Host Intestinal Wall Research Articles

Molecular Characterization of the Interplay between Fasciola hepatica Juveniles and Laminin as a Mechanism to Adhere to and Break through the Host Intestinal Wall.

Fasciola hepatica is the main causative agent of fasciolosis, a zoonotic parasitic disease of growing public health concern. F. hepatica metacercariae are ingested by the host and excyst in the intestine, thereby releasing the newly excysted juveniles (FhNEJ), which traverse the gut wall and migrate towards the biliary ducts. Since blocking F. hepatica development is challenging after crossing of the intestinal wall, targeting this first step of migration might result in increased therapeutic success. The intestinal extracellular matrix (ECM) is constituted by a network of structural proteins, including laminin (LM) and fibronectin (FN), that provide mechanical support while acting as physical barrier against intestinal pathogens. Here, we employed ELISA and immunofluorescent assays to test for the presence of LM- and FN-binding proteins on a tegument-enriched antigenic fraction of FhNEJ, and further determined their identity by two-dimensional electrophoresis coupled to mass spectrometry. Additionally, we performed enzymatic assays that revealed for the first time the capability of the juvenile-specific cathepsin L3 to degrade LM, and that LM degradation by FhNEJ proteins is further potentiated in the presence of host plasminogen. Finally, a proteomic analysis showed that the interaction with LM triggers protein changes in FhNEJ that may be relevant for parasite growth and adaptation inside the mammalian host. Altogether, our study provides valuable insights into the molecular interplay between FhNEJ and the intestinal ECM, which may lead to the identification of targetable candidates for the development of more effective control strategies against fasciolosis.

Analysis of trematodes and cestodes in humans

The Phylum Platyhelminthes is divided into two groups: cestodes (tapeworms) and trematodes (flukes). Tapeworms live in vertebrate intestines, and their larval forms can be found in the flesh of animals that these animals eat. The adult tapeworm has no digestive tract and instead absorbs nutrients through its body surface. The worm's head, or scolex, has a mechanism for attaching to the host's intestinal wall. Knowledge of basic epidemiological characteristics and distinguishing radiographic findings can improve the chances of detecting and treating parasitic infections of the nervous system. This article discusses the clinical presentation, diagnosis, and treatment of some of the more a common cestode and trematode diseases of the central nervous system.

Whole genome and acid stress comparative transcriptome analysis of Lactiplantibacillus plantarum ZDY2013.

Previous study has reported that Lactiplantibacillus plantarum ZDY2013 which was screened from traditional Chinese fermented soybeans has a strong acid resistance. The purpose of this study was to uncover the genes potentially related to its genetic adaptation and probiotic profiles, based on comparative genomic and comparative transcriptome analysis. We got the basic information about L. plantarum ZDY2013 and identified genes which are related to genetic adaptation and probiotic profiles, including carbohydrate transport and metabolism, cell wall/membrane/envelope biogenesis, proteolytic enzyme systems and amino acid biosynthesis, CRISPR adaptive immunity, stress responses, ability to adhere to the host intestinal wall, exopolysaccharide (EPS) biosynthesis, and bacteriocin biosynthesis. Comparative transcriptome showed CK group (normal MRS culture L. plantarum ZDY2013) and SCL group (pH 3.0 MRS culture L. plantarum ZDY2013) had 652 significant differentially expressed genes including 310 up-regulated genes and 342 down-regulated genes. Besides that, these genes had been classified through KEGG and GO functional annotation. In addition, we also found top 20 KEGG pathways adjusted to acid stress. Then, some genes were selected to verify the transcriptome analysis and explore the mechanism of how L. plantarum ZDY2013 tolerate acid stress. We found that some genes of ABC transporter, phosphotransferase system, oxidation reduction process, membrane transporter and phosphorylation metabolism process had a significant change. These results suggested that comparative characterization of the L. plantarum ZDY2013 genome and transcriptome provided the genetic basis for further elucidating the functional mechanisms of it.

Suppression of inflammatory genes expression in the injured host intestinal wall during Mesocestoides vogae tetrathyridium larvae migration.

