Sites of encystment by the metacercariae of Echinoparyphium recurvatum in Lymnaea peregra.

Experimental infection of Echinoparyphium recurvatum von Linstow (Digenea: Echinostomatidae) cercariae in the snail second intermediate host Lymnaea peregra Müller shows that metacercarial encystment takes place on the lining of the mantle cavity, pericardial cavity and kidney lumen, with the mantle cavity the most preferred site. All three sites are accessible via the body openings. The metacercariae appear to be more susceptible to encapsulation in the visceral mass than in the cavity of the mantle, pericardium and the lumen of the kidney.     

Toxic effects of cadmium and zinc on the transmission of Echinoparyphium recurvatum cercariae

The toxicity of cadmium, zinc and Cd/Zn mixtures to the transmission of Echinoparyphium recurvatum (Digenea: Echinostomatidae) cercariae into the snail second intermediate hosts was investigated at concentrations ranging from 100 microg l-1 to 10 000 microg l-1 in both soft and hard water. A differential response in the infectivity of metal-exposed cercariae into Lymnaea peregra and Physa fontinalis was demonstrated which was dependent on the snail species being infected. Exposure of L. peregra, P. fontinalis, and L. stagnalis to heavy metals caused a differing susceptibility to E. recurvatum cercariae depending on the snail species being exposed. The mechanism and effects of metal toxicity, together with the importance of the parasite/host strain on cercarial transmission are discussed.     

Tegumental ultrastructures of Echinoparyphium recurvatum according to developmental stages

The present study was performed to observe tegumental ultrastructure of Echinoparyphium recurvatum according to developmental stages. Worms (1, 3, 5 and 15-day old) were recovered from chicks experimentally infected with metacercariae from Radix auricularia coreana. One-day old worms were elongated and ventrally concave, and covered with peg-like tegumental spines except the adjacent areas of the head crown and excretory pore. Type I sensory papillae were distributed on the lip of the oral sucker, and grouped ciliated papillae were around the oral sucker. Peg-like tegumental spines were densely distributed on the anterior surface of the ventral sucker level. The ventral sucker had an aspinous tegument and no sensory papillae. Tegumental spines on the posterior surface of the ventral sucker level were sparsely distributed and disappeared posteriorly. In 3 and 5-day old worms, the tegument around the oral sucker was aspinose and wrinkled concentrically. The ventral sucker had a wrinkled tegument and many bulbous papillae. Type I sensory papillae were distributed between the bulbous papillae. Tegumental spines were spade-shaped with a terminal tip. A total of 45 collar spines including 4 end group ones on both ventral corners was alternately arranged in 2 rows. The 15-day old worms were very stout and their tegumental spines were tongue-shaped without a terminal tip. From the above results, it is confirmed that the surface ultrastructure of E. recurvatum was generally similar to that of other echinostomatid flukes. However, some features, i.e., morphological change of tegumental spines and appearance of sensory papillae on the ventral sucker according to development, and number, shape and arrangement of collar spines, were characteristic, which may be of taxonomic and bioecological significance.     

Echinostoma revolutum and Echinoparyphium recurvatum recovered from house rats in Yangyang-gun, Kangwon-do

During an investigation on intestinal flukes of house rats in Yangyang-gun, Kangwon-do, a total of 6 species of trematodes belonging to 3 families; Echinostomatidae (Echinostoma hortense, E. cinetorchis, E. revolutum and Echinoparyphium recurvatum), Diplostomidae (Fibricola seoulensis) and Plagiorchiidae (Plagiorchis muris), were recovered from two adult rats. E. revolutum and E. recurvatum were new trematode faunae of rats in Korea. E. revolutum had an elongated body, 5.3-6.0 mm long and 1.0-1.3 mm wide. The total number of collar spines was 35-37 including 5 end group ones on each ventral corner. Its coiled uterus contained numerous eggs. E. recurvatum also had an elongated body, 3.5-4.7 mm long and 0.50-0.65 mm wide. It had total 45 collar spines including 4 end group ones. The uterus was short with only a few eggs. It has been first confirmed by this study that E. revolutum and E. recurvatum are indigenously distributed among house rats in Korea.     

The effects of temperature on the distribution and establishment of Echinoparyphium recurvatum metacercariae in Lymnaea peregra

The establishment and distribution of Echinoparyphium recurvatum metacercariae in the second intermediate host, Lymnaea peregra, were investigated at a temperature range of 5-29 degrees C. Preliminary studies on the survival and infectivity of E. recurvatum cercariae showed that both parameters were temperature dependent. No cercarial transmission occurred at 5 or 10 degrees C. Nevertheless, the transmission efficiency (1/H0) indicated that transmission was temperature independent in the temperature range 17-25 degrees C and was much lower than in previous studies using this host-parasite system. These differences were attributed to low cercarial densities used in this study. The effect of temperature on encystment site choice (mantle cavity, kidney, pericardium) by metacercariae showed that the mantle cavity was the prime site of encystment, followed by the pericardium and the kidney. Temperatures at the lower and upper ranges (14 and 29 degrees C), however, caused a significant reduction in encystment in the mantle cavity but not in the pericardium or kidney. The importance of cercarial densities, the physiological mechanisms influencing metacercarial distribution and their implications for parasite transmission to the definitive host are discussed.     

