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PubMed1977

[Cercaria ogunis n. sp. (echinostomatidae) from Bulinus globosus in West Africa (author's transl)].

Cercaria ogunis n. sp. (Echinostomatidae) is described. The cercaria has 47 collar spines, 2 X 15 flame cells, a small dorsal and a small ventral finfold near the tip of the tail. A peculiar organ located dorsally next to the brain is explained, hypothetically, as a statocyst. In the behaviour of the cercaria there are some conspicuous features, i.e. a rapid swimming-velocity, a striking positive geotaxis and a positive phototaxis. Second intermediate hosts are gastropods and amphibians. The metacercarial cysts exist in two distinct modifications: Cysts from Bulinus are globular, cysts from amphibians are elongated-ellipsoid. The Bulinus population of the habitat shows at the same time a high prevalence of Schistosoma haematobium. C. ogunis has never been observed as being involved in double infections. This seems to suggest that the rediae of this species are incompatible with other trematodes in the snail.

Africa, Western↗
PubMed1979

[Sequence of reconversion of the sporocysts of Schistosoma mansoni producing cercariae, to the production of new generations of sporocysts (author's transl)].

During the life cycle of Schistosoma mansoni the production of sporocysts of a higher order than secondary is a normal mode of larval multiplication which intervenes in asexual reproduction of the parasite. The sequence of reconversion of sporocysts producing cercariae to those producing sporocysts III, IV, etc... can be divided into three principal steps: (1) cessation of cercariae production; (2) degeneration of cercariae contained in the sporocyst, and (3) production of the new generation of sporocysts. Degeneration of intrasporocystic larval material seems to be an indispensable step for the new orientation of production. The signifance of this method os multiplication in the ecology of transmission is discussed.

Animals↗
PubMed1995

An immunocytochemistry study comparing the occurrence of neuroactive substances in the nervous system of cercariae and metacercariae of the eye fluke Diplostomum spathaceum.

The nervous system of two larval stages (cercariae, metacercariae) of eye fluke Diplostomum spathaceum was investigated immunocytochemically by the application of antisera to the amino acid glutamate and to neuropeptides isolated from invertebrates (Mollusca) and from vertebrates to whole-mount preparations. In cercariae, positive immunoreactivity (IR) was observed with antisera raised against Catch-relaxing peptide (CARP), FMRFamide, alpha-caudodorsal cell peptide (alpha-CDCP), substance P, vasotocin, and vasopressin. In metacercariae, in addition to positive staining with these antisera, the ones raised against glutamate, APGWamide, caudodorsal cell hormone I (CDCH-I), and small cardiac peptide B (SCPB) also gave positive IR in the nervous system. In the two larval stages the most extensive pattern of IR was observed with anti-FMRFamide and anti-CARP. In the nervous system of metacercariae the same immunoreactive neurosubstances appeared to be present as in that of cercariae. The increase in the variety of immunoreactive neurosubstances in the more complex nervous system of metacercariae is discussed in relation to parasite development and to host adaptation.

Animals↗
PubMed1993

Immunizing potential of ultraviolet-attenuated cercariae of Schistosoma mansoni in rodent hosts.

Schistosoma mansoni cercariae attenuated with ultraviolet (UV) irradiation (254 nm) at a dose of 18 mJ/cm2 induced partial resistance against a homologous challenge in male ICR mice and male Hartley guinea pigs. The reduction in the adult worm burden was 51% and 37% +/- 13%, respectively. On the other hand, male and female Mongolian gerbils (Meriones unguiculatus) vaccinated with UV-attenuated cercariae exhibited marginal resistance (13% +/- 9% and 22% +/- 10%, respectively). This raises the possibility that gerbils might have an unknown immune-characteristic nature. The usefulness of UV-attenuated cercariae is discussed with respect to the control of the disease.

Animals↗
PubMed2003

Ultrastructure of pigmented and unpigmented photoreceptors in cercariae of Trichobilharzia ocellata (Plathelminthes, Trematoda, Schistosomatidae): evidence for the evolution of parasitism in Neodermata.

