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PubMed1982

Characterization of chemical stimuli for the penetration of Schistosoma mansoni cercariae. I. Effective substances, host specificity.

The stimulation of penetration of Schistosoma mansoni cercariae into agar was studied. This depends exclusively on chemical triggers whose specificity is analyzed in experiments with 230 chemicals. Only aliphatic hydrocarbon chains which have a polar as well as a nonpolar end group are effective. The effectiveness of saturated substances is limited, at pH 7.0, to chain lengths between 10 and 15 carbon atoms. Unsaturated substances are active at longer chain lengths. Their effectiveness is increased by the number of double bonds in the cis position, and these should not be placed too close to the nonpolar end of the chain. As well as double bonds, halogens, hydroxyl groups, and methyl side chains are equally effective. All penetration stimulating substances kill cercariae in free water, and the appropriate chemicals cause this lethality at very low concentrations. It is shown that the host recognition pattern at the stage of penetration is especially adapted to invasion of the human skin.

Agar↗
PubMed1982

Characterization of chemical stimuli for the penetration of Schistosoma mansoni cercariae. II. Conditions and mode of action.

The mode of action of chemical substances which trigger the penetration of S. mansoni cercariae into agar substrata is studied. The effectiveness of these substances is largely independent on their polarity and water solubility. Thus, they do not seem to act by a passive membrane permeation process, but they may interact with specific receptor sites, which are characterized. The receptor sites seem to respond to the following chemical characteristics of the stimulating aliphatic hydrocarbon chain: Carboxylic end group, lipophilic end group, chain length, cis-double bond. The penetration stimulating substances cause, even in cercariae in free water, a transformation of the tegument, manifested as a reduction of the Cercarienhüllen-Reaktion and a loss of osmotic protection.

Agar↗
PubMed1979

Evaluation of lung recovery assay for schistosomula in mice immunized with x-irradiated cercariae of Schistosoma mansoni.

The lung recovery assay for schistosomula has recently been used as a rapid method for measuring the state of immunity of a challenged animal. Its merit rests on the fact that the peak day of schistosomular recovery in the lungs of both normal and immune hosts falls on the same day and the degree of immunity can be measured by the percent of schistosomular recovery on this particular day. An evaluation of this method for mice immunized with highly X-irradiated cercariae of Schistosoma mansoni was made. The results indicate that in the immunized mice the peak day for the schistosomular recovery was delayed and the number of schistosomula recovered on the peak day was decreased. The delay of the peak day was increased by the degree of host immunity, so its identification for a host of an unknown immunologic status was not a simple matter. In addition, this method measured only the immune effect which took place in the skin and on prepeak days in the lungs. It was not as competent as the conventional liver perfusion method which measures the total result of the immune effect of the skin, lungs, and liver. Our conclusion is that for measuring the immunizing effect of irradiated cercariae, the lung recovery method is not suitable for the determination of the state of immunity induced.

Animals↗
PubMed1982

Isoenzyme studies on cercariae from monoinfections and adult worms of Schistosoma mansoni (10 isolates) and S. rodhaini (one isolate) by horizontal polyacrylamide gel electrophoresis and staining of eight enzymes.

The enzyme phosphoglucose isomerase (PGI), phosphoglucomutase (PGM), hexokinase (HK), adenylate kinase (AK), fructokinase (FK), mannose-6-phosphate isomerase (MPI), glucose-6-phosphate dehydrogenase (G-6-PDH) and malate dehydrogenase (MDH) were chosen to study the variation between isolates, cercariae and adults, individuals, and sexes of Schistosoma mansoni and S. rodhaini, using horizontal polyacrylamide gel electrophoresis. The method described allows combinations of six of the eight enzymes to be scored in the homogenate from one adult worm. In adult S. mansoni one phenotype of the eight enzymes was observed in all isolates. In addition, the enzyme PGI showed polymorphism in the isolates from Tala, Kenya and Uganda. PGM in the isolates from Tala, Kenya and South Africa showed polymorphism. The cercarial phenotype differs from the adult phenotype in G-6-PDH, where the cercarial enzyme mobility is slower than that in the adult worm. The low amount of intrastrain variation observed in this species is explained by the limited amount of material used to establish the laboratory stocks, whereas the genetic similarity between geographically widely separated stocks does suggest that only limited geographical variation is likely to occur in S. mansoni. It is suggested that the gene controlling the PGI polymorphism is located on the sex chromosomes of S. mansoni. Mobility differences were observed between S. mansoni and S. rodhaini in the enzyme PGI and PGM, and these characteristics might be useful for a quick identification of schistosome cercariae emerging from Biomphalaria sp. in Africa.U

Adenylate Kinase↗
PubMed1994

A cysteine proteinase in the cercariae of Diplostomum pseudospathaceum (Trematoda, Diplostomatidae).

