Academic literature on the topic 'Bulinus truncatus'

Bulinus truncatus rohlfsi is a snail host of the human blood fluke Schistosoma haematobium. Observations on the dynamics of laboratory cultures of B. t. rohlfsi are presented from a series of experiments that investigated the effects of population density, pH, and oxygen concentration, and the inhibitory effects of old snail culture media. The data suggest that survival and fecundity are density dependent and that the cause of this effect is a fairly thermostable compound with a molecular weight <1000.

SUMMARYThe snail Bulinus nasutus 1214 possesses a potent haemagglutinin (end-point titre with human erythrocytes, 2−18) in its cell-free haemolymph which also binds to the miracidia (but not other larvae) of the incompatible parasite Schistosoma margrebowiei. We have purified a protein possessing this haemagglutinating property from the plasma of this snail. The native Mr of this protein was estimated by SDS polyacrylamide gel electrophoresis to be 210 kDa; under denaturing conditions in a 7.5% PAGE gel it ran as a major band of 135 kDa. Proteins of similar Mr were also found in the haemolymph of 16 other Bulinus spp. (the major intermediate hosts of human and veterinary schistosomiasis in Africa) although the plasma of none of these agglutinated human erythrocytes. Nonetheless, Cleveland mapping of the Mr 135 kDa bands from these different Bulinus spp. revealed 4 identical major peptide fragments (30, 28, 19 and 16 kDa) in each, thus demonstrating a similarity in the primary structure of these plasma proteins. Antisera from Balb/C mice immunized with the 135 kDa polypeptide from Bulinus truncatus 1521 cross-reacted in Western blots with the 135 kDa band of other members of the same truncatus/tropicus species complex but not with species from the africanus or forskalii species groups.

Freshwater snails of the genera Biomphalaria, Bulinus, and Oncomelania are intermediate hosts of schistosomes that cause human schistosomiasis, one of the most significant infectious neglected diseases in the world. Identification of freshwater snails is usually based on morphology and, potentially, DNA-based methods, but these have many drawbacks that hamper their use. MALDI-TOF MS has revolutionised clinical microbiology and has emerged in the medical entomology field. This study aims to evaluate MALDI-TOF MS profiling for the identification of both frozen and ethanol-stored snail species using protein extracts from different body parts. A total of 530 field specimens belonging to nine species (Biomphalaria pfeifferi, Bulinus forskalii, Bulinus senegalensis, Bulinus truncatus, Bulinus globosus, Bellamya unicolor, Cleopatra bulimoides, Lymnaea natalensis, Melanoides tuberculata) and 89 laboratory-reared specimens, including three species (Bi. pfeifferi, Bu. forskalii, Bu. truncatus) were used for this study. For frozen snails, the feet of 127 field and 74 laboratory-reared specimens were used to validate the optimised MALDI-TOF MS protocol. The spectral analysis yielded intra-species reproducibility and inter-species specificity which resulted in the correct identification of all the specimens in blind queries, with log-score values greater than 1.7. In a second step, we demonstrated that MALDI-TOF MS could also be used to identify ethanol-stored snails using proteins extracted from the foot using a specific database including a large number of ethanol preserved specimens. This study shows for the first time that MALDI-TOF MS is a reliable tool for the rapid identification of frozen and ethanol-stored freshwater snails without any malacological expertise.

Ebodi AYE, Ahmed MM. 2017. Toxicity of Randia nilotica fruit extract on Schistosoma mansoni, Biomphalaria pfeifferi and Bulinus truncatus. Cell Bio Dev 1 (1): 23-30. The aqueous filtered and unfiltered extract of the fruits of Randia nilotica (locally name as Shagarat El-Murfaein) were assessed as molluscicides against Biomphalaria pfeifferi and Bulinus truncatus as well as their effect on cercariae and miracidia of Schistosoma mansoni. The plant was tested on uninfected B. pfeifferi and B. truncatus, the results showed that unfiltered extracts were found relatively more potent than filtered one (i.e. 100% was attained at 90 ppm and 80 ppm) respectively. While, filtered extract tested on uninfected B. pfeifferi and B. truncatus (100% was attained at 100 ppm and 90 ppm) respectively. The effect of unfiltered extract on infected B. pfeifferi produced 100% mortality in concentration of 70 ppm. The activity of the plant on cercariae and miracidia revealed that cercariae was more resistance than miracidia (i.e.50 ppm killed all cercariae within 3 hours while killed miracidia within 2 hours. The results were statistically analyzed and discussed, and the findings were promising and could open new avenues for the practical use of the plant at the field.

