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PubMed2006

Encystment and metacercariae development of Echinostoma cinetorchis cercariae in an in vitro culture system.

For some species of 37-collar-spined Echinostoma, their cercariae successfully encyst and develop to metacercariae in vitro. In our study, we cultured Echinostoma cinetorchis cercariae in 12 different media to study the formation of metacercariae. Locke's solution, medium 199, and RPMI 1640 were used as media for culture. RPMI 1640 produced the highest encystment and normal metacercariae development. The osmolality of the media was related to their ability to encyst and develop. The 0.5 X media induced higher encystment and normal metacercaria formation than the 1x media. The addition of fetal bovine serum to RPMI 1640 increased the level of encystment and normal metacercariae development. In the mixture of 0.5 x RPMI 1640 and 10% fetal bovine serum, encystment was highest, at 96.0%, and the development ratio of normal metacercariae was also the highest, at 91.5%, after 48 hr of cultivation. In a viability test, 7 day- and 14 day-cultured metacercariae were successfully matured to adult worms in experimentally infected rats. These results showed that E. cinetorchis cercariae could be cultured to viable metacercariae in an in vitro culture system and that 0.5 x RPMI 1640 plus 10% fetal bovine serum was the most useful medium for cultivation. This culture system can be adapted for additional studies on the E. cinetorchis life cycle, especially to supply large numbers of metacercariae for other studies on this echinostome.

Animals↗

PubMed1975

Clonorchis sinensis in Kyungpook Province, Korea: 1. Distribution and demonstration of the cercaria of Clonorchis sinensis from snail, Parafossarulus manchouricus Bourgigant.

Studies were conducted in rivers in Kyungpook Province, Korea from July 1970 to September 1974 to determine the stations where Parafossarulus manchouricus, the intermediate snail host of Clonorchis sinensis, are abundant, and the infection rates of these snails with the cercaria of Clonorchis sinensis. Snail collections were made during four consecutive summers(July to September in each year). Ten snail habitats were found. The population density of the snails per square meter of the river bottom ranged from 25 to 250. The highest population of snails was encountered at the Dong-chon station. Cercaria studies by means of the immersing and crushing technics indicated surprisingly low rate of Clonorchis sinensis infection among the snails examined. The proportion of infected snails in Kyungpook Province was 0.8 per thousand of all snails examined. Results indicated that the Parafossarulus manchouricus exists in limited areas within the rivers under study and the infection of the snail with the cercaria of Clonorchis sinensis is very low.

Journal Article↗

PubMed1978

Immunization of mice with cobalt-60 irradiated Schistosoma mansoni cercariae.

Parameters of immunization of mice with 60Cobalt-irradiated Schistosoma mansoni cercariae are described and related to protection against subsequent challenge infection. Such immunization was found to be dependent on dose of irradiation, number of immunizing cercariae, and number and time course of infections. Low levels of resistance were obtained with low irradiation doses, in contrast to previous studies in mice. In general, resistance increased with increasing irradiation doses, up to approximately 48-56 Kr. Maximal resistance (70-80%) was induced by a single exposure to 250-500 cercariae, irradiated at a dose rate of 2 Kr/minute to a total dose of 56 Kr, administered percutaneously 4-6 wk prior to challenge. Challenge could be delayed for at least 15 wk after immunization without a decrease in resistance. The resistance obtained was not attributable to a delayed migration of challenge worms.

Animals↗

PubMed1980

Cercaria-induced histamine release: a factor in the pathogenesis of schistosome dermatitis?

Cercariae, but not schistosomules, of Schistosoma mansoni are capable of activating the release of histamine from rat peritoneal mast cells in vitro. This activation occurs in the absence of serum and does not require adherence to mast cells. The amount of histamine released is proportional to the number of cercariae present. This mast-cell triggering factor from cercariae remains to be characterized biochemically, but may well play a causal role in the "swimmer's itch" associated with primary schistosome exposure.

Animals↗

PubMed1981

Attempts to transfer the resistance of Schistosoma mansoni-infected and irradiated cercaria-immunized mice by means of parabiosis.

Acquired resistance to Schistosoma mansoni infection was measured in S. mansoni-infected or irradiated cercaria-immunized mice, and in normal mice to which the former had been surgically joined. Such parabiotic partners were shown to freely exchange humoral and cellular blood constituents. There was no detectable transfer of resistance from mice infected for 8, 12, or 28 weeks to their uninfected partners, even if parabiosis was established before the initial infection and maintained to autopsy. In comparison with parabiosed controls, the number of adult worms surviving from a challenge infection was reduced by 51-96% in the previously infected mice but was not significantly reduced in their uninfected partners. In contrast, mice immunized with irradiated cercariae and their nonimmunized parabiotic partners showed similar levels of resistance. These data indicate that the resistance induced in mice by irradiated cercariae can be transferred, confirm that at least under some experimental conditions the resistance induced in mice by a previous S. mansoni infection is not readily transferred, and provide additional evidence that the resistance induced by normal infection and irradiated cercarial immunization differ in some fundamental way.

