Humoral and cellular response to infection with Echinostoma revolutum in the golden hamster, Mesocricetus auratus

Echinostomes and Other Intestinal Trematode Infections

Intestinal trematodes are among the most common types of parasitic worms. About 76 species belonging to 14 families have been recorded infecting humans. Infection commonly occurs when humans eat raw or undercooked foods that contain the infective metacercariae. These parasites are diverse in regard to their morphology, geographical distribution and life cycle, which make it difficult to study the parasitic diseases that they cause. Many of these intestinal trematodes have been considered as endemic parasites in the past. However, the geographical limits and the population at risk are currently expanding and changing in relation to factors such as growing international markets, improved transportation systems, new eating habits in developed countries and demographic changes. These factors make it necessary to better understand intestinal trematode infections. This chapter describes the main features of human intestinal trematodes in relation to their biology, epidemiology, host-parasite relationships, pathogenicity, clinical aspects, diagnosis, treatment and control.

Foodborne intestinal flukes in Southeast Asia

In Southeast Asia, a total of 59 species of foodborne intestinal flukes have been known to occur in humans. The largest group is the family Heterophyidae, which constitutes 22 species belonging to 9 genera (Centrocestus, Haplorchis, Heterophyes, Heterophyopsis, Metagonimus, Procerovum, Pygidiopsis, Stellantchasmus, and Stictodora). The next is the family Echinostomatidae, which includes 20 species in 8 genera (Artyfechinostomum, Acanthoparyphium, Echinochasmus, Echinoparyphium, Echinostoma, Episthmium, Euparyphium, and Hypoderaeum). The family Plagiorchiidae follows the next containing 5 species in 1 genus (Plagiorchis). The family Lecithodendriidae includes 3 species in 2 genera (Phaneropsolus and Prosthodendrium). In 9 other families, 1 species in 1 genus each is involved; Cathaemaciidae (Cathaemacia), Fasciolidae (Fasciolopsis), Gastrodiscidae (Gastrodiscoides), Gymnophallidae (Gymnophalloides), Microphallidae (Spelotrema), Neodiplostomidae (Neodiplostomum), Paramphistomatidae (Fischoederius), Psilostomidae (Psilorchis), and Strigeidae (Cotylurus). Various types of foods are sources of human infections. They include freshwater fish, brackish water fish, fresh water snails, brackish water snails (including the oyster), amphibians, terrestrial snakes, aquatic insects, and aquatic plants. The reservoir hosts include various species of mammals or birds.The host-parasite relationships have been studied in Metagonimus yokogawai, Echinostoma hortense, Fasciolopsis buski, Neodiplostomum seoulense, and Gymnophalloides seoi; however, the pathogenicity of each parasite species and host mucosal defense mechanisms are yet poorly understood. Clinical aspects of each parasite infection need more clarification. Differential diagnosis by fecal examination is difficult because of morphological similarity of eggs. Praziquantel is effective for most intestinal fluke infections. Continued efforts to understand epidemiological significance of intestinal fluke infections, with detection of further human cases, are required.

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.

The expulsion of Echinostoma trivolvis from C3H mice: differences in glycoconjugates in mouse versus hamster small intestinal mucosa during infection

Mucosal glycoconjugates were examined in C3H mice and in hamster small intestines infected with Echinostoma trivolvis and in uninfected rodents, using periodic-acid Schiff (PAS) and high-iron diamine-alcian blue (HID-AB) staining and three different fluorescein-conjugated lectins: Triticum vulgaris agglutinin (WGA), Helix pomatia agglutinin (HPA) and Griffonia simplicifolia agglutinin (GSA-II). Lectin-labelling by electron microscopy was also undertaken with WGA and HPA lectin-gold probes. HID-AB stain demonstrated that the most mature goblet cells of the mouse villi contain sulfomucins, whereas those of hamsters contain sialomucins. The expression of lectin-binding sites and the intensity of the lectin binding in the small intestines were changed by echinostome infection. Specific differences in the reaction to mucin glycoproteins were clearly observed between the mouse and hamster intestines infected with E. trivolvis; lectin-binding to hyperplastic goblet cells and crypts in the infected mice increased, while no marked increase in the number of goblet cells and reaction to the glycoconjugates were observed in the infected hamsters. These findings indicate that the expression of terminal N-acetyl-D-galactosamine, sialic acid and N-acetyl-D-glucosamine increased in mucins secreted from hyperplastic goblet cells associated with E. trivolvis infection in mice. No marked increase in these glycoconjugates occurred in hamster infections. These findings reflect clear differences in infectivity of E. trivolvis in C3H mice versus hamsters.

