Expulsion of Echinostoma trivolvis (Cort, 1914) Kanev, 1985 and retention of E. caproni Richard, 1964 (Trematoda: Echinostomatidae) in C3H mice: pathological, ultrastructural, and cytochemical effects on the host intestine

Immunology and pathology of echinostomes and other intestinal trematodes

Intestinal trematodes constitute a major group of helminths that parasitize humans and animals with relevant morbidity and mortality. Despite the importance of the intestinal trematodes in medical and veterinary sciences, immunology and pathology of these helminth infections have been neglected for years. Apart from the work focused on the members of the family Echnistomatidae, there are only very isolated and sporadic studies on the representatives of other families of digeneans, which makes a compilation of all these studies necessary. In the present review, the most salient literature on the immunology and pathology of intestinal trematodes in their definitive hosts in examined. Emphasis will be placed on members of the echinostomatidae family, since it is the group in which the most work has been carried out. However, we also review the information on selected species of the families Brachylaimidae, Diplostomidae, Gymnophallidae, and Heterophyidae. For most of these families, coverage is considered under the following headings: (i) Background; (ii) Pathology of the infection; (iii) Immunology of the infection; and (iv) Human infections.

Changes in resident microbiota associated with mice susceptibility or resistance to the intestinal trematode Echinostoma caproni

Echinostoma caproni (Trematoda: Echinostomatidae) is an intestinal trematode with no tissue phases in the definitive host that has been extensively used as an experimental model to study the factors that determine resistance against intestinal helminths. In E. caproni infections in mice, interleukin-25 (IL-25) plays a critical role and it is required for the resistance to infection. However, little is known on the factors that determine its production. Primary E. caproni infection in mice is characterized by the development of chronic infections and elevated worm recovery, in relation to a local Th1 response with elevated production of interferon-γ. However, partial resistance against secondary E. caproni infections in ICR (Institute of Cancer Research) mice is developed after the chemotherapeutic cure of a primary infection and the innately produced IL-25 after pharmacological treatment. In this paper, we analyse the potential role of intestinal microbiota in the production of IL-25, and the subsequent resistance to infection. For this purpose, we analysed the production of IL-25 under conditions of experimental dysbiosis and also the changes in the resident microbiota in primary infections, pharmacological curation and secondary infections. The results obtained showed that resident microbiota play a major role in the production of IL-25 and the appearance of members of the phylum Verrucomicrobia as a consequence of the curation of the primary infection could be related to the partial resistance to secondary infection.

Neglected Food-Borne Trematodiases: echinostomiasis and gastrodiscoidiasis

In the present paper, we review two of the most neglected intestinal food-borne trematodiases: echinostomiasis, caused by members of the family Echinostomatidae, and gastrodiscoidiasis produced by the amphistome Gastrodiscoides hominis. Both parasitic infections are important intestinal food-borne diseases. Humans become infected after ingestion of raw or insufficiently cooked molluscs, fish, crustaceans, amphibians or aquatic vegetables. Thus, eating habits are essential to determine the distribution of these parasitic diseases and, traditionally, they have been considered as minor diseases confined to low-income areas, mainly in Asia. However, this scenario is changing and the population at risk are currently expanding in relation to factors such as new eating habits in developed countries, growing international markets, improved transportation systems and demographic changes. These aspects determine the necessity of a better understanding of these parasitic diseases. Herein, we review the main features of human echinostomiasis and gastrodiscoidiasis in relation to their biology, epidemiology, immunology, clinical aspects, diagnosis and treatment.

