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PubMed2004

Description and surface topography of the cercaria of Austrobilharzia sp. (Digenea: Schistosomatidae).

The cercaria of Austrobilharzia sp. from the marine prosobranch gastropod Planaxis sulcatus in Kuwait Bay is described. The surface microtopography and pattern of the tegumentary sensory receptors are examined using scanning electron microscopy. The general microtopography of the surface of the cercaria is similar to that previously observed in cercariae of mammalian schistosomes, although differences are recorded in the types, numbers and distribution of the sensory receptors. The study identified more than 13 types of receptors comprising aciliated, uniciliated and for the first time a multiciliated receptor in a strigeid cercaria. The ciliated receptor types differ in the cilium length and structure of the surrounding collar and tegumentary base. The receptor types are site specific: (1) the aciliated and pitlike on the anterior organ-neck region and ventral sucker; (2) the uniciliated with a long flexible cilium with or without collar or a tegumentary base on the body and tail; and (3) the uniciliated with a short rigid cilium and a robust collar and tegumentary base, and the multiciliated with 6 flexible cilia and a high cylindrical collar on the anterior organ tip. The reported SEM information on the sensory receptors may contribute to elucidating their functional role and to establishing morphological characters for the phylogeny of the family Schistosomatidae.

Animals↗
PubMed2005

Cercariae of a species of Philophthalmus detected in a freshwater snail, Semisulcospira libertina, in Japan.

Cercariae belonging to the genus Philophthalmus (Digenea: Philophthalmidae) were detected in a freshwater snail Semisulcospira libertina collected from Innai Town, Oita Prefecture, Kyusyu, Japan. This is the first record of the cercaria of this genus from East Asia and from Semisulcospira. Daughter rediae and cercariae are briefly described and morphologically compared with similar but unidentified ones reported from Japan. Cercariae were found encysting on the surface of the bottom of the container and metamorphosed into a flask-like metacercaria characteristic of Philophthalmus.

Animals↗
PubMed2002

Diplostomum spathaceum cercariae respond to a unique profile of cues during recognition of their fish host.

During its normal life cycle, Diplostomum spathaceum cercariae attach to and invade fish intermediate hosts. They are also known to attach to various other aquatic animals in response to water currents, touch and carbon dioxide. The purpose of this study was to identify the specific stimuli used by D. spathaceum cercariae to recognise the appropriate fish host. We characterised the host cues which stimulate them to remain on the host (enduring contact) and to penetrate the skin. Cercariae were exposed to animal skin tissues and fish skin surface mucus, their extracts and chemical modifications integrated into agar or offered via membrane filters. Enduring contact was stimulated by hydrophilic extracts Mr<3kDa, which were sensitive to oxidation of carbohydrates. The stimulating cues are probably small molecular carbohydrates, as monosaccharides stimulated enduring contacts, but amino acids, urea, electrolytes and peptides did not. Penetration was stimulated by hydrophilic macromolecules, Mr>30kDa, and by lipids. The hydrophilic stimuli were protease resistant and precipitable with Alcian blue and they were sensitive to alkaline cleavage, to digestion with lysozyme and neuraminidase as well as to oxidation of sialic acids. They were considered to be glycoproteins with O-glycosidically linked carbohydrate chains and bound sialic acids as signal structures. The lipophilic penetration stimuli were contained exclusively in the fatty acid fractions, and the stimulating characteristics of these fatty acids resembled the stimulating penetrations in other cercarial species. Diplostomum spathaceum cercariae respond to a unique profile of cues in their sequence of host-recognition phases. These cues differ from those used in other fish parasites studied to date and underline the diversity of fish recognition strategies.

Animals↗
PubMed1997

Immunization of mice with ultraviolet-attenuated cercariae of Schistosoma mansoni transiently reduces the fecundity of challenge worms.

In the present study cohorts of ICR and BALB/c mice were immunized with u.v.-irradiated cercariae of S. mansoni and challenged 5 weeks later, in parallel with unimmunized control mice, with approximately 100 cercariae. Total worm burdens at 5, 6, 7 and 8 weeks after challenge were significantly reduced by 27-65% in immunized mice. The total number of eggs and the number of eggs/female worm trapped in liver and small intestine were reduced significantly at 6 and 7 weeks post challenge in immunized, as compared to unimmunized mice. Decrease in tissue egg load could be achieved in BALB/c mice passively transferred with spleen cells from u.v.-attenuated cercaria-immunized mice. The proportion of female worms laying eggs in vitro was diminished only in worms recovered from highly resistant mice. The reduction in worm oviposition in immunized mice was no longer apparent at 8 weeks. The data taken together indicate that highly effective immunization of outbred and inbred mice with attenuated cercariae leads to significant, but transient, impairment in challenge worm egg production.

