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PubMed1992

The effects of age, temperature, light quantity and wavelength on the swimming behaviour of the cercariae of Cryptocotyle lingua (Digenea: Heterophyidae).

Laboratory experiments indicated that the active life-span of the cercariae of Cryptocotyle lingua was temperature-dependent. An increase in water temperature and population age both correlated with a tendency for the organisms to become decaudate. The larvae were strongly photoresponsive to lateral light but with time, horizontal swimming rates (HSRs) from release point to light source progressively declined. When measured over a range of light quantities, HSRs peaked at 30 microM/m2/s. HSRs were also influenced by water temperature. A rapid increase occurred up to 15 degrees C after which there was a precipitous decline. HSRs to coloured light were negatively correlated with increasing wavelength. When offered a choice between colours, cercariae favoured the shorter wavelengths. The implications of these responses for successful transmission are discussed.

Animals↗
PubMed1990

The influence of second intermediate host dispersion pattern upon the transmission of cercariae of Echinoparyphium recurvatum (Digenea: Echinostomatidae).

Transmission of cercariae of the echinostome digenean Echinoparyphium recurvatum was observed in experimental populations of the second intermediate host snail Lymnaea peregra. Populations of 100 snails were distributed among plastic mesh cages in an infection arena to produce different patterns of host dispersion. Cercarial transmission was investigated in host populations showing three separate patterns of host dispersion; Ideal Regular, Random and Contagious ('Clumped'). Levels of cercarial transmission in populations showing each type of dispersion pattern were found to be significantly different. The highest rate of cercarial transmission occurred in the contagiously dispersed host population, and the lowest in the randomly dispersed population. Analysis of results from the randomly dispersed population also showed that both the mean percentage prevalence of infection, and also the mean number of cysts recovered per snail, increased significantly with the number of snails per cage. The positive relationship between the mean number of cysts per snail and the number of snails per cage was found to be best described by an exponential function. Chemosensory location of L. peregra snail hosts by E. recurvatum cercariae may provide an explanation for the patterns of cercarial transmission observed.

Animals↗
PubMed1997

The cysteine proteinases of Schistosoma mansoni cercariae.

Based on substrate preferences, cercariae of Schistosoma mansoni were seen to express both cathepsin L and cathepsin B cysteine proteinases, although the former activity was many-fold greater. Two cathepsin L activities identified in cercarial extracts by zymography co-migrated with activities in extracts of 3 h and 24 h schistosomula and in extracts of adult worms. Since these enzymes have been implicated in haemoglobin digestion by adult worms, they may perform a similar function in schistosomula. Immunolocalization using scanning electron micrographs showed that cathepsin L and cathepsin B proteinases were present in the cercarial post-acetabular glands. In addition, cercarial serine proteinase activities considered to facilitate skin penetration efficiently cleaved the substrates Z-Gly-Pro-Arg-NHMec and Z-Gly-Pro-Lys-NHMec. Cercariae release most of this serine proteinase activity when induced to secrete the contents of their acetabular glands. In contrast, newly transformed 3 h and 24 h schistosomula did not express this activity.

Animals↗
PubMed2000

Characterization, cloning and immunogenicity of antigens released by transforming cercariae of Schistosoma mansoni.

A schistosome infection is initiated when the parasite penetrates the skin of a susceptible host. Relatively large quantities of protein are released by transforming cercariae compared to later larval stages. This represents the first parasite material to which the host's immune system is exposed, yet little is known about the proteins which are released during the first few hours post-transformation. We have shown that antiserum raised against such molecules was capable of imparting protection against a schistosome challenge infection upon passive transfer to naïve mice. By screening a cercarial cDNA library with this serum, 38 positive clones were identified. Sequence analysis showed these to represent 8 different molecules which included Schistosoma mansoni 21-7 kDa antigen, calcium-binding-protein and the vaccine candidate glutathione S-transferase (Sm28GST). In addition, 5 clones were isolated, 1 of which had significant homology to many cytochrome C proteins, another with leukocyte elastase inhibitors and 3 which represented novel molecules. Four clones were expressed in a prokaryotic high-level expression vector, sera produced against each purified recombinant protein and used subsequently to probe Western blots and parasite sections. The leukocyte elastase inhibitor homologue and 2 unknowns induced significant proliferation by lymph node cells recovered from mice vaccinated with irradiated cercariae. More strikingly, the 2 novel proteins stimulated very high levels of interferon gamma (IFNgamma) secretion both by lymph node cells and those recovered by broncho-alveolar lavage from the lungs of vaccinated mice. Such results will be discussed in the context of vaccine development.