The effect of dexamethasone on the course of Echinostoma caproni and E. trivolvis infections in the golden hamster (Mesocricetus auratus)

Golden hamsters (Mesocricetus auratus) were given intramuscular injections of dexamethasone and infected with Echinostoma caproni or E. trivolvis. All animals were necropsied on day 14 postinfection. Dexamethasone treatment at high doses resulted in increased parasite recovery. Decreased total white blood cell counts and decreased relative splenic weights were observed in corticosteroid-treated hamsters. Dexamethasone-treated animals also demonstrated significantly lower mean parasite dry weights for E. caproni. Specific serum IgG against the parasites was not detected in corticosteroid-treated hamsters on day 14 postinfection.

An enzyme-linked immunosorbent assay for detecting anti-Echinostoma trivolvis (trematoda) IgG in experimentally infected ICR mice. Cross-reactivity with E. caproni

An enzyme-linked immunosorbent assay (ELISA) utilizing surface glycocalyx-membrane crude antigen of adult Echinostoma trivolvis was developed for the detection of circulating anti-E. trivolvis IgG in experimentally infected ICR mice. An antigen concentration of 10.0 micrograms/ml was used, and it was possible to detect anti-E. trivolvis IgG at a dilution of 1/3,200. On day 10 postinfection (p.i.), all infected mice had anti-E. trivolvis IgG reactive with the surface glycocalyx antigen. The IgG level varied over a 40-day period, showing a time-dependent pattern with a peak on day 16 p.i. The results concerning reciprocal cross-reactivity indicate that adult E. trivolvis and E. caproni share at least some of the surface antigens and express species-specific antigenic determinants in ICR mice at similar, nonsignificantly (P = 0.76) different levels.

Antibodies in the serum of golden hamsters experimentally infected with the intestinal trematode Echinostoma caproni

The serum antibody response in golden hamsters (Mesocricetus auratus) infected with the intestinal trematode Echinostoma caproni was examined with ELISA, SDS-PAGE and Western blot, and IFAT techniques. All methods showed that the hamsters responded slowly but developed a clear positive humoral response to the infection. In most hamsters, an antibody response to infection could not be detected earlier than 11-13 weeks after infection with 6 or 25 metacercariae, and responses were weak when compared to previous results from mice infected with the same parasite. IFAT with positive hamster sera on live juvenile E. caproni showed only fluorescence at the posterior tip, which is a different pattern from that seen using from infected mice, indicating a different response to antigens on the juvenile parasites by these two hosts. The results are discussed in relation to the limited selfcure and development of resistance which is observed in golden hamsters infected with E. caproni.

Echinostoma caproni in mice: studies on the attachment site of an intestinal trematode

During infection in mice Echinostoma caproni is attached to the mucosa of the small intestine with the ventral sucker (acetabulum). The morphology, histology and dynamics of attachment sites from primary infections were examined. The sites were highly characteristic microscopically, and consisted of a plug of grasped mucosa occupying the cavity of the ventral suckers. The mucosa in the area of the small intestine where the parasite resided showed marked villous atrophy and crypt hyperplasia. The cellular composition of the attachment sites did not appear significantly different from what was seen in other parts of the mucosa in the residential area, and the study did not reveal any specific cellular host response at the attachment site. After mechanical removal of the parasites from unfixed tissue in saline, the attachment sites gradually reduced in size and disappeared. It is suggested that the attachment sites are only temporary structures, formed by the mechanical grasp of the ventral sucker as the parasites move about in the residential area of the intestine.