Adoptive Transfer↗
PubMed2002

Effects of cadmium upon longevity of Diplostomum sp. (Trematoda: Diplostomidae) cercariae.

Laboratory experiments were conducted to examine the impact of cadmium (Cd) on survival of Diplostomum sp. cercariae. Freshly emerged cercariae were exposed to Cd solutions at concentrations ranging between 0.2 and 200 microg/l. The mortality patterns and mean survival times (MSTs) of the exposed parasites were determined by the Kaplan-Meier estimator and were compared (Log-Rank test) to corresponding patterns and estimators of the unexposed controls. Cd concentrations >20 microg/l caused statistically significant changes in the mortality pattern of Diplostomum sp. cercariae and reduced MST by at least five hours compared to the control group, where MST was 52 h. The results show that longevity of the free-living Diplostomum sp. cercariae can be reduced by direct exposure to heavy metals. Cd contamination of aquatic habitats thus potentially can have an impact on parasite populations and communities.

Animals↗
PubMed1992

Effect of the organophosphorous insecticide, chlorpyrifos (Dursban), on growth, fecundity and mortality of Biomphalaria alexandrina and on the production of Schistosoma mansoni cercariae in the snail.

Exposure of Biomphalaria alexandrina to sublethal concentrations (0.125, 0.25 and 0.05 ppm) of the organophosphorous insecticide, chlorpyrifos (Dursban), induced a reduction in egg production and egg hatchability. Exposure of Schistosoma mansoni miracidia to the insecticide (60 min, 0.50 ppm) prior to infection of B. alexandrina did not affect the subsequent production of cercariae. However, exposure of S. mansoni-infected snails to the insecticide until day 55, from day 20 to day 62 and from day 35 to 62 following infection resulted in blockage of cercarial shedding. Cercarial shedding commenced in some snails when the treatment stopped. Exposure to the insecticide in concentrations of 0.125 and 0.25 ppm during the first 20 days following infection did not affect the subsequent production of cercariae, but exposure to 0.5 ppm during the first 20 days affected markedly the production of cercariae due to a high snail mortality. The findings indicate that the cercaria is the target stage for the activity of chlorpyrifos on the intramolluscan larval development. It is suggested that S. mansoni cercarial production in B. alexandrina may be a useful system for monitoring the effect of low concentrations of pesticides on the aquatic environment, and that the ability by chemical means to interrupt the cercarial production might be a useful tool in further analyses of important aspects of the snail/parasite relationship.

Animals↗
PubMed1985

The induction of specific immunity against Schistosoma japonicum by exposure of mice to ultraviolet attenuated cercariae.

Mice can be partially protected against Schistosoma japonicum by prior exposure to ultraviolet (UV)-attenuated infections which fail to survive to the adult stage and produce no overt pathology in the host. Optimum resistance was induced by parasites exposed to 40 seconds of UV, significantly lower levels of resistance being stimulated by both shorter and longer exposures. No consistent relationship between the degree of resistance induced and the number of irradiated cercariae given could be demonstrated and equivocal results were obtained when comparing the efficacy of single and multiple vaccinations. Vaccinations with UV-attenuated cercariae given intraperitoneally (i.p.) were as efficacious as those given percutaneously but mice were as or more resistant to challenges given by the i.p. route, the possible reasons are discussed. There was no observed delay in the migration of the challenge, vaccinated mice being as resistant when perfused 6 or 3.5 weeks after challenge. Vaccination was species specific since mice exposed to either UV-attenuated S. japonicum cercariae or gamma-attenuated S. mansoni cercariae were resistant to homologous but not heterologous challenge.

Animals↗
PubMed1985

Changes in the surface antigen profile of Schistosoma mansoni during maturation from cercaria to adult worm.

