914), E. jurini (Skvortsov, 1924), E. caproni Richard, 1964, Moliniella anceps (Molin, 1859), Echinochasmus beleocephalus (Linstow, 1873) and other echinostome species. For nearly a century, incorrect morphological, biological, life-cycle and host information has been attributed to E. revolutum, and at times these data have contributed to the diagnoses of the species. Occasionally, authors actually working with E. revolutum have ascribed their results to other species. Based on extensive experimental life-cycle studies beginning with infected snails from type-localities, it is shown that (1) the first intermediate host is a lymnaeid snail; (2) the second intermediate hosts are various pulmonate and prosobranch snails, mussels, frogs and freshwater turtles; (3) the final hosts are birds; (4) E. revolutum cercariae and adults have 37 collar spines; (5) the species occurs only in Europe and Asia; (6) Cercaria echinata Siebold, 1937, Echinostoma echinatum (Zeder, 1803) and E. jurini (Skvortsov, 1924) are the closely related 37-spined allies in Europe; and (7) species specific characteristics are expressed only in the larvae and the host-parasite relationships. The adults of E. revolutum cannot be identified using morphological criteria and it is proposed that worms with 37 collar spines belonging to the genus Echinostoma and occurring in naturally infected birds in Europe and Asia be referred to an “E. revolutum group.”     

Segmentina hemisphaerula: a new molluscan intermediate host for Echinostoma cinetorchis in Korea.

Three species of Planorbidae have been reported from Korea, e.g., Gyraulus convexiusculus, Hippeutis (Helicorbis) cantori, and Segmentina (Polypylis) hemisphaerula. Of these, only H. cantori was reported as the first and second intermediate host for Echinostoma cinetorchis, an important human intestinal parasite in Korea. Segmentina hemisphaerula has also been found to be an intermediate host. In field-collected planorbids, only S. hemisphaerula was found shedding echinostome cercariae and infected with metacercariae of E. cinetorchis, whereas no G. convexiusculus and H. cantori were found to be infected. In experiments with laboratory-bred snails, G. convexiusculus and S. hemisphaerula were susceptible to infection by miracidia of E. cinetorchis, but H. cantori could not be infected. Tadpoles of Rana nigromaculata and laboratory-bred snails of the 3 planorbid species were exposed to E. cinetorchis cercariae shed from field-collected S. hemisphaerula. All tadpoles, S. hemisphaerula, and G. convexiusculus became infected, but no H. cantori were infected. Metacercariae from tadpoles, S. hemisphaerula, and G. convexiusculus were fed to rats per os, and eggs of E. cinetorchis were detected in the rat feces 1 wk later. The rats were killed, and adult E. cinetorchis were recovered from the small intestines. This is the first report of G. convexiusculus as a potential first and second intermediate host and of S. hemisphaerula as a new first and second intermediate host for E. cinetorchis in Korea.     

Photo- and geo-orientation by Echinostome cercariae results in habitat selection.

The effect of light and gravity on orientation was studied in cercariae of 4 echinostome species: Pseudechinoparyphium echinatum, Echinostoma revolutum, Hypoderaeum conoideum, and Isthmiophora melis. The cercariae were placed into vertical and horizontal cuvettes, illuminated with 2 different light intensities from various directions, and their distribution recorded for 6 hr Each species showed its individual pattern of horizontal photo-orientation and geo-orientation, with distinct changes during the time after emerging. The geo-orientation was controlled differently in each species by the intensity and the direction of light radiation. The different orientation patterns suggest functions such as leaving the habitats of the host-snails emitting the cercariae, dispersal, and frequenting the microhabitats of potential hosts. The high diversity of orientation patterns among the species that originated from the same first intermediate host Lymnaea stagnalis in the same ponds and that invade similar host spectra suggests adaptations to different ecological conditions.     