Interleukin-25 Induces Resistance Against Intestinal Trematodes

Echinostoma caproni is an intestinal trematode that has been extensively used as an experimental model to investigate the factors determining the resistance to intestinal helminths or the development of chronic infections. ICR mice are permissive hosts for E. caproni in which chronic infections are developed, concomitantly with local Th1 responses, elevated levels of local IFN-γ, inflammation and antibody responses. However, mice develop partial resistance to homologous challenge infections after cure of a primary infection, which converts this subject into an adequate model for the study of the mechanisms generating resistance against intestinal helminths. The purpose of the present study was to compare the immune response induced in primary and secondary infections to elucidate the factors determining the different outcome of the infection in each type of infection. The results obtained indicate that susceptibility is determined by the lack of IL-25 expression in response to primary infection. In contrast, infection in an environment with elevated levels of IL-25, as occurs in challenge infection, results in a Th2 phenotype impairing parasite survival. This was confirmed by treatment of naïve mice with exogenous IL-25 and subsequent infection. Changes induced in goblet cell populations and mucin glycosylation could be implicated in resistance to infection.

Subcutaneous injection of exosomes reduces symptom severity and mortality induced by Echinostoma caproni infection in BALB/c mice

Recent studies have shown the importance of exosomes in the host-parasite relationship. These vesicles are an important part of the excretory/secretory pathway for proteins with the potential to alter immune responses. Therefore, in the present study, we examined the immunomodulatory role of exosomes in BALB/c mice using Echinostoma caproni as an experimental model of intestinal helminth infection. For this purpose, BALB/c mice were injected twice s.c. with purified exosomes of E. caproni, followed by experimental infection. We report a delay in the development of the parasite in mice immunised with exosomes, a concomitant reduced symptom severity and increased survival upon infection. Immunisations with exosomes evoked systemic antibody responses with high levels of IgM and IgG. IgG1, IgG2b and IgG3 are the subtypes responsible for the IgG increase. These antibodies showed specific recognition of exosomal proteins, indicating that these vesicles carry specific antigens that are involved in the humoral response. The administration of exosomes induced an increase of IFN-γ, IL-4 and TGF-β levels in the spleen of mice prior to infection. The subsequent infection with E. caproni resulted in a further increase of IL-4 and TGF-β, together with an abrupt overproduction of IL-10, suggesting the development of a Th2/Treg immune response. Our results show that the administration of exosomes primes the immune response in the host, which in turn can contribute to tolerance of the invader, reducing the severity of clinical signs in E. caproni infection.

Partial resistance to homologous challenge infections of the digenean Echinostoma caproni in ICR mice

In the present paper, we analyse the effect of a primary infection of ICR mice with Echinostoma caproni (Trematoda: Echinostomatidae) on the generation of resistance against homologous challenge infections. In ICR mice, E. caproni induces chronic infections concomitantly with strong responses characterized by the development of T-helper 1 (Th1)-type local immune responses with elevated levels of local interferon-gamma (IFN-γ) and inflammatory and antibody responses. Here, the effect of the response generated against a primary infection with E. caproni in the generation of resistance against subsequent homologous infections was analysed. For this purpose, ICR mice were challenged with metacercariae of E. caproni and the results obtained showed that primary infection induces partial resistance against subsequent homologous infections in ICR mice. This resistance was expressed as a reduced rate of infection, worm recovery and worm size, indicating that primary infection induces changes in the host, making a hostile environment for the development of the parasite.

Differential alterations in the small intestine epithelial cell turnover during acute and chronic infection with Echinostoma caproni (Trematoda)

Background

The intestinal epithelium plays a multifactorial role in mucosal defense. In this sense, augmented epithelial cell turnover appears as a potential effector mechanism for the rejection of intestinal-dwelling helminths.

Methods

A BrdU pulse-chase experiment was conducted to investigate the infection-induced alterations on epithelial cell kinetics in hosts of high (mouse) and low (rat) compatibility with the intestinal trematode Echinostoma caproni.

Results

High levels of crypt-cell proliferation and tissue hyperplasia were observed in the ileum of infected mice, coinciding with the establishment of chronic infections. In contrast, the cell migration rate was about two times higher in the ileum of infected rats compared with controls, with no changes in tissue structure, indicating that an accelerated cell turnover is associated with worm expulsion.

