Transplantation of in vitro-generated Schistosoma mansoni mother sporocysts into Biomphalaria glabrata.

Specific studies on schistosome gene functions require both access to the parasite stages, preferably the larvae, and to complete the life cycle. In the present study, we investigated whether short-term in vitro cultivation of sporocysts and surgical transplantation into snails could be combined to produce cercariae. Miracidia were maintained in vitro in the presence of Biomphalaria glabrata embryonic (Bge) cells or, alternatively, in Bge-cell-conditioned medium. The transformation of miracidia to mother sporocysts was observed in both cases. Two day-old sporocysts were transplanted into the cephalopedal sinus of recipient snails. Transplantation efficiencies varied between 16% and 43%, depending on the culture of the sporocysts in terms of the number of cercariae producing snails. Cercariae recovered from these snails were used to successfully infect hamsters, demonstrating that short term in vitro-generated sporocysts undergo normal cercariogenesis following transplantation. This combination of in vitro cultivation and transplantation may be useful for novel experimental approaches to investigate the genes involved in larval development or host-parasite molecular interactions.

Schistosoma intercalatum: an endangered species in Cameroon?

Despite the extremely wide distribution of both intermediate (snail) and definitive hosts, the species Schistosoma intercalatum has a highly restricted distribution in parts of West Africa (Cameroon, Equatorial Guinea, Gabon, Nigeria, Democratic Republic of Congo and São Tomé). Recent studies showed that the epidemiology of this species is very dynamic, including invasions and extinctions. This article reviews the epidemiology of S. intercalatum in Cameroon, where the species is endangered, and analyses its overall status in Africa. The possible reasons for the limited distribution of S. intercalatum are discussed.

Schistosoma mansoni and Schistosoma haematobium: identification and characterization of glycoconjugate antigens in the hemolymph of infected vector snails.

Two carbohydrate epitopes were identified by monoclonal antibodies (KCS and E2) and characterized with respect to their immunoreactivity, monosaccharide structure, and location. Immunofluorescence demonstrated the presence of both epitopes on the surfaces of sporocysts, cercariae, and miracidia of Schistosoma mansoni, Schistosoma haematobium, and Schistosoma japonicum. However, spatial distribution and density of expression varied among species and developmental stages, and neither epitope was detectable on adult worm surfaces. Both glycans were found in the hemolymph of infected, but not uninfected, intermediate snail hosts. The presence of epitopes in hemolymph, as well as in schistosome eggs, is species-specific for KCS, recognizing only S. mansoni, and partly specific for E2, which reacted predominantly with S. haematobium. Immunoaffinity purification of target antigens for KCS and E2 from hemolymph of infected Biomphalaria and Bulinus, respectively, followed by carbohydrate composition analysis revealed a high content of fucose in both glycans. Methylation analysis demonstrated exclusively terminal fucose for the target antigen of KCS and terminal as well as internal fucose for the one of E2. Removal of terminal fucose abolished reactivity with both monoclonal antibodies. Both glycans are different from previously characterized schistosome carbohydrates. Their biological function(s) remain to be defined.

Recent studies on Schistosoma intercalatum: taxonomic status, puzzling distribution and transmission foci revisited

Schistosoma intercalatum, which causes human rectal schistosomiasis in Africa, still presents a great interest for its imprecise taxonomic status and its puzzling distribution in Africa. Two geographically isolated strains of S. intercalatum are recognized, the Lower Guinea strain and the Congo strain, which differ from each other in a number of morphological, biological and biochemical characteristics. Recent molecular data using RAPD markers indicate high divergence between the two strains, with values of Nei and Li's similarity indice allowing recognition of two genetically distinct taxa: experiments on pre- and post-isolating mechanisms are in progress in order to re-evaluate the taxonomic status of this polytypic species. With regard to its geographical distribution, S. intercalatum is characterized by the existence of two stable endemic areas (localized in Lower Guinea and North East of Democratic Republic of Congo) which correspond to the historical areas of species discovery, and the emergence during the last 15 years of new foci of the Lower Guinea strain outside previously known endemic areas. The absence of local adaptation of the Lower Guinea strain to its intermediate host, supported by experimental studies, may help to facilitate the spread of this strain. Nevertheless, the present restricted distribution of this species remains puzzling, because its potential snail hosts (bulinids) are widely distributed throughout much of Africa. Recent experimental and epidemiological studies suggest that interspecific sexual interactions between human schistosomes could have a role in limiting the distribution of S. intercalatum: the competitive sexual processes acting among human schistosomes show that S. haematobium and S. mansoni are always competitively dominant over S. intercalatum. These epidemiological observations lead the authors to distinguish three kinds of transmission foci for S. intercalatum

ADAPTIVE SEX ALLOCATION IN A SIMULTANEOUS HERMAPHRODITE.

When applied to hermaphrodite organisms, the local mate competition hypothesis predicts an increase of the ratio of sperm to ova produced as the number of mates increases. Here we test this prediction using a hermaphroditic platyhelminth parasite (trematode), Echinostoma caproni. This worm inhabits the small intestine of vertebrates, inevitably inducing the formation of highly subdivided populations, a condition known to promote local mate competition. Moreover this echinostome exhibits an unrestricted mating pattern involving both selfing and outcrossing as well as multiple fertilizations. We quantified the investment in reproductive organs by estimations of testes, cirrus sac, ovary, and egg size and fecundity when echinostomes were isolated alone, in pairs, or in groups of 20 worms. Adult body size was also recorded as a covariate. When mating group size increases (singles, pairs, or groups) we observed a significant increase in resource allocation to male function in addition to a significant decrease in ovary size. Smaller ovaries do not seem to affect egg size, but do result in a reduction in fecundity. Finally, our results are in accordance with the expected theoretical relationship between male allocation and the number of potential mates given local mate competition.

The evolution of life-history traits in parasitic and free-living platyhelminthes: a new perspective.

Parasite life histories have been assumed to be shaped by their particular mode of existence. To test this hypothesis, we investigate the relationships between life-history traits of free-living and parasitic platyhelminthes. Using phylogenetically independent contrasts we examine patterns of interspecific covariation in adult size, progeny volume, daily fecundity, total reproductive capacity, age at first reproduction and longevity. The correlations obtained indicate a similar causal chain of life history variations for free-living and parasitic platyhelminthes. These results suggest that increased longevity favours delayed reproduction. Furthermore, growth pattern determines adult body size and age at maturity. For platyhelminthes, whether free-living or parasitic, the total reproductive capacity is found to be directly determined by the size of the worm. Within this group the parasitic way of life does not seem to influence the basic patterns of life history evolution.