A cysteine proteinase was detected in extracts from cercariae of the trematode Diplostomum pseudospathaceum. The enzyme preferred protein substrates over synthetic, chromogenic peptides. The optimal pH for hydrolysis of substrates was 7.2 for azocoll, 6.4 and 7.6 for azocasein, 7.6 for azoalbumin, and 6.8 for N-benzoyl-L-arginine-4-nitroanilide. Elastin-Congo red and certain N-blocked L-aminoacyl- and L-peptidyl nitroanilides bearing L-phenylalanine, L-alanine, L-tyrosine, and L-leucine at the P1 subsite were not hydrolyzed. Thiol-reducing and divalent cation-complexing agents stimulated the proteinase activity, whereas thiol-blocking agents inhibited it. The relative molecular weight of the enzyme was approximately 40,000 as determined by SDS-PAGE. Detection of an identical proteinase in water after treatment of living cercariae with praziquantel suggests that the enzyme occupied the penetration glands in the larvae. Thus, when secreted by the parasite during invasion of an appropriate host, the enzyme might act as a penetration-promoting factor.

Animals↗
PubMed2003

Tegumentary papillae of Echinostoma caproni cercariae (Trematoda: Echinostomatidae).

Argentophilic staining and scanning electron microscopy were used to study the tegumentary papillae of Echinostoma caproni cercariae. The most abundant tegumentary papillae were uniciliate, but multiciliate papillae were also found, mainly on the ventral aspect of the oral collar. The distribution pattern of the papillae on the body and tail was in general similar to that seen in the cercariae of other 37-collar-spined Echinostoma species. Some differences were noted between E. caproni and the allopatric species, E. trivolvis. E. caproni has a greater number of papillae associated with the collar spines than does E. trivolvis. E. caproni has uniciliate papillae on the acetabulum, whereas E. trivolvis does not. Chaetotaxy is useful to distinguish subtle morphological differences in cercarial species in the 37-collar-spined Echinostoma complex.

Animals↗
PubMed2003

Analysis of the gene expression profile of Schistosoma japonicum cercariae by a strategy based on expressed sequence tags.

We present an analysis of the expression profile of Schistosoma japonicum cercariae by a strategy based on expressed sequence tags (ESTs). A cDNA library from S. japoniucm cercariae was constructed and was used to generate ESTs. In total, 201 clones randomly selected from the library were sequenced; 136 ESTs were successfully obtained and sent to the BLAST server for homology searching. Among the 136 ESTs, 85 (62.50%) did not match any protein or gene sequence published in the BLAST databases; these comprised 75 (55.15%) ESTs matched (or partly matched) S. japonicum and Schistosoma mansoni ESTs, 4 (2.94%) matched human ESTs and 6 (4.41%) that did not match any sequence. Fifty-one (37.50%) ESTs were identified by the BLAST server; these consisted of 8 (5.88%), 9 (6.62%) and 34 (25.00%) that showed high homology with genes or proteins reported from S. japonicum, S. mansoni and other organisms, respectively. These identified ESTs can be grouped into nine categories: transporters (1.96%), secretory proteins (1.96%), kinases (3.92%), proteases (5.88%), structural and cytoskeletal proteins (13.73%), metabolism-related proteins (9.80%), regulatory and signaling proteins (11.76%), transcription and translation machinery (25.50%), and others (25.50%). Several interesting new genes cloned from this cDNA library are discussed here. These findings will be valuable for the understanding of the biology of this parasite.

Animals↗
PubMed2004

Navigation within host tissues: cercariae orientate towards dark after penetration.

The survival of skin penetrating cercariae depends on information on the direction to move toward deeper layers in the epidermis (the direction of further migration) and toward the surface (direction which must be avoided when migrating). We tested the hypothesis that parasites can use their photo-sensitivity for orientation away from the light-exposed skin surface towards darker locations. Cercariae of species invading humans ( Schistosoma mansoni), birds ( Trichobilharzia ocellata) and fish ( Diplostomum spathaceum) oriented towards light sources when free swimming in cuvettes. However, they shifted to a negative photo-orientation when migrating in agar substrates after penetration and transformation to schistosomula. This is a first hint that parasites may use photo-orientation when they navigate in host tissues.