Conclusion

Our results indicate that E. caproni infection induces a rapid renewal of the intestinal epithelium in the low compatible host that may impair the establishment of proper, stable host-parasite interactions, facilitating worm clearance.

Echinostoma caproni (Trematoda): differential in vivo mucin expression and glycosylation in high- and low-compatible hosts

Enhanced mucus production and release appears to be a common mechanism for the clearance of intestinal helminths, and this expulsion is normally mediated by Th2-type immune responses. To investigate the factors determining the expulsion of intestinal helminths, we have analysed in vivo expression of mucin genes at the site of infection in two host species displaying different compatibility with Echinostoma caproni (Trematoda). Surprisingly, a general down-regulation on mucin mRNA expression was detected in low-compatible hosts (rats) coinciding with the development of Th2/Th17 responses and the early rejection of the worms from the intestinal lumen. This suggests the existence of a mechanism by which the parasites can modulate the mucus barrier to favour their survival. In highly compatible hosts (mice), some mucin genes were found to be up-regulated throughout the infection, probably, to protect the intestinal epithelium against the infection-induced inflammation developed in this host species. Moreover, infection-induced changes on mucin glycans were also studied by lectin histochemistry. Similar alterations were detected in the ileum of infected mice and rats, except with SNA lectin, indicating that sylated mucins might play an important role in determining the evolution of the infection in each host species.

The effect of glycosylation of antigens on the antibody responses against Echinostoma caproni (Trematoda: Echinostomatidae)

In the present study, we analyse the effect of glycosylation in Echinostoma caproni (Trematoda: Echinostomatidae) antigens in antibody responses against the parasite in experimentally infected mice. It has been previously demonstrated that the mouse is a host of high compatibility with E. caproni and develops elevated responses of IgG, IgG1, IgG3 and IgM as a consequence of the infection, though the role of glycans in these responses remains unknown. To this purpose, the responses generated in mice against non-treated excretory/secretory antigens of E. caproni were compared with those observed after N-deglycosylation, O-deglycosylation and double deglycosylation of the antigens by indirect ELISA and western blot. Our results suggest that E. caproni-expressed glycans play a major role in the modulation of the immune responses. The results obtained indicate that IgG subclass responses generated in mice against E. caproni are essentially due to glycoproteins and may affect the Th1/Th2 biasing. The reactivity significantly decreased after any of the deglycosylation treatments and the N-glycans appears to be of greater importance than O-glycans. Interestingly, the IgM response increased after N-deglycosylation suggesting that carbohydrates may mask peptide antigens.

Th17 responses in Echinostoma caproni infections in hosts of high and low compatibility

In order to investigate the factors determining the expulsion of intestinal helminths, we have analyzed the in vivo expression of IL-17, TGF-β and IL-23 in several tissues of two host species displaying different compatibility with Echinostoma caproni (Trematoda). We did not observe upregulation of these cytokines in any of the tissues of the high compatible host (mice). In contrast, the responses in the host of low compatibility (rats) with the parasite were markedly different. Significant increases in the expression of IL-17 and TGF-β were observed in the Peyer's patches and the intestine from the 2 to 8 weeks post-infection. The expression of IL-23 was upregulated from 2 to 4 weeks post-infection in the spleen, Peyer's patches and the intestine. Considering together our results with those published previously the development of chronic infections appears to be related with the development of local Th1 responses, whereas the early rejection of the worms is mediated by the development a biased Th17/Th2 phenotype. The Th17 response generated in rats may facilitate the worm expulsion via the suppression of the inflammatory Th1 responses and the increase in intestinal contractility.

