Cercarial Body Research Articles

Search, find, and penetrate: ultrastructural data of furcocercariae of Cardiocephaloides longicollis (Digenea, Strigeidae) explain their transmission and infection strategy into fish hosts.

The present study provides an overview of the structures linked to fish host finding, recognition, and invasion of one of the most commonly occurring morphotypes among trematodes, furcocercariae. For this, we use free-swimming cercariae of the strigeid Cardiocephaloides longicollis (Rudolphi 1819) Dubois, 1982. Their elongated cercarial body and bifurcated tail are covered by a tegument with an irregular surface, showing numerous folds arranged in different directions and a typical syncytial organization. Both the body and the bifurcated tail are covered with short spines, rose-thorn shaped, as well as four types of sensory papillae, distinguished by the presence or absence of a cilium, its length, and their position on the cercarial body. These papillae are especially important for free-living stages that rely on external stimuli to locate and adhere to the host. A specialized anterior organ is located at the anterior part of the cercariae and is encircled by a triangle-shaped group of enlarged pre-oral spines followed by a transverse row of enlarged post-oral spines that, together with the sensory papillae, allow active finding, recognition, and penetration into fish. The ventral sucker, covered with inner-oriented spines, sensory papillae, and cilia, helps during this process. The cercariae of C. longicollis possess three types of gland cells (a head gland and two types of penetration glands), each containing different types of secretory granules that play a role in host invasion. The protonephridial excretory system consists of an excretory bladder, a system of collecting tubules, flame cells, and two excretory pores in the middle of each furcae, which serve to control osmoregulation in their marine environment, as well as to eliminate metabolic waste. Together with the four types of sensory endings, the central ganglion forms the nervous system. Our results add novel information on the ultrastructure of strigeid furcocercariae, being essential to interpret these data in relation of their functional role to better understand the transmission and penetration strategies that cercariae display to infect their fish hosts.

Photoactivated water-disinfecting, and biological properties of Ag NPs@Sm-doped ZnO nanorods/cuttlefish bone composite: In-vitro bactericidal, cercaricidal and schistosomicidal studies

Herein, eco-friendly composite was synthesized by embedding silver (Ag) nanospheres onto aragonitic cuttlefish bone (CB)-stabilized samarium doped zinc oxide (Sm-doped ZnO) nanorods. The operating interaction profile and the photoactive behavior of this nanocomposite were assessed via XRD, FTIR, Raman, TEM, FE-SEM, DLS, DRS and PL techniques. Locality of Sm-doped ZnO and its attaching modes to the cuttlefish bone lamella were highly dominated by embedding Ag NPs that encouraged Zn2+ Lewis acid sites to electrostatically interact with aragonite carbonates in the channeled porous CB system. Such interacting approach enhanced photoactivity of Sm-doped ZnO by lowering its energy band gap (from 3.26 eV for Sm-doped ZnO/CB to 2.12 eV for Ag@Sm-doped ZnO/CB). Besides, plasmon-induced silver electrons provided Sm-doped ZnO by extra photosensitivity. Ag@Sm-doped ZnO/CB nanocomposite exhibited pronounced photo-activated disinfection efficiencies for Staphylococcus aureus (80%), Pseudomonas aeruginosa (60%), and Schistosoma mansoni cercariae (100%) linked with progressive demolition in cercarial body. Such nanocomposite also possessed exterminating action against Schistosoma mansoni adult worms serving near 100% worm-mortality accompanied by significant disintegration of worm body. These findings were successfully drawn Ag@Sm-doped ZnO/CB as an efficient weapon in the biocides arsenal being even capable of destructing pathogenic bacteria and parasites in dark- and photo- conditions.

The sexual adult of Cercaria praecox Walker, 1971 (Digenea: Fellodistomidae), with the proposal of Oceroma n. g.