Mesocestoides vogae is a cestode parasite of the family Mesocestoididae (order Cyclophyllidea). Its larvae, tetrathyridium, are approximately 1 mm long and 300 μm wide and infect a wide range of host species including humans. Tetrathyridium migrate through the intestinal wall to invade the peritoneal cavity. Despite intestinal penetration by such a large-sized parasite, symptomatic intestinal disorders are not common during the migration period. In this study, the dynamics of tetrathyridia migration and their pathogenicity towards intestinal tissues were examined in mice infected orally with these parasites. Most tetrathyridia were found to migrate through the intestinal wall, moving into the peritoneal cavity or liver 24 to 48 hours after the oral infections. Next, the pathogenicity of tetrathyridium in the intestinal wall was histopathologically evaluated, and tissue injury from tetrathyridium migration was confirmed. Inflammatory foci were observed as tetrathyridium migration tracks from 48 hours after oral infection; however, the number of inflammatory foci had decreased by half more than 48 hours later. Therefore, we examined the gene expression levels of the macrophage driving cytokine, IL-1β, and the eosinophil recruiting chemokine, CCL11, by quantitative reverse-transcriptase PCR. The expression levels of these genes in the infected group were significantly lower than those of the non-infected group at 48 hours post-infection. Although the immunomodulating ability of the excretory-secretory products released from tetrathyridium has been previously shown by in vitro assays, the significance of this ability in their lifecycle has remained unclear. In this study, we discovered that tetrathyridium causes temporal inflammation in the intestinal wall during penetration and large-scale migration in this organ, but tetrathyridium simultaneously suppresses the host’s inflammatory gene expression, might to be a strategy that reduces inflammatory responses and increases survival of the parasite.

An ELISA based on soluble egg antigens for the serodiagnosis of animal schistosomiasis turkestanica.

BackgroundThe existing diagnostic techniques for detecting schistosomiasis turkestanica, such as aetiological assays, identify infection by parasitic worms via the incubation of miracidia from faeces or observing eggs under microscopy. However, they are limited in the diagnosis of low-grade and prepatent infections, which lead to a high misdetection rates. Therefore, a new method for parasite diagnosis with increased sensitivity is urgently needed.MethodsGoats in Nimu County (Tibet, China) infected with Schistosoma turkestanicum in an epidemic area were selected according positivity for the infection by faecal examination. Adult worms were collected, eggs were extracted by the sodium hydroxide (NaOH) erosion method, and soluble worm antigen preparation (SWAP) and soluble egg antigen (SEA) were isolated. The best coating concentration of the antigens and the best degree of dilution for serum were determined by square array experiments, and the optimal blocking solution and serum diluents were selected. The specificity, sensitivity and crossover of the ELISA method were determined using 48 samples of goat sera positive for S. turkestanicum, 100 samples of goat sera negative for S. turkestanicum, and 54 samples of buffalo sera positive for S. japonicum. Serological assays were established with samples from goats naturally grazed in a rural area of Nimu County, Tibet Province, by using the indirect ELISA method for the diagnosis of schistosomiasis, and faeces were collected for miracidia hatching. The sensitivity of the two detection methods was compared.ResultsEggs of S. turkestanicum were distributed in the host duodenum and small intestine. Eggs in the host intestinal wall were extracted by the NaOH erosion method, which provided intact eggs with reduced impurities. The testing results obtained by isolating SEA were more stable than those obtained by using SWAP and less affected by the coating concentration and serum dilution. Additionally, the value of positive serum/negative (P/N) serum for SEA was much higher than that for SWAP. The optimal coating concentration of SEA was 0.5 μg/ml, and the optimal serum dilution was 1:100. The specificity and sensitivity of the indirect ELISA based on SEA (S. turkestanicum) were both 100%, and no cross-reactivity was found with schistosomiasis japonica. An epidemiological survey of goats in naturally infected areas showed that the prevalence rate of schistosomiasis turkestanica was 93%, and the infection rate increased with the ages of the goats.ConclusionWe aimed to develop a sensitive method to utilize in the mass field screening of livestock. As a diagnostic antigen, SEA (S. turkestanicum) was more suitable for serological testing than SWAP (S. turkestanicum). The indirect ELISA using SEA (S. turkestanicum) exhibited good sensitivity, specificity and no cross-reactivity with schistosomiasis japonica. The degree of infectivity and prevalence of S. turkestanicum infection in endemic areas are serious and should be a focus of concern among local departments.