The lens-covered pigment cup ocelli in free-swimming cercariae of Trichobilharzia ocellata were re-examined and the differentiation of the lenticular elements was studied in cercariae still enclosed in sporocysts. Each eye consists of a single rhabdomeric sensory cell, a single cup cell harboring pigment granules and the lens. This lens is developed step by step by the fusion of numerous dark platelets not enclosed by a bordering membrane. The material is presumably proteinaceous. There is no evidence that the lenses are of mitochondrial origin. Besides the pigment cup ocelli, a special type of unpigmented rhabdomeric photoreceptor was discovered. Three unicellular photoreceptors arranged in a three-dimensional configuration exist. These light-sensing organs show a principle of construction similar to that of phaosomous photoreceptors. We hypothesize that both types of photoreceptors are relevant for distinct reactions in the host-finding behaviour of the cercariae. The special type of lensing in the pigmented eyes seems to be restricted to Trichobilharzia species, whereas the phaosomous-like receptors may be more widespread in members of the Schistosomatidae. The obvious absence of any mitochondrial lensing in T. ocellata, and probably all other species of the Digenea, may be correlated with the evolution of endoparasitism in the Trematoda.

Animals↗
PubMed2005

Three-dimensional reconstruction of the distribution of flame cells in a trematode cercaria.

In order to reveal the vertical distribution of flame cells in a trematode cercaria, horizontal serial semi-thin sections were reconstructed by an image analyzer and a manual procedure. The ascending main excretory tubes extended forward, meandering up and down at the digestive system level from the excretory bladder. At the posterior end of the ventral sucker, they curved dorsally, passed through the dorsal side, returning to the mid level at the anterior end of the ventral sucker. They then ran forward to the posterior part of the oral sucker, and turned back. The flame cells were more abundant in the ventral region than in the dorsal region. The majority of pairs of right and left flame cells were present at the same distance from the digestive system or ventral (or dorsal) surface. This method, using conventional techniques, has some advantages for determining the horizontal and vertical distributions of flame cells in cercaria and may, therefore, promote research on cercaria.

Animals↗
PubMed2001

Recognition of cattle skin by cercariae of Orientobilharzia turkestanica.

The cercariae of Orientobilharzia turkestanica attached to isolated cattle skin and penetrated it. The attachment was stimulated by warmth and by hydrophilic and lipophilic chemical cues of skin surface extracts. The enduring contact with the skin was also stimulated by the chemical cues, but not by warmth. Penetration of the cercariae into agar substrates was triggered by skin surface lipids, and free fatty acids were identified as the exclusively active compounds of the lipids. That the cercariae attach and remain on the skin by responding to at least two different chemical host cues is unique among the schistosomatids studied so far. It might reflect an adaptation to invade the hosts in clear water or near the water surface where chemical mud compounds will not interfere with host recognition.

Animals↗
PubMed1997

Chaetotaxy and armature of Ichthyocotylurus erraticus (Rudolphi, 1809) and I. variegatus (Creplin, 1825) cercariae (Digenea, Strigeidae).

The armature and chaetotaxy of Ichthyocotylurus erraticus (Rudolphi 1809) and I. variegatus (Creplin 1825) cercariae were studied using scanning electron microscopy (SEM) and silver staining of the argentophilic sensilla. This represents the first detailed investigation of the surface structures of cercariae belonging to this genus. Both species exhibited a similar armature, although differences were recorded in the number of spines comprising the pre-oral tuft and the number of rows of spines in the post-oral collar. The number and the distribution of sensilla were found to be identical for both species of cercariae. Four types of sensilla, common to both species, were identified that differed in cilia length and in the structure of the surrounding collar. The distribution of particular sensillary forms was found to be consistent in both species.

Animals↗
PubMed1989

Schistosoma mansoni: increasing saline concentration signals cercariae to transform to schistosomula.