A sexual adult trematode that is considered to be conspecific with the distinctive larval trematode Cercaria praecox Walker, 1971 is reported from the kyphosid fish Scorpis lineolata Kner in Moreton Bay, Queensland, Australia. The sexual adult is consistent with the cercarial body of Cercaria praecox in having a single caecum with an asymmetrical appendix, symmetrical testes immediately posterior to the ventral sucker, and the ovary and vitellarium both well posterior to the testes. This combination of characters is distinct within the Fellodistomidae Nicoll, 1909 and requires the proposal of a new genus, Oceroma n. g. Analysis of 28S rDNA sequences demonstrates that this species forms a clade with Coomera Dove & Cribb, 1995 within the Fellodistomidae. The life-cycle of the species is predicted to require two hosts and to involve the direct ingestion of the cercaria.

New insight into the morphology of Eurytrema coelomaticum (Trematoda, Dicrocoeliidae) cercariae by light, scanning, and transmission electron microscopies

Eurytrema coelomaticum is a digenetic trematode that parasitizes the pancreatic ducts of ruminants. In the present study, the morphology of the cercariae was analyzed using light, scanning, and transmission electron microscopies. The size of the larvae was larger than that reported in the literature. An oral sucker with many papillae and an oral aperture in its center and a ventral sucker with few discrete papillae on the edge were observed. No stylet at the anterior end of the larval body and spines on the tegument of the end of the tail were observed. The cercariae had lateral penetration glands and (central) pre-acetabular glands, from which ducts lead to the anterior region and open into a small anterior pocket. The flame cells were located laterally and communicated with fine branches, converging to two lateral excretory collecting ducts that opened into an excretory bladder, centrally located at the posterior end of the body. The tegument presented an external layer loosely attached to the larval body, below which an amorphous syncytial outer layer with many mitochondrial profiles was observed. This region exhibited many secretions and released secretory granules, indicating intense secretory activity. The circular and longitudinal muscle layers were arranged in sequence below the outer layer. The outer layer was connected by cytoplasmic bridges crossing the muscular layers to the internal region of the tegument, where the cell body with nucleus was located. In the cercarial body, it was possible to observe a typical flame cell with the barrel region, where cilia and the internal and external ribbed regions were found. The somatic cells seem to have an active metabolism, with a well-developed endoplasmic reticulum, secretory granules, and evident nuclei. The results are discussed in the light of the biology and taxonomy of this species.

Disentangling phylogenetic constraints from selective forces in the evolution of trematode transmission stages

The transmission stages of parasites are key determinants of parasite fitness, but they also incur huge mortality. Yet the selective forces shaping the sizes of trans- mission stages remain poorly understood. We ran a comparative analysis of interspecific variation in the size of transmission stages among 404 species of parasitic trematodes. There are two transmission steps requiring infective stages in the life cycle of trematodes: transmission from the definitive to the first intermediate (snail) host is achieved by eggs and/or the miracidia hatched from those eggs, and transmission from the first to the second intermediate host is achieved by free-swimming cercariae. The sizes of these stages are under strong phylogenetic constraints. Our results show that taxonomy explains (50% of the unaccounted variance in linear mixed models, with most of the variance occurring at the superfamily level. The models also demonstrated that mollusc size is positively associated with egg volume, miracidial volume and cercarial body volume, but not with the relative size of the cercarial tail. In species where they encyst on substrates, cercariae have significantly larger bodies than in species penetrating chordates, although the relative size of the cercarial tail of species using chordates as second intermediate hosts was larger than in other trematode species. Habitat also matters, with larger cercarial tails seen in fresh- water trematodes than in marine ones, and larger miracidial volumes in freshwater species than in marine ones. Finally, the latitude (proxy for local temperature) at which the trematode species were collected had no effect on the sizes of transmission stages.

