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PubMed1990

Penetration of Schistosoma japonicum cercaria into host skin.

The anterior part of Schistosoma japonicum cercaria is a specialized head organ which can slightly stretch out and retract. There are three different types of large unicellular glands in cercarial body, consisting of one head gland, 2 pairs of pre- and 3 pairs of postacetabular glands. These glands differ in position, gross feature, histochemistry and functions. Both polysaccharase and protease activities are demonstrated in the secretions from these glands. Mode of cercarial penetration is described in detail and the penetration is effected by a combination of lytic secretions and mechanical movements. The schematic representation of the process of cercarial penetration is presented. The dynamic distributions of schistosomula in skin at different time intervals after skin penetration in various mammalian hosts are shown. Some newly transformed schistosomula die while penetrating into the skin of 7 mammalian species and the mortality rate varies with the host species, and that can also be affected by the age of cercariae following emergence from the snail. Some physiological aspects between cercariae and newly transformed schistosomula are compared. In contrast to cercariae, schistosomula are saline-adapted and water-intolerant. They were modified histochemically and antigenically.

Animals↗
PubMed1990

Local anaphylactic reactions to the penetration of cercariae of Schistosoma mansoni.

1. In order to study local tissue anaphylactic responses to infection with Schistosoma mansoni cercariae, mice of three different strains (C57BL/10J, Balb/cJ and CBA/J) were infected by subcutaneous injection of 15 to 20 cercariae. Eleven to 16 weeks later the animals were reinfected through one ear with 250 to 350 cercariae. 2. Throughout the infection period, the histamine content of the ears increased up to 150% of control values. Upon reinfection, the penetration of cercariae through the ear reduced its histamine content to near normal values. 3. Reinfection causes inflammation as judged by a 1.5 to 2.3-fold increase in the amounts of plasma leaking through the ear vessels as measured by leakage of Evans blue dye. 4. These results suggest that the local inflammatory reaction mediated by mast cells is important in the resistance of mice to reinfection with S. mansoni.

Anaphylaxis↗
PubMed1987

Argentophilic and scanning electron microscopic observations of the tegumentary papillae of Echinostoma revolutum (Trematoda) cercariae.

Argentophilic staining and scanning electron microscopy (SEM) were used to study the tegumentary papillae of Echinostoma revolutum cercariae. The most abundant papilla was uniciliate and arranged bilaterally on the body and tail of the cercaria. The distribution of these papillae was similar to that seen in other 37-collar spined echinostome cercariae. SEM revealed a total of 18 multiciliate papillae--16 on the anterior end and 2 at the middle of the body. These papillae contained up to 18 cilia per papilla and have not been reported previously from any cercaria.

Animals↗
PubMed1989

[A study on mechanism of skin penetration by cercaria of S. japonicum and screening of preventive drugs].

Mice pretreated with PG cyclo-oxygenase inhibitor aspirin, at 300 mg/kg/d x 5, and ibuprofen, at 100 mg/kg/d x 5 orally and 20 mg/kg/d x 3 intraperitoneally revealed moderate chemoprophylactic effects and the reduction of the penetration of worms by 23% when compared to controls. Daily oral administration of aspirin, at 300 mg/kg for 15 days the worms reduction increased to 41.7%. In estimation of PGE1 in cercariae of S. japonicum by radioimmunoassay, the PGE1 was 49 pg/100 cercariae. In normal mouse skin PGE1 has been measured to amount to 3105 +/- 691.7 pg/10 mg on average. In cercarial penetrated mouse skin, 1.5 hours after exposure the PGE1 assessed in 100 and 250 cercariae in the infected skin were 5506 +/- 1127.1 and 12085 +/- 2622.9 pg/10 mg respectively, which were significantly higher than that of the non-penetrated skin. These studies in conjunction with our previous work indicate that: 1.PGs, similar to S. mansoni, were probably necessary for cercarial penetration. 2.PG inhibitors could reduce cercarial penetration. Receptors antagonist etc. e.g. diphenhydramine, chlorpheniramine, atropine, practolol could not reduce cercarial penetration, but praziquantel in the pretreated mice could reduce cercarial penetration significantly. e.g. 400 mg/kg orally 2 hours prior to affection of cercariae about 100% reduction of the penetration, but if pretreated with praziquantel, 4, 8, 24, 36 hours prior to the affection the reduction penetration decreased to 51.7, 46.1, 9.4, 8.9% respectively.

Alprostadil↗
PubMedDate not supplied

[Comparative efficiency of infecting laboratory animals via intravenous and subcutaneous administration of Schistosoma mansoni cercaria].