Antigenic proteins on the surfaces of different developmental stages of Schistosoma mansoni were radio-iodinated by the Iodogen-catalysed method and identified by immunoprecipitation with a panel of antisera. The sera comprised specific immune serum from mice harbouring a chronic schistosome infection or vaccinated with gamma-irradiated cercariae; serum from rabbits immunized with adult schistosome tegumental outer membranes or a partially purified Mr 32 K glycoprotein from adult worm membranes; and a monoclonal antibody recognizing an Mr 20 K antigen on the surface of schistosomula. The Mr 38-32 K glycoproteins were the major antigens identified in surface-labelled cercariae and their probable association with the glycocalyx is discussed. Schistosomula transformed from cercariae either mechanically or by penetration of host skin in vitro, expressed a similar pattern of surface antigens to that identified for cercariae, but low molecular weight antigens of Mr 20, 17 and 15 K were also detected. The Mr 38-32 K glycoproteins, although present on newly transformed schistosomula, were progressively replaced with time, by a single dominant glycoprotein (Mr 32 K) expressing identical epitopes to those on the Mr 38-32 K complex. Moreover, the data confirm that the Mr 32 K glycoprotein persists on the tegument after in vivo maturation and is conserved, together with Mr 20 and 15 K antigens, through to the adult stage. New antigens (Mr 97 and 25 K) were also detected during in vivo maturation and were present in late-stage schistosomes recovered from infected hosts. In addition, the enzyme alkaline phosphatase is expressed on the surfaces of 3-week-old liver worms as a dominant antigen (Mr 65 K); this feature may be related to nutritional and/or physiological processes in the tegument of this metabolically active stage of development.

Alkaline Phosphatase↗
PubMed1990

Schistosoma mansoni and S. japonicum: comparison of levels of ultraviolet irradiation for vaccination of mice with cercariae.

When cercariae of Schistosoma mansoni and of S. japonicum were irradiated with various levels of u.v. light at 254 nm, their development to perfusable worms was reduced to below 1% at about 200 microW min cm-2. Cercariae attenuated with about 300 microW min cm-2 induced partial resistance against an homologous challenge infection in mice. No differences were observed between the two schistosome species when the same treatment was given to the cercariae. Thus the same u.v. dose can confer immunizing ability to cercariae of both S. mansoni and S. japonicum.

Animals↗
PubMed1998

Cercaria-schistosomulum surface transformation of Trichobilharzia szidati and its putative immunological impact.

Schistosome cercariae of the genus Trichobilharzia are the causative agent of swimmers' itch. In order to characterize the changes in parasites during and after the penetration of the host skin, in vitro and in vivo (in ducks and mice) transformations of T. szidati cercariae to schistosomula were performed. Ultrastructural observation revealed that cercariae possess a simple outer tegumental membrane with a thick glycocalyx. As with human schistosomes, the latter structure disappears during transformation and a new double membrane with putative protective function is formed. Our biochemical and immunological observations showed that the carbohydrate-rich glycocalyx of cercariae is readily bound by lectins and antibodies. The in vitro transformation to schistosomula can be detected by enhanced reactivity of 2 lectin probes (PNA and ConA) with the surface. The in vivo-transformed (skin and lung) schistosomula appear to have few surface ligands for the 12 lectin probes being tested. Similarly, the cercarial surface and its remnants on the in vitro-produced schistosomula is recognized by sera from immunized mice and humans with cercarial dermatitis; the tissue schistosomula fail to react with these antibodies. The loss of surface targets as a part of parasite immune evasion within the host is discussed.

Animals↗
PubMed2000

The cercaria of Galactosomum bearupi Pearson, 1973 (Trematoda: Heterophyidae) at Heron and Masthead Islands, Great Barrier Reef, Australia.

Magnacercous cercariae, all morphologically identical but with different coloured tails, were found naturally infecting the intertidal prosobranch gastropod Clypeomorus batillariaeformis Habe & Kosuge (Cerithiidae) at Heron and Masthead Islands. Several species of coral-dwelling fishes were exposed to magnacercous cercariae. Active ingestion by the fish, followed by the complete development of the metacercaria in the optic lobes, occurred in Pomacentrus molluccensis Bleeker, but not in Dascyllus aruanus (L.), where development stopped short after encystment. All cercariae turned out to belong to the same species, Galactosomum bearupi Pearson, 1973. Natural infections of G. bearupi metacercariae were found in eight species of fish at Heron Island: Pomacentrus molluccensis, P. wardi Whitley, P. bankanensis Bleeker, P. flavicauda Whitley, Stegastes cf. fasciolatus (Ogilby), Sillago maculata Quoy & Gaimard, S. cf. ciliata Cuvier and Crenimugil crenilabris (Forsskål). This represents the fourth account of the cercaria of a species of Galactosomum.

