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PubMed2002

The attachment of Schistosoma mansoni cercariae to human skin cells.

Most of our knowledge about the process of penetration of skin, by cercariae of Schistosoma mansoni, has been gained from studies carried out in vivo with laboratory animals. Human skin is significantly different from that of other animals but there are obvious practical difficulties in directly studying attachment and penetration with human skin. Techniques have been developed which enable a 3-dimensional skin equivalent to be grown in tissue culture, made from different types of human skin cells. The aim of the present study was to investigate cercarial interactions with confluent cultures of the individual skin cell types that make up normal human skin and which will be used to construct a multi-component model. Cercariae behaved differently towards the various cell types tested. They responded least to monolayers of endothelial cells and most to primary keratinocytes, derived from human foreskin and differentiated at an air/liquid interface. This study demonstrates, therefore, that cercariae are capable of distinguishing between different types of skin cells and they preferentially attach to differentiated cells which form the epidermis.

Animals↗
PubMed2000

Host-finding in Echinostoma caproni: miracidia and cercariae use different signals to identify the same snail species.

The snail host signals releasing host-finding responses in miracidia and cercariae of Echinostoma caproni were analysed by fractionation of snail-conditioned water (SCW). Cercariae responded non-specifically to organic and hydrophilic, low molecular weight components of SCW showing their typical turning response. Hydrolysis of peptides in SCW had no effect on cercarial responses. An artificial mixture of amino acids in concentrations determined from SCW as well as glycine alone in a concentration corresponding to the total concentration of amino acids in SCW showed nearly the same efficacy as SCW itself. Miracidia responded to a high molecular weight glycoprotein fraction, which could be isolated from SCW by ion-exchange and size-exclusion chromatography. In contrast to an Egyptian Schistosoma mansoni strain, the echinostome miracidia were not able to differentiate between different snail species. The results show for the first time that miracidia and cercariae of the same species may use different signals to identify the same snail host species. This indicates an independent evolution of host-finding mechanisms in the two parasite stages.

Animals↗
PubMedDate not supplied

[Chaetotaxy of cercariae of two Microphallid Trematodes, Microphallus gracilis Baer, 1943 and Maritrema pyrenaica Deblock and Combes, 1965 parasiting Neomys fodiens (author's transl)].

The distribution of papillae on the cercariae of Microphallus gracilis and Maritrema pyrenaica parasites of Neomys fodiens is studied. The comparison between several cercariae of Microphallidae parasites of Birds had allowed to separate the ciliary characters of the two genera Microphallus and Maritrema. The ciliary characters of the two cercariae parasites of Mammals described in this paper, and those previously pointed out in Microphallidae of Birds are identical.

Animals↗
PubMed1981

[Superficial argentophilic structures of miracidium and cercaria of Paramphistomum phillerouxi Dinnik, 1961 (Trematoda, Paramphistomidae) (author's transl)].

Superficial argentophilic structures of the miracidium and cercaria of Paramphistomum phillerouxi Dinnik, 1961, are descrifed in detail. Concerning the miracidium they are similar to those of the miracidia of some species belonging to the genus. On the other hand the chaetotaxy of the cercaria is different from that of the cercaria of P. togolense (Alberet et coll., 1978) and therefore this appears to constitute a good criterium for the taxonomy of this group.

Animals↗
PubMed2002

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.

Animals↗
PubMed2002

Emergence of cercariae of Echinostoma caproni and Schistosoma mansoni from Biomphalaria glabrata under different laboratory conditions.

Release of Echinostoma caproni cercariae and Schistosoma mansoni from experimentally infected Biomphalaria glabrata snails maintained under different laboratory conditions was studied. Infected snails were isolated individually for 1 h in Stender dishes containing 5 ml of artificial spring water and the number of cercariae released during this time was recorded. Of numerous conditions tested, the addition of lettuce, the use of water conditioned by B. glabrata snails and a temperature of 35 degrees C significantly increased the release of E. caproni cercariae. A significant increase in cercarial release of S. mansoni was seen only in cultures fed lettuce. A temperature of 12 degrees C caused a significant decrease in cercarial release of both E. caproni and S. mansoni. Increased snail activity associated with feeding behaviour was probably responsible for the enhanced cercarial sheds observed in this study.