Comparative study on effectiveness of intravenous and subcutaneous methods of infection of animals has shown that infection rate of helminths after the injection of equal dozes of cercariae under skin, into portal and femoral veins of golden hamsters does not differ significantly (42.6 +/- 4.2, 37.8 +/- 5.8 and 26.0 +/- 6.6 schistosomes, respectively). When using the above methods for cotton rats the infection rate was lower than that in golden hamsters. The most insignificant infection rate of parasites was recorded in both species after the injection of cercariae into the femoral vein. Results of the infection of golden hamsters with different dozes of cercariae have shown that with the increase of dozes of infectious material the infection rate of helminths rises during the experimental intestinal schistosomiasis only to a definite level, which is attained by the injection of cercariae into the portal vein in dozes lower than those used for subcutaneous infection.

Animals↗
PubMed1988

Pulmonary leukocytic responses are linked to the acquired immunity of mice vaccinated with irradiated cercariae of Schistosoma mansoni.

Pulmonary cellular responses in C57BL/6 mice exposed to Schistosoma mansoni have been investigated by sampling cells from the respiratory airways with bronchoalveolar lavage. Mice exposed to cercariae attenuated with 20 krad gamma-radiation developed stronger and more persistent pulmonary leukocytic responses than animals exposed to equal numbers of normal parasites. Although vaccination with irradiated cercariae also stimulated T cell responses of greater magnitude and duration than normal infection, the lymphocytic infiltrate elicited by each regimen did not differ substantially in its composition, 5 wk after exposure. Studies with cercariae attenuated by different treatments established that a link exists between the recruitment of leukocytes to the lungs of vaccinated mice and resistance to reinfection. There was a strong association between pulmonary leukocytic responses and the elimination of challenge infections by vaccinated mice. Animals exposed to irradiated cercariae of S. mansoni were resistant to homologous challenge infection but were not protected against Schistosoma margrebowiei. Homologous challenge of vaccinated mice stimulated anamnestic leukocytic and T lymphocytic responses in the lungs, 2 wk postinfection, but exposure of immunized animals to the heterologous species failed to trigger an expansion in these populations of cells. Our studies indicate that pulmonary leukocytes and T lymphocytes are intimately involved in the mechanism of vaccine-induced resistance to S. mansoni. It remains unclear whether these populations of cells initiate protective inflammatory reactions against challenge parasites in the lungs, or accumulate in response to the activation of the protective mechanism by other means.

Animals↗
PubMed1972

Evaluation of an overlay technique for the recovery of Schistosoma mansoni cercariae.

The consistent recovery of schistosome cercariae from turbid water may be an important observation in the study of schistosomiasis transmission. The phototactic behaviour of cercariae was used as the basis of a technique in which cercariae were induced to migrate into a layer of clear water overlying the turbid sample; the clear layer was then filtered and the cercariae counted. The recovery rate, however, does not appear to justify the use of this technique, at least in the field.

Animals↗
PubMed1972

Seasonal abundance of trematode cercariae in Bulinus truncatus in a small focus of schistosomiasis in the Nile Delta.

Bulinus truncatus was most numerous from June to August, and echinostome cercariae, present in 19.3% of snails, were the most prevalent of the 4 types of trematode cercariae found. The echinostomes occurred throughout the year, other cercariae only in certain months. Double infections were uncommon. The findings suggest that echinostome cercariae exercise some biological control of Schistosoma haematobium in the area studied.

Animals↗
PubMedDate not supplied

[Longevity of marine cystophorous cercariae in the environment].

Experiments were conducted on the duration of life in sea water of three species of cystophorous cercariae from the Barents sea. The expenditure of reserve nutritive substances (glycogene) in the process of the vital activity of cercariae was followed. The life duration of cystophorous cercariae is considerably longer than that cited in literature for other groups of cercariae that is associated with their morphological and biological peculiarities.

Animals↗
PubMed1981

Schistosoma bovis, S. intercalatum and S. haematobium: methods for in vivo radiolabelling of cercariae with radioselenium.

Cercariae of Schistosoma bovis, S. intercalatum and S. haematobium were radiolabelled by individual exposure of their respective host snails to 75Se-methionine in 1 ml water for a period of 20 hours. Maximum cercaria-bound radioactivity was obtained four to seven days after labelling of snails, but detectable levels of radioactivity incorporation were obtained with all three species for a period of 32 days. The radiolabelling procedure did not interfere with the production of cercariae or with the biological characteristics of the labelled larvae. The described research opens the way for the application of various radioisotope tracer systems in studies on host-parasite relationships between cercariae and schistosomula of terminal-spined species of schistosomes and the final host.

