Dominant character of the molecular marker of a Biomphalaria tenagophila strain (Mollusca: Planorbidae) resistant to Schistosoma mansoni

Abstract

Biomphalaria tenagophila is a planorbid with a wide distribution in South America (Paraense 1984), and has epidemiological importance, since this species maintains the cycle of the trematode Schistosoma mansoni in some areas in Brazil. In spite of its dominance in some areas, B. tenagophila is found in the nature with low rates of infection, however, it is responsible for the majority of the autochthonous cases of schistosomiasis in the state of São Paulo, as well as for the foci of the disease in the states of Minas Gerais and Santa Catarina (Paraense 1986). This last focus is maintained by a highly susceptible population (Joinville) of molluscs to S. mansoni. On the other hand, there is a population coming from the Ecological Reservoir from Taim (state of Rio Grande do Sul), that has systematically been found resistant to different strains of S. mansoni (Coelho 1995). This population has been maintained under laboratory conditions for more than twenty years, without any selective pressure favoring the resistance. Vidigal et al. (1998), using the polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) of the ribosomal RNA internal transcribed spacer region (ITS) with restriction DdeI enzyme, were able to separate molecularly the molluscs genus Biomphalaria, such as B. glabrata, B. tenagophila, and B. straminea, which are intermediate hosts of S. mansoni in Brazil. Those authors obtained species-specific profiles for this three species, observing besides that various Brazilian populations of B. tenagophila showed a characteristic profile, with two fragments (800 and 470 pb). Barbosa (2001), using the same technique, observed that the Taim population, in addition to the characteristic species-specific profile of B. tenagophila, as described by Vidigal et al. (1998), has a 350 pb fragment too.In the present study, cross-breedings between molluscs from B. tenagophila (Taim) and B. tenagophila (Joinville) were carried out, aiming at verifying whether the marker of the Taim population has a dominant character.Studies in order to obtain F1 generation were undertaken using a specimen of B. tenagophila Taim and another one of albino B. tenagophila Joinville. They were maintained together in order to achieve cross-breeding (4 pairs). The albino recessive character was used, in this case, as a phenotypic marker. The molluscs with 5 mm in diameter, approximately, sexually immature, were put together into a plastic recipient with 100 ml dechlorinated water for 50 days. Afterwards, the respective pairs were separately put into glasses in order to obtain F1 descendants. In this experiment, the egg-layings from the albino snails, as well as from the pigmented ones, were collected for four weeks. The egg-layings from F1 generation were transferred to an aquarium until the molluscs could reach 5 mm in diameter. F2 generation was obtained by means of cross-breedings between F1 individuals according to the same procedures previously described.A fragment from the cephalopodal region of the molluscs was col...

Biomphalaria tenagophila: dominant character of the resistance to Schistosoma mansoni in descendants of crossbreedings between resistant (Taim, RS) and susceptible (Joinville, SC) strains

“…To this end we used the RAPD technique, and 24 primers were tested, but no molecular marker could be detected. Recently, our staff was able to detect a molecular marker, which is typical of Taim lineage and presents a mendelian behavior (Rosa et al 2004). This marker, although not associated to resistance, is represented by the presence of a band with 350 base pairs of the ITS region in the ribosomal mitocondrial DNA detected by means of PCR-RFPL technique, using the Ddel I enzyme.…”

Phylogenetic analysis of Biomphalaria tenagophila (Orbigny, 1835) (Mollusca: Gastropoda)

“…1979, Bezerra et al 2003, Rosa et al 2004, Coelho & Bezerra 2006. Several studies have been carried out in order to gain a better understanding of resistance traits, including molecular approaches using nuclear DNA regions (Pires et al 1997, Spatz et al 1999, Barbosa 2001, Rosa et al 2005, Barbosa et al 2006), but little is known about the genes related with the resistance phenotype in this population (Santos et al 1979, de Freitas et al 1985, Rosa 2002.…”

Interaction between primary and secondary sporocysts of Schistosoma mansoni and the internal defence system of Biomphalaria resistant and susceptible to the parasite

“…In addition, the mortality of B. tenagophila Taim was higher than that of the other snails. It has been well established that B. tenagophila Taim is completely resistant to S. mansoni (Corrêa et al 1979, Santos et al 1979, Bezerra et al 1997, 2003, Martins-Souza et al 2003, Rosa et al 2004, 2005, Barbosa et al 2006, Pereira et al 2008. Table II shows that B. tenagophila Taim kills sporocysts more effectively than the Cabo Frio strain or B. glabrata.…”

“…Biomphalaria glabrata, Biomphalaria tenagophila and Biomphalaria straminea are the three species responsible for the transmission of schistosomiasis in Brazil (Paraense 1