Animals↗
PubMed2002

Daily emergence of Schistosoma mansoni and S. haematobium cercariae from naturally infected snails under field conditions.

The daily emergence of Schistosoma mansoni and S. haematobium cercariae was investigated under field conditions. Intermediate host snails of both schistosome species were collected during the rainy season, cold dry season and warm dry season and kept separately in test tubes in habitat water. Shed cercariae were collected from each of the test tubes at two hourly intervals, transferred to Petri dishes and counted. Mice were exposed to these cercariae to establish the identity of the schistosome parasites. Peak shedding for both species was observed at 1100 h during the rainy and warm dry seasons and at 0900 h during the cold dry season. Shedding before 0900 h was found only for S. haematobium in the rainy season while shedding after 1700 h occurred only during this season at both species. Shedding observed during 1900 h observation period was in the low category for both species. No shedding was observed during the 2100 h observation period for any of the species and the investigation was discontinued after this period. Only S. haematobium ova were found in the exposed mice.

Animals↗
PubMed2004

Effects of copper sulphate on in vitro encystment of the cercariae of Echinostoma caproni.

The effects of various concentrations of copper sulphate were studied on in vitro encystment of Echinostoma caproni in a Locke's-artificial spring water (ASW) (1:1) medium. Cercariae were killed in 10,000 mg l(-1) CuSO4 in Locke's-ASW (1:1) within 24 h and extruded cystogenous material to produce an abnormal cyst wall. The 'emergency response' of encystment to high concentrations of copper reported for Parorchis acanthus cercariae did not occur in E. caproni. Concentrations of 1000 mg l(-1) and 100 mg l(-1) CuSO4 in Locke's-ASW (1:1) also killed the cercariae without encystment by 48 h. A concentration of 10 mg l(-1) CuSO4 in Locke's-ASW (1:1) allowed for normal in vitro encystment within 48 h and these cysts were capable of excystation in a trypsin-bile salts medium.

Animals↗
PubMed2003

Identification of trematode cercariae carrying Neorickettsia risticii in freshwater stream snails.

We provide evidence of Neorickettsia (Ehrlichia) risticii Holland, the agent of Potomac horse fever, in trematode larval stages found in aquatic snails and insects collected from a stream in Korea, using nested polymerase chain reaction (PCR) and sequence analysis of the 16S rRNA gene fragment amplified from several cercaria species. It was observed that of 423 (13.1%) of 3,219 snails infected with cercariae, 77 (20.8% of the 371) were infected with N. risticii. Five families of trematode cercariae, Schistosomatidae, Echimostomatidae, Heterophyidae, Microphallidae, and Acanthocopidae were identified morphologically within Semisulcospira libertina, Radix auricularia coreana, and S. gottschei snails. Echinostoma cinetorchis, E. hortense, and Metagonimus sp. were identified based on both the cercarial morphology as well as by phylogenetic analysis of the amplified 18S rRNA gene sequences. Adult aquatic insects were also collected from the same sites and were sorted into five species, Ischnura asiatica in Coenagrionidae and Calopteryx japonica, Sympetrum darwinianum, Symptrum eroticum, and Symptrum parvulum in Calopterygoidae. One thousand and two hundred eighty five metacercariae (classified into groups A through F) were isolated from 310 adult aquatic insects, and the average number of metacercariae per aquatic insect was 4.1. However, there was no amplification of N. risticii from these metacercariae.

Anaplasmataceae Infections↗
PubMed1993

Acquired resistance to Schistosoma japonicum in IgE-deficient SJA/9 mice immunized with irradiated cercariae.

Participation of IgE in protective immunity against Schistosoma japonicum was examined by comparing congenital IgE-deficient SJA/9 and IgE-producing SJL/J mice. Mice immunized with 100 irradiated cercariae 7 weeks previously were infected with 50 live cercariae. In SJL/J mice at 40 days after infection, a 3-to 4-fold increase of total IgE levels and anti-S, japonicum egg IgE antibody production were observed with no significant difference between immunized and nonimmunized mice. IgE was not detected in SJA/9 mice throughout the experiments. Protective immunity evaluated by recovery of adult worms was found in SJA/9 mice and was comparable to that of SJL/J mice. These results suggest that acquired immunity in mice with irradiated cercariae of S. japonicum was not dependent on IgE in these strains of mice.

