The structure of the helminth cuticle

Migration and ultrastructure of the acanthocephalan Echinorhynchus gadi Zoega in Müller, 1776 in intermediate host under experimental conditions

Amphipods Eogammarus tiuschovi were experimentally infected by the acanthocephalan Echinorhynchus gadi (Acanthocephala: Echinorhynchidae). Within the first four days post-infection, acanthors of the acanthocephalan caused the cellular response of the host, which ended with their complete encapsulation on day 4 post-infection. The acanthors obtained through the experiment were examined ultrastructurally. Two syncytia (frontal and epidermal) and a central nuclear mass are found in the acanthor's body. The frontal syncytium has 3-4 nuclei and contains secretory granules with homogeneous, electron-dense contents. Since the secretory granules occupy only the anterior one-third of this syncytium, it is suggested that the contents of these granules are involved in the acanthor's migration through the gut wall of the amphipod. The central nuclear mass consists of an aggregation of fibrillar bodies and a few electron-light nuclei distributed on the periphery. Some of these nuclei, located near the central nuclear mass, are assumed to be a source of the acanthocephalan's internal organs. The epidermal syncytium surrounds the frontal syncytium and the central nuclear mass. It is represented by a superficial cytoplasmic layer, but the bulk of the cytoplasm is concentrated in the posterior one-third of the acanthor's body. Syncytial nuclei are evenly distributed throughout the cytoplasm. The muscular system of the acanthors consists of 10 longitudinal muscle fibers located below the superficial cytoplasmic layer and two muscle retractors crossing the frontal syncytium.

Feeding on clean food? Potential effects of electric organ discharges by Torpedo spp. (Torpediniformes: Torpedinidae) on their trophically transmitted parasites

Members of the Torpedinidae (torpedoes) and Hypnidae (coffin ray) use electric organ discharges (EOD) to stun or kill their prey before consumption. We investigated whether EOD could also negatively affect the helminth larvae infecting these preys through a surrogate model: we applied electric discharges to individuals of blue whiting, Micromesistius poutassou, that harbored live larvae of Anisakis. Larval mortality throughout a 6-h period was significantly higher in the treatment group, suggesting that EODs could significantly hamper helminth recruitment. We then tested whether torpedinids and hypnids ("strong-EOD" families) harbored species-poor helminth (cestode) assemblages compared with "weak-EOD" Torpediniformes (Narcidae and Narkidae) and other Batoidea. Based on comparisons on estimated species diversity and mean species richness of tapeworms at host individual level we found that (i) Torpediniformes had the lowest tapeworm diversity of all Batoidea orders; (ii) Torpedo spp. consistently had the lowest mean cestode richness at host individual level, and this could not be related to other host factors influencing cestode diversity in chondrichthyans, that is body size, trophic level or dietary breath. However, a preliminary comparison between "strong-EOD" and "weak-EOD" Torpediniformes did not detect clear differences of cestode richness. Thus, evidence supporting an unambiguous contribution of EODs to depauperate cestode assemblages requires further research.

Electron microscopy of the separated outer tegument of the sparganum and its antigenicity

The author reported previously on separation of the outer tegument of the spargana (plerocercoids of Spirometra mansoni) using high concentration of urea solution. To determine which layer of the tegument is separated by this method, an electron microscopic analysis has been processed in this study. It was confirmed that the basement layer of the tegument is separated from the parenchyme of the sparganum. In addition, the antigenicity of the separated outer tegument against the human sparganosis patient sera was evaluated. Numerous antigenic proteins, including 16 and 55 kDa proteins, were noticed in the separated tegument; however, there were no diagnostic 31/36 kDa molecules in this tegument. The molecules reactive with the patient sera in the tegument are to be characterized in future studies.

Observations on the structure and function of the haemoglobin from the cuticle of Nippostrongylus brasiliensis (Nematoda)