Animals↗
PubMed1980

[Evaluation of the drift of cercariae by a single daily sampling in the site of schistosomiasis transmission. Example of Guadeloupean sites of Schistosoma mansoni transmission (author's transl)].

Research on cercarian density in running water transmission sites of intestinal schistosomiasis in Guadeloupe has allowed the construction of a representative model of the rhythm of presence of Schistosoma mansoni cercariae. This model allows, with a single daily sampling between 11 a.m. and 2 p.m., the evaluation of the daily sum of hourly densities. We propose to measure the parasite component of the risk of contamination in a bilharzial site by the drift of cercariae expressed in cercariae/day. The drift of cercariae takes account of variations in cercarian density and of the flow of the channel. It expresses the daily quantity of cercariae available for human contamination.

Animals↗
PubMed1995

Prevalence and transmission of cercariae causing schistosome dermatitis in Flathead Lake, Montana.

Numerous studies have been conducted on swimmer's itch, but very few have been in Montana and none on Flathead Lake, the largest, natural freshwater lake in the western United States. We conducted a study to determine the prevalence of hosts transmitting cercariae causing swimmer's itch in this lake. Hosts for this life cycle were determined by direct observation of fresh waterfowl fecal material for the presence of miracidia, and snails for the presence of cercariae. Swimmer's itch-producing cercariae were verified directly by placing various species on the arms of human volunteers and waiting for a reaction. Results of the study were further substantiated using a controlled experiment in which snails were individually infected with miracidia from the suspected waterfowl host and then checked for infection after a 6-wk incubation period. Our findings show that the common merganser (Mergus merganser) and the snail Stagnicola elrodi were natural hosts of the swimmer's itch parasite (Trichobiharzia ocellata) with prevalences of 84% and 2.0%, respectively. To our knowledge this is the first documented case of S. elrodi transmitting the swimmer's itch cercariae.

Animals↗
PubMed1993

A description of a pleurolophocercous cercaria of Procerovum sp from the Haplorchis group of heterophyid trematodes.

Freshwater snails, Stenomelania denisoniensis (Brot) from Tinaroo Dam, North Queensland, Australia were found to be infected with a heterophyid cercaria identified as Procerovum sp. The tail of the cercaria has finfolds which are bilateral anteriorly and dorso-ventral posteriorly, features which separate it from other genera in the Haplorchis-group. This group is differentiated from the cercariae of all the other heterophyid genera by the presence of the penetration glands that extend to the posterior end of the body lateral to the excretory bladder. This paper presents a full description of the cercaria, together with comparisons with other known species of Procerovum.

Animals↗
PubMed1993

Comparison of the protective efficacy on mekongi schistosomiasis in mice induced by antigens derived from cercariae, schistosomulae and adult worms.

Protective efficacy of the extracts of cercariae, schistosomulae and adult worms of S. mekongi was studied in mice receiving immunizations with these extracts emulsified with Freund's complete adjuvant initially and incomplete adjuvant subsequently, and compared with mice receiving physiological saline with or without adjuvants as controls. After challenge with cercariae, the animals were sacrificed and the larvae or adult worms harvested by lung recovery and perfusion techniques on day 5 and weeks 6-8, respectively. Worm reduction rates were significantly higher in mice receiving extracts of schistosomula (59%) and adult worms (51%) than in those receiving the cercarial extracts (31%). Similar findings were obtained with the perfusion technique showing worm reduction rates of 57%, 53% and 30% in mice receiving extracts of schistosomulae, adult worms and cercariae, respectively. ELISA antibody titers were correspondingly increased in mice receiving extracts of schistosomulae and adult worms, but not in those receiving cercariae. This apparent association may be inadequate to suggest that the increase in ELISA titer be used as an indicator for resistance in mekongi schistosomiasis.

Animals↗
PubMed1996

Emergence of cercariae of Echinostoma trivolvis from Helisoma trivolvis under different conditions.

Release of Echinostoma trivolvis cercariae from naturally infected Helisoma trivolvis snails maintained under different laboratory conditions was studied. Infected snails were isolated for 1 hr in Stender dishes containing 5 ml of artificial spring water and the number of cercariae released during this time was recorded. Of the conditions tested, i.e., light versus dark, day versus night, volume of water, snail maintenance temperature prior to isolation, temperature during isolation, food versus no food, aeration of water, disturbance of water, and isolation in snail conditioned water, the only significant factors in the emergence of E. trivolvis cercariae were temperature related. Observations on cercariae released in vitro from isolated rediae maintained in Locke's solutions were in accord with the in vivo results.