Agar↗
PubMed2000

Influence of mechanical tail-detachment techniques of schistosome cercariae on the production, viability, and infectivity of resultant schistosomula: a comparative study.

Two decaudation methods used by Schistosoma mansoni cercariae for the production of schistosomula by in vitro transformation were comparatively tested. Both low-pressure syringe passage and vortex mixing of the cercariae produced schistosomula of similar percentages of viability, and the levels of worm recovery following subcutaneous injection in mice were also comparable, though low. By all criteria tested, including simplicity and time requirement, the two methods are equally efficient and are well applicable for mass production of schistosomula.

Animals↗
PubMed2001

Prevalence of cercariae from Lymnaea stagnalis snails in a pond system in Southern Germany.

Lymnaea stagnalis snails were collected from 174 individual ponds of an extensive pond system in South Germany; 43,441 snails collected during 1980 2000 were examined for shedding cercariae. The species richness (at least 18 species of cercariae) and the high cercarial prevalence (at least 44.9%) may result from the high abundance and diversity of vertebrate and invertebrate hosts in the area. The mean prevalence (% +/- SEM) of most cercarial species increased from May-June to August-October, e.g. in Diplostomum spathaceum from 4.1% to 18.6%, in all echinostomatids from 5.6% to 18.0%, in Pseudechinoparyphium echinatum from 3.0% to 11.2%, in Xiphidiocercariae from 2.2% to 13.4%, and the overall prevalence shifted from 13.7% to 53.5%. There was no change in the prevalence of the different cercarial species over the last 20 years. The agents of cercarial dermatitis showed a constant low prevalence, 0.17% in Trichobilharzia ocellata (43,441 L. stagnalis examined) and 0.24% in other Trichobilharzia species (4,245 Radix examined). Such low prevalences seem to be normal in areas where cercarial dermatitis occurs in humans.

Animals↗
PubMed1983

Schistosoma mansoni: stimulus and transformation of cercariae into schistosomules.

Schistosoma mansoni schistosomules prepared from cercariae by seven in vitro techniques had not all reached the same state of development at the end of the incubation period as scored by seven parameters: water tolerance; Cercarienhüllen Reaktion; presence of the glycocalyx; condition of the surface membrane; nuclear state; granule migration; and cryopreservability. At the end of the specific incubation period for each technique, the level of development was judged with respect to schistosomules which had developed in situ for 1 hr after penetration of the ear skin of mice. In descending order of their correspondence to in vivo schistosomules, those derived in vitro (by the procedures listed) ranked as follows: first, penetration of dried rat skin; second, centrifuging and vortexing, or incubation in serum-supplemented medium; and third, syringe passage, omnimixing, centrifuging, and incubating, or incubating alone. The only treatment common to all techniques was incubation in 37 C culture medium for 2 hr or more. This is suggested as the stimulus for the cercaria-to-schistosomule transformation.

Animals↗
PubMed1986

Schistosoma mansoni: a new parenchymal cell in cercariae.

A new type of cell has been identified in cercariae of Schistosoma mansoni. The perikarya (cell bodies) of these cells were located in the body (midsegment), in an area oral to the acetabulum (ventral sucker). Cytoplasmic processes extending from the perikarya ramified throughout the parenchyma of the anterior organ (oral sucker), body, and tail segments by following the path of the nerve processes from the neuropile. The perikarya of these cells had heterochromatic nuclei and a predominance of particulate material and granules (240-360 nm) in their cytoplasm. Aggregates of granules (240-360 nm) and associated vesicles (34 nm) were scattered throughout the cytoplasmic processes of the cells and formed distinct varicosed areas. These processes often connected to the tegument in the midsegment (body) of the cercariae. The granules and associated vesicles reacted (became electron dense) with fixatives reported to be detectors of biogenic amines: The glutaraldehyde/osmium tetroxide fixation procedure rendered the granules electron dense while the glutaraldehyde/chromate/osmium tetroxide fixation procedure rendered the granules and the associated vesicles electron dense. The chromate solution of the latter procedure was responsible for the electron density of the associated vesicles. The morphology of these cells (their long ramifying cytoplasmic processes) and their reaction to chromium suggests that they are probably biogenic aminergic sensory cells.

Animals↗
PubMed1990

Opisthorchis viverrini: finding and recognition of the fish host by the cercariae.