Secretory glands in cercaria of the neuropathogenic schistosome Trichobilharzia regenti - ultrastructural characterization, 3-D modelling, volume and pH estimations

BackgroundCercariae of schistosomes employ bioactive molecules for penetration into their hosts. These are released from specialized unicellular glands upon stimuli from host skin. The glands were previously well-described in the human pathogen Schistosoma mansoni. As bird schistosomes can also penetrate human skin and cause cercarial dermatitis, our aim was to characterize the architecture and ultrastructure of glands in the neurotropic bird schistosome Trichobilharzia regenti and compare it with S. mansoni. In the context of different histolytic enzymes used by these two species, we focused also on the estimations of gland volumes and pH in T. regenti.ResultsThe architecture and 3-D models of two types of acetabular penetration glands, their ducts and of the head gland are shown here. We characterized secretory vesicles in all three gland types by means of TEM and confirmed accuracy of the models obtained by confocal microscopy. The results of two independent approaches showed that the glands occupy ca. one third of cercarial body volume (postacetabular glands ca. 15%, circumacetabular 12% and head gland 6%). The inner environment within the two types of acetabular glands differed significantly as evidenced by dissimilar ability to bind fluorescent markers and by pH value which was higher in circumacetabular (7.44) than in postacetabular (7.08) glands.ConclusionsAs far as we know, this is the first presentation of a 3-D model of cercarial glands and the first exact estimation of the volumes of the three gland types in schistosomes. Our comparisons between T. regenti and S. mansoni implied that the architecture and ultrastructure of the glands is most likely conserved within the family. Only minor variations were found between the two species. It seems that the differences in molecular composition have no effect on general appearance of the secretory cells in TEM. Fluorescent markers employed in this study, distinguishing between secretory vesicles and gland types, can be useful in further studies of mechanisms used by cercariae for host invasion. Results of the first attempts to estimate pH within schistosome glands may help further understanding of regulation of enzymatic activities present within the glands.

Novel derivatives of niclosamide synthesis: Its bioactivity and interaction with Schistosoma japonicum cercariae

Two novel niclosamide derivatives were synthesized by adding polyethylene glycol groups of differing lengths to a niclosamide core. The modified niclosamide derivatives were characterized using 1H NMR and HRMS spectra. Anti-cercarial bioactivity results showed that the niclosamide derivative constructed to float on the surface of the water was able to kill cercariae when the number of hydrophilic groups was >3. A fluorescent niclosamide derivative containing naphthalimide was further synthesized to observe the interaction between the cercaricide and Schistosoma japonicum cercariae. Confocal fluorescence microscopy revealed that the fluorescent niclosamide derivative could easily penetrate into the cercarial body beyond the circulatory system leading to the rapid death of cercariae.

Phenotypic plasticity in the cercarial indices of human and rodent samples ofSchistosoma mansoni(Digenea: Schistosomatidae)

In the epidemiology of schistosomiasis, the cercarial index (CI) has been used for several purposes, including the identification of the species of vertebrate host involved in transmission in a particular setting. The CI of samples of Schistosoma mansoni of human (BH) and rodent (CMO) origin have now been compared, in an attempt to identify morphological markers on cercariae that would indicate whether the eggs from which the cercariae have developed were produced in humans or in rodents. After silver-nitrate impregnation of the cercariae, the CI (and their reaction norms) for the antero-dorsal (AD), antero-lateral (AL) and tail-stem (U) sensory receptors were investigated. The data analysis was based on linear-regression methods, Levene's test for the equality of variances, pooled-variance independent t-tests, and discriminant analysis. The results indicated that CI varied with vertebrate-host origin, that the AD reaction norms were more consistent and plastic than the other reaction norms investigated, that there appeared to be no simple allometric relationship between any of the CI investigated and cercarial body length, and that the BH sample gave larger standard deviations and a higher incidence of mis-classification than the CMO, indicating some developmental instability in the sample of human origin. The relative instability of the BH sample was, however, possibly the result of the experimental procedures. As the parasites used to produce the BH sample had been isolated from humans fairly recently and then routinely maintained in mice, host-induced selection could have affected the sample, altering its CI and their reaction norms. The results of the discriminant analysis indicated that, of the indices investigated, AD was the best morphological marker for distinguishing human and rodent samples of S. mansoni.