Ecotoxicoparasitology of the gastrointestinal tracts of pinnipeds: the effect of parasites on the potential bioavailability of total mercury (THg)

Acanthocephalans, cestodes, and some species of nematodes acquire nutrients from the lumen contents in the gastrointestinal (GI) tract of their definitive host. These parasites are exposed to toxicants, such as mercury (Hg), through passive or active feeding mechanisms; therefore, the focus of this study was to determine if there is an effect of parasites on the dietary availability of total mercury (THg) within piscivorous pinniped hosts. THg concentrations ([THg]) in selected host tissues, parasites, and GI lumen contents from 22 California sea lions (Zalophus californianus), 15 ringed seals (Phoca hispida), and 4 spotted seals (Phoca largha) were determined. Among all pinnipeds, [THg] in acanthocephalans of the large intestine were significantly higher than concentrations in other samples (host lumen contents, other parasites and host intestinal wall), irrespective of location within the host GI tract. δ15N values of parasites depended both on parasite group and location within the GI tract. δ15N values were consistently higher in parasites inhabiting the large intestine, compared to elsewhere in the GI tract, for both sea lions and seals. δ13C values in parasites did not differ significantly from host GI tissues. Based on both [THg] and stable isotope values, parasites are likely affecting the Hg bioavailability within the GI lumen contents and host tissues, and toxicant-parasite interactions appear to depend on both parasitic taxon as well as their location within the host intestine.

On the Migration of Cystacanths Sphaerirostris Picae (Acanthocephala, Centrorhynchidae) in Paratenic host Lacerta Agilis, Histopathology

On the Migration of CystacanthsSphaerirostris Picae(Acanthocephala, Centrorhynchidae) in Paratenic hostLacerta Agilis, HistopathologyThe penetration mechanism ofSphaerirostris picaecystacanths in intestinal wall of the paratenic hostLacerta agilisand characteristic features of inflammatory changes in host intestinal wall are examined. Inflammatory reaction is characterized by predomination of eosinophiles and comparatively small amount of neutrophiles. The reaction is much more pronounced when cystacanth is placed in parallel to the wall of intestine. Extensive edema, plethora, stases in vessels, and slight hemorrhages are observed in submucous membrane. Inflammatory infiltration is less pronounced in case of perpendicular orientation of the proboscis. The secretory glands in cystacanths were not found, secretion on the tegumental surface was not seen, as well as no morphological effect of lytic enzymes on host tissues. The penetration of host intestinal wall is shown to be mechanic, advancement of the cystacanth through the wall of intestine is due to alterations of partial evagination and invagination of the presoma in combination with contractions of the metasoma.

Intestinal distribution of worms and host ingesta in Nippostrongylus brasiliensis.

The gastrointestinal nematode Nippostrongylus brasiliensis is thought to feed on host ingesta, and it is generally thought that the presence of ingesta determines the distribution of this parasite within the host intestine. However, these assertions have not been supported by direct evidence. The purpose of this study was to test the hypothesis that N. brasiliensis worms are preferentially found in regions of the host small intestine containing ingesta. The relationship between worm and ingesta distribution was investigated using mice infected with N. brasiliensis and killed on day 8 postinfection at 0130, 0730, 1330, or 1930 hr. There was an inverse relationship between worm and ingesta distributions, and the worms were distributed significantly more anteriad in the intestine than host ingesta, at all times during the 24 hr. To determine what the worms fed on, host ingesta, tissue, and blood were differentially labeled with the fluorescent dyes rhodamine B and Fluoresbrite. The results of this study suggest that N. brasiliensis feeds on the host's intestinal wall, and that habitat distribution of this parasite within the small intestine is not directly related to the presence of luminal ingesta.

Identification and partial characterization of the proteases from different developmental stages of schistocephalus solidus (cestoda: Pseudophyllidae

The proteolytic activities of extracts prepared from procercoids and plerocercoids as well as adults of the pseudophyllidean cestode Schistocephalus solidus were examined using several proteins and synthetic peptides as substrates. Whole bodies of procercoids and the isolated syncytial tegument of plerocercoids and adults prepared by freeze-thaw were studied. Extracts of procercoids contained a chymotrypsin-like proteinase exhibiting a molecular weight of 23,500 determined by gel filtration chromatography. The proteinase showed collagenolytic activity and had a pH optimum at 8. Such a proteinase was absent in plerocercoids and adults. In these developmental stages leucine aminopeptidases were detected in the isolated syncytial tegument having molecular weights of 93,500 (plerocercoids) and 89,000 (adults), respectively. The aminopeptidases in both stages displayed optimal activity at pH 8.5. The chymotrypsin-like proteinase of the procercoid is possibly necessary for the penetration of the host's intestinal wall, whereas the aminopeptidases of the plerocercoid and the adult of S. solidus may aid in parasite nutrition by degrading oligopeptides at the tegumental surface.