Surface ultrastructure of Stictodora tridactyla (Trematoda: Heterophyidae) from Kuwait Bay

The surface morphology of Stictodora tridactyla recovered from a kitten that was fed the killifish, Aphanius dispar, naturally infected with the metacercariae was studied using scanning electron microscopy. The body comprised a rounded head, elongate neck, and widely pyriform hind-body. The head bore a circular oral sucker on the ventral side, and concentric rows of peg-like cephalic spines on the dorsal side. The oral sucker was armed with pre-oral spines similar in shape and size to the cephalic spines. The neck and hind-body were densely covered with scale-like multipointed spines, the size and density of which decreased from anterior to posterior parts of the body. Ciliated dome-shaped papillae were found solitarily or as conjugated groups on the head apex and lips of the oral sucker. Non-ciliated dome-shaped papillae were restricted to the lower lip of the oral sucker. The body was devoid of a ventral sucker. The genital opening appeared as a round depression of the tegument at about the anterior third of the body. This is the first record of the occurrence of S. tridactyla in the Arabian Gulf region and A. dispar is a new second intermediate host.     

Stephanostomum lophii sp. nov. (Digenea: Acanthocolpidae), intestinal parasite of Lophius piscatorius, with reference to seasonal fluctuations of metacercariae in intermediate second hosts (Gadidae)

We describe the adult and metacercaria of a new species of digenetic trematode, Stephanostomum lophii sp. nov., an intestinal parasite of the angler fish, Lophius piscatorius . The species is distinguished from the similar Stephanostomum kovalevi by the numerous peristomial spines in the latter and from S. baccatum by the oral sucker being larger than the ventral sucker and by the fact that the principal intermediate hosts are gadids, not pleuronectids as in the case of Stephanostomum baccatum . We also report the prevalence of S. lophii metacercariae in various potential angler fish prey species caught off the coast of Galicia (NW Spain).     

Echinostoma mekongi: Discovery of Its Metacercarial Stage in Snails,Filopaludina martensi cambodjensis,in Pursat Province,Cambodia

Echinostoma mekongi was reported as a new species in 2020 based on specimens collected from humans in Kratie and Takeo Province, Cambodia. In the present study, its metacercarial stage has been discovered in Filopaludina martensi cambodjensis snails purchased from a local market nearby the Tonle Sap Lake, Pursat Province, Cambodia. The metacercariae were fed orally to an experimental hamster, and adult flukes were recovered at day 20 post-infection. They were morphologically examined using light and scanning electron microscopes and molecularly analyzed by sequencing of their mitochondrial cox1 and nad1 genes. A total of 115 metacercariae (1–8 per snail) were detected in 60 (60.0%) out of 100 Filopaludina snails examined. The metacercariae were round, 174 μm in average diameter (163–190 μm in range), having a thin cyst wall, a head collar armed with 37 collar spines, and characteristic excretory granules. The adult flukes were elongated, ventrally curved, 7.3 (6.4–8.2)×1.4 (1.1–1.7) mm in size, and equipped with 37 collar spines on the head collar (dorsal spines in 2 alternating rows), being consistent with E. mekongi. In phylogenetic analyses, the adult flukes showed 99.0–100% homology based on cox1 sequences and 98.9–99.7% homology based on nad1 sequences with E. mekongi. The results evidenced that F. martensi cambodjensis snails act as the second intermediate host of E. mekongi, and hamsters can be used as a suitable experimental definitive host. As local people favor to eat undercooked snails, these snails seem to be an important source of human infection with E. mekongi in Cambodia.     

Austropeplea ollula (Pulmonata: Lymnaeidae): a new molluscan intermediate host of a human intestinal fluke, Echinostoma cinetorchis (Trematoda: Echinostomatidae) in Korea

Three freshwater snail species of the family Lymnaeidae have been reported from Korea, Radix auricularia coreana, Austropeplea ollula and Fossaria truncatula. Out of 3 lymnaeid snail species, A. ollula was naturally infected with the Echinostoma cinetorchis cercariae (infection rate = 0.7%). In the experiments with the laboratory-bred snails, F. truncatula as well as A. ollula was also susceptible to the E. cinetorchis miracidia with infection rates of 25% and 40%, respectively. All of three lymnaeid snail species exposed to the E. cinetorchis cercariae were infected with the E. cinetorchis metacercariae. It is evident that A. ollula acts as the first molluscan intermediate host of E. cinetorchis in Korea, and F. truncatula may be a possible candidate for the first intermediate host of this intestinal fluke. Also, three lymnaeid snail species targeted were experimentally infected with E. cinetorchis metacercariae.     