Animals↗

PubMed1983

Immunization of mice with ultraviolet-irradiated Schistosoma mansoni cercariae: a re-evaluation.

Mice immunized by percutaneous exposure to ultraviolet-irradiated Schistosoma mansoni cercariae developed levels of resistance to subsequent S. mansoni infection comparable to those induced by gamma-irradiated cercariae (50-70% reduction in adult worm burden). Cercariae treated with ultraviolet doses ranging from one to three times the minimum dose required to prevent long-term survival induced the highest levels of resistance.

Animals↗

PubMed1986

Site requirements and kinetics of immune-dependent elimination of intravascularly administered lung stage schistosomula in mice immunized with highly irradiated cercariae of Schistosoma mansoni.

Experiments were performed to compare the migration and survival of 75Se-labeled schistosomes, introduced by percutaneous cercarial exposure or by intravascular administration of 7-day-old lung stage schistosomula, in control and irradiated cercaria-immunized mice. Schistosomula were intravascularly introduced into the lungs, systemic organs and liver by injection via the femoral vein (FV), left ventricle (LV), and superior mesenteric vein (SMV), respectively. The fate of challenge larvae was examined by autoradiography of host tissues and by recovery of adult worms. It was found that both normal and immune elimination were site-dependent. In control mice 45%-60% of cercarial penetrants and lung schistosomula injected into the FV and LV were recoverable as adult worms, while a significantly greater number (70%-85%) were recoverable when lung schistosomula were injected into the SMV. In immunized mice, parasites introduced as either cercariae or FV-injected schistosomula were both highly sensitive to immune elimination. LV-injected schistosomula were also sensitive but to a slightly lesser degree. In contrast, schistosomula placed directly in the liver by SMV injection were totally insensitive to immune elimination. It was concluded that elimination of schistosomula in irradiated cercaria-immunized mice occurs in the lungs and/or in the systemic organs, but not in the liver. Also, it was concluded that immune elimination is not a rapid process, since more than 7 days were required after intravascular challenge for the development of demonstrable differences between control and immunized mice.

Animals↗

PubMed1992

Combined microautoradiographic and histopathologic analysis of the fate of challenge Schistosoma mansoni schistosomula in mice immunized with irradiated cercariae.

Combined microautoradiographic and histopathologic methods were used to locate and examine schistosomula of Schistosoma mansoni in the lungs of irradiated cercaria-immunized mice 21 days after percutaneous challenge infection with 75Se-labeled cercariae. Of 75 schistosomula examined in serial sections, 53% were located in the pulmonary microvasculature, 23% in alveolar spaces, 3% with one end in a vessel and the other in an alveolar space, and the locations of 21% were not identified. Inflammatory reactions of variable intensity were observed around schistosomula in both vascular and alveolar sites, although the most intense category of reactions was associated almost entirely with alveolar larvae. All autoradiographic foci contained recognizable schistosomula. Although the concentration of reduced silver grains precluded cyto-structural analysis, observations on schistosomular contour and shape provided no evidence of larval damage. Our findings suggest that immune elimination of schistosomula in mice immunized with irradiated cercariae is partly or largely effected by a process of alveolar extrusion of viable parasites during their lung migration.

Animals↗

PubMed1999

Blockage of skin invasion by schistosome cercariae by serine protease inhibitors.

Invasion of skin by schistosome cercariae is facilitated by a serine protease secreted from the acetabular cells of cercariae in response to skin lipid. Specific inhibitors of the protease, when applied to human skin in formulations designed to retain the inhibitor on and in the upper stratum corneum layers, block cercarial invasion of human skin. Both peptide-based, irreversible inhibitors and non-peptide, reversible inhibitors block cercarial invasion when applied in a propylene glycol:isopropyl alcohol (3:1) formulation in vitro. Arrest of cercarial invasion could be achieved even after immersion of treated skin in water for 2 hr. Peptide-based irreversible inhibitors in the presence of three different Topicare Delivery Compounds optimized arrest of cercarial invasion. The three Topicare Delivery Compounds applied alone prevented 80-100% of cercarial invasion. With inclusion of the inhibitor, there was 97-100% inhibition in vitro. The optimal formulation with inhibitor was then applied to the tails of BALB/c mice, and the mice were exposed to 120 cercariae by tail immersion. With the carrier lotion alone, there was a 50% reduction in worm burden and a 70% reduction in egg burden. When inhibitor was included, an 80% reduction in worm burden and a 92% reduction in egg burden was observed.