Autoradiographic and morphological studies on the uptake of the triglyceride [3H]-glyceroltrioleate by acanthocephalans

Two eoacanthocephalans, four palaeacanthocephalans, including the infective larvae of one species, and one archiacanthocephalan were exposed in vitro to a labelled triglyceride. The nutrient was almost exclusively incorporated by the tegument of the presoma. The uptake of [3H]-glyceroltriolete started at the anterior half of the presoma, followed by a consecutive labelling of the entire presoma tegument and the lemnisci. In the archiacanthocephalan, however, the general uptake was comparatively low. In the final host of the acanthocephalans, the absorbed nutrient must derive from the host's intestinal wall, injured by the parasite. In the eoacanthocephalans and the palaeacanthocephalans, the labelled nutrient was most intensively taken up by the tegument of the hooks. Inside the hook tegument, the basal membrane and the outer membrane form a labyrinth of entangling crypts and protuberances. In the surrounding proboscis tegument as well as in the neck tegument, the lipid seemed to be transported along these two membranes. In addition to its absorption by the presoma tegument, the labelled nutrient was intensively incorporated by the apical organ and the paired lateral organ of the eoacanthocephalan presoma and by the terminal part of the uterine endothelium of all female eoacanthocephalans and palaeacanthocephalans. The use of the nutrient by the parasites is discussed.

Ultrastructural studies on the plerocercoid ofSpirometra erinacei in experimental sparganosis

The gland cell and the tegument of the Spirometra erinacei plerocercoid following parasite migration in hamsters were observed by electron microscopy. Gland cells released secretory granules mainly into the frontal pit during each stage of migration. The density of the perinuclear secretory granules decreased markedly just after parasite penetration through the host intestinal wall. Therefore, gland cells seem to play an essential role in penetration. During migration in the host, lipid-like droplets appeared in the subtegumental cells and tegument and increased in number and size during migration in the abdominal cavity, but they had disappeared from plerocercoids recovered from subcutaneous tissues. Myelin-like bodies also occurred in the tegument, subtegumental cells and medullary matrix; they were released directly through the tegument into the frontal pit. Discoidal bodies gathered in the distal part of the tegument, where filamentous microtriches appeared in regions from which microtriches had been peeled off during penetration.

Fatty acid composition of plerocercoid and adult of Spirometra erinacei and the host-parasite relationship

Fukushima T., Abe K., Nakagawa A. and Yamane Y. 1988. Fatty acid composition of plerocercoid and adult of Spirometra erinacei and the host-parasite relationship. International Journal for Parasitology 18: 27–31. Different patterns of fatty acids were identified in the two growth stages, plerocercoid and adult, of S. erinacei and considered from the viewpoint of the host-parasite relationship. Differences in fatty acid compositions of C 16:0 (palmitate), C 18:0 (stearate), C 18:1 (oleate), C 18:2 (linoleate), C 20:0 (arachidate), C 20:2 (eicosadienoate) and C 20:5 (eicosapentaenoate) were observed in different proglottides of adult worm. C 16:0 and C 18:0 in scoleces, C 18:2 and C 20:5in mature proglottides approximated the proportions of those in the host intestinal wall. Proportions of C 16:0, C 18:0, C 18:2, C 20:4 (arachidonate) and C 22:5 (docosapentaenoate) of plerocercoids were found to be influenced by the proportions of fatty acids in the host serum. c 20:0 was higher in plerocercoids from snakes than those from hamsters in spite of the fact that C 20:0 in snake and hamster sera was almost equal. We discuss these differences of fatty acid composition in relation to the absorption and metabolism of lipids.

The histopathology of Neoechinorhynchus hutchinsoni Datta, 1936 (Neoacanthocephala): Neoechinorhynchidae) infection in Nemacheilus kashmirensis Hora.

Histopathological studies of Neoechinorhynchus hutchinsoni infection in Nemacheilus kashmirensis show partial or complete damage of the host intestinal wall, depending upon the degree of penetration. Increased number of goblet cells are seen at the site of unperforated wounds but where the intestinal wall is completely perforated the goblet cells were undifferentiated. The parasite destroys the mucosa, lamina propria, muscle layer and serosa leading to perforation. This report of perforation by Neoechinorhynchus hutchinsoni is the first in the genus Neoechinorhynchus.