Animals↗
PubMed1982

[Distribution of argentophilic structures in two strigeid cercariae, Cotylurus brevis Dubois et Rausch, 1950 and Apatemon (A.) minor Yamaguti, 1933].

Two furcocercariae respectively Colylurus brevis Dubois et Rausch, 1950 from Segmentina nitida and Apatemon (A.) minor Yamaguti, 1933 from Gyraulus acronicus were studied and identified morphologically. Ciliary papillae distribution was studied after staining with silver nitrate solution and compared with that of cercariae known in the same genus. Colylurus brevis was compared to Cotylurus lutzi Basch, 1969 and Cotylurus sp. Kruger, 1978. Apatemon (A.) minor was compared to Apatemon sp. Kruger, 1978, Apatemon graciliformis Szidat, 1928, and Cercaria 1 Richard, 1971. Cercariae of the genus Cotylurus and Apatemon were easily identified from the number and distribution of acetabular papillae: 4 SI + 6 SII in Cotylurus and 3 SI + 3 SII in Apatemon. These characteristics further enabled the identification of a cercaria belonging to the genus Diplostomum since all the carcariae studied in this genus have 3 SI + 6 SII.

Animals↗
PubMed1994

Fasciola hepatica: a study of the shedding of cercariae from Lymnaea truncatula raised under constant conditions of temperature and photoperiod.

Investigations on the shedding of cercariae of Fasciola hepatica were carried out in Lymnaea truncatula in order to verify the existence of a low-frequency periodicity in the numerical distribution of metacercariae per snail and per day when the snails are raised under controlled conditions. Preadult L. truncatula were thus collected in the field, individually exposed to two miracidia, and subsequently raised until their death under constant temperature (20 degrees C) and photoperiod (12 h/12 h diurnal rhythm). The 102 snails shedding parasites produced 24,325 metacercariae of which 5% were floating cysts. The daily production of cercariae was maximal during the first 30 days of the patent period, subsequently decreased until day 114, and ceased on day 124. No infradian-type rhythm was noted in the daily distribution of mean values. The snails shed their cercariae in one to 14 waves; 20.6% and 15.7% of the snails produced their parasites in four and five periods respectively. The authors suggest that the seven-day periodicity found by Audousset et al. (1989) in the daily distribution of cercariae produced by three colonies of L. truncatula raised in seminatural conditions must be attributed only to the influence of environmental factors.

Animals↗
PubMed2001

Genetic variability among cercariae of the Schistosomatidae (Trematoda: Digenea) causing swimmer's itch in Europe.

Ribosomal DNA sequences of the internal transcribed spacer 1 (ITS1) were obtained from schistosome cercariae responsible for swimmer's itch in Europe. Two types of ITS1 (1100 and 1400), which differ by the number of repeated patterns were found among cercariae shedded by Lymnaea ovata and L. auricularia (Lymnaeidae). A phylogenetic analysis of the ITS1 region showed that sequences of each type form two well-defined clades. An adult of Trichobilharzia regenti isolated from the nasal vessels of Anas platyrhynchos (Anatidae) was found to correspond to the cercaria type 1400. The sequencing of several ITS1 clones from a single cercaria of each type, as well as a specific PCR-based test suggested that both ITS1 types do not co-occur within a single individual.

Animals↗
PubMed1987

Two heat-induced proteins are associated with transformation of Schistosoma mansoni cercariae to schistosomula.