The cercaria of Opisthorchis viverrini finds and recognizes its fish host by using at least four steps of behavioral patterns. (1) Dispersal and selection of plant-free water microhabitat are achieved by intermittent swimming behavior with positive phototactic orientation. (2) Attachment to the host is stimulated by water currents and a hydrophilic component of fish skin surface which has a molecular weight of more than 30,000. This component is sensitive to digestion with hyaluronidase and seems to be a glycosaminoglycan other than hyaluronic acid and chondroitin sulfate. (3) Remaining on the host's surface is induced by an unknown chemical component of fish skin surface mucus. (4) Penetration into the host is triggered by a hydrophilic component of fish skin surface of a molecular weight of more than 30,000. This host signal has a proteinaceus character as it is sensitive to proteinase digestion but not to hyaluronidase and glycosidases. The requirement of O. viverrini cercariae for complete glycosaminoglycans and proteins as signals in host identification may have the advantage that the numerous small molecules in mud and decaying materials in the water cannot interfere with host-finding.

Animals↗
PubMed1979

Factors affecting the acquisition of resistance against Schistosoma mansoni in the mouse: III. The failure of primary infections with cercariae of one sex to induce resistance to reinfection.

Mice which were given a primary infection consisting of male or female Schistosoma mansoni cercariae alone failed to acquire the same degree of resistance against homologous challenge as did mice with a bisexual primary infection. The degree of resistance acquired by "single-sex"-infected mice was not augmented either by increasing the number of cercariae administered in the primary infection, or by increasing the interval between primary infection and challenge, or by injection of S. mansoni eggs. The results are discussed in relation to previous observations on the capacity of "single-sex" schistosome infections to induce resistance.

Animals↗
PubMed1995

The irradiated cercariae vaccine model: looking on the bright side of radiation.

Schistosomes infect between 200 and 300 million people at any one time. A major strategy to reduce the impact of schistosomiasis on human health is the development of a defined antigen vaccine. Protective immunity induced in mice by irradiated cercariae may serve as a model for the development of a vaccine. In such vaccinated mice, worm burdens resulting from challenge infection can be reduced by more than 90% compared to non-vaccinated mice. During the past three decades, the irradiated-carcariae vaccine model has been dissected in the detail in order to determine factors that may be relevant to vaccination, such as the participating immune compartments, the site and kinetics of the immune response, and the antigens recognized. In this review, Dania Richter, Donald A. Harn and Franz-Rainer Matuschka highlight the research on the vaccine model, focusing on the murine model using gamma-irradiated cercariae of Schistosoma mansoni.

Journal Article↗
PubMed2004

Detection of Schistosoma mansoni cercariae in plankton samples by PCR.

A PCR assay on the basis of a tandemly repeated DNA sequence was employed for the detection of Schistosoma mansoni in artificial plankton samples. It was highly specific, since as few as 1fg DNA from this species were sufficient to obtain a clear signal, while 10pg DNA of Schistosoma rodhaini were required and no PCR products were obtained with even 10ng DNA of planktonic organisms and any other trematode species tested. In areas with transmission of different Schistosoma species 10pg DNA should be used for amplification, which would allow detection of 20 S. mansoni cercariae in 0.05g plankton without interference caused by DNA of other Schistosoma species. In other areas 10ng DNA from plankton samples can be amplified, detecting less than one S. mansoni cercaria specifically in 0.05g plankton. This assay might help to identify S. mansoni in samples from field studies, where a multitude of different organisms hinder a correct species identification.

Animals↗
PubMed2006

Serum cytokines of the 20 Krad-irradiated S. mansoni cercariae vaccinated, primary and superinfected Cercopethicus aethiops aethiops.

Appropriate animal models are necessary to better understand the immune response in schistosomiasis. Schistosoma mansoni infection was established using irradiated cercariae in Cercopithecus aethiops aethiops (Grivet monkey) to describe immune responses of the serum cytokines, IL-4, IL-10, IL-12, IFN- gamma, and TNF-alpha. Intraperitoneal irradiated cercariae immunization on three occasions resulted in some differences of cytokine production. In primary infection, IL-4 was significantly raised (p=0.03) in the immunized monkeys, and there was an insignificant increase (p>0.05) in IL-10. However, ova excretion did not influence the cytokines, except in the controls where both IL-4 and IL-10 were significantly increased (p<0.05). In the controls, IL-12 and INF-gamma levels were lower after ova excretion, but the inflammatory TNF-alpha increased (p=0.049) and these findings can be associated with more liver pathogenesis in the group. Thus, this work has indicated the potential importance of anti-schistosome vaccine studies on the grivet monkeys.

Animals↗