Cercariae of S. mansoni shed the surface glycocalyx, form a double lipid bilayer on their surface, and transform to schistosomula when tails are removed and parasites are transferred from pond water to 300 mOsm phosphate-buffered saline. To determine whether the absolute concentration of saline or the relative change in saline concentration was the signal for surface transformation, cercariae were isolated from the snail hepatopancreas, sheared to remove the tails, and incubated in defined media for 3 hr at 37 degrees C. Surface transformation was assayed using the binding of the fluorescein-conjugated lectin concanavalin A to the schistosomular double unit membrane but not to the cercarial glycocalyx. An increase in salinity either from 18 mOsm (artificial pond water) to 120 mOsm (the snail osmolarity) or from 120 to 300 mOsm (the mammalian osmolarity) triggered transformation to schistosomula. Organisms constantly exposed to 120 mOsm or shifted from 120 mOsm to pond water did not transform their surfaces. The signal for transformation appeared to be increasing salinity rather than increasing osmolarity because cercarial bodies did not become schistosomula in 300 mOsm mannitol. Surface transformation was inhibited when cercariae were incubated with the acetylcholinesterase inhibitor eserine sulfate during a 10 min time when the osmolarity was raised. We conclude that increasing salinity rather than the absolute saline concentration is the signal for surface transformation and that eserine sulfate may inhibit the receipt of this signal.

Animals↗
PubMed1991

Schistosoma mansoni: protein phosphorylation during transformation of cercariae to schistosomula.

Infectivity of the multicellular pathogen Schistosoma mansoni for the human host is dependent upon the ability of free-living cercariae to transform rapidly into parasitic schistosomula. The biochemical pathways that regulate this transitional period are unknown. The role of protein phosphorylation was investigated by examining the incorporation of [32Pi]phosphate into proteins of S. mansoni. A sevenfold increase in total phosphorylation was found in 3-hr-old schistosomula as compared to cercariae. Analysis of radiolabeled proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography demonstrated that a 14-kDa protein served as a marker for transformation, being phosphorylated in schistosomula but not cercariae. The protein was phosphorylated on a serine residue. Phosphorylation was stimulated by a shift of parasites from water to salt-containing medium at 23 degrees C. Incubation of organisms in water at 37 degrees C did not initiate phosphorylation of this protein. The 14-kDa phosphoprotein was extracted from parasite homogenates with 1 M NaCl but was insoluble in 1% Triton X-100. Protein phosphorylation during the cercarial-schistosomula transformation may represent an important biochemical event that regulates infectivity of the parasite for the human host.

Animals↗
PubMed1993

Expression of Schistosoma mansoni genes involved in anaerobic and oxidative glucose metabolism during the cercaria to adult transformation.

Schistosomes switch rapidly from the use of stored glycogen to a reliance on host glucose during the transformation from free-living cercariae to parasitic schistosomula. We have cloned a set of cDNAs encoding proteins involved in glucose metabolism to allow us to examine the expression of these genes during this transformation. We first obtained and characterized Schistosoma mansoni cDNA clones encoding the tricarboxylic acid cycle enzyme, mitochondrial malate dehydrogenase (SMDH) and the mitochondrial encoded electron transport protein, cytochrome oxidase subunit 1 (SCOX1). Northern blots were then prepared using mRNA isolated from whole cercariae, cercarial tails, schistosomula, adult males and adult females. The Northern blots were successively hybridized with a variety of probes including those for SMDH, SCOX, the glycolytic enzymes, hexokinase, triosephosphate isomerase and glyceraldehyde-3-phosphate dehydrogenase and several control probes. Probes were additionally hybridized to mRNA dot blots and the signals were quantified using storage phosphor technology. These studies reveal that transcripts encoding these metabolic enzymes are localized at much higher levels in cercarial tails than in whole cercariae or transformed schistosomula, and support the notion of a dominant aerobic metabolism in tails. Male and female adult worms express each of the mRNAs at roughly equal levels. Adults express the metabolic mRNAs, including those involved in oxidative glucose metabolism, at relatively high levels suggesting that adult schistosomes retain a significant capacity to produce energy through aerobic metabolism.

Amino Acid Sequence↗
PubMed2002

Expressed sequence tag (EST) analysis of a Schistosoma japonicum cercariae cDNA library.