Objectif : Identifier les espèces Schistosoma haematobium, S. bovis et leurs hybrides et, évaluer la compatibilité des schistosomes avec les mollusques hôtes intermédiaires et la souris blanche (Mus musculus albinos), hôte définitif, en infestation expérimentale. Méthodologie et résultats : Des schistosomes ont été obtenus à partir de bulins infestés naturellement ou expérimentalement avec des miracidiums provenant des urines de l’homme. Ils ont permis d’étudier la compatibilité de quatre populations de Bulinus truncatus avec deux souches du groupe S. haematobium. La chronobiologie cercarienne a été étudiée à partir de quatre tranches horaires : 6-10h, 10-12h, 12-15h et 15- 18h. Des souris blanches infestées expérimentalement, ont été perfusées pour dénombrer les vers adultes. Une meilleure compatibilité schistosome-mollusque a été observée au niveau des infestations sympatriques. Le pic d’émergence cercarienne pour les mollusques naturellement infestés a été observé entre 6-10h, 10h15h et à 15-18h, tandis que celui des bulins infestés expérimentalement a été majoritairement observé entre 10-15h. En termes de nombre de vers collectés, les souris blanches ont été plus permissives aux schistosomes provenant des mollusques naturellement infestés. Conclusion et application des résultats : Les pics d’émergence cercarienne précoce (6-10h) et tardif (15-18h) pourraient être liés à S. bovis, tandis que celui de 10-15h correspondrait à S. haematobium. De même, en raison de la très faible compatibilité connue entre Mus musculus albinos et S. haematobium, les schistosomes auxquels les souris blanches ont été plus permissives sont fort probablement des S. bovis et/ou hybrides S. bovis x S. haematobium. Ainsi, les espèces anthropophiles et celles zoophiles du groupe Schistosoma haematobium peuvent être distinguées de manière routinière par deux approches. La première, en disséquant des souris de laboratoire (Mus musculus albinos) 4 mois après leur mise au contact de l’eau contenant des cercaires obtenues après exposition à la lumière de mollusques infestés prélevés sur le terrain ; la seconde en comparant les profils obtenus après dénombrement des cercaires émises au cours de quatre tranches horaires bien choisies. Mots clés : Bulinus truncatus, Schistosoma haematobium, Schistosoma bovis, Caractérisation, Chronobiologie. Glitho et al., J. Appl. Biosci. 2021 Caractérisation biologique de Schistosoma haematobium, S. bovis et leurs hybrides chez l’homme et chez les mollusques Bulinus truncatus naturellement infestés, au Centre et Nord de la Côte d’Ivoire. 16341 ABSTRACT Objective: Identify the species Schistosoma haematobium, S. bovis and their hybrids; to evaluate the compatibility of schistosomes with intermediate host snails and the white mouse (Mus musculus albinos), the definitive host for experimental infestation. Methodology and results: Schistosomes have been obtained from naturally or experimentally infested snails with miracidiums from human urine. The compatibility of four populations of Bulinus truncatus with two strains of the S. haematobium group was studied. The chronobiology of cercariae was studied in four time slots: 6- 10h, 10-12h, 12-15h and 15-18h. Experimentally infested white mice were perfused and adult worms were collected. A better schistosome-snail compatibility was observed in sympatric infestations. The peak of cercarial emergence for naturally infested snails was at 6-10h, 10h-15h and 15-18h, while that of the snails experimentally infested was mostly observed at 10-15h. In terms of number of worms collected, white mice were more permissive to schistosomes from naturally infested snails. Conclusion and application of results: Early (6-10h) and late (15-18h) cercarial emergence peaks can be related to S. bovis, while the 10-15h peak correspond to S. haematobium. Due to the reported low compatibility between the white mice Mus musculus albinos and S. haematobium, the observed schistosomes permissive to the white mice are most likely S. bovis and/or hybrids S. bovis x S. haematobium. Therefore, anthropophilic and zoophilic species of the Schistosoma haematobium group can be routinely distinguished by two approaches. The first, dissecting laboratory mice (Mus musculus albinos) 4 months after their contact with water containing cercariae obtained after exposure to light from infested snails collected in the field; the second by comparing the profiles obtained after enumeration of cercariae emitted during four well-chosen time slots. Keywords: Bulinus truncatus, Schistosoma haematobium, Schistosoma bovis, hybrid, Characterization, Chronobiology.