The fluid layer within the cuticle of the nematode Nippostrongylus brasiliensis contains haemoglobin. The absorbance spectra of the haemoglobins extracted from whole nematodes were measured spectrophoto-metrically and the spectra of cuticular haemoglobin in individual living nematodes was obtained by microdensitometry. Adult female nematodes were confined under cover-slips in oxygenated saline and measurements of optical density of a small area of the cuticular haemoglobin were taken at 10 sec intervals. The optical density decreased over a period of 4 min at 543 nm and increased at 553 nm indicating deoxygenation of the cuticular haemoglobin; irrigation with fresh saline restored the haemoglobin to its oxygenated state. This demonstrates that cuticular haemoglobin loads and unloads oxygen in the living animal. Isoelectric focusing showed that mature nematodes have haemoglobins which are isoelectric around pH 7·0 and at pH 9·8. Isolated cuticular fluid contained the haemoglobin which was isoelectric at pH 9·8, but no other haemoglobin, and immature adults, which do not have cuticular haemoglobin, contained only those haemoglobins which were isoelectric at pH 7·0. Sodium dodecyl sulphate polyacrylamide gel electrophoresis and column chromatography showed that the molecular weight of the cuticular haemoglobin sub-unit is 16·9–17·5 × 103 Daltons and that the haemoglobin exists primarily as a tetrameric molecule with a molecular weight of 65–75 × 103 Daltons. The presence of cuticular haemoglobin may allow adult Nippostrongylus to exploit oxygen-deficient areas within the environment of the rat's intestine where it would otherwise be unable to survive for prolonged periods.

The development of the tegument and cercomer of the polycephalic larvae (cercoscolices) ofParicterotaenia paradoxa(Rudolphi, 1802) (Cestoda: Dilepididae) at the ultrastructural level

The development of the tegument and cercomer ofParicterotaenia paradoxapolycephalic larvae was examined using electron microscopy. Larvae are formed by budding from the inner surface of the tegument of the degenerating hexacanth embryo. A new secondary tegument formed around the larvae is probably produced from the original hexacanth sub-tegumental cells. Microvilli covering the surface of young larvae are converted directly into microtriches, as the larvae develop, by addition of electron-dense material to the proximal part of the microvillus. Remnants of the original microvillus are visible at the distal surface of each new microthrix, but they eventually degenerate. The cercomer homologue is represented by scattered follicular cells, bearing microvilli, lying just within the containing cyst wall. The continuity of tegumentary tissue from one developmental stage to the next is discussed.

Separation of the syncytial layer of spargana using urea

The tegument of tapeworms is known to be composed of an outer syncytial cytoplasm layer which includes microtriches and cytoplasmic organelles (= syncytial layer), and a parenchymatous cytoplasm layer that contains subtegumental cell nuclei (= subtegumental layer) and organelles. In the present study, separation of the syncytial layer of the sparganum, the plerocercoid stage of Spirometra mansoni, was tried using urea as the chemical reagent. Histological sections were prepared to visualize the status of separation after staining with hematoxylin and eosin. The results showed that the syncytial layer of the sparganum tegument which includes microtriches and cytoplasmic organelles were successfully separated from the parenchyma using 3 M urea.

[Transmission electron microscopic ultrastructure of the tegument of Fibricola seoulensis]

An electron microscopic study was performed to observe the ultrastructure of the tegument of F. seoulensis. The outer surface of the tegument was covered with a trilaminated plasma membrane. The electron-dense cytoplasmic layer was 2.5 microns wide in the anterior portion and contained numerous vacuoles, mitochondria and granular materials in its matrix. The basement layer was 330 nm wide or so, and its numerous extensions protruded into the cytoplasmic layer. The sensory organ was composed of a small vesicle of 1.7 x 1.1 microns in dimensions, which possessed a cilium of 1.2 x 0.19 micron in size. The pharynx was composed of the epithelial layer of about 0.5 micron wide, well developed muscle layer and basement layer. The tegument of the oral sucker was composed of a cytoplasmic layer of 0.4-0.5 micron width, a narrow basement layer, a well developed muscle layer and tegumental cells. Some kinds of secretory granules that seemed to be originated from the cells of the oral sucker were observed in the parenchymal portions of the adjacent cells. The tribocytic organ consisted of numerous microvilli. The microvilli were 5 nm wide and heptalaminated. Two types of secretory granules originated from the gland cells of tribocytic organ were observed in the tegument and parenchyme. The tegumental cells were irregular in shape, and of which nuclei were multifarious.

Sparganum proliferum: an overview of its structure and ultrastructure

A detailed study of the structure and ultrastructure of Sparganum proliferum was made possible for the first time thanks to the successful in vitro and in vivo maintenance of this rare parasite. Although S. proliferum exhibits many of the classical tegumental and parenchymal structures previously described for other larval cestodes, these are either arranged in a distinct fashion or, in some cases, may be completely different. Among the latter and of special interest are the single or multiple parenchymal cavities, surrounded by tegument, which in some instances appear to act as a primitive digestive tract.