Interaction between the blood fluke,Sanguinicola inermisand humoral components of the immune response of carp,Cyprinus carpio

The effect of Sanguinicola inermis on serum antibody and complement activity in Cyprinus carpio was assessed using an ELISA and haemolytic assays. Possible immune evasion strategies were assessed using immunodetection of host proteins on the surface of the parasite. Carp acclimatized to 20 or 25 degrees C were infected by exposure to 500 cercariae or injected intraperitoneally with 150 cercariae, and serum monitored over a 63-day period. In cercariae-injected carp, irrespective of time and temperature, a significant increase occurred in complement activity being greatest at 25 degrees C. In addition, fish exposed to the cercariae of S. inermis and maintained at 20 degrees C the level of complement activity was significantly higher after 5 weeks compared to controls. At 20 degrees C intraperitoneal injections of parasites increased serum antibody levels which peaked after 7 days. In contrast, at 25 degrees C, antibody levels were maintained over 63 days. Exposure of fish to infection did not appear to stimulate antibody production. Immunofluorescence studies revealed 'host-like' molecules on the surface of the cercarial body exposed to carp serum and adult flukes obtained directly from the fish or cultured for 24 h in L15 medium. The possible role of 'host-like' molecules in immune evasion is discussed and the response at different temperatures is related to infection dynamics.

An ultrastructural study of excretory system development in the cercariae of Prosorhynchoides gracilescens (Rudolphi, 1819) and Prosorhynchus squamatus Odhner, 1905 (Digenea, Bucephalidae).

The ultrastructure of the developing excretory system of Prosorhynchoides gracilescens and Prosorhynchus squamatus cercariae is described. The development pattern was similar in both species. In early embryos the two main collecting tubes were composed of a layer of cells which were wrapped around the lumen. Later, the tubes fused and the excretory epithelium of the fusion zone and that of the lateral caudal ducts became a syncytium. The collecting tubes in the cercarial body retained their cellular organization. As the tails grew, additional excretory pores were formed in the tail stem where thickened portions of the caudal duct epithelium contacted the surface tegument. Following this, the distal portions of the lateral caudal ducts lost contact with the primary excretory pores and progressively degenerated. Excretory atrium development started with differentiation of secretory active cytons peripheral to the fusion zone. These cells gave rise to cytoplasmic extensions that penetrated the fusion zone wall to eventually form a continuous cytoplasmic layer. This layer eventually replaced some of the fusion zone excretory epithelium and became the lining of the excretory atrium. The anterior end of the fusion zone differentiated into an excretory bladder and a short posterior portion gave rise to the caudal vesicle.

An ultrastructural study of the cercarial excretory system in Bucephaloides gracilescens and Prosorhynchus squamatus.

The ultrastructure of the flame cells, capillaries, collecting tubes, excretory bladder, excretory atrium, caudal vesicle, lateral caudal ducts and excretory pores of cercariae of Bucephaloides gracilescens (Rudolphi, 1819) Hopkins, 1954 and Prosorhynchus squamatus Odhner, 1905 (Digenea: Bucephalidae) is described. Both species are essentially similar except for some details. The terminal parts of the protonephridia have all the structural features that are typical of trematodes. The collecting tubes in the cercarial body are composed of cells that are wrapped around the lumen. The main collecting tubes are joined to the excretory bladder syncytium by septate junctions. Features of P. squamatus excretory bladder epithelium indicate that it is involved in secretory activity, but this is not the case in B. gracilescens. In both species the luminal surface of the excretory bladder epithelium is increased by lamellae, and the basal plasma membrane forms invaginations. In the bladder syncytium of P. squamatus both apical lamellae and basal invaginations are more developed and mitochondria are also more numerous. The excretory atrium is lined by a syncytium with nucleated cytons located in the surrounding parenchyma. The atrium lining is not continuous with the body tegument and possesses specific secretory inclusions and a thick glycocalyx. Septate junctions connect the atrium syncytium to the excretory bladder epithelium at its anterior end and to the syncytial excretory epithelium lining the caudal vesicle and the lateral caudal ducts at its posterior. In the excretory pores the caudal duct syncytium is joined to the tegument by septate desmosomes.

