Egg laying in vitro of Echinostoma caproni (Trematoda) in nutritive and nonnutritive media

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.

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.

Refractoriness of host haemocytes to parasite immunosuppressive factors as a putative resistance mechanism in the Biomphalaria glabrata-Echinostoma caproni system

In contrast to the growing knowledge accumulated on plant resistance to pathogens, mechanisms of parasite resistance largely remain to be elucidated in animal species. In the present study we investigated mechanisms underlying resistance/susceptibility in the snail-trematode system Biomphalaria glabrata-Echinostoma caproni. In particular, we compared the effect of the parasite excretory-secretory (E-S) products on the defence functions of haemocytes from 2 susceptible and 2 resistant snail strains. In vitro experiments showed that E. caproni E-S products inhibit adhesion and phagocytosis of haemocytes from susceptible snails. A partial biochemical characterization also suggested that the interfering factor(s) is (are) heat-labile glycosylated polypeptides of molecular mass between 10 and 30 kDa. Interestingly, haemocytes from resistant snails remained unaffected by the parasite E-S products, suggesting that a constitutive difference results in their refractoriness to the parasite's immunosuppressive factor(s).