Dirofilaria immitis: molting process of third-stage larvae

The objective of this study was to determine the molting process of Dirofilaria immitis third-stage larvae (L-3) to fourth-stage larvae (L-4), as it occurred in vitro. After 48 hr in vitro, the L-4 epicuticle was completely formed, and by 72 hr there was a clear separation between the L-3 and L-4 cuticles. The thickness of the newly formed L-4 cuticle was significantly less than that which has been described for larvae recovered from dogs after a similar incubation time period. If culture conditions were lacking in bovine albumin or proper temperature, larvae successfully developed the L-4 epicuticle but did not complete ecdysis. The molting process of D. immitis L-3 was thus shown to be multistepped with different factors required to induce the various developmental phases.

Ultrastructure and cytochemistry of the tegument of Orthocoelium scoliocoelium and Paramphistomum cervi (Trematoda: Digenea)

The tegument of Orthocoelium scoliocoelium and Paramphistomum cervi was examined using histochemical techniques and electron microscopy. On the basis of the distribution of acid and alkaline phosphatase (E.C. 3.1.3.2, E.C. 3.1.3.1), non-specific esterase (E.C. 3.1.1.1), cholinesterase (E.C. 3.1.1.7) and succinate dehydrogenase (E.C. 1.3.99.1) at light microscope level two distinct regions were recognized, an outer and an inner zone. Electron microscopy revealed that the tegument comprises an outer surface syncytium underlain by a thick subsyncytial zone and musculature. Deeper still occur the nucleated "tegumental cells". The latter are in cytoplasmic continuity with the surface syncytium via vacuolated cytoplasmic trabeculae which traverse the muscle layers and the subsyncytial zone. Three types of tegumental cells each lacking mitochondria were observed. The T1 cells synthesize discoid and electron dense T1 bodies while T2 cells produce oval and electron lucent T2 bodies. The third type of tegumental cells apparently produce no secretory bodies and may represent an embryonic cell type. The surface syncytium contains T1 and T2 secretory bodies and is bounded apically by a plasma membrane invested externally by a fuzzy and filamentous glycocalyx. The surface syncytium lacks mitochondria and is traversed by infoldings of the basal plasma membrane. Beneath the surface syncytium the subsyncytial zone is largely comprised of fibrous interstitial material. This zone, which is particularly thick in the amphistomes, is traversed by trabeculae and extensions of underlying parenchymal cells which usually contain mitochondria and lysosomes. The subsyncytial zone overlies numerous circular and longitudinal muscle fibres. The absence of mitochondria and enzymes associated with active transport suggests that the amphistome tegument may be mainly specialized for protection of the worm against mechanical and chemical conditions prevailing in the rumen. Active uptake of nutrients is probably not a primary function.

Regional specialization of the surface of a parasitic nematode

A monoclonal antibody (NIM-M7) has been prepared which reacts with a major surface antigen of adult males and females of Trichinella spiralis. This specificity is only demonstrable when the antigen is liberated by detergent solubilization of surface-labelled worms. When reacted with living adults, on the other hand, NIM-M7 reacts well with only the eversible cloaca, or copulatory bell, of the male, binding weakly, if at all, to other surface areas of male or female worms. A similar staining pattern is also given by Concanavalin A. The differential staining given by NIM-M7 must indicate a molecular difference between the organization of the same surface antigen on the cuticular surface of the copulatory bell and other areas of the worm surface. This example of regional specialization demonstrates that the nematode cuticle is not necessarily chemically uniform.

[Studies On The Bladder Worm, Cysticercus Cellulosae: The Ultrastructure Of C. Cellulosae]

An electron microscopic study was performed to know the basic tegumental structure of Cysticercus cellulosae. The scolex and bladder portions of cysticerci (human and porcine strains) were prepared for transmission and scanning electron microscopy by conventional procedures. In general, the tegument of C. cellulosae showed the basic ultrastructure of cestode tegument on electron micrographs. The teguments of both scolex and bladder portions consisted of such components i.e., an outer vesicular layer with numerous microtriches and inner fibrous layer. Below the fibrous layer, there were layers of muscle bundles and tegumental cells. The microtriches which covered the surface of cysticercus revealed two distinctly different shapes. The characteristic bladder-like, elongated pyramid shaped 'tetrahedral form' was observed on the surface of the scolex portion, whereas the elongated cylindrical 'filamentous form' was distributed on the surface of bladder portion. In spite of the difference of isolated host and location, the cysticerci showed the same result. But dimensional variations of the tegument according to topography of the worm were observed. The possibility of application in making differential diagnosis from other larval cestodes and possible functions of this larval tegument were discussed.