Infection with Schistosoma mansoni, a parasitic fluke, is acquired when cercariae found in freshwater bodies at ambient temperature penetrate human skin. In this study the response of S. mansoni cercariae to change in temperature from ambient to that of mammalian hosts was compared to the response of other stages that do not experience such dramatic temperature shifts. In cercariae, temperature increases from 23 degrees C to either 37 degrees C or 42 degrees C primarily induced the synthesis of two proteins unique to this stage, of Mr 60,000 and 58,000. Neither protein could be induced by similar treatment in the other two stages of the parasite found in mammalian hosts. Instead, these stages predominantly synthesized a Mr 70,000 protein that crossreacted with monoclonal and polyclonal antibodies against the Mr 70,000 heat shock protein of Drosophila and chicken. No crossreactive material was detected in cercariae, suggesting that a protein homologous to the highly conserved heat shock protein of Mr 70,000 is absent or induced to very low levels by temperature increase at this stage. The induction of the Mr 60,000 and 58,000 proteins was confined to the initial 3-hr period during cercarial transformation to the schistosomula stage.

Animals↗
PubMed2005

Changes in survival characteristics of Diplostomum spathaceum cercariae emerged from cadmium-exposed Lymnaea stagnalis.

The effect of exposing Lymnaea stagnalis (Gastropoda: Pulmonata), infected with Diplostomum spathaceum (Trematoda: Diplostomatidae), to 100 microg l(-1) cadmium for 7 days on survival characteristics (survival, tail loss, decaudized cercarial life-span) of emerged cercariae was investigated. Exposure of L. stagnalis to cadmium resulted in significantly increased D. spathaceum cercarial survival and an inhibited tail loss compared to controls. The normal parallel relationship which exists over time between decreasing cercarial survival and increasing tail loss in controls was changed in cercariae from cadmium-exposed hosts with an increased proportion of cercarial deaths occurring without tail loss. The decaudized cercarial life-span over the survival period of the cercarial population did not significantly change. However comparisons between individuals decaudized during the initial 24 h time period with those which were decaudized during the final period of cercarial survival showed a significantly altered life span which did not occur in the control population. As a potential indicator of penetration 'fitness' comparisons were also undertaken between control and exposed cercariae decaudized during the initial 24 h time period, which revealed that the decaudized cercarial life-span from the exposed hosts was significantly different from controls. This may have important implications for the ability of cercariae to migrate through the tissues of their target host. The importance and relevance of these results to parasite transmission are discussed.

Animals↗
PubMed2004

Effect of aestivation of Biomphalaria pfeifferi on the survival and infectivity of Schistosoma mansoni cercariae.

Schistosoma mansoni cercariae from post-aestivated Biomphalaria pfeifferi remain motile for 20 hours after release. Thereafter, their activity decreases with age. The difference in mortality rate of cercariae from aestivated and non-aestivated B. pfeifferi studied here proved to be statistically significant (P < 0.05) within the first 10 hours of the experimental period. Results of the percentage recovery of worms from different mouse organs infected with cercariae from aestivated and non-aestivated snails varied. The two main organs infected were the liver and intestine. In conclusion, the penetration, migration and maturation of cercariae into adult worms were not affected by the aestivation of B. pfeifferi.

Animals↗
PubMed1983

Studies on the development of anti-schistosomular surface antibodies by mice exposed to irradiated cercariae, adults and/or eggs of S. mansoni.

Levels of antibody a binding to the schistosomulum surface and b mediating in vitro eosinophil-dependent cytotoxicity of schistosomula were studied and compared to the in vivo levels of resistance to cercarial challenge in mice infected with irradiated cercariae, unirradiated cercariae of single or mixed sex, or injected with eggs. Antibody-binding was assessed by counting the number of IgG-Fc-receptor bearing cells (P388D1 cells) adhering to mechanically-transformed schistosomula. Significant levels of adherence occurred with sera taken from 1--2 weeks following exposure to irradiated cercariae, the level increasing gradually thereafter and being enhanced by repeated exposure. Sera from the bisexual infection showed a dramatic increase in binding activity between weeks 5--8, and with the single sex infections there was a steady rise up to week 10 followed by a sharp rise between weeks 10--12. Weekly injections of eggs produced a steady rise in serum binding activity. Sera taken just before challenge were also tested for their ability to mediate killing of schistosomula by eosinophil-enriched preparations of heterologous rat peritoneal exudate cells in vitro. Significant levels of killing occurred with all sera, but the greatest lethal activity was found in sera from the egg-injected, chronically-infected and 200 male cercariae-infected groups. This ranking did not correlate with in vivo resistance against challenge as assessed by worm recovery, the egg-injected and single sex-infected groups failing to manifest significant resistance.

Animals↗