Animals↗
PubMed1991

[Relationship between the pathogenicity of Schistosoma mansoni in mice and the susceptibility of the vector mollusc. I. Cercariae infectivity and worm burden].

The possible influence of the immune mechanisms of the molluscs on the development of the sporocysts and the resultant behavior of the adult worm in the vertebrate host were studied. Two strains of Schistosoma mansoni (BH and SJ) were used. These were genetically selected for their susceptibility and maintained, respectively, in Biomphalaria glabrata and Biomphalaria tenagophila, the natural invertebrate hosts. Experimental groups of mice infected with cercariae proceeding from the two species of molluscs, belonging to generations P, F1, F2, F3 and F4, were formed. The infection rates of the snails, the number of the penetrant cercariae and the worm burden in mice were evaluated. It was concluded that the higher susceptibility of Biomphalaria tenagophila results in a greater ability on the part of the cercarial to develop into adult worms. The higher susceptibility of B. glabrata results in greater power of penetration into mice tegument on the part of the cercariae.

Analysis of Variance↗
PubMedDate not supplied

[Schistosoma mansoni: quantitative aspects of the development of irradiated cercariae in the skin, lungs and portal system, in mice].

The migration of Schistosoma mansoni (LE and SJ strains) has been studied in eight groups of outbred Swiss albino mice (Mus musculus), which were previously infected with ca 450 cercariae, transcutaneously. The infection of mice was performed with non irradiated cercariae (control groups), or with gamma-irradiated cercariae, at the schedule of 3, 20 and 40 Krad. Regarding the skin, a progressive decrease was detected for the recovery rates, related to the time of infection. As far as the lungs and portal system are concerned, a significant inverse correlation was observed between the total recovery rate and the irradiation dosages. The dose of 20 Krad practically hinders the migration of the parasites (in both strains) from the lungs to the portal system, whereas the dose of 40 Krad prevents the migration of most of the parasites from the skin to the lungs.

Animals↗
PubMedDate not supplied

Schistosoma mansoni: the effect of dexamethasone on the cercaria-schistosomulum transformation, in vivo.

Treatment with dexamethasone (DMS) in the early phases of the experimental Schistosoma mansoni infection causes an indirect effect on the cercaria-schistosomulum transformation process. This is observed when naive albino mice are treated with that drug (50 mg/Kg, subcutaneously) and infected intraperitoneally 01 hour later with about 500 S. mansoni cercariae (LE strain). An inhibition in the host cell adhesion to the larvae, with a simultaneous delay in the cercaria-schistosomulum transformation, is observed. This effect is probably due to a blockade of the neutrophil migration to the peritoneal cavity of mice, by an impairment of the release of chemotactic substances. Such delay probably favors the killing of S. mansoni larvae, still in the transformation process, by the vertebrate host defenses, as the complement system.

Animals↗
PubMed2005

Influence of saccharose on the development of cercariae from Schistosoma mansoni strains BH and SJ.

The development of cercariae from Schistosoma mansoni strains BH and SJ in Biomphalaria glabrata and Biomphalaria tenagophila treated with saccharose was studied. The molluscs were maintained in dechlorinated tap water containing 0.01% saccharose. After one week of treatment with saccharose, B. glabrata and B. tenagophila were exposed to ten S. mansoni miracidia, from BH and SJ strains respectively. Control snails of both species were maintained in dechlorinated tap water without saccharose and exposed to the same number of miracidia. There was no significant difference between the infection rates of snails treated or not with saccharose. However, the two groups of B. glabrata had significantly greater infection rates than the corresponding B. tenagophila groups. Molluscs treated with saccharose had a lower survival rate, with the greatest mortality occurring immediately before and at the beginning of cercariae release. Treatment with saccharose did not result in the release of more cercariae, but larvae from molluscs so treated showed a greater capacity to penetrate mouse skin, which was attributed to the greater energy supply during larval development in the mollusc.

Animals↗
PubMed2000

Argentophilic structures of miracidia and cercariae of Philophthalmus lucipetus (Philophthalmidae: Trematoda) from Israel.