Non-covalent interactions result in aggregation of surface antigens of the parasitic nematode Trichinella spiralis

Surface antigens of three stages of the nematode worm Trichinella spiralis has been labelled with iodine and examined by sodium dodecyl sulphate (SDS)/polyacrylamide-gel electrophoresis under reducing and non-reducing conditions. A variety of interactions were defined: the infective larva surface antigens formed a spectrum of aggregates from 50kDa to greater than 1000kDa from subunits of 47kDa and 90kDa; in the adult worms of 60kDa complex arose fron interaction between two dissimilar molecules of 40kDa and 20kDa; the new-born larvae components formed homologous dimers from a 58kDa molecule. Aggregating molecules were adherent to lentil lectin-Sepharose and are therefore glycoproteins. The interactions observed were completely abolished by boiling in SDS/mercaptoethanol, but only partially destroyed by boiling in SDS/iodoacetamide. Based upon this, the associations can be characterized as non-covalent, but disulphide-bond-dependent. It is suggested, but not proved, that the aggregates arise from strong non-covalent hydrophobic interaction sites which are stabilized by intrachain disulphide bonds in the molecules concerned.

[Electron Microscopical And Histochemical Studies On The Epicuticle Of Echinorhynchus Gadi (Acanthocephala)]

For the purpose of observing ultrastructure of the epicuticle of Echinorhynchus gadi, the present electron microscopical studies had been made. Also the histochemical methods of Morwy, Bauer, Smith, Lison, Taft, and those of lead and uranyl acetate had been used in order to see the distribution of glycogen, mucopolysaccharides, lipid and nucleic acid in the cuticle of Echinorhynchus gadi. The results obtained by the above studies were as follows: 1. Glycogen, mucopolysaccharides were found in the outermost, middle and inner layers, especially abundant in the middle layer of the cuticle. 2. Lipid was found in the middle and inner layer, and it was found abundantly around the lacunal canal in the cuticle. 3. Nucleic acid was found around the lacunal canal in the middle layer, and also distributed in the cell nucleus of inner layer in the cuticle. 4. Electron microscopically, the cuticle of Echinorhynchus gadi had three outer layers, being outermost, middle and inner ones. The outermost layer was medium electron dense, composed with plasmalemma and filaments. The middle layer was homogeneous one which was electron pale. The inner layer, which was electron dense, consisted of felt layer and radial layer. The electron dense glycogen, lipid granules were distributed in radial layer.

Changing proteins on the surface of a parasitic nematode

Most of the organisms of the phylum Nematoda are free living, but some are animal or plant parasites of major importance to man. During their life cycle all nematodes undergo a series of moults in which they shed an external cuticle, consisting of an outermost membrane-like layer of unknown composition and a series of fibrillar layers similar to collagens. Because of this structure, the cuticle has been viewed as an acellular exoskeleton with rather inert molecular components. However, observations have shown that it contains enzymes and sometimes haemoglobin, and that nutrients are absorbed through it in the infective larvae and adut stages of Brugia pahangi. It is bound by complement and antibody, resulting in the adherence of leukocytes, and antibody-dependent cell-mediated reactions damage the cuticle of newborn larvae of Trichinella spiralis and the microfilariae of Dipetalonema viteae and Litomosoides carinii. We report here that the surface of the cuticle of the parasitic nematode Trichinella spiralis expresses protein molecules which change qualitatively following the moulting process, and quantitatively during growth of the worms within one stage. Also, surface proteins are released in vitro at a rate which depends on the conditions of culture of the worms.

Fine Structure Of Cysticercus Celluosae From Human Brain

A transmission electron microscopic study was conducted in order to know basic tegumental structure of Cysticercus cellulosae which was obtained from the ventricles of human brain. In general, the electron microscopic appearance of the tegument resembled that of the body wall of adult and larval forms of other cestodes. The tegument both of the parenchymatous portion (scolex and spiral canal) and bladder portion consisted of such components, i.e., an outer vesicular layer with microtriches, and an inner fibrous layer. The subtegumental tissue below the fibrous layer was filled with muscle bundles and tegumental cells. The surface of the larva was covered by the microtriches of two distictly different types. The characteristic pyramid-shaped "tetrahedral" form was observed on the surface of the scolex portion, whereas the elongated, slender "filamentous" microtriches were distributed on the regions of the spiral canal and bladder portion. The tegumental and subtegumental tissues varied in thickenss from one region to the next. The possibility of application in making differential diagnosis from other larval cestodes and possible fuction of this larval tegument were discussed.