Host-Parasite Relationships of Helminth Parasites in Leeches of the Genus Haemopis. I. Associations at the Individual Host Level

Specimens of six species of leeches of the genus Haemopis were necropsied and examined histologically in an attempt to elucidate the in situ host-parasite relationships between the leeches and their helminths. Specimens of five species of mature trematodes were recovered from the gastrointestinal ceca. The histological organization of the gastrointestinal ceca was found to be quite similar to that of the small intestine of ictalurid fishes, and it is suggested that ancestral macroderoidid parasites of leeches may have been preadapted to the intestinal environment of catfishes. This explanation is proposed to account for the continued existence of members of the genus Alloglossidium in the intestine of both piscine and hirudinean hosts. Extreme interand intraspecific crowding of enteric trematodes also was observed; a possible mechanism for reduction of competition through habitat partitioning is examined. Immature trematodes and nematodes were observed to be encysted along the blood vessels of the gastrointestinal ceca. A nonspecific fibrous encapsulation response to these cysts was observed frequently; in some cases, this host response appeared to induce disintegration of the larval trematodes. Six species of mature digenetic trematodes from leeches of the genus Haemopis Savigny, 1822 have been described recently (Demshin, 1968; Fish & Vande Vusse, 1976; Neumann & Vande Vusse, 1976; Schmidt & Chaloupka, 1969; Timmers, 1979). With the exception of a brief description of the attachment of some of these trematodes to the host intestinal wall (Taft & Kordiyak, 1973), no effort has been made to examine the nature of these unusual host-parasite systems. Therefore, studies were undertaken in an attempt to describe the in situ relationships between helminth parasites, both enteric and parenteric, and leeches of the genus Haemopis. Data on prevalence, abundance, and host-specificity also were obtained and are presented in part II (Riggs & Ulmer, 1983). MATERIALS AND METHODS Leeches were collected at night during late spring and early summer of 1976 and 1977 in the shallows and from marshy shorelines of several lakes 1We would like to thank Drs. Frederick Vande Vusse, Roy T. Sawyer, Marvin Meyer, and L. R. Richardson for contributing their knowledge of and experience with the hirudineans and their parasites. We are especially grateful to Dr. Gerald W. Esch for his careful reviews of the manuscript and his helpful suggestions during its preparation. 2 Publication costs, in part, are being met by a grant from the Spencer-Tolles Fund of the American Microscopical Society. 3 Present address: Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109, U.S.A. TRANS. AM. MICROSC. SOC., 102(3): 213-226. 1983. () Copyright, 1983, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.180 on Tue, 27 Sep 2016 05:27:58 UTC All use subject to http://about.jstor.org/terms TRANS. AM. MICROSC. SOC. and ponds located in north-central Minnesota and northwestern Iowa. Necropsies were conducted 24-48 h after collections; gross observations on living worms in tlhe host gut were made using a stereo microscope equipped with 30x and 60x magnification. The techniques of Fried et al. (1970) were employed in the study of encysted metacercariae. The posterior one-third of the intestines of five specimens each of Haemopis marmorata (Say, 1824) Moore, 1901, H. grandis (Verrill, 1874), H. plumbea Moore, 1912 were removed, extended, and fixed in 10% buffered-formalin at 70?C and embedded in paraffin. Sagittal sections of the intestines from two specimens of each host species were cut serially at 10 /m and the remaining intestinal preparations were sectioned tranversely at 15 /um. All sections were stained in Harris' hematoxylin and eosin Y.

Host-Parasite Relationships of Helminth Parasites in Leeches of the Genus Haemopis. I. Associations at the Individual Host Level