Amino Acid Sequence↗
PubMed1998

Th1 cytokine mRNA expression dominates in the skin-draining lymph nodes of C57BL/6 mice following vaccination with irradiated Schistosoma mansoni cercariae, but is down-regulated upon challenge infection.

Vaccination of C57BL/6 mice with irradiated cercariae of Schistosoma mansoni results in the induction of high levels of immunity to subsequent infection. The events occurring in the lymph nodes draining the exposure site have been analysed ex vivo by reverse transcription-polymerase chain reaction (RT-PCR) and the timing of cytokine gene expression following exposure has been established. After vaccination, spatial separation of the T-helper type 1 (Th1) and Th2 responses was evident, with interferon-gamma (IFN-gamma), interleukin-2 (IL-2) and IL-12 mRNA peaking earlier than mRNA for IL-4, IL-5 and IL-10. In contrast to the profiles observed post-vaccination, following challenge the IL-4 mRNA was predominant in the draining lymph nodes, with IFN-gamma message levels barely detectable above the naive level. These observations are confirmed by the analysis of IL-4 and IFN-gamma mRNA using competitive PCR. From these studies it is clear that irradiated cercariae are more able to promote a protective Th1 response, with normal parasites eliciting higher IL-4 and IL-5 expression upon both primary and secondary stimulation.

Animals↗
PubMed1996

Homologous and heterologous protective immunity to Egyptian strains of Schistosoma mansoni and S. haematobium induced by ultraviolet-irradiated cercariae.

C57BL/6 and Balb/c mice were immunized with ultraviolet-irradiated cercariae of Egyptian strains of Schistosoma mansoni and S. haematobium, challenged with nonirradiated cercariae of the homologous or heterologous species, and assayed for protection against challenge infection by comparing the adult worm burdens of immunized and non-immunized mice. Homologous protection (per cent reduction in worm recovery) ranged from 56% to 69% for S. mansoni and 88% to 99% for S. haematobium. Significant heterologous protection was consistently induced against S. haematobium by immunization with S. mansoni, but not against S. mansoni by immunization with S. haematobium. These results are discussed in relation to those of previous studies and in terms of implications for vaccine development.

Animals↗
PubMed2001

Protective immunity to Schistosoma japonicum infection depends on the balance of T helper cytokine responses in mice vaccinated with gamma-irradiated cercariae.

Although the strain difference in protection of mice to Schistosoma mansoni infection has been described, limited information is available in the case of Schistosoma japonicum. In the present study, we compared the protective immunity to S. japonicum infection and cytokine production in various strains of mice vaccinated with gamma-irradiated cercariae. A significant reduction in worm recovery was observed in male and female mice of DBA/2 at a 6-week interval between vaccination and a challenge infection, whereas vaccinated mice of C57BL/6, C57BL/10, (C57BL/6 x DBA/2) F1 (B6D2F1) and (C57BL/10 x DBA/2) F1 (B10D2F1) showed no detectable level of protection. No sex-linked difference in development of resistance was observed in any of the strains so far examined. Vaccination with gamma-irradiated cercariae twice with a 3-week interval also induced significant protection against a challenge infection in DBA/2 but not in BALB/c or C57BL/6 strains. Further studies demonstrated that spleen cells of vaccinated C57BL/6 mice produced lower levels of IFN-gamma compared to the cells of vaccinated BALB/c and DBA/2. On the other hand, production of IL-10 by spleen cells was relatively higher in BALB/c mice than in the other two strains. Macrophages that had been stimulated with spleen cell culture supernatants derived from vaccinated DBA/2 damaged schistosomula more effectively than cells stimulated with supernatants derived from the other strains. These results suggest that different levels of protection observed among strains of mice depend on the balance of cytokine responses which consequently activate or suppress macrophage-mediated damage to schistosomula.