2-Propanol↗

PubMed1999

Production and chronobiology of emergence of the cercariae of Euparyphium albuferensis (Trematoda: Echinostomatidae).

The production and the chronobiology of emergence of the cercariae of Euparyphium albuferensis from Gyraulus chinensis experimentally infected with a single miracidium were established during 28 consecutive days from the first day of cercarial shedding. Moreover, the effect of a sudden change in light-dark cycling was investigated. Although the daily cercarial shedding rates show great variability, a progressive increase in cercarial production was observed in the first weeks of the cercarial shedding periods, probably in relation to the demography of intramolluscan larval stages. Under 12:12 light-dark cycling conditions, E. albuferensis cercariae emerged in the light, and the rhythm was circadian. The sudden change in the light-dark cycle resulted in corresponding alterations in emergence patterns, which shows that cercarial emergence was correlated to light-dark alternation. The ecological consequences of daily emergence by mobile cercariae whose target hosts are organisms that regularly occur in the same habitat with the molluscan emitting host, such as those of E. albuferensis, are discussed with reference to the hypotheses proposed to date, and an alternative hypothesis is proposed.

Animals↗

PubMed1999

Survival and infectivity of Hypoderaeum conoideum and Euparyphium albuferensis cercariae under laboratory conditions.

The survival characteristics of the cercariae of Hypoderaeum conoideum and Euparyphium albuferensis (Trematoda: Echinostomatidae) at 20 degrees C and 30 degrees C are described, and the age dependency of their infectivity at 20 degrees C is studied to determine their respective transmission efficiencies. Cercarial survival was found to be age-dependent and was higher at 20 degrees C. For both cercariae, the maximum life-span was 26 h at 20 degrees C and 16 h at 30 degrees C, and their respective times to 50% mortality were similar at each temperature. Both cercariae seem to be well adapted to transmission in their natural habitat, though cercarial infectivity of H. conoideum was higher than that of E. albuferensis, this being correlated with their prevalences in nature. The age-dependency of cercarial survival may be related to steadily diminishing endogenous energy levels, though the delay in attaining maximum infectivity suggests that other factors not related to energy considerations are involved in the delimitation of the cercarial infective period. However, this latter observation may constitute an adaptative mechanism allowing cercarial dissemination.

Animals↗

PubMed1999

Scanning electron microscopical studies on cercariae and metacercariae of Fasciola gigantica.

The surface topography of Fasciola gigantica cercariae and metacercariae was studied by scanning electron microscopy. The head of F. gigantica cercaria is covered with several small knobs and its tail is provided with two lateral folds, fused ventrally, near the distal end of the tail. The oral sucker is smaller than the ventral one and possesses a characteristic surface structure. The outermost layer (layer I) of the outer cyst wall of the metacercaria is roughened with irregular furrows. The inner surface of the outer cyst wall (layer II) is more homogeneous and nearly smooth. The outermost layer of the inner cyst wall (layer III) is smooth and lacks any furrows or tubercles. The differences between F. gigantica and F. hepatica cercariae and metacercariae are discussed.

Animals↗

PubMed2000

[The protective immunity in mice immunized with FhGST or AsGST against Schistosoma japonicum cercariae].

OBJECTIVE: To study the protective immunity against Schistosoma japonicum (Sj) cercariae challenge in mice immunized with FhGST or AsGST. METHODS: There groups of Kunming mice were immunized three times with rSjGST, FhGST and AsGST, respectively. Then 30 cercariae of Schistosoma japonicum were given per mouse by abdominal skin inoculation. Six weeks later, all mice were killed to collect adult worms, liver, spleen and large intestine for worm count and egg count. RESULTS: The worm burden was reduced by 27.8%-36.4% in the three immune groups compared with the two control groups (P < 0.05). rSj26GST, FhGST and AsGST significantly decreased the number of eggs deposited in the tissues. CONCLUSION: FhGST and AsGST could induce protection against S. japonicum cercariae infection.

Animals↗

PubMed2002

[Construction and characterization of the cDNA library from Schistosoma japonicum cercariae].

OBJECTIVE: To construct a cDNA library from Schistosoma japonicum cercariae. METHODS: Total RNA was extracted from 500,000 S. japonicum cercariae and used to synthesize the double-stranded cDNA and cloned into the TriplEx2 vector using "SMART cDNA Construction Kit". RESULTS: The primary titer of the constructed cDNA library is 1.8 x 10(7) pfu/ml and the titer of amplified library is 2.5 x 10(10) pfu/ml. The average size of inserts is 1.075 kb. The recombinant efficiency is 94.4%. The full length cDNA of S. japonicum TPI and JF-2 genes was successfully amplified from the library. CONCLUSION: A cDNA library of S. japonicum cercariae has been constructed successfully.