The transmission of some schistosome parasites is dependent on the planorbid snail hosts. Bulinus truncatus is important in urinary schistosomiasis epidemiology in Africa. Hence, there is a need to define the snails’ phylogeography. This study assessed the population genetic structure of B. truncatus from Giza and Sharkia (Egypt), Barakat (Sudan) and Madziwa, Shamva District (Zimbabwe) using mitochondrial cytochrome oxidase subunit 1 gene (COI) and internal transcribed spacer 1 (ITS 1) markers. COI was sequenced from 94 B. truncatus samples including 38 (Egypt), 36 (Sudan) and 20 (Zimbabwe). However, only 51 ITS 1 sequences were identified from Egypt (28) and Sudan (23) (because of failure in either amplification or sequencing). The unique COI haplotypes of B. truncatus sequences observed were 6, 11, and 6 for Egypt, Sudan, and Zimbabwe, respectively. Also, 3 and 2 unique ITS 1 haplotypes were observed in sequences from Egypt and Sudan respectively. Mitochondrial DNA sequences from Sudan and Zimbabwe indicated high haplotype diversity with 0.768 and 0.784, respectively, while relatively low haplotype diversity was also observed for sequences from Egypt (0.334). The location of populations from Egypt and Sudan on the B. truncatus clade agrees with the location of both countries geographically. The clustering of the Zimbabwe sequences on different locations on the clade can be attributed to individuals with different genotypes within the population. No significant variation was observed within B. truncatus populations from Egypt and Sudan as indicated by the ITS 1 tree. This study investigated the genetic diversity of B. truncatus from Giza and Sharkia (Egypt), Barakat area (Sudan), and Madziwa (Zimbabwe), which is necessary for snail host surveillance in the study areas and also provided genomic data of this important snail species from the sampled countries.

Planorbarius metidjensis e Bulinus truncatus, identificados como hospedeiros intermediários de Schistosma haematobium e S. bovis, foram o objecto do nosso estudo. Este trabalho está dividido em seis capítulos que de certo modo, se encontram relacionados entre si. No Capítulo 1, faz-se uma abordagem geral sobre estas duas espécies de moluscos com importância em medicina, com breves considerações sobre a sua classificação, características morfológicas e distribuição no mundo e em Portugal. Do mesmo modo, a revisão de literatura realça aspectos importantes relacionados com interacção do molusco, hospedeiro intermediário e o tremátode parasita e a aplicação das novas técnicas moleculares nesta área. No intuito de rever a distribuição geográfica destas duas espécies de moluscos em Portugal continental, foi realizado um levantamento malacológico em vários distritos, cujos resultados são apresentados no Capítulo 2. Os distritos em estudo foram Beja, Coimbra, Évora, Faro, Guarda, Lisboa, Portalegre, Setúbal e Viseu, tendo sido colhidos 3219 exemplares de P. metidjensis, enquanto para B. truncatus não foi encontrado nenhum exemplar. Por isso, a segunda parte do trabalho decorreu com exemplares de B. truncatus, mantidos há várias gerações no Laboratório de Malacologia da Unidade de Helmintologia e Malacologia Médicas, e tendo origem em exemplares colhidos pela Profª Doutora Maria Amélia Grácio, Directora da Unidade. Ainda neste capítulo e com base nos dados recolhidos, foi feita a caracterização dos habitats segundo o seu tipo físico, natureza e aspectos bioecológicos. No Capítulo 3, destaca-se a variabilidade encontrada nas características morfométricas da concha de P. metidjensis nos diferentes distritos, o que permitiu evidenciar dois grupos distintos. O primeiro engloba as regiões do Alentejo, Algarve e Estremadura e o segundo, as regiões das Beiras e Sado. O tipo físico dos habitats e as características das conchas dos