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Aquatic snails play a key role in the transmission of parasites such as the human blood or liver flukes (Schistosomes and Fasciola sp.). During the last decade, particular efforts have been made by a small number of scientists to progress in our understanding of the molecular mechanisms underlying snail immune responses and/or host parasite interactions. Complementary approaches using the gastropod snail Biomphalaria glabrata, an intermediate host of Schistosoma mansoni, have yielded a number of unexpected results such as the existence of highly diversified pathogen-binding proteins (FREPs), or potential immune regulators similar to mammalian cytokines. Although molecular immune processes largely remain to be elucidated, accumulating data support the idea that snail innate immunity is much more complex than originally thought.

Distomatoses due to Fasciola spp. and Fasciolopsis buski are very common in the developing countries of Southeast Asia. The flukes in Laos have not yet been completely studied and described, however. In 2004, we began screening for these two distomatoses in the province of Savannakhet, in southern Laos. Our initial results showed that the causal agent of fascioliasis in humans and animals is Fasciola gigantica. The infestation rate of fascioliasis in cattle in slaughterhouses ranged from 17 to 57%, with higher percentages in buffalo (75-100%) than in cows (0-25%). In Laotian villages, the prevalence of human fascioliasis reached 2.4 % after a stool examination and 13.8 % after systematic serology testing. The prevalence of intestinal distomatosis from F. buski was 33.7%. The rate of villagers with hepatobiliary and intestinal events exceeded 2% but the involvement of these two forms of distomatosis varied highly, ranging from 1.7% (stool diagnosis) to 16.4% (serodiagnosis) for F. gigantica and 11.2% for F. buski. We have described the first cases of fascioliasis and intestinal distomatosis from F. buski in Laos.

Proteases catalyse the cleavage of internal peptide bonds within peptides and proteins. They are classified into four major classes and are involved in a broad range of eukaryotic processes. Proteases have also been found to play a number of critical roles in the virulence of pathogenic agents, particularly of nematode parasites. Parasitic proteases are involved in different aspects of host-parasite interactions. They facilitate the invasion of host tissues and allow nutrition as well as the survival of the parasite in its host. Proteases also participate in the parasite's evasion from the host's immune response. The functional diversity and complexity of these enzymes are described in this review, with a particular focus on the principally identified proteases of four helminths: Schistosoma sp., Fasciola sp., Taenia sp. and Haemonchus sp. Some of these proteases, especially the cysteine proteases secreted by the parasitic trematode Fasciola hepatica, have been successfully tested in experimental immunodiagnosis. Proteases identified in different parasites are currently under study for a use as recombinant vaccines. In this respect, proteases are proposed as major potential targets for immunotherapy and chemotherapy against parasitic diseases.

International audience; Proteases in helmintic parasites. Proteases catalyse the cleavage of internal peptide bonds within peptides and proteins. They are classified into four major classes and are involved in a broad range of eukaryotic processes. Proteases have also been found to play a number of critical roles in the virulence of pathogenic agents, particularly of nematode parasites. Parasitic proteases are involved in different aspects of host-parasite interactions. They facilitate the invasion of host tissues and allow nutrition as well as the survival of the parasite in its host. Proteases also participate in the parasite's evasion from the host's immune response. The functional diversity and complexity of these enzymes are described in this review, with a particular focus on the principally identified proteases of four helminths: Schistosoma sp., Fasciola sp., Taenia sp. and Haemonchus sp. Some of these proteases, especially the cysteine proteases secreted by the parasitic trematode Fasciola hepatica, have been successfully tested in experimental immunodiagnosis. Proteases identified in different parasites are currently under study for a use as recombinant vaccines. In this respect, proteases are proposed as major potential targets for immunotherapy and chemotherapy against parasitic diseases.; Les protéases catalysent le clivage de liaisons peptidiques internes au sein de peptides et protéines. Classées en quatre grandes familles, ces enzymes sont impliquées dans de nombreuses fonctions des cellules eucaryotes. De plus, elles jouent un rôle critique dans la virulence des pathogènes et plus particulièrement des parasites. Elles interviennent à différents niveaux de l'interaction hôte-parasite. Elles facilitent la pénétration du parasite au sein de l'hôte et y assurent sa nutrition ; elles participent également à l'échappement du parasite vis à vis du système immunitaire de l'hôte. La diversité et la complexité fonctionnelle de ces molécules sont illustrées dans cette revue qui décrit les principales protéases identifiées chez quatre helminthes : Schistosoma sp., Fasciola sp., Taenia sp. et Haemonchus sp. Certaines de ces protéases et notamment plusieurs cystéine protéases du trématode Fasciola hepatica semblent être de bons candidats pour l'immunodiagnostic. De même des protéases identifiées chez différents parasites et utilisées comme vaccin recombinant font actuellement l'objet d'études. Ainsi les protéases apparaissent comme des cibles potentielles majeures en thérapie et vaccination antiparasitaire.