Schistosoma mansoni proteases Sm31 (cathepsin B) and Sm32 (legumain) are expressed in the cecum and protonephridia of cercariae.

Adult Schistosoma mansoni parasites live in the bloodstream of their vertebrate hosts where they consume red blood cells. Hemoglobin, released from the ingested red blood cells, is degraded by a variety of parasite proteases, including Sm31 (cathepsin B) and Sm32 (schistosome legumain). In this study the localization pattern of the Sm31 and Sm32 enzymes in cercariae (the infectious life cycle stage) was examined. Antibodies generated against recombinant Sm31 and Sm32 recognize their respective proteins in Western blots of soluble parasite extracts. Highest levels are seen in adult female extracts, whereas the level of both proteins is below detection in cercarial extracts. However, in fixed, whole cercariae, both proteins are seen in the cecum and protonephridia. In the cecum, the staining pattern has a granular appearance, suggesting that the proteins are packaged in vesicles. In the protonephridial system, Sm31 and Sm32 are detected in all 8 flame cells in the cercarial body and in both flame cells in the cercarial tail. The distribution of the 2 proteins differs in the flame cells. Examination of immunostained cercariae using laser scanning confocal microscopy shows that whereas Sm31 is located in the tubule cell, Sm32 is found in both the tubule cell and its adjoining cap cell. These findings suggest that the proteins are involved in the proposed excretory and osmoregulatory roles of flame cells.

The cercarial tail in Proterometra macrostoma (Digenea: Azygiidae): permeability and fine structure of the tegument.

Permeability of the cercarial tail in Proterometra macrostoma was examined in vitro with 1 mM 3H-glucose, which tails absorb by diffusion alone. Naturally emerged cercariae (bodies withdrawn into tails) were permeable, but they rapidly (3 min) equilibrated with glucose in the bathing medium and maintained steady state for 4 hr. Metabolism of absorbed glucose was not detectable until after 90 min, and radioactivity in bodies dissected from tails after 4 hr was negligible. On the basis of cercarial water content (90% of total weight) and absorbed isotope at steady state, the calculated volume of the equilibrating compartment was 4% of an intact cercaria. This value correlated well with that of the tegument (3-5%), which was 1-2 microm thick as seen by transmission electron microscopy. A continuous, electron-dense basal membrane/lamina separated the tegument from subtegument. We conclude that the glycocalyx and external plasma membrane are freely permeable, whereas the basal membrane is the barrier that effectively isolated the subtegument from exogenous glucose. The basal membrane also may be the primary structure that protects the subtegument and cercarial body from effects of osmotic stress.

Bacciger bacciger (Trematoda, Fellodistomidae) infection in commercial clams Donax trunculus (Bivalvia, Donacidae) from the sandy beaches of the Western Mediterranean