Argentophilic structures of Philophthalmus lucipetus miracidia and cercariae from Israel are described. Eighty-four of 87 miracidia examined displayed an epidermal plate arrangement of 6:8:4:2 = 20, similar to other Philophthalmus species. Twenty papilla-like structures are arranged on the terebratorium in 3 groups, along 1 axis. Sixteen body papillae are located at the bases of epidermal plates of row 1. Eyespots are mediodorsal, between rows 1 and 2. Excretory pores are lateral, between rows 2 and 3. Features common to Israeli and Bulgarian isolates, differentiating them from other species, include the presence of 16 body papillae as opposed to 10 in other species, and a maximum of 20 papillae on the terebratorium as opposed to 19 in the others. About 3% of the miracidia displayed different plate arrangements. Among the argentophilic structures of P. lucipetus cercariae, the Israeli and Bulgarian P. lucipetus show a common pattern of 2-4 excretory pores in the tail, but arrangement of cephalic CI3 and CI5 papillae in the 2 isolates is insufficiently unequivocal for species determination. The data presented show that miracidial characteristics, rather than those of cercariae, aid in determining the species of philophthalmids. They also support former evidence attesting to the identity of the Bulgarian and Israeli species.

Animals↗
PubMed2001

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.

Animals↗
PubMed2001

Schistosoma mansoni proteases Sm31 (cathepsin B) and Sm32 (legumain) are expressed in the cecum and protonephridia of cercariae.

Adult Schistosoma mansoni parasites live in the bloodstream of their vertebrate hosts where they consume red blood cells. Hemoglobin, released from the ingested red blood cells, is degraded by a variety of parasite proteases, including Sm31 (cathepsin B) and Sm32 (schistosome legumain). In this study the localization pattern of the Sm31 and Sm32 enzymes in cercariae (the infectious life cycle stage) was examined. Antibodies generated against recombinant Sm31 and Sm32 recognize their respective proteins in Western blots of soluble parasite extracts. Highest levels are seen in adult female extracts, whereas the level of both proteins is below detection in cercarial extracts. However, in fixed, whole cercariae, both proteins are seen in the cecum and protonephridia. In the cecum, the staining pattern has a granular appearance, suggesting that the proteins are packaged in vesicles. In the protonephridial system, Sm31 and Sm32 are detected in all 8 flame cells in the cercarial body and in both flame cells in the cercarial tail. The distribution of the 2 proteins differs in the flame cells. Examination of immunostained cercariae using laser scanning confocal microscopy shows that whereas Sm31 is located in the tubule cell, Sm32 is found in both the tubule cell and its adjoining cap cell. These findings suggest that the proteins are involved in the proposed excretory and osmoregulatory roles of flame cells.

Animals↗
PubMed2002

In vitro and in vivo encystment of the cercariae of Echinostoma caproni.

In vitro and in vivo studies were conducted on the cercariae of Echinostoma caproni. Of the 15 media tried, 2 resulted in effective in vitro encystment in petri dish cultures maintained at 23 +/- 1 C. They were a Locke's--artificial springwater (ASW) (1:1) medium (67% encystment) and a Biomphalaria glabrata embryonic cell line medium (23% encystment). To obtain large numbers of in vitro--formed cysts, finger bowl cultures containing 40 ml of the Locke's-ASW (1:1) medium were used at 23 +/- 1 C. Of 3,000 cercariae tested, 1,890 (63%) were encysted in this medium by 48 hr. Most of these cysts looked similar to those formed in vivo, although some showed abnormalities in the outer cyst wall and other malformations. A total of 200 in vitro-formed cysts treated in an alkaline trypsin-bile salts (TB) medium for 2 hr at 41 C showed 94% excystation. In vitro-formed cysts fed to mice produced ovigerous adults within 2 wk postinfection (PI). Eggs from these worms gave rise to miracidia that produced patent intramolluscan infections in B. glabrata snails. In vivo encystment was studied in lab-raised juvenile Helisoma trivolvis (Colorado strain) snails, 1-3 mm in shell diameter. From 6 to 24 hr PI, 93-100% of the cercariae were recovered as metacercarial cysts in the snail tissue. Treatment of these cysts in the TB medium resulted in 96% excystation within 2 hr at 41 C.

Animals↗