moluscos colhidos parecem ser os factores explicativospara esta similaridade. Neste capítulo também é feita uma abordagem sobre a dinâmica populacional de quatro habitats seleccionados com base nas características físicas de cada um deles (dois do distrito de Évora e dois do distrito de Faro). No Capítulo 4, estudam-se os moluscos em relação a uma eventual infecção natural por tremátodes, bem como, a sua susceptibilidade à infecção por Schistosoma haematobium (estirpe de Angola) e S. mansoni (estirpe do Brasil). No total de 3219 P. metidjensis examinados, 1456 (45,2%) eliminaram xifideocercárias. Quanto à susceptibilidade de P. metidjensis a S. haematobium, os resultados vieram, mais uma vez, confirmar a não susceptibilidade desta espécie de moluscos à estirpe angolana de S. haematobium. Em relação a S. mansoni, alguns exemplares de P. metidjensis desenvolveram infecção até à fase de esporocisto, apesar de não chegarem a eliminar cercarias. Estes resultados não se verificaram nos moluscos B. truncatus. No Capítulo 5, é feito pela primeira vez, um estudo molecular de P. metidjensis. Neste estudo foram usados exemplares de P. metidjensis de diferentes habitats e agrupados em cinco distritos, para analisar a sua posição sistemática e relação filogenética com outras espécies homólogas cujas sequências se encontram no GenBak. Nesta análise foram usadas as sequências parciais dos genes mitocondriais COI e 16S, tendo-se identificado um total de nove haplotipos para o gene COI e quatro para o gene 16S. Estes resultados mostraram que o maior número de haplotipos foi encontrado no distrito de Coimbra, para ambos os genes, significando que os habitats deste distrito foram mais polimórficos que os restantes. Com base nos resultados obtidos para os genes COI e 16S, P. metidjensis de Portugal apresentaram uma elevada homologia (81%) com outras espécies de Planorbarius spp, bem como, com espécies de Biomphalaria spp das regiões Neotropical e Africana, hospedeiros intermediários de S. mansoni e de outros tremátodes. Para avaliar qual o grau de diversidade genética de P. metidjensis foram usados marcadores de RAPD nos moluscos colhidos em 19 habitats (de nove distritos). Os resultados evidenciaram não só uma elevada variabilidade genética, determinada pelo Índice de Shannon (Ho=0,4981),como também, uma alta diferenciação genética (Gst=0,238) inter e intrapopulacional (de acordo com os pressupostos de Wright, 1978). À semelhança do capítulo anterior, no Capítulo 6, faz-se pela primeira vez uma caracterização molecular de B. truncatus de Portugal. Como já foi referido anteriormente, não foi possível colher exemplares desta espécie durante o trabalho de campo, por isso este estudo realizou-se com as populações mantidas no laboratório. Os resultados do estudo, em que se aplicou a técnica de RAPD, evidenciaram uma elevada diferenciação genética entre as populações (Gst=0,28), assim como, uma elevada variabilidade genética intrapopulacional determinada pelo Índice Shannon (0,5294 ± 0,1787) a qual parece estar relacionada com o baixo número de migrantes. Foram também utilizados como marcadores moleculares o gene COI do ADN mitocondrial e ITS (Região Interna Transcrita) do ADN ribossomal para análise da posição sistemática e relação filogenética com outras espécies homólogas (hospedeiras intermediárias de Schistosoma spp) cujas sequências se encontram no GenBank, as quais evidenciaram homologia muito elevada com as espécies B. truncatus (Sudão) e B. tropicus. Além disso, foi identificado um total de sete haplotipos para a região ITS e nove para o gene COI, sendo a população de moluscos de Estói a que apresentou três haplotipos, enquanto as restantes populações apresentaram quatro haplotipos distintos. Os resultados globais para Fst foram muito baixos, sugerindo tratar-se de uma mesma população.