Animals↗

PubMed1992

Schistosoma mansoni cercaria and schistosomulum antigens in serodiagnosis of schistosomiasis.

Schistosoma mansoni cercaria and schistosomulum obtained in vitro were used in immunofluorescence (IF) tests and indirect hemagglutination (IHA) tests of 137 study sera, 44 from subjects infected with S. mansoni and 93 from healthy subjects residing outside areas endemic for the disease. The results of these tests were compared with those obtained by testing the same sera using conventional adult worm antigen, and also with the initial clinical and parasitologic diagnoses of the 137 subjects providing the study sera. Regarding sera from acute versus chronic cases, IF testing of the acute sera consistently detected IgA antibodies along with IgM and IgG, the last two being found consistently in chronic sera. Also, the geometric mean of the IgM antibody titers found in the IF tests was higher for acute than for chronic sera. Excluding IF IgA, which was negative for chronic cases, the sensitivity of the other types of tests (IF IgG, IF IgM, and IHA) using cercaria and schistosomulum antigens, both under evaluation, ranged from 0.773 to 0.955, the specificity ranged from 0.957 to 1.000, the efficiency ranged from 0.927 to 0.985, the predictive value of positives ranged from 0.909 to 1.000, and the predictive value of negatives ranged from 0.903 to 0.979. No statistical differences were observed between these results and those obtained with conventional adult worm antigen. This suggests that cercaria and schistosomulum antigens, both of which can be produced more quickly and cheaply than adult worm antigen, could serve as reliable alternatives to adult worm antigen in the serodiagnosis of schistosomiasis mansoni.

Acute Disease↗

PubMed1992

Ultrastructural aspects of intramolluscan developing cercariae of Echinostoma liei.

The ultrastructure of the daughter redia of Echinostoma liei inside their host Biomphalaria alexandrina is described. The tegument consists of one layer, bearing numerous microvilli on its outer surface. Besides, the description of the ultrastructure of the developing cercariae within the daughter rediae is also included in the present study. The young cercariae are covered with a thin nucleated primitive temporary epithelium, which is lost when the true tegument is formed beneath it. The mechanism of spine formation was not apparent, but there is some indication that the spines are associated with a thickened part of the basal membrane of the tegument. Section through these cercariae showed that the tissues lying below the tegument are disposed in consecutive layers, suggestively representing developing muscle tissues.

Animals↗

PubMed2005

Reduction of infectivity of schistosome cercariae by application of cercaricidal oil to water.

Schistosomiasis continues to plague populations living in disease-endemic areas, and exposure to infective cercariae results in more than 200 million cases worldwide. Laboratory experiments were conducted to test whether a cercaricidal film applied directly to the water surface can reduce viability of cercariae. A distillate from inexpensive cedarwood oil enriched for cedrol in a mixed oil fraction was formulated (1:5) with the surfactant Tween 80. When applied to the surface of clean and turbid water in test vessels, the formulation spread across and just below the air-water interface, causing inactivation of Schistosoma mansoni cercariae within minutes. The active ingredient was heat stable and reduced schistosome survival and infectivity by 90% and 99.2%, respectively in a mouse model. The effective dose (13 mug/cm(2)) was dependent on surface area rather than volume of water treated. We conclude that application of the biodegradable formulation to the surface of schistosome-infested waters may be an effective, economical, and safe means of reducing human infections.

Animals↗

PubMed1991

[Scanning electron microscopic observations on Clonorchis sinensis cercariae].

The surface structure of Clonorchis sinensis cercariae was observed under scanning electron microscope. The cercaria was of the parapleuro-lophocercous type. The measurements of the cercariae were as follows: body 137-240 x 62-90 microns, tail 320-470 x 21-34 microns, oral sucker 27-46 x 23-33 microns. The ventral sucker was incompletely developed and much smaller than the oral one. The whole body surface was covered with backward pointing spines. Four horizontal rows of oral spines were found around the mouth opening of the oral sucker. These spines diminished in size with the distance of the rows from the opening and their numbers were 12, 18, 19 and 18 respectively. Transverse and longitudinal plicae formed from tegument were found on the surface of the tail, being in connection with dorsal and ventral fins along posterior half of the tail. Many sensory structures or papillae were observed on the body. They were of three different types: 1) papillae with long or short cilia distributed widely on the body surface and around the mouth opening, the number of papillae with cilia on the body surface being greater than that described by Komiya et al (1940); 2) a few sensory fossa on the tail, measuring 1.0 x 0.6 microns; 3) a few ring-type papillae with knob on the body surface with pore of 0.5 micron in diameter.

Animals↗