Development and pathology of Echinostoma caproni in experimentally infected mice

In the present article, several parasitological features of mice, each experimentally infected with 75 metacercariae of Echinostoma caproni (Trematoda: Echinostomatidae), were studied during the first 12 wk postinfection. Moreover, the early pathological responses also were analyzed and compared with data previously published on other host species of E. caproni to gain further insight into the factors determining worm rejection or establishment of chronic infections. The results obtained show that the pattern of E. caproni infection in mice is consistent with a highly compatible host-parasite system. This combination is characterized by a high worm establishment, high egg output, and long survival of the worms. However, some differences with respect to other highly compatible hosts have been observed, particularly in relation to the survival of the adult worms. Histological studies suggest that the kinetics of goblet cells, mucosal neutrophils, and mononuclear inflammatory cells in the mesentery seem to be essential in determining the course of E. caproni infection in mice.

Echinostoma caproni (Trematoda): differential in vivo cytokine responses in high and low compatible hosts

In order to investigate the factors determining the expulsion of intestinal trematodes, we have analyzed the in vivo cytokine responses at several levels and the local responses against Echinostoma caproni (Trematoda) in two host species displaying different compatibility with the parasite. The response of the high compatible host (mice) is characterized by a mixed Th1/Th2 phenotype in the spleen, Peyer's patches and mesenteric lymph nodes. At the intestine, a marked Th1 response with a marked increase of IFN-γ together with elevated number of mucosal neutrophils and expression of induced nitric oxide synthase were observed. The responses in the host of low compatibility (rats) with the parasite at the spleen, Peyer's patches and mesenteric lymph node did not show clear differences with regard to the mice. However, the response in the intestine was markedly different. In rats, a Th2 response with increase in the levels of IL-5, IL-6 and IL-13 expression was detected. According to these results, the local production of IFN-γ and the local inflammatory responses with neutrophilic infiltration are associated with the development of chronic infections, whereas the worm expulsion is related with the development of Th2 responses and appears to be based on effects on non-bone narrow-derived cells.

Immunology and pathology of intestinal trematodes in their definitive hosts

This review examines the significant literature on the immunology and pathology of intestinal trematodes in their definitive hosts. We emphasize information on selected species in six families for which the literature on these topics is extensive. The families are Brachylaimidae, Diplostomidae, Echinostomatidae, Gymnophallidae, Heterophyidae, and Paramphistomidae. For most of these families, coverage is considered under the following headings: (i) background; (ii) pathology of the infection; (iii) immunology of the infection; (iv) immunodiagnosis; and (v) human infection. Some of these heading have been subdivided further, based on the literature available on a particular topic. Following this coverage, we include a final section on the important topical literature on selected trematodes in families other than the six mentioned above.

Biological variation between two Brazilian geographical isolates of Echinostoma paraensei

The biological behaviour and morphometric data from two allopatric isolates of Echinostoma paraensei (Rio Bonito - RB and Sumidouro - SU) collected from naturally infected Nectomys squamipes from two secluded Atlantic Forest fragments were studied. Mice that had been experimentally infected with ten encysted metacercariae of each isolate were monitored weekly in two trials to analyse worm burden and the kinetics of worm distribution along the intestine. The total number of uterine eggs, wet weights and measurements of the worms and body, acetabulum, testes and ovaries were also analysed. The RB isolate showed a higher worm burden, 7.7+/-0.8, and a longer life span, 16 weeks, compared to a worm burden of 5.8+/-1.1 and life span of 9 weeks for the SU isolate. Worms of the RB isolate were clustered in the duodenum and in the bile duct while the SU isolate worms were dispersed along the small intestine of infected mice. Both isolates developed similarly as regards morphometric data and wet weight, although the total number of uterine eggs was greater in RB. The degree of intraspecific variation observed in the worm distribution along the intestine, worm burden and life span raises questions regarding the use of these criteria for species differentiation. These findings suggest that variation in biological parameters found between the E. paraensei isolates could result from geographical isolation and, in particular, the environmental conditions of transmission. Further studies on E. paraensei polulations from different forest fragments will contribute towards an understanding of the speciation of this parasite.