Influence of cadmium exposure on the incidence of first intermediate host encystment by Echinoparyphium recurvatum cercariae in Lymnaea peregra

The effect of cadmium exposure of the snail first intermediate host Lymnaea peregra on the incidence of encystment of Echinoparyphium recurvatum (Digenea: Echinostomatidae) cercariae without emergence from the snail was investigated. Exposure to 100 microg l(-1) Cd for 72 h caused a significant increase in the incidence of first host encystment when compared to controls. In addition, autometallographic staining of E. recurvatum daughter rediae and developing cercariae showed that there was metal accumulation within their body tissues. The significance of these findings to parasite transmission in metal-polluted environments is discussed.     

Metacercarial utilization of a naturally infected single species (Lymnaea peregra) snail community by Echinoparyphium recurvatum

Utilization of a single-species molluscan community of Lymnaea peregra by metacercariae of Echinoparyphium recurvatum over a summer (July-September) period in south-east England showed an increase in the mean number of cysts per host with host size and time of exposure. Aggregation resulting from host and habitat-related factors increased with host size and time of exposure. Encystment within the host was restricted to the peripheral organs in smaller juvenile snails but as snails increased in size, metacercariae were distributed throughout the tissues.     

Scanning electron microscopy of adult Echinoparyphium recurvatum (Von Linstow, 1873) (Digenea: Echinostomatidae) from Britain

The surface topography of 15-day-old adult Echinoparyphium recurvatum (Von Linstow, 1873) sensu stricto, from an isolate of the parasite utilizing Lymnaea peregra as first intermediate host in southern England, is described and illustrated using scanning electron microscopy, and is compared to those of other Echinoparyphium species from Europe, and with those of E. recurvatum of East Asian origin. The general morphology of tegumental features was found to be very similar to that of worms of the same age observed in a previous study on a Korean isolate of E. recurvatum. Comparison of collar and body spination of E. recurvatum with other 45-collar-spined members of the genus in Europe revealed some significant differences in morphology. Collar spines of E. recurvatum were found to be shorter and more pointed than those of Echinoparyphium mordwilkoi. The body spines of E. recurvatum are rounded and scale-like, extending just beyond the ventral sucker, contrasting with the pointed, thorn-shaped body spines of E. mordwilkoi, extending posteriorly to the level of the second testis. Body spine shape and distribution in E. recurvatum were found to be more similar to those of Echinoparyphium pseudorecurvatum. The value of SEM studies in elucidating the relationship between members of the genus Echinoparyphium in Britain/Europe and those in Africa, Asia and North America is suggested.     

Effects of cadmium and zinc toxicity on orientation behaviour of Echinoparyphium recurvatum (Digenea: Echinostomatidae) cercariae

The effects of cadmium and zinc toxicity on orientation behaviour (photo- and geo-taxis) of Echinoparyphium recurvatum cercariae was investigated at concentrations ranging from 10 to 1000 microg l(-1). Exposure to the toxicants at all metal concentrations caused a change in orientation to negative phototaxis and positive geotaxis during the submaximal dispersal phase (0.5 h cercarial age). Autometallography staining of cercariae exposed to 1000 microg l(-1) cadmium or zinc showed selective binding of heavy metals to tegumental surface sites associated with sensory receptors. The significance to parasite transmission of changes in cercarial orientation behaviour in metal polluted environments is discussed.     

In vivo efficacy of praziquantel against Echinoparyphium aconiatum (Trematoda: Echinostomatidae) parasitizing the great pond snails Lymnaea stagnalis (Gastropoda: Lymnaeidae)

The present study had a practical goal. I aimed to determine whether praziquantel could reduce the production of Echinoparyphium aconiatum (Trematoda: Echinostomatidae) cercariae in infected snails Lymnaea stagnalis (Gastropoda: Lymnaeidae) without killing the hosts. Praziquantel is a broad-spectrum antihelminth agent. It caused a total cessation of cercaria shedding when the praziquantel concentration in the treatment bath was 10 mg/L and the treatment time was 30 h or longer. A next research step which has to be taken before giving detailed recommendations about using praziquantel for ceasing production of E. aconiatum cercariae in parasitized snails is to follow the survivorship and performance of treated snails after a praziquantel exposure for longer than in this medium-term (3 days) experiment.     