DAO Diseases of Aquatic Organisms Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials DAO 35:37-46 (1999) - doi:10.3354/dao035037 Bacciger bacciger (Trematoda, Fellodistomidae) infection in commercial clams Donax trunculus (Bivalvia, Donacidae) from the sandy beaches of the Western Mediterranean Montserrat Ramón1,*, Mercedes Gracenea2, Olga González-Moreno2 1Institut de Ciències del Mar, Passeig Joan de Borbó, s/n, E-08039 Barcelona, Spain 2Laboratori de Parasitologia, Facultat de Farmàcia, Universitat de Barcelona, E-08028 Barcelona, Spain *E-mail: mramon@icm.csic.es ABSTRACT: Sporocysts of the Fellodistomidae trematode Bacciger bacciger were embedded in gonadal tissue of the bivalve Donax trunculus from the Mediterranean coast of Spain. The overall prevalence of infection was 8.4%, increasing with host size to 23% in D. trunculus from 35 to 36 mm in shell length. Individuals <19 mm long were not infected. No clear seasonality was recognized in prevalence of infection. The proportion of infected individuals of both sexes was similar (6.56% in males and 8.04% in females), although the highest prevalence was in clams of unknown sex (13.47%). The proportion of infected clams reduced to virtual castrates of unknown sex reached 28%. The tegument of the sporocyst and shed cercariae was studied by light and electron microscopy. Scanning electron microscopy revealed a smooth surface on the sporocyst tegument, the area of which was greater due to the presence of circumferential infolds and numerous pits. A birth pore on one side of the sporocyst, uniciliate sensory organs and cup-shaped sensory-like structures were present on the tegument. The cercarial body had spines and uniciliate sensory organs. The ventral sucker of the cercariae had 2 rings of uniciliate sensory organs and tegumental spines. KEY WORDS: Bacciger bacciger · Donax trunculus · Trematode infection · SEM observations · Western Mediterranean Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in DAO Vol. 35, No. 1. Publication date: January 07, 1999 Print ISSN:0177-5103; Online ISSN:1616-1580 Copyright © 1999 Inter-Research.

Comparative Observations on Cercariae and Metacercariae of Echinostoma trivolvis and Echinoparyphium sp.

Comparative observations were made on cercariae of Echinoparyphium sp. from Physa gyrina in Charlie's pond, Stokes County, North Carolina and cercariae of Echinostoma trivolvis from Helisoma trivolvis in Northampton County, Pennsylvania. The cercaria of Echinoparyphium sp. has 43 collar spines, lacks penetration and paraesophageal glands, and has a conical tail without fin folds. The cercaria of E. trivolvis has 37 collar spines, penetration and paraesophageal glands, a finger-like process at the tip of the tail and fin folds. The length of the cercarial body and tail of E. trivolvis was significantly greater than that of Echinoparyphium sp. Cercariae of both species encysted in Biomphalaria glabrata snails in single and concurrent infections. In concurrent infections with a single cercaria of each species, 2 encysted metacercariae were adjacent to each other in the saccular kidney of the snail at 24 hr postinfection. The diameter of encysted metacercariae of E. trivolvis was significantly greater than that of Echinoparyphium sp. Echinoparyphium sp. metacercariae excysted at 39 C in an alkaline trypsin-bile salts medium used previously to excyst E. trivolvis. The length of excysted metacercariae of E. trivolvis was significantly greater than that of Echinoparyphium sp.

Life history of Echinoparyphium recurvatum (Trematoda: Echinostomatidae) in Korea.

The present study was performed to observe characteristics of the life history of Echinoparyphium recurvatum under both natural and laboratory conditions in Korea. A batch of Radix auricularia coreana was collected from Sunamchon, one of the stream of West Naktonggang (River), in Kangso-gu, Pusan during August and September 1992. Out of 106 snails examined by crushing, 52 (49.0%) were infected with larval E. recurvatum, i.e. rediae, cercariae and metacercariae. Cercariae naturally shed from snails encysted in the snails of same species and loaches, but not in mud-snails. Adult worms were detected from chicks and ducks experimentally infected with metacercariae, but not from rats and mice. The average recovery rate of adults from chicks was 13.1%. Rediae were sac-like, 2.437 x 0.317 mm in average size, with a muscular pharynx and a brownish cecum which reached the anterior half of the body. Cercariae consisted of a spindle-shaped body (0.262 x 0.129 mm in average) and a rod-like tail (0.528 x 0.056 mm in average). In the cercarial body, 45 collar spines were observed on the head crown, and double rows of excretory ducts with fine granules were laterally arranged between the pharynx and the ventral sucker. Metacercariae were spherical, 0.144 x 0.142 mm in average size, with thick hyaline outer and thin elastic inner walls, and many excretory granules. Adults were slender and more attenuated in the anterior end, 2.760 x 0.550 mm in average size, and had 45 collar spines including four end group spines on both ventral corners. From the above results, it was confirmed that R. auricularia coreana plays a pivotal role in the life cycle of E. recurvatum as the first and/or second intermediate hosts in Korea.