Echinostoma caproni: intestinal pathology in the golden hamster, a highly compatible host, and the Wistar rat, a less compatible host

The histopathological changes induced by Echinostoma caproni (Trematoda: Echinostomatidae) in a high (golden hamster) and a low compatible host (rat) were compared at 15 and 30 days post-infection. Infection of rats was characterized by a progressive increase in erosion of villi and elevated numbers of goblet cells, which could be related to the early expulsion of the parasite in a host of low compatibility. In contrast to rats, the number of goblet cell in E. caproni-infected hamsters was low, but increased numbers of neutrophils and mesenteric inflammatory cells were observed. This indicated that local inflammatory responses in hamsters were greater than in rats. An immunohistochemical study using polyclonal IgG anti-E. caproni excretory-secretory antigens demonstrated a greater level of passage of E. caproni antigens through the intestinal mucosa in hamsters than in rats, probably in relation to the greater inflammatory response. Our results indicate the fact that early inflammatory responses could be important for the establishment of E. caproni chronic infections in highly compatible hosts.

Kinetics of Antibodies and Antigens in Serum of Mice Experimentally Infected with Echinostoma caproni (Trematoda: Echinostomatidae)

The present study reports on the kinetics of antibodies and antigens in serum of mice experimentally infected with 75 metacercariae of Echinostoma caproni during the first 12 wk postinfection (wpi). Antibody titers in the serum of mice were determined by an indirect enzyme-linked immunosorbent assay (ELISA) using excretory/secretory (ES) antigens of E. caproni. The early detection of antibodies against ES antigens of E. caproni is feasible using indirect ELISA. Mice developed significant antibody responses at 2 wpi, and the values progressively increased until the end of the experiment. This may be related to the intestinal absorption of adult worm antigens that induces humoral responses. The presence of E. caproni circulating antigens was determined by a capture ELISA based on polyclonal rabbit antibodies against ES antigens of E. caproni. High levels of seroantigens in mice were detected by 1-2 wpi, probably because of the local inflammatory responses in mice induced by the adult worms. A drop in circulating antigen levels was observed at 9 wpi, which could reflect changes in the intestinal tissues over the course of the infection.

Immunity induced by the radiation-attenuated schistosome vaccine

As a paradigm for the development of a vaccine against human schistosomiasis, the radiation-attenuated (RA) vaccine has enabled the dissection of different immune responses as putative effector mechanisms. This review considers advances made in the past, and updates our knowledge with reference to recent studies that have provided new information relevant particularly to the early innate events after vaccination, and to the nature of the protective effector mechanism. Priming of a protective response by RA larvae is a highly co-ordinated series of events starting in the skin, draining lymph nodes and lungs, leading to the development of various effector responses, ranging from Th1-associated cell-mediated activity, to anti-parasitic antibodies, all of which contribute to the elimination of challenge larvae to varying extents. In this respect, the RA vaccine elicits a multifaceted immune response, from which we can derive valuable insights relevant to the future design of novel delivery systems and adjuvants for recombinant and subunit vaccines.

Growth and development of Massaliatrema misgurni (Trematoda: Heterophyidae) in mice and its metacercarial morphology

The morphology of metacercariae of Massaliatrema misgurni Ohyama et al. (Ohyama et al., Parasitol Int 2001; 50; 267-71) was described, and their infectivity, egg output, growth and development in mice until day 35 post infection (PI) were studied. Metacercarial cysts from loaches imported from China to Japan were 199-349 microm in diameter and consisted of a very thick translucent outer layer and a refractile inner layer. Excysted metacercariae basically had the shape of miniature adults, and a pair of pre-developed testes but no other genital organs were recognized. The worm recovery rate from mice was 36.7-51.7% during days 3-7 PI, and decreased remarkably to 2.5 and 1.7% at days 28 and 35 PI. The prepatent period was 3-4 days, and the egg output quickly increased and sustained high levels at days 5-7 PI, then decreased suddenly at day 8 PI, and continued at a low level until day 28 PI. The size of the body and inner organs such as the oral sucker, pharynx, acetabulum, testes, ovary and seminal receptacle quickly increased until day 3 PI, and sustained at a plateau level until day 21 PI except testes which gradually decreased until 21 PI. The number of the uterine eggs increased with a short time lag compared to other genital organs and sustained a plateau level until day 21 PI. Compared with other Heterophyidae species, M. misgurni was characterized by the remarkably fast growth and development.