The spatial relationship between the musculature and the NADPH-diaphorase activity, 5-HT and FMRFamide immunoreactivities in redia, cercaria and adult Echinoparyphium aconiatum (Digenea)

The spatial relationship between the musculature and the NADPH-diaphorase (NADPH-d) activity, 5-HT and FMRFamide immunoreactivities in redia, cercaria and adult Echinoparyphium aconiatum was studied using scanning electron microscopy (SEM), NADPH-d histochemistry, immunocytochemistry, and confocal scanning laser microscopy (CSLM). TRITC-conjugated phalloidin was used to stain the musculature. Staining for NADPH-d was observed in the central (CNS) and peripheral nervous system (PNS) of all three stages. NADPH-d positive nerves occurred very close to muscle fibres. 5-HT-immunoreactive (5-HT-IR) nerve cells and fibres occurred in the CNS and PNS and close to muscle fibres. FMRFamide-IR nerve fibres were observed in the CNS and PNS of adult worms. This is the first time, the presence of the NADPH-d has been demonstrated in the larval as well as the adult stages of a fluke.     

Echinoparyphium elegans (Looss, 1899) (Digenea: Echinostomatidae): the life cycle and redescription of the adult with a revision of the 43-spined members of the genusEchinoparyphium

The adult morphology ofEchinoparyphium elegans is redescribed. The life cycle is described. The first intermediate host is the freshwater snail,Bulinus truncatus. This and other freshwater snails, such asBulinus globosus, Physa acuta and albinoBiomphalaria glabrata, serve as second intermediate hosts. Adult worms were obtained experimentally from canaries, chicks, pigeons and albino rats, but not from albino mice. The 43-spinedEchinoparyphium species with a collar spined arrangement 5-5-3-3-27,E. bioccalerouxi, E. ralphaudyi andE. combesi, are placed into synonymy withE. elegans after examination of the paratypes.     

An ectosymbiotic flatworm, Temnocephala chilensis, as second intermediate host for Echinoparyphium megacirrus (Digenea: Echinostomatidae) in Patagonia (Argentina)

During a survey of parasites of the Patagonian freshwater crab Aegla neuquensis neuquensis, its ectosymbiont Temnocephala chilensis was found parasitized with an echinostomatid metacercaria with 43 collar spines. Of the 414 T. chilensis collected, 106 were parasitized with metacercariae of Echinoparyphium sp. Ovigerous adults of E. megacirrus were obtained from domestic chicks experimentally infected with metacercariae obtained from temnocephalans. This is the first record of temnocephalans being parasitized by digeneans.     

Molecular characterisation of four echinostomes (Digenea: Echinostomatidae) from birds in New Zealand,with descriptions of <Emphasis Type="Italic">Echinostoma novaezealandense</Emphasis> n. sp. and <Emphasis Type="Italic">Echinoparyphium poulini</Emphasis> n. sp.

Morphological and molecular characterisation of echinostome specimens (Digenea: Echinostomatidae) recovered in one Anas platyrhynchos L. and one Cygnus atratus (Latham) (Anseriformes: Anatidae) from New Zealand revealed the presence of two known species, Echinostoma miyagawai Ishii, 1932 and Echinoparyphium ellisi (Johnston & Simpson, 1944) and two species new to science. Comparative morphological and phylogenetic analyses supported the distinct species status of Echinostoma novaezealandense n. sp. ex Branta canadensis (L.), A. platyrhynchos and C. atratus, and Echinoparyphium poulini n. sp. ex C. atratus. Echinostoma novaezealandense n. sp., a species of the “revolutum” species complex characterised by the possession of a head collar armed with 37 spines, keyed down to E. revolutum but was distinguished from the latter in having a much narrower body with almost parallel margins, longer oesophagus, wider cirrus-sac, larger seminal vesicle, much smaller ventral sucker, ovary, Mehlis’ gland and testes, more anteriorly located ovary and testes, and distinctly smaller eggs (81–87 × 42–53 vs 106–136 × 55–70 µm). This new species appears similar to Echinostoma acuticauda Nicoll, 1914 described in Australia but differs in having a longer forebody, more posteriorly located ovary and testes, and much smaller eggs (81–87 × 42–53 vs 112–126 × 63–75 µm). Echinoparyphium poulini n. sp. is differentiated from the four species of Echinoparyphium possessing 37 collar spines considered valid as follows: from E. chinensis Ku, Li & Chu, 1964 in having a much smaller body, four (vs five) angle spines and simple seminal vesicle (vs bipartite); from E. schulzi Matevosyan, 1951 in having a less robust body at a comparable body length, much smaller ventral sucker, ovary and testes, and longer but narrower eggs (87–109 × 50–59 vs 70–85 × 60–84 µm); and from the two smaller forms, E. serratum Howell, 1968 and E. aconiatum Dietz, 1909, in a number of additional metrical features correlated with body size and especially in the possession of much larger collar spines. Partial fragments of the mitochondrial nad1 and 28S rRNA genes were amplified for representative isolates of the four species and analysed together with sequences for Echinostoma spp. and Echinoparyphium spp. available on GenBank. Phylogenetic analyses based on the mitochondrial nad1 gene revealed congruence between the molecular data and species identification/delineation based on morphology; this was corroborated by the 28S rDNA sequence data.