The object of our study were Planorbarius metidjensis and Bulinus truncatus, identified as the intermediate hosts of Schistosoma haematobium and S. bovis. This work is divided into six chapters that are to an extent related with one another. Chapter 1 are general considerations regarding these two species of mollusc with importance in medicine, including brief considerations about its classification, morphological characteristics and distribution worldwide and in Portugal. The literature review also highlights important aspects related to the interaction between mollusc, intermediate host and parasitic trematode, and the application of new molecular techniques to the area. With the purpose of reviewing the geographic distribution of these two species of molluscs in continental Portugal, we present results of a malacologic survey of various districts, namely Beja, Coimbra, Évora, Faro, Guarda, Lisboa, Portalegre, Setúbal and Viseu in to Chapter 2. We collected a total of 3219 specimens of P. metidjensis, but no B. truncatus were found. For this reason, the second part of the work used specimens of B. truncatus kept for several generations in the Malacology Laboratory of the Medical Helminthology and Malacology Unit, derived from specimens originally collected by Profª Doutora Maria Amélia Grácio, Director of the Unit. This chapter also characterizes, based on the collected data, the habitats according to physical, natural and bioecological aspects. Chapter 3 focuses on the variability in morphometric characteristics of the shell of P. metidjensis in the different districts, which allowed us to revealed two distinct groups. The first in the regions of Alentejo, Algarve and Estremadura and the second in the regions of the Beiras and Sado. The physical characteristic of the habitats and the collected mollusc’s shells seems to be the factors explaining this similarity. This chapter also refers the population dynamics of four habitats selected for their physical characteristics (two from the district of Évora, two from the district of Faro).Chapter 4 is the study of the molluscs in relation to a possible natural infection by trematodes, as well as their susceptibility to infection by Schistosoma haematobium (strain from Angola) and S. mansoni (strain from Brazil). Out of a total of 3219 specimens of P. metidjensis examined, 1456 (45,2%) eliminated xiphideocercaria. With regard to the susceptibility of P. metidjensis to S. haematobium, the results confirm, once again, the non susceptibility of this species of mollusc to the Angolan strain of S. haematobium. Concerning, S. mansoni, some specimens of P. metidjensis developed infection to the stage of sporocyte, but did not eliminate cercariae. These results did not take place in the mollusc B. truncatus In Chapter 5, we report the first molecular study of P. metidjensis. In this study we used several specimens of P. metidjensis from different habitats, grouped in five districts, to analyse their systematic position and phylogenetic relation with other homologous species, whose sequences were available in GenBank. We used partial sequences of the mitochondrial COI and 16S genes, having found nine haplotypes of COI and four of 16S. These results show a greater number of haplotypes in the Coimbra district, for both genes, implying greater polymorphism in the habitats of this district. Based on the results with the COI and 16S genes, P. metidjensis from Portugal presents a high homology (81%) with other species of Planorbarius spp, as species Biomphalaria spp from the Neotropical and African regions, intermediate hosts of S. mansoni and other trematodes. To evaluate the degree of genetic diversity of P. metidjensis, RAPD markers were collected from molluscs of 19 habitats (out of nine districts). Results suggest not only a hight genetic variability, determined by the Shannon Index (Ho=0, 4981), but also high inter- and intra-populational genetic differentiation (Gst=0,229) (Wright, 1978). The Chapter 6 reports the first molecular characterization of B. truncatus. As referred to earlier, we were not able to collect specimens of this species from the field, having studied lab-maintained populations. The results of this study, with theapplication of RAPD techniques, revealed a high genetic differentiation among populations (Gst=0, 28), as well as a high intrapopulational genetic diversity determined through Shannon’s index (0, 5294 ± 0, 1787), which seems to be related to a low number of migrants. The mitochondrial COI and the ribosomal Internal Transcribed Spacer (ITS) were used for analyzing the systematic position and phylogenetic relation with homologous species (intermediate hosts of Schistosoma spp) whose sequences are available in GenBank. These revealed very high homology with the B. truncatus (Sudan) and B. tropicus (Zambia). Furthermore, a total of seven ITS haplotypes and nine COI haplotypes were identified. The mollusc population of Estói possessed three haplotypes, while the remaining populations presented four distinct haplotypes. The global results for Fst were very low, suggesting a single population.