Contribution to the knowledge of species of the genus Stephanostomum Looss, 1899 (Digenea: Acanthocolpidae) from teleosts of the Western Mediterranean,with the description of S. gaidropsari n. sp.

Four species of the acanthocolpid genus Stephanostomum are redescribed from the digestive tract of teleosts in the Western Mediterranean: the type-species, S. cesticillum from Lophius piscatorius is described with a ventrally interrupted ring of 35 circum-oral spines and as lacking a uroproct; S. bicoronatum from Sciaena umbra has a ventrally interrupted ring of 31 circum-oral spines and a uroproct; S. pristis from Phycis phycis has an uninterrupted ring of 36 oral spines and no uroproct; S. minutum from Uranoscopus scaber has an uninterrupted ring of 36 oral spines and a uroproct. A new species, S. gaidropsari from Gaidropsarus mediterraneus, is described with an uninterrupted ring of 36 oral spines and an apparent uroproct. It differs from all other Stephanostomum species with similar oral spine numbers in the armament of the ejaculatory duct, and from various of these species by vitelline distribution, length of the genital atrium, oesophageal length and sucker-ratio.     

Invaders of an invader - Trematodes in Potamopyrgus antipodarum in Poland

The subject of the following study was the natural and experimental invasion of trematode larvae in Potamopyrgus antipodarum from Bory Tucholskie National Park (Poland). Only one out of the 14,908 dissected specimens had oval sporocysts and mature cercariae of fish fluke, which belongs to the Sanguinicolidae family. It is the first recorded case in the European population of P. antipodarum living in inland water. The experimental study showed the possibility of native metacercariae (Echinostoma revolutum, Echinoparyphium aconiatum and Hypoderaeum conoideum) settlement in those immigrant snail species; however, exposure to parasites resulted in an increase in snail mortality. The three out of six used cercariae species were able to transform into metacercariae in P. antipodarum as in the second intermediate host, but the exposure to parasitic larvae of four of the used species resulted in an increase in snails’ mortality. It may suggest that not only metacercariae settlement but also the attack of cercariae (Rubenstrema opisthovitellinum at a temperature of 22 °C) affected the low survival of experimental snails in comparison to control animals. The subject of discussion presented in this paper is also the hypothesis on probable effect of the interaction between P. antipodarum and native snail species (as a source of invasive larvae of parasites) living in the same habitat.     

First record and description of metacercariae of Curtuteria arguinae n. sp. (Digenea: Echinostomatidae), parasite of cockles Cerastoderma edule (Mollusca: Bivalvia) in Arcachon Bay, France

A new Himasthlinae species, Curtuteria arguinae, is described as metacercariae from the cockle Cerastoderma edule (L.), collected at Banc d'Arguin (southwestern France). These metacercariae encysted preferentially in the mantle and also in the foot of cockles. Encysted and chemically excysted metacercariae were studied by light microscopy and scanning electron microscopy, respectively. Excysted metacercariae were elongated and curved ventrally. They bore a 33-spine circumoral collar. Sensory papillae were arranged around the oral sucker and also symmetrically along the ventral surface body, from the collar to the acetabulum. The dorsal and ventral tegument surfaces were densely packed with similar pointed spines. The posterior end of the body was without any spines. Among the Curtuteria species described previously, only Curtuteria haematopodis Smogorjewskaja and Iskova, 1966 had the same number of circumoral collar spines. A 6-yr field survey showed that the cockle population at Banc d'Arguin was subjected to a summer infection of C. arguinae. Curtuteria arguinae phenology of infection is characterized by interannual variability and seasonality (beginning in July-August and maximum in autumn). The first intermediate and final hosts remain unknown.