Animals↗
PubMed1981

[Argyrophilic integumentary structures of the miracidium, redia and cercaria of Paramphistmun daubneyi Dinnik, 1962 (Trematoda, Paramphistomidae)].

Paramphistomum microbothrium and P daubneyi are two sibling-species. The value of morphological criteria which have been used to distinguish the adults is not accepted by all authors. On the contrary, criteria based upon larval stages, except miracidia, permit an easy diagnosis. P. microbothrium parasitizes Bulinids, the rediae have a long intestine, germ-balls are inequal in size, cercariae are long-tailed and possess numerous lateral somatic bristles: about 9 by a half-body and numerous caudal bristles: about 17 pairs. P. daubneyi parasitizes Lymneids, the rediae have a short intestine, germ-balls are of equal size, cercariae are short-tailed and posses few lateral somatic bristles (about 4 by a half-body) and relatively few caudal bristles: about 6 pairs. In addition to the cercaviae, argentophilic structures of miracidia and rediae of P. daubneyi are described.

Animals↗
PubMed1985

[Survey on Schistosomes of man and livestock in Senegal using specific identification given by chetotaxy of cercaria. I. New arguments for the validation of S. curassoni Brumpt, 1931, parasite of man and domestic Bovidae].

Study of Senegal cercariae emitted by naturally infected snails or by snails experimentally infected using eggs from human urine or from sheep liver, and study of the corresponding eggs. The relative position of the dorsal sensillae of cercariae is described by an "AD index" and the ratio length/width of eggs by an "L/l index." At the present time, we have not finished the epidemiological studies, certain experiments are imperfect and the isoenzyme analysis of the corresponding adults is incomplete. Nevertheless information given by the indices AD and L/l agree and lead us to admit the existence of a Schistosome different to mattheei, haematobium and bovis and which, following Brumpt and Gretillat we refer to as Schistosoma curassoni. If one relies on the indices, the study indicates that: a) S. mattheei has not been found in Senegal, b) S. bovis is quite rare, c) S. haematobium apparently exists in pure infections in Casamance and in mixed infections with S. curassoni in man in the north and in the east, d) S. curassoni is apparently the dominant species in domestic ruminants and in man in the north and in the east, e) Bulinus umbilicatus is the principal vector of S. curassoni and S. haematobium.

Animals↗
PubMed1987

[Chaetotaxy of the cercaria of Paramphistomum sp., a parasite of cattle in Vendée].

The cercaria was shed by an Anisus rotundatus experimentally infected with a parasite of Bos taurus in Vendée (France). This Trematode was identified as Paramphistomum cervi. The snail natural host is unknown. The chaetotaxy of the cercaria differs from that of other European species of Paramphistomum and particularly from P. leydeni and P. daubneyi both species which occur in Vendée. The morphology of the adult precludes any relationship with P. ichikawai also present in Vendée. Therefore it very likely represents a species which was synonymised with P. cervi or a new species.

Animals↗
PubMed1992

Larval stages of medically important flukes (Trematoda) from Vientiane province, Laos. Part II. Cercariae.

The cercariae of five flukes, which are potential human parasites, Opisthorchis viverrini (family Opisthorchiidae), Haplorchis taichui (Heterophyidae), Schistosoma spindale (Schistosomatidae), Fasciolopsis buski, and Fasciola gigantica (Fasciolidae) were found in freshwater snails from Laos. The cercariae of the above species, recorded in Laos for the first time, are illustrated and their morphology is briefly described. The snail Helicorbis umbilicalis represents a new intermediate host of F. buski. The occurrence of medically important snails in the Vientiane province will also be discussed.

Animals↗
PubMed2006

Identification of novel proteases and immunomodulators in the secretions of schistosome cercariae that facilitate host entry.