Specimens of six species of leeches of the genus Haemopis were necropsied and examined histologically in an attempt to elucidate the in situ host-parasite relationships between the leeches and their helminths. Specimens of five species of mature trematodes were recovered from the gastrointestinal ceca. The histological organization of the gastrointestinal ceca was found to be quite similar to that of the small intestine of ictalurid fishes, and it is suggested that ancestral macroderoidid parasites of leeches may have been preadapted to the intestinal environment of catfishes. This explanation is proposed to account for the continued existence of members of the genus Alloglossidium in the intestine of both piscine and hirudinean hosts. Extreme interand intraspecific crowding of enteric trematodes also was observed; a possible mechanism for reduction of competition through habitat partitioning is examined. Immature trematodes and nematodes were observed to be encysted along the blood vessels of the gastrointestinal ceca. A nonspecific fibrous encapsulation response to these cysts was observed frequently; in some cases, this host response appeared to induce disintegration of the larval trematodes. Six species of mature digenetic trematodes from leeches of the genus Haemopis Savigny, 1822 have been described recently (Demshin, 1968; Fish & Vande Vusse, 1976; Neumann & Vande Vusse, 1976; Schmidt & Chaloupka, 1969; Timmers, 1979). With the exception of a brief description of the attachment of some of these trematodes to the host intestinal wall (Taft & Kordiyak, 1973), no effort has been made to examine the nature of these unusual host-parasite systems. Therefore, studies were undertaken in an attempt to describe the in situ relationships between helminth parasites, both enteric and parenteric, and leeches of the genus Haemopis. Data on prevalence, abundance, and host-specificity also were obtained and are presented in part II (Riggs & Ulmer, 1983). MATERIALS AND METHODS Leeches were collected at night during late spring and early summer of 1976 and 1977 in the shallows and from marshy shorelines of several lakes 1We would like to thank Drs. Frederick Vande Vusse, Roy T. Sawyer, Marvin Meyer, and L. R. Richardson for contributing their knowledge of and experience with the hirudineans and their parasites. We are especially grateful to Dr. Gerald W. Esch for his careful reviews of the manuscript and his helpful suggestions during its preparation. 2 Publication costs, in part, are being met by a grant from the Spencer-Tolles Fund of the American Microscopical Society. 3 Present address: Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109, U.S.A. TRANS. AM. MICROSC. SOC., 102(3): 213-226. 1983. () Copyright, 1983, by the American Microscopical Society, Inc. This content downloaded from 157.55.39.180 on Tue, 27 Sep 2016 05:27:58 UTC All use subject to http://about.jstor.org/terms TRANS. AM. MICROSC. SOC. and ponds located in north-central Minnesota and northwestern Iowa. Necropsies were conducted 24-48 h after collections; gross observations on living worms in tlhe host gut were made using a stereo microscope equipped with 30x and 60x magnification. The techniques of Fried et al. (1970) were employed in the study of encysted metacercariae. The posterior one-third of the intestines of five specimens each of Haemopis marmorata (Say, 1824) Moore, 1901, H. grandis (Verrill, 1874), H. plumbea Moore, 1912 were removed, extended, and fixed in 10% buffered-formalin at 70?C and embedded in paraffin. Sagittal sections of the intestines from two specimens of each host species were cut serially at 10 /m and the remaining intestinal preparations were sectioned tranversely at 15 /um. All sections were stained in Harris' hematoxylin and eosin Y.

Characostomum howelli n.sp. (Nematoda: Strongylidae) from the giant African rat Cricetomys gambianus and other helminths from Tanzania.

5 males and 5 females of this species were collected from the intestine of the giant African rat Cricelomys gambianus from Minaki Secondary School, near Pugu, Tanzania. Some of the specimens have parts of the host's intestinal wall tissues in their buccal capsules and some specimens have the anterior part of the intestine dark in colour. This may suggest that these nematodes attach themselves to their host's intestinal wall and probably feed on its blood.The elongated body is cylindrical, tapering at both ends, the anterior end recurved dorsally. The cuticle is transversely striated and the buccal aperture is round, lacking a radial crown but the cuticle of the external surface of the buccal capsule forms several annular thickenings around the buccal aperture. There are 4 main external cuticular bands extending to near the buccal aperture. The buccal capsule is funnel-shaped with extremely thick and highly chitinized walls, the dorsal wall notably shorter than the ventral. The thickness of the walls is uneven, with maximum thickness posteriorly. The capsule lacks teeth and the dorsal oesophageal gland terminates near the anterior edge of the buccal capsule. The oesophageal funnel is chitinized. The oesophagus is claviform owith a wider posterior part and ends in a triradiate valve.

The Post-embryonic Developmental Stages of Cestodes

This chapter discusses the advances in knowledge made in some aspects of the biology of post-embryonic stages of cestodes in the past 15 years. It summarizes the information on development and structure, emphasizing overall similarities (or differences) among the major groups of cestodes, and indicating some areas in which further research is deemed essential or profitable. Some of the factors, which form the basis of the physiological host specificity or susceptibility are suggested in this chapter. These include (1) enzyme concentration in the host intestine, which determines the hatching of the oncosphere; (2) intestinal emptying time in relation to time required for the hatching and establishment of the oncosphere; (3) the thickness or consistency of the host intestinal wall to be penetrated by the embryo, and (4) the environment of the host's body cavity which may permit or inhibit continued growth after the initiation of post-embryonic development.