The comparative development of Echinostoma caproni (Trematoda: Echinostomatidae) adults in experimentally infected hamsters and rats

The aim of the present study was to compare the development of Echinostoma caproni (Trematoda: Echinostomatidae) adults in two host species displaying different degrees of compatibility with this parasite. For this purpose, the variability in the worm recovery, egg output, and morphology of E. caproni adults during the course of experimental infections in hamsters and rats was analyzed. Student's t-tests and two-factor ANOVA analysis with the time post-infection and the host species as independent variables, and Bonferroni t-tests as post hoc analysis were used for the study. Worm recovery and egg output were host species dependent. The values were significantly higher in the worms established in hamsters than those in rats. The oral sucker area, pre-pharynx length, and pharynx area were the most conservative features, and no significant variability related to the host species was detected. In contrast, body area, collar width, esophagus length, cirrus sac area, ventral sucker area, ovarian area and anterior and posterior testicular areas were significantly higher in those worms collected from hamsters. Moreover, significant worm age-host species interactions were found for body area, ovarian area, ventral sucker area, and anterior and posterior testicular areas.

Recent Advances in the Biology of Echinostoma species in the “revolutum” Group

This review examines the significant literature on the biology of Echinostoma species in the "revolutum" group. We have considered 10 species belonging to this group. There is a considerable body of literature for four of the species, i.e. Echinostoma caproni, E. trivolvis, E. paraensei and E. revolutum. For these species we have arranged coverage to include the following headings: (1) systematic and descriptive studies; (2) experimental, manipulative and ecological studies; (3) physiological and biochemical studies; (4) immunological and molecular studies. For the remaining six species, i.e. E. friedi, E. miyagawai, E. echinatum, E. parvocirris, E. luisyrei and E. jurini, the literature is not very extensive, and headings were not used. Considerable information in various areas of modern parasitology can be obtained from species in the "revolutum" complex for which the entire life cycle is maintained in the laboratory. The review includes a list of researchers and their addresses who currently maintain such life cycles.

DEVELOPMENT OF AN ANTIBODY-BASED CAPTURE ENZYME-LINKED IMMUNOSORBENT ASSAY FOR DETECTING ECHINOSTOMA CAPRONI (TREMATODA) IN EXPERIMENTALLY INFECTED RATS: KINETICS OF COPROANTIGEN EXCRETION

The present study reports on the development of a coproantigen capture enzyme-linked immunosorbent assay (ELISA) for detecting Echinostoma caproni in experimentally infected rats. The capture ELISA was based on polyclonal rabbit antibodies that recognize excretory-secretory (ES) antigens. The detection limit of pure ES was 3 ng/ml in sample buffer and 60 ng/ml in fecal samples. The test was evaluated using a follow-up of 10 rats experimentally infected with 100 metacercariae of E. caproni, and the results were compared with those of other diagnostic methods such as parasitological examination and antibody titers determined by indirect ELISA. Coproantigens were detected in all the infected rats from the first day postinfection (DPI). The period of maximal coproantigen excretion was between 7 and 21 DPI. The values remained positive until 49-56 DPI, coinciding with the disappearance of the eggs in the stool samples of the infected rats. The kinetics of coproantigen detection were correlated with those of egg output. The present assay provides an alternative tool for the diagnosis of the echinostome infections. The proposed capture ELISA makes possible an earlier diagnosis than that provided by parasitological examination and indirect ELISA and also allows for the differentiation of past and current infections. Our results show that this assay can also be used to monitor the course of echinostome infections.

