Resistant (Taim, RS) and susceptible albino (Joinville, SC) Biomphalaria tenagophila populations were kept together, at different proportions, throughout a 18-month-period. Some of the snail groups were submitted to Schistosoma mansoni infection. The targets of this study were (a) to analyze the populational dynamics among resistant and susceptible individuals to S. mansoni; (b) to study the resistance phenotype in descendants of cross-breeding; (c) to observe whether the parasite could exert any kind of selection in those snail populations. Throughout the experiment it could be observed that the susceptible B. tenagophila strain (Joinville) underwent a selective pressure of the parasite that was negative, since the individuals showed a high mortality rate. Although B. tenagophila (Taim) population presented a higher mortality rate without pressure of the parasite, this event was compensated by a reproductive capacity. B. tenagophila Taim was more fecund than B. tenagophila Joinville and was able to transmit the resistance character to their descendants. F1 generation obtained by cross-breeding between resistant and susceptible lineages was completely resistant to S. mansoni infection, irrespective of the Taim proportion. Moreover, less than 5% of F2 progeny were susceptible to S. mansoni infection.
"The results obtained in studies dealing with the populational dynamics of resistant and susceptible B. tenagophila lineages, at different proportions and with or without pressure of S. mansoni infection, showed the predominance of the resistant Taim lineage, mainly in the presence of S. mansoni infection (Rosa et al., 2006 "
[Show abstract][Hide abstract] ABSTRACT: Biomphalaria tenagophila Taim lineage has proved to be consistently resistant to Schistosoma mansoni. Several published works have shown that this resistance is due to the innate defence system of that strain, and in cross-breedings with susceptible strains the Taim lineage presents dominant character. These findings led to the hypothesis that, introducing this strain in areas where transmission of schistosomiasis is maintained by this species, the introduced lineage would perform cross-breeding with the local snails, thus generating offsprings resistant to the parasites. The perspectives of the proposed approach, as well as some preliminary results and problems related to the first introduction without a previous use of molluscicide are discussed.
[Show abstract][Hide abstract] ABSTRACT: Digenetic trematodes use molluscs, almost always a Gastropoda, in their evolutive cycle, as intermediary hosts. The genus Schistosoma, with three main species that infect humans - S. mansoni, S. japonicum, and S. haematobium – shows a prevalence of 200 million patients in various countries worldwide, and 600 million people are still at risk of infection. S. mansoni is the most prevalent species, and Biomphalaria snails are its intermediary hosts. Although the campaigns of schistosomiasis control based on chemotherapy have reduced the morbidity and prevalence of this disease, transmission continues in almost all the areas submitted to intervention. One of the factors that has influence on the susceptibility of Biomphalaria to S. mansoni infection is ability of the host internal defense system (IDS) to recognize and destroy the parasite. In Biomphalaria, the IDS is composed of cellular elements named hemocytes that act jointly with soluble components present in hemolymph, which could affect directly the larvae, or act in the recognition of the parasite, and activation of hemocytes. The susceptibility level of the mollusc has been attributed to the hemocyte capacity of involving and destroying the parasite, and this will be the centre of interest of this review.The study of S. mansoni and Biomphalaria interaction in resistant snail strains is important not only due to the academic-scientific value of this fascinating research area, but also to the potentially possible alternatives for the control of this endemia.
[Show abstract][Hide abstract] ABSTRACT: For a better comprehension of the parasite-host interaction, proteins expressed by the cardiac and pericardial tissues were compared between susceptible (Cabo Frio) and resistant (Taim) Biomphalaria tenagophila populations, challenged (c) and non-challenged (nc) with Schistosoma mansoni. Proteins were separated by two-dimensional gel electrophoresis (2DE) and stained with Coomassie blue. A total of 146 and 135 spots were observed in Cabo Frio (CFnc) and in Taim (Tnc) non-challenged populations, respectively, whereas 153 spots were detected in both Cabo Frio (CFc) and Taim (Tc) challenged populations. Regarding comparisons between CFnc and CFc, the numbers of exclusive spots obtained were one and nine, respectively, whereas Tnc yielded 17 and Tc eight exclusive spots. By comparing the total of spots in CF (nc+c) with T (nc+c) populations, we obtained: four exclusive spots for CFc; zero for CFnc; four for Tc and; one for Tnc. A quantitative comparison (reason>2.5) of the total spots of CF (nc+c) with T (nc+c) populations allowed us to distinguish five more intense spots for Tc, 14 for Tnc, 15 for CFnc and 11 for CFc. In the CFnc population, two proteins were identified: actin and ATP synthase alpha chain; in the CFc population, four proteins: actin, calmodulin, HSP70, and dehydrogenase; in the Tnc population, five proteins: matrilin, HSP70, actin, ATP synthase alpha chain and intermediate filament of the protein; and in the Tc population, three proteins: actin, alpha-S1 casein and ATP synthase alpha chain. Out of a total of 79 spots, only nine proteins were identified due to the low number of available nucleotide sequences in the GenBank. Nevertheless, knowing proteins regarded as differentially expressed is indispensable for hitherto unidentified genes implicated in B. tenagophila resistance and or susceptibility to S. mansoni infection.
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