Les schistosomoses constituent encore un problème de santé publique au Cameroun. La forme urinaire due à S. Haematobium est la plus répandue et est transmise à l'homme par des mollusques hôtes intermédiaires dont les plus importants sont Bulinus truncatus et B. Globosus. Pour tenter d'expliquer la diversité observée dans le fonctionnement des foyers de schistosomoses urinaires, une étude de la structure génétique des populations de B. Truncatus et de B. Globosus a été menée en utilisant le polymorphisme de plusieurs loci microsatellites. Dans les populations de B. Truncatus, la diversité génétique à certains loci est relativement élevée mais aucun hétérozygote n'a été observé, expliqué probablement par un taux d'autofécondation très élevé. Une forte structuration génétique a été observée entre les populations, pouvant résulter des actions combinées de l'autofécondation, de la dérive génétique et d'un faible taux de migration. Dans les populations de B. Globosus, le niveau de variabilité est plus faible mais certains loci ont une diversité génétique élevée. On note la présence des hétérozygotes mais en proportion insuffisante si bien que toutes les populations sont en déséquilibre de Hardy-Weinberg. Une corrélation positive et significative est observée entre les distances géographiques et génétiques si bien que les paires de populations éloignées sont structurées alors que les paires rapprochées ne le sont pas. La structuration des populations, forte chez B. Truncatus et moyenne chez B. Globosus a pu être à l'origine d'évolutions différentielles des populations de bulins, pouvant expliquer la diversité observée dans les schémas de transmission de la schistosomose urinaire dans les foyers de cette endémie au Cameroun
Schistosomiasis is still a public health problem in Cameroon. Urinary form caused by S. Haematobium is the most widespread and is transmitted to humans by snails which serve as intermediate host. Bulinus truncatus and B. Globosus being the most important. In an attempt to explain the observed diversity in the functioning of urinary schistosomiasis focy, a genetic study of B. Truncatus and B. Globosus population's structure was conducted using microsatellite markers. In B. Truncatus populations, genetic diversity at some loci is relatively high but no heterozygotes were observed, probably due to a very high rate of self-fertilization. A strong genetic structure was observed between populations, it may results from the combined actions of self-fertilization, genetic drift, and low migration rate. In B. Globosus populations, the level of variability is lower, but some loci have a high genetic diversity. Heterozygotes are present in law proportion such that all populations are in Hardy-Weinberg disequilibrium. A significant positive correlation was observed between geographic and genetic distances. While the distant population's pairs are structured, the close ones are not. Population structure is strong in B. Truncatus and average in B. Globosus. This could be at the origin of the differential development in Bulinus populations and may explain the observed diversity in patterns of urinary schistosomiasis transmission in the endemic foci in Cameroon

L'objectif de cette these est de comprendre l'evolution d'un polymorphisme sexuel tres particulier, l'aphallie, chez le gasteropode pulmone bulinus truncatus. Ce polymorphisme se caracterise par la coexistence de deux morphes sexuels dans les populations naturelles: des individus hermaphrodites normaux (euphalliques) et des individus depourvus d'organe copulateur male (aphalliques). Les deux morphes peuvent s'autofeconder. Mais, en allofecondation, les individus aphalliques ne peuvent jouer que le role de femelle. Ainsi, l'evolution de l'aphallie et de l'autofecondation sont intimement liees. Dans un premier temps, nous avons montre que la determination de l'aphallie presente une forte composante genetique, meme si la temperature influence egalement le determinisme du morphe sexuel. Une forte variabilite genetique pour l'aphallie a ete observee entre les populations naturelles et a l'interieur de quelques populations. Dans un deuxieme temps, nous avons mis en evidence une tres faible difference de valeur selective entre les deux morphes. De forts taux d'autofecondation ont ete observes, sans avoir d'effets nefastes sur les traits d'histoire de vie des individus. Enfin, nous avons montre que des taux d'aphallie intermediaires pouvaient etre observes a l'equilibre meme pour de forts taux d'autofecondation, par une approche par modelisation. L'importance relative des facteurs selectifs et stochastiques pour le maintien et l'evolution de l'aphallie et de l'autofecondation dans les populations naturelles ont ete discutes

Une etude de la genetique des populations (structure genetique et systemes de reproduction) de bulinus truncatus et de b. Globosus, principaux hotes intermediaires des schistosomes du groupe a uf a eperon terminal, a ete menee, a partir d'echantillons de cote d'ivoire et du niger. Chez b. Globosus, le polymorphisme enzymatique est faible. Les populations sont en general, en equilibre de hardy-weinberg. Le faible polymorphisme a ete explique par la derive genetique suite aux variations saisonnieres de l'effectif des populations. Chez b. Truncatus, le polymorphisme enzymatique est encore plus faible, et a ete explique par l'action conjuguee de la derive genetique et de l'autofecondation. Chez les deux especes, une variation geographique de allozymes a ete mise en evidence et a ete expliquee par la distance geographique et les barrieres physiques creees par l'anthropisation du milieu. L'etude des systemes de reproduction confirme chez b. Truncatus, une reproduction par autofecondation et par allofecondation. Chez b. Globosus, la reproduction par allofecondation a ete confirmee dans une population alors que l'autofecondation partielle a ete mise en evidence dans l'autre. Les descendants hybrides entre les individus des populations du niger et de cote d'ivoire ont un taux de susceptibilite a s. Haematobium montrant un fort effet de l'origine de l'individu mere. L'interet de ces resultats pour la lutte biologique contre les schistosomoses par introduction de mollusques resistants est analyse