Expressed sequence tags (ESTs) constitute a rapid and informative strategy for studying gene-expression profiles of specific stages of schistosomes. To date, only approximately equal 2000 ESTs of Schistosoma japonicum have been deposited in databases. This is insufficient to understand the biology and development of this species. In this report, a cDNA library constructed from S. japonicum cercariae RNA was used to generate ESTs. Cercariae are the larval forms of Schistosoma responsible for infection of the vertebrate host and one of the main objectives of this research was to discover and characterize new and unique genes from this stage. The expression products of those stage-specific genes can potentially be useful as new drugs or vaccine targets applicable for controlling Asian schistosomiasis. In our study, 101 cDNA clones were sequenced either from 5' or 3' end of the cDNAs. Some 42 ESTs (42%) matched known genes, while 59 ESTs did not match with any known genes. Among the 42 former ESTs, 29 (informative ESTs) matched to functional genes and 13 matched with ribosomal proteins or RNA genes. Among the latter 59 ESTs, 21 matched with published ESTs of S. japonicum or S. mansoni, two matched with human ESTs and the other 18 did not match with any published sequences. The informative ESTs could be grouped into nine categories: regulatory and signaling proteins (24.1%), transcription and translation machinery proteins (13.8%), RNA binding proteins (6.9%), structural and cytoskeletal proteins (6.9%), DNA binding proteins (3.4%), DNA scaffold proteins (3.4%), transporter proteins (3.4%) and others (31%). Some functional genes relevant to the physiology of cercariae are discussed.

Animals↗
PubMed2000

Induction cues for tegument formation during the transformation of Schistosoma mansoni cercariae.

Adult schistosomes are parasitic blood flukes that have a continuous double lipid bilayered membrane surrounding the entire worm. This tegumental membrane is synthesised during invasion of the vertebrate host by free-swimming infectious forms called cercariae. As cercariae invade their final hosts they lose their tails and encounter a changing environment that includes altered temperature, sugar concentration and osmolarity. We have identified a glucose transporter protein designated SGTP4 that is found exclusively in the outer adult tegument and on membranous vesicles within the tegumental cytoplasm. By using immunofluorescence analysis to monitor the appearance and distribution of SGTP4 we can track the process of new tegumental membrane formation and examine the cues that trigger this developmental pathway. Cercariae in water do not transform their tegument while those incubated in rich medium do so rapidly. We have examined which of the many constituents of rich medium are responsible for triggering this transformation. Incubation in a solution of moderate osmolarity (120 mOsM PBS) is sufficient by itself to trigger tegument transformation, albeit at a slower rate relative to incubation in rich medium. Adding either glucose (to 100 mM) to the solution or increasing the temperature of incubation (from 22 degrees C to 37 degrees C) further increased the rate of tegument biogenesis. The introduction of glucose together with an increase in the incubation temperature further accelerated the process, suggesting that these factors act synergistically to promote transformation rates. The critical nature of osmolarity in inducing the process is highlighted by the fact that transformation proceeds as efficiently in 360 mOsM alone as it does in rich medium. While the fatty acids linolenic acid (cis-9, cis-12, cis-15-octadecatrienoic acid at 1 mM) and capric acid (Decanoic acid, at 0.1 mM) have both been proposed to stimulate tegumental transformation, we show that neither promotes the morphogenesis of a normal schistosomulum tegument. The schistosomicide praziquantel (to 1 mM) has no detectable effect on new tegument formation.

Animals↗
PubMed1997

Metacercarial encystment and in vivo cultivation of Cercaria lebouri Stunkard 1932 (Digenea: Notocotylidae) to adults identified as Paramonostomum chabaudi Van Strydonck 1965.

Cercariae found occurring in naturally infected gastropod molluscs, Littorina littorea, were identified as Cercaria lebouri Stunkard 1932. They were induced to form metacercarial cysts on the surface of glass Petri dishes. Each cercaria became attached by its oral sucker and adopted a disc-like shape before discarding its tail. A transparent cyst wall was secreted over and around each organism, inside which developmental changes were observed for up to 4 weeks. Six-week-old metacercariae were fed to 1-day-old chickens which yielded adult worms 12 days later. The worms were measured, photographed and described. Initially, attempts to identify the adult worms using a key and catalogue proved ineffective. However, comparison of the adult flukes grown from C. lebouri with the definitive description of Paramonostomum chabaudi van Strydonck 1965 indicated that the two organisms are synonymous. The larval stages of P. chabaudi had not, until now, been identified.