Tegumentary papillae of Echinostoma caproni cercariae (Trematoda: Echinostomatidae)

Argentophilic staining and scanning electron microscopy were used to study the tegumentary papillae of Echinostoma caproni cercariae. The most abundant tegumentary papillae were uniciliate, but multiciliate papillae were also found, mainly on the ventral aspect of the oral collar. The distribution pattern of the papillae on the body and tail was in general similar to that seen in the cercariae of other 37-collar-spined Echinostoma species. Some differences were noted between E. caproni and the allopatric species, E. trivolvis. E. caproni has a greater number of papillae associated with the collar spines than does E. trivolvis. E. caproni has uniciliate papillae on the acetabulum, whereas E. trivolvis does not. Chaetotaxy is useful to distinguish subtle morphological differences in cercarial species in the 37-collar-spined Echinostoma complex.

Changes on Schistosoma mansoni (Digenea: Schistosomatidae) worm load in Nectomys squamipes (Rodentia: Sigmodontinae) concurrently infected with Echinostoma paraensei (Digenea: Echinostomatidae)

The water rat, Nectomys squamipes, closely involved in schistosomiasis transmission in Brazil, has been found naturally infected simultaneously by Schistosoma mansoni and Echinostoma paraensei. Laboratory experiments were conducted to verify parasitic interaction in concurrent infection. It was replicated four times with a total of 42 water rats and essayed two times with 90 mice pre-infected with E. paraensei. Rodents were divided into three groups in each replication. A wild strain recently isolated from Sumidouro, RJ, and a laboratory strain of S. mansoni from Belo Horizonte (BH) was used. Rats infected with E. paraensei were challenged 4 weeks later with S. mansoni and mice 2 or 6 weeks after the infection with S. mansoni. Necropsy took place 8 weeks following S. mansoni infection. The N. squamipes treatment groups challenged with S. mansoni RJ strain showed a significant decrease (80 and 65%) in the S. mansoni parasite load when compared with their respective control groups. There was a significant change or no change in the hosts challenged with the BH strain. The persistence time of E. paraensei within host was extended in relation to control groups, with a consequent enhancement of the number of recovered worm. An E. paraensei strain-specific influence on S. mansoni parasitism is reported. This paper presents some experimental data about this interaction in N. squamipes and Mus musculus.

Rapid expulsion of the intestinal trematodes Echinostoma trivolvis and E. caproni from C3H mice by trapping with increased goblet cell mucins

Echinostoma trivolvis (Cort, 1914) adults were rejected from C3H mice by 15 days post-exposure, corresponding to the increase in the number of goblet cells. Homologous and heterologous infections with the allopatric species E. caproni (Richard, 1964) were used to confirm the effect of increased secretion of goblet cell mucins in rejecting metacercariae of challenge infections of E. trivolvis or E. caproni on days 10, 16 and 20 p.i. after primary infections of E. trivolvis metacercariae. Five-day-old juveniles of E. trivolvis and E. caproni, which were recovered from C3H mice or hamsters, were also used for challenge infections on day 10 p.i. The metacercariae and juveniles, which were challenged homologously and heterologously on day 10 p.i., were almost all expelled. The metacercariae of E. trivolvis, which were challenged homologously on day 16, were completely rejected, but only a few challenged metacercariae of E. caproni in heterologous infection were recovered. Considerable numbers of E. caproni were recovered when challenge infections with the metacercariae were done on day 20 p.i., while only a small number of E. trivolvis was recovered. All controls without primary infections showed a recovery rate of over 50% of the worms. These results indicate that increased secretion of mucins by hyperplastic goblet cells associated with primary infections of E. trivolvis may be responsible for the expulsion of worms challenged homologously with E. trivolvis and heterologously with E. caproni from the mouse host.

A comparison of Echinostoma trivolvis and E. caproni using random amplified polymorphic DNA analysis

The random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) technique was applied to two closely-related echinostome species, Echinostoma trivolvis and E. caproni, demonstrate interspecific polymorphisms of genomic DNA. Band patterns generated using five individual primers showed that these two echinostomes were genetically distinct, although they share genomic DNA to some extent.