Schistosomiasis, caused by parasitic helminths, remains a serious human disease in the tropics. Cercariae of Schistosoma mansoni infect their hosts by direct skin penetration, aided by secretions from acetabular and head glands. Both proteolytic and immunomodulatory properties have been ascribed to the released material, but to date only five isoforms of elastase and one putative anti-inflammatory protein (Sm16) have been cloned. We analyzed secretions from mechanically transformed cercariae by two-dimensional electrophoresis. An average gel image was created and compared with a separation of soluble larval extract, revealing a less complex spot pattern in the secretions with 60% of the spots matched to the larval extract. Subsequent tandem mass spectrometric analysis identified 48 spots from the released material, representing approximately 80% of its normalized volume. Twenty-nine of these are likely to originate in the vesicles, and 18 are likely to originate in the cytosol of the glands (the latter class being present due to holocrine secretion); one is unknown. The vesicular proteins were significantly more enriched than the cytosolic proteins in the released material when compared with the larval extract. A novel metalloproteinase (termed SmPepM8) was the second most abundant constituent after three isoforms of cercarial elastase. In addition, a dipeptidyl peptidase IV (SmDPP IV) was discovered but in much smaller quantity. A new serine protease inhibitor (SmSerp_c) was also prominent. Along with Sm16, four potential immunomodulators were identified, three with similarity to venom allergens (SmSCP_a, _b, and _c) and one with homology to the potassium channel blockers in scorpion venom (SmKK7). Interrogation of the expressed sequence tag database found transcripts encoding the majority of vesicular proteins present solely in the intramolluscan stages of the life cycle. Distinct patterns of radiolabel incorporation suggested three separate origins for the vesicular proteins. All the novel constituents merit investigation as vaccine candidates, and the potential immunomodulators merit investigation as therapeutic agents.

Amino Acid Sequence↗
PubMed2004

Influence of cadmium exposure on the incidence of first intermediate host encystment by Echinoparyphium recurvatum cercariae in Lymnaea peregra.

The effect of cadmium exposure of the snail first intermediate host Lymnaea peregra on the incidence of encystment of Echinoparyphium recurvatum (Digenea: Echinostomatidae) cercariae without emergence from the snail was investigated. Exposure to 100 microg l(-1) Cd for 72 h caused a significant increase in the incidence of first host encystment when compared to controls. In addition, autometallographic staining of E. recurvatum daughter rediae and developing cercariae showed that there was metal accumulation within their body tissues. The significance of these findings to parasite transmission in metal-polluted environments is discussed.

Animals↗
PubMed1998

Identification of an alpha3-fucosyltransferase and a novel alpha2-fucosyltransferase activity in cercariae of the schistosome Trichobilharzia ocellata: biosynthesis of the Fucalpha1-->2Fucalpha1-->3[Gal(NAc)beta1-->4]GlcNAc sequence.

Fucose is a major constituent of the protein- and lipid-linked glycans of the various life-cycle stages of schistosomes. These fucosylated glycans are highly antigenic and seem to play a role in the pathology of schistosomiasis. In this article we describe the identification and characterization of two fucosyltransferases (FucTs) in cercariae of the avian schistosome Trichobilharzia ocellata, a GDP-Fuc:[Galbeta1-->4]GlcNAcbeta-R alpha1-->3-FucT and a novel GDP-Fuc:Fucalpha-R alpha1-->2-FucT. Triton X-100 extracts of cercariae were assayed for FucT activity using a variety of acceptor substrates. Type 1 chain (Galbeta1-->3GlcNAc) based compounds were poor acceptors, whereas those based on a type 2 chain (Galbeta1-->4GlcNAc), whether alpha2'-fucosylated, alpha3'-sialylated, or unsubstituted, and whether present as oligosaccharide or contained in a glycopeptide or glycoprotein, all served as acceptor substrates. In this respect the schistosomal alpha3-FucT resembles human FucT V and VI rather than other known FucTs. N-ethylmaleimide, an inhibitor of several human FucTs, had no effect on the activity of the schistosomal alpha3-FucT, whereas GDP-beta-S was strongly inhibitory. Large scale incubations were carried out with Galbeta1-->4GlcNAc, GalNAcbeta1-->4GlcNAcbeta-O -(CH2)8COOCH3 and Fucalpha1-->3GlcNAcbeta1-->2Man as acceptor substrates and the products of the incubations were isolated using a sequence of chromatographic techniques. By methylation analysis and 2D-TOCSY and ROESY1H-NMR spectroscopy the products formed were shown to be Galbeta1-->4[Fucalpha1-->2Fucalpha1-->3]GlcNAc, GalNAcbeta1-->4[Fucalpha1-->2Fucalpha1-->3]GlcNAcbe ta-O-(CH2)8COOCH3, and Fucalpha1-->2Fucalpha1-->3GlcNAcbeta1-->2Man, respectively. It is concluded that the alpha2-FucT and alpha3-FucT are involved in the biosynthesis of the (oligomeric) Lewisx sequences and the Fucalpha1-->2Fucalpha1-->3GlcNAc structural element that have been described on schistosomal glycoconjugates.