Animals↗
PubMed2002

Detection of Neorickettsia (Ehrlichia) risticii in tissues of mice experimentally infected with cercariae of trematodes by in situ hybridization.

Neorickettsia (Ehrlichia) risticii was demonstrated to occur in cercariae developing in Juga yrekaensis snails by experimental transmission, genetic detection and histopathology. Cercariae were isolated from the digestive glands of snails collected in a fresh stream water area of Siskiyou County, CA, and inoculated into CF1 mice. Mice developed clinical signs, splenomegaly and histopathologic abnormalities. The agent was maintained by serial passages of whole blood in CF1 mice. A 527-bp product of the 16S rRNA gene of N. risticii was serially detected by nested PCR in blood, feces, salivary gland, suprarenal gland, spleen, intestine and bone marrow of inoculated mice. N. risticii DNA was detected by in situ hybridization with DIG-labeled probe in PCR-positive salivary gland, intestine and spleen tissue sections of experimental mice on day 30 after inoculation. Infection in mice was established when cercariae were inoculated by either IP or SC routes but not established following intraoral route. N. risticii was detected by PCR in spleen, intestine and bone marrow even after 73 days post-inoculation whereas blood from the same animals became negative at 58 days. N. risticii was observed by in situ hybridization in salivary gland, spleen and intestine of mice infected by IP or SC inoculation. This ISH protocol should aid investigations on the host range of the Neorickettsiosis and pathogenesis of neorickettiosis in vector, animal or human.

Animals↗
PubMed2002

Ultrastructure of the Schistosoma mansoni cercaria.

The cercaria of the schistosome parasite is a short-lived, free-swimming larval stage that is infective for the mammalian, definitive host. This atlas describes the ultrastructure of the cells that comprise the cercaria of Schistosoma mansoni, a leading causative agent of human schistosomiasis. In addition to the cells which make up the various organ systems, such as the nervous, tegumental, osmoregulatory, muscular and primordial digestive systems, also we show the ultrastructure of those cells whose organization or location are not as well defined structurally but are essential nevertheless for the success of the parasite. These latter include the various support cells, and those cells that, upon differentiation into the adult worm, serve reproductive functions. A description is also given of the cells whose sole functions are realized only at the cercarial stage, chiefly involved in the vigorous act of skin penetration. Although we include a detailed review of the ultrastructure of S. mansoni cercariae, much of the information reported has not been previously published. In summary, this paper brings together an ultrastructural description of all the cell types presently known that make up the much studied larval stage of this medically important trematode.

Animals↗
PubMed2000

Neutral lipids in cercariae, encysted metacercariae, and rediae of Echinostoma caproni.

High performance thin-layer chromatography (HPTLC) was used to analyse the neutral lipids in the rediae, cercariae, and encysted metacercariae of Echinostoma caproni from Biomphalaria glabrata snails. Visual observations of the chromatograms showed that the most abundant lipid fraction in all stages was free sterol. Quantification of the free sterol revealed mean weights of 2.7 +/- 0.64 ng per redia, 0.53 +/- 0.023 ng per cercaria, and 0.081 +/- 0.0098 ng per encysted metacercaria. Oil Red O staining of the larval stages confirmed the presence of lipids within the rediae and cercariae but did not show lipids in the encysted metacercariae. The dimunition in neutral lipids from the cercarial to the encysted metacercarial stage does not support a previous observation that fat increases in successive phases of the digenean life cycle.

Animals↗
PubMed1978

A study of the relationship between the energy contents of Schistosoma mansoni cercariae and their death during penetration of mammalian host skin.

Immersion of Biomphalaria pfeifferi in 1.5% glucose solution showed that the snails did not absorb any glucose during the first six hours but that almost 30% of the glucose was absorbed after 24 hours. The glycogen content of such "glucose-fed" snails was much higher than that of control normal snails. Cercariae of S. mansoni collected from the former snails exhibited a much lower level of death (20%), during penetration of mouse skin, than that of control normal cercariae (36%). It is suggested that death of S. mansoni cercariae during penetration of mammalian host skin is probably due to exhaustion of their energy reserves.

Animals↗