Finding of specific anti-Fasciola antibodies in persons living in the central area of the delta of Niger shows that human fascioliasis is a reality in Mali. Fasciola gigantica, the single species affecting livestock is probably the parasite concerned. We think that this parasitic disease in humans is underestimated, obscured by schistosomiasis which is hyperendemic in the country. Complementary studies are much needed for better identification of the problem.

The authors study parasites of the six most commonly consumed species of fishes in Côte-d'Ivoire. Analysis of gills, alimentary canal and blood of 188 fishes reveal the presence of extremely diverse families of parasites.

The life cycle of a senegalese strain of Fasciola gigantica was carried out in France from adults recovered in the liver of naturally infected cattle (Bos taurus). Laboratory-reared Lymnaea natalensis experimentally infected shed numerous cercariae. Metacercariae were used for successful infection of sheep. In the miracidium, variations are observed in the disposition of the medio-ventral epithelial cell of the second tier. The distribution of the superficial argentophilic structures is similar to that of the miracidium of F. hepatica. The chaetotaxy of the cercaria is very closely related to that of the cercaria of a strain of F. gigantica from Madagascar shed by Lymnaea hovarum but it differs clearly from that of the cercaria of F. hepatica. The encystment of a great number of cercariae (25 %) on the surface of water suggests that this is an important factor in the extension of the foci of contamination, and therefore increases greatly the risks of infection not only for animal but also for man. It is possible that human fascioliasis caused by F. gigantica is a disease, the importance of which is under-estimated.

Four lyophilizated liver flüke antigens and one of hydatid fluid were examined for the presence of blood group like antigens P1, A, B, M and N by an hemagglutination inhibition test with hyperimmune and natural hemagglutinating sera. P1 or P1-like substance was found in the extracts of "Fasciola hepatica" and "F. gigantica" in a lower concentration than in echinoccocal fluid. This presence may explain the occurrence of anti-P1 antibodies in patients infected with liver flüke and belonging to the P2 blood group. However biochemical studies will be necessary to determine if the P1 activity is due to the blood group P1 substance of the red cell itself or due to a P1 like substance.

Integumentary argentophilic structures of the miracidium and cercaria are described and with those of F. gigantica compared. In the miracidia, the pattern of the organites of the terebratorium and the arrangement of the papillae between the first and second tier of epidermal plates are similar for the two species. However, the disposition of the medio-ventral plate of the second tier allows the miracidia of the two related species to be distinguished statistically. In the cercariae, the chaetotaxy differs between F. hepatica and F. gigantica in two cephalic regions and on the tail (presence of UD papillae in F. hepatica, absence in F. gigantica). The chaetotaxy of a daughter-redia of F. hepatica is also described. There is an important concentration of papillae around the buccal aperture, whereas at the pharyngeal and post pharyngeal levels, papillae are more spaced on the side supposed to be ventral, and scarce on the side considered dorsal.

Des oeufs de "Fasciola gigantica" et "Ascaris suum" peuvent rester viables plus de 48 heures dans l'intestin de certain Ardeidae. "Ardeola idae", espece migratrice d'Afrique a Madagascar, pourrait donc theoriquement participer au transfert d'helminthoses correspondantes a plus de 1.000 kilometres. (Resume d'auteur)