Animals↗
PubMed1997

Schistosoma mansoni cercariae: stimulation of acetabular gland secretion is adapted to the chemical composition of mammalian skin.

The chemical signals of mammalian skin that stimulate the secretion of acetabular gland contents of Schistosoma mansoni cercariae were determined by exposing cercariae to fractions of human and pig skin surface obtained by thin-layer chromatography. Postacetabular gland secretion was stimulated by hydrophilic skin extracts but was often combined with a secretion of preacetabular glands. Secretion of preacetabular glands, which contain enzymes for skin lysis, could be selectively stimulated with skin surface lipids. Two different mechanisms of lipid-stimulated preacetabular gland release could be distinguished. First, secretion in combination with penetration behavior and probably tegument transformation was stimulated by the fraction of free fatty acids. Second, secretion independent of penetration behavior and tegument transformation was exclusively stimulated by glucosylceramides and phospholipids, probably phosphatidylcholines. The secretion mechanisms seem to allow a continuous lysis of epidermal macromolecules during the skin passage of the cercariae. Free fatty acids occur in the uppermost skin layers and may stimulate the combination of the first response; phospholipids and glucosylceramides are restricted to deeper epidermal layers and may stimulate the enzyme secretion there. An active preacetabular gland release was also stimulated by toxic chemicals, which could suggest an emergency penetration program for impaired cercariae.

Adaptation, Physiological↗
PubMed1997

Observation of developing cercaria of Schistosoma japonicum on ultrastructural level and remarks at its morphology of mature stage.

OBJECTIVE: To study the developing cercaria of Schistosoma Japonicum (S. japonicum) on ultrastructural level by transmission electron microscope (TEM) for analyzing the morphological dynamic changes of the tegument, glands and musculature. METHODS: Artificial infected Oncomelania hupensis were dissected under dissecting microscope and the daughter sporocysts picked up for studying the germinal cells stage (S1). The other embryonic cercaria were selected according to the modified parameter of Chen and Bier (1972). The specimens were prepared by conventional procedure of the laboratory of TEM and were observed by Hitachi H600. RESULTS: Beside the germinal cell stage (S1), this is the first chronological study on the morphological development of S. japonicum cercaria from S2-S5 concerning the tegument and its elements (glycocalyx, sensory papilla, basal lamina and spine), head and acetabular gland and musculature of the body and tail. This article discusses the ultrastructural morphological differences from prior authors and emphasizes on the postacetalar gland and the pattern of tail musculature of the matured stage cercaria. CONCLUSIONS: According to the cell division and differentiation, the process of development may be divided into 5 stages: S1, the single germinal cell stage; S2, the germinal ball stages: major multiplication and minor differentiation; S3, tail budding embryonic stage, both active in multiplying and differentiating; S4, the pre-matured stage, major differentiation and minor multiplication; and S5, the fully matured stage (completing the differentiation).

Animals↗
PubMed1993

Schistosoma mansoni: identification and protective immunity of adult worm antigens recognized by T lymphocytes of outbred Swiss mice immunized with irradiated cercariae.

Percutaneous exposure of outbred Swiss mice to 500 Schistosoma mansoni (Egyptian strain) cercariae attenuated by 25,000 rad gamma radiation, twice at a 4-week interval, led to 80% protection against challenge with 100 live unattenuated cercariae compared to unimmunized control mice. The S. mansoni molecules that induce protective immunity in this model are not as yet identified. The capacity of an immunogen to induce efficient protective immunity depends largely on its T-cell-activating potential, as T cells are required both for eliciting long-lasting antibody formation and for antibody-independent cell-mediated immunity. To define such T cell antigen in S. mansoni, soluble adult worm antigens (SAWA) were separated by SDS-PAGE and electrotransferred onto nitrocellulose paper. Thirteen bands, identified by their M(r) were tested in T cell Western assays for their ability to stimulate proliferation of lymph node cells from 23 mice immunized with irradiated cercariae for the second time 2-5 weeks earlier. Lymphocytes from all mice responded to only a few (maximum of 6) bands. The response rate for the 13 SAWA bands tested ranged from 0-43%. These findings suggest a heterogeneity in T cell responses of individual mice to each of the SAWA bands and have implications that should be considered in the selection of immunogens to be assayed for anti-Schistosomiasis mansoni protective capacity. A highly significant protection against S. mansoni challenge in outbred Swiss mice was obtained exclusively following vaccination with a cocktail of soluble adult worm T cell immunogens that are recognized by 30-40% of individuals.

Animals↗