Cytochemical localization of cytochrome c oxidase activity in mitochondria in the tegument and tegumental and parenchymal cells of the trematodes Echinostoma trivolvis, Zygocotyle lunata, Schistosoma mansoni, Fasciola gigantica and Paragonimus ohirai

Cytochrome c oxidase in the mitochondria of the tegument and tegumental and parenchymal cells was examined cytochemically in Echinostoma trivolvis, Zygocotyle lunata, Schistosoma mansoni, Fasciola gigantica and Paragonimus ohirai, trematodes that inhabit different sites in their vertebrate hosts. Clear differences in enzyme activity occurred in the mitochondria of these species, probably reflecting the different energy metabolisms of these worms. Marked aerobic metabolism occurred in S. mansoni and P. ohirai adults that inhabit the host mesenteric veins and the lungs, respectively. The tegument and parenchymal cells of S. mansoni possess relatively few, small mitochondria with tabular cristae which are heavily reactive for cytochrome c oxidase. In P. ohirai, the activity for cytochrome c oxidase in tegumental mitochondria increased gradually from juveniles to adults, reflecting that the respiratory activity increased with growth and the aerobic metabolism is activated when the worms reach the lung. P. ohirai juveniles and adults had two types of mitochondria with different shapes and enzyme activities that were located in two different types of parenchymal cells. The intestinal species, E. trivolvis had mitochondria in the basal aspect of the tegument, and some variations in enzyme activity of their mitochondria in the tegumental and parenchymal cells were observed, suggesting that they possess both aerobic and anaerobic metabolic systems. Z. lunata that live in rodent caeca are devoid of mitochondria in the tegument and have many characteristic mitochondria with undeveloped cristae in the parenchymal cells. Mitochondria of F. gigantica showed weak or no activity for cytochrome c oxidase, suggesting that the worm is well-adapted to an anaerobic environment in the host bile duct.

Light and scanning electron microscopic observations of the eggs, daughter rediae, cercariae, and encysted metacercariae of Echinostoma trivolvis and E. caproni

Light microscopy (LM) and scanning electron microscopy (SEM) were used to determine interspecific differences between various larval stages of 2 allopatric species of 37-collar-spined echinostomes, Echinostoma caproni and E. trivolvis. The abopercular and embryo diameters of the eggs of E. trivolvis were significantly different from those of E. caproni. The abopercular knobs of E. caproni and E. trivolvis have shallow and deep infoldings in the eggshells, respectively. Interspecific differences were noted in the tegument, tegumentary papillae, and spherical bodies around the mouth and in the papilliform process of the two rediae. The cercaria of E. caproni has one ventral tail fin-fold, whereas that of E. trivolvis has two; both species have two dorsal tail fin-folds. The outer metacercarial cyst diameter of E. caproni was significantly greater than that of E. trivolvis. E. caproni has a smoother outer cyst wall than does E. trivolvis.

The expulsion of Echinostoma trivolvis (Trematoda) from ICR mice: extension/retraction mechanisms and ultrastructure of the collar spines

Ultrastructural observations of collar spines and surrounding tissues associated with extension/retraction mechanisms of the spines were made on Echinostoma trivolvis recovered from ICR mice or golden hamsters. The spine consisted mainly of a homogeneous, crystalline structure of moderate to heavy electron density. The spine was surrounded by an outer layer of tegument-like material. Interstitial material was located between this outer layer and the surrounding tegument. Muscle bundles associated with spine movements were anchored by hemidesmosomes to interstitial material. Contraction of these muscles caused an invagination of the tegument surrounding a spine, resulting in spinal protrusion. Relaxation of these muscles resulted in spinal retraction. An immunocytochemistry technique using colloidal gold confirmed the presence of actin in the collar spines. Most of the collar spines of excysted metacercariae and juveniles maintained in a defined medium supplemented with fresh hamster serum were extended, whereas worms maintained in mouse serum mainly showed retracted spines. Apparently, factors in mouse serum are involved in spinal retraction.