Ultrastructure of sensory endings in Diplostomum pseudospathaceum Niewiadomska, 1984 cercariae (Digenea, Diplostomidae)

Using TEM techniques, 13 types of sensory endings were revealed on the body and tail of cercariae of D. pseudospathaceum. They differ in the presence or absence of cilia, number of cilia, number of electron-dense rings, basal body type and collar shape. The following groups of sensory endings were distinguished: uniciliate with a short (5 types), moderately long (one type) or long cilium (4 types); multiciliate sensory pits (2 types); and nonciliate sensory bulbs. Most sensory endings with long cilium and nonciliate sensory bulbs were found on the tail stem. All the breviciliate sensory endings and multiciliate sensory pits, as well as 1 type with long cilium, were situated on the cercarial body. The uniciliate sensory endings with a moderately long cilium were found on the furcae. The ultrastructural variety of sensory endings in different groups of Digenea, as well as their supposed functions, are discussed.

Surface Ultrastructure of the Cercaria of Neodiplostomum seoulense (Trematoda: Neodiplostomidae)

The surface ultrastructure of Neodiplostomum seoulense cercariae was studied by scanning electron microscopy. The cercarial body was cylindrical and its tail bifurcated. Short tegumental spines, with a broad base and single pointed tip, were dense anteriorly but sparse posteriorly on the lateral margins of the body. The acetabulum had stout spikelike spines, centripetally oriented on the inner surface. Sensory papillae, each with a short cilium, were concentrated around the oral sucker; they could be tangoreceptors or chemoreceptors, or both. Many sensory papillae, each with a long cilium, were observed on the tail; these might be rheo- or tangoreceptors. It is suggested that the sensory papillae of N. seoulense cercariae provide for attachment and penetration into the skin of tadpoles, which are the second intermediate host.

Schistosoma mansoni: Fractionation and Characterization of the Glycocalyx and Glycogen-like Material from Cercariae

The glycocalyx (GCX) that covers schistosomal cercariae is a complex molecule that has immunomodulating properties. Here, we purified milligram amounts of GCX using Anguilla lectin which binds to the GCX covering the cercarial body and tail. Typically, 10 million cercariae were extracted with phenol, dialyzed, and chromatographed on a Sepharose 2B-CL column. An average of 39 mg of total carbohydrate eluted near the void volume from which 31 mg of glycogen-like material was further separated by lectin affinity chromatography. Its identity was established by compositional analysis, sensitivity to amylase digestion, and its nuclear magnetic resonance spectrum. The lectin-bound GCX was eluted with 0.1 M fucose with a final yield of 5.3 mg carbohydrate. Fucose composed 40% of the total GCX carbohydrate with lesser but approximately equal amounts of galactose, glucosamine, and galactosamine present. NMR data indicated that the amino sugars were N-acetylated. Glucose was also present but in varying amounts in different preparations of GCX. Oligosaccharides were released from GCX by hydrazinolysis and separated by electrophoresis after reductive amination to 8-aminonaphthalene-1,3,6-trisulfonic acid (ANTS). Bands comigrating with standards containing 11, 12, 16, and 17 sugar residues were detected. Thus, the GCX is a complex structure composed of oligosaccharides, probably linked to a peptide.

Transmission electron microscopy of sensory receptors of Echinostoma revolutum (Froelich 1802) cercaria (Digenea: Echinostomatidae).

Nonciliate, uniciliate, and multiciliate receptors were shown by transmission electron microscopy to occur in the body tegument of Echinostoma revolutum (Froelich 1802) cercariae. Detailed studies revealed three types of nonciliate, four types of uniciliate, and one type of multiciliate sensory endings. Most receptors were singly distributed. Only a few of them formed paired receptor complexes in three regions of the cercarial body. These receptor complexes were found to possess nonciliate, uniciliate, and multiciliate sensory endings.