Animals↗
PubMed1984

Mechanisms of protective immunity against S. mansoni infection in mice vaccinated with irradiated cercariae. VI. Influence of the major histocompatibility complex.

Inbred mouse strains develop different levels of resistance to challenge infection with Schistosoma mansoni in response to vaccination with irradiated cercariae. The role of the major histocompatibility complex (MHC) in determining this genetic polymorphism in acquired resistance was investigated. Previous studies suggested that inbred mice bearing either the b or d MHC haplotypes develop a higher level of vaccine induced resistance than do mice with other MHC haplotypes. An analysis of an F1 cross between an H-2b strain (C57BL/6) and an H-2k strain (C3H/HeJ) indicated that the ability to develop high levels of immunity is inherited in a dominant fashion. In order to confirm that the development of high resistance is an MHC associated trait, B10, C3H, BALB and B6 congenic mice bearing different H-2 haplotypes were compared. On either the B10, B6, or BALB background, substitution of b or d with k or a MHC alleles resulted in a decreased level of vaccine induced immunity. The observed decreases were more pronounced in BALB and B6 than in B10 congenics suggesting an influence of background (non-MHC linked) genes on protective immunity. Similarly, C3H.SW (H-2b) mice developed a significantly higher level of acquired resistance than C3H/HeSn (H-2k) mice. Cross and backcross experiments between H-2b and H-2k B6 congenic mice confirmed the dominant inheritance of high resistance as well as the MHC linkage of the trait. These data indicate that the MHC locus exerts a quantitative influence on vaccine induced resistance in certain inbred mouse strains and provide further support for the concept that the protection elicited by irradiated cercariae is the manifestation of a specific host immune response.

Alleles↗
PubMed1989

Variable species and stage specificity of schistosomulum surface epitopes recognized by mice vaccinated with highly irradiated cercariae.

Antibodies from mice vaccinated with highly irradiated Schistosoma mansoni or S. haematobium cercariae were used to characterize schistosomulum surface epitopes which were found to be diverse in their species and stage specificities. The epitopes recognized on the Mr greater than 200,000 and 15,000 schistosomulum surface antigens of S. mansoni and the Mr greater than 200,000 schistosomulum surface antigen of S. haematobium were found to be cross-specific whereas those on the Mr 38,000, 32,000 and 20,000 schistosomulum surface antigens of S. mansoni and the Mr 35,000, 30,000 and 24,000 schistosomulum surface antigens of S. haematobium were only immunoprecipitated by homologous antibody and are thus possible targets of the protective species-specific immunity stimulated by highly irradiated cercariae. The epitopes recognized on the Mr greater than 200,000 and 38,000 antigens of S. mansoni were shown to cross-react with both the egg and the adult worm whereas those on the Mr 32,000 and 20,000 antigens only cross-reacted with the adult worm, and those on the Mr 15,000 antigen cross-reacted with neither the adult worm nor the egg. In addition the epitopes on the Mr 38,000 and 32,000 antigens were demonstrated to be polypeptide in nature. Those on the Mr greater than 200,000, 20,000 and 15,000 antigens, on the other hand, could not be conclusively defined.

Animals↗