Comparative histochemical observations on the lipids in the immature and mature stages of Cotylophoron cotylophorum Paramphistomatidae: Digenea

Immature and mature stages of the sheep amphistome Cotylophoron cotylophorum have been analysed histochemically for their lipids. Excretory ducts of the immature worms were the common sites for the accumulation of neutral lipids (triglycerides) and phospholipids which showed very sparse distribution at the corresponding sites in the adult. Phospholipids and lipoproteins observed in the tegument of the adult could not be seen in the immature form. Intestinal caecae of both forms showed the presence of diffused and granular lipids which were relatively less in the immature. The possible physiological significance of these differences in the lipid contents of the immature and mature forms has been discussed.

The origin and development of the epidermis and associated structures in the cercaria of Cryptocotyle lingua (Creplin) (Digenea: Heterophyidae) from Littorina littorea (L.)

Cercariae of Cryptocotyle lingua develop from intraredial germinal cells which divide to form ‘naked’ cell aggregates and later germ balls covered, first, by a syncytial primitive epithelium and later a syncytial epidermis formed, in sequence, from superficial cells of the embryo. The primitive epithelium is soon lost. The original nuclei of the syncytial epidermis degenerate when the first series of epidermal cell bodies, formed immediately below and having the characters of protein synthesizing cells, become connected with it. The first cell bodies are replaced by a series of five types of epidermal (secretory) cell bodies developing in the parenchyma and giving off cytoplasmic processes which become connected, in sequence, with the outer cytoplasmic layer. Secretion bodies from four of the five types are discharged into the outer cytoplasmic layer, before the cercaria leaves the molluscan host, and remain there in the free swimming cercaria. The secretions of the fifth type are retained in their epidermal (secretory) cell bodies. The arrangement of the secretion bodies in the outer cytoplasmic layer and their histochemical reactions suggest possible functions concerned, later, with entry into and encystment within the second intermediate fish host.

An electron microscope study of the tegument of the metacercaria and adult of Leucochloridiomorpha constantiae (Trematoda: Brachylaemidae)

The tegumentary ultrastructure of Leucochloridiomorpha constantiae metacercariae and adults has been described. A filamentous glycocalyx invests the tegument of metacercariae and large numbers of biconcave, disk-shaped secretion vesicles are found in its outer zone, cytoplasmic bridges and cytons. Mitochondria within the outer tegumentary zone of metacercariae are restricted to its basal half. The transformation of metacercariae to adults involves the loss of the glycocalyx, a decrease in the number of disk-shaped secretion vesicles, a more uniform distribution of mitochondria through the outer tegumentary zone, an apparent degeneration of cytons, a thinning of the fibrous basal lamina and a decrease in the number of visible cytoplasmic bridges traversing it. The significance of these events for a metacercaria which does not encyst within the molluscan host is discussed. In addition, crystalline, spine-like inclusions in the outer tegumentary zone of adult L. constantiae are described and their possible function discussed.

Penetration of mammalian skin by the infective larva of Nippostrongylus brasiliensis

The behaviour of the third-stage larvae ofNippostrongylus brasiliensishas been studied on rat, mouse and human skin. Locomotion in thin films of moisture is by two-dimensional, undulatory propulsion on skin, and by three-dimensional, undulatory propulsion on hairs. In drops of water or in thick films of moisture locomotion is less efficient than in thin films. It is suggested that the thin film of moisture around larvae on the skin may become coated with a thin monolayer of lipid which could reduce evaporation from the surface of the nematode and from the film of moisture, thus extending the period before desiccation begins. Studies with the electron microscope have shown that the larvae move horizontally into the stratum corneum and later penetrate the epidermis and dermis by separating the constituent cells of these tissues. In the dermis there is dissolution of collagen around the larvae. It is suggested that this separation of cells and dissolution of collagen need not be brought about by enzyme action, as similar effects can be brought about by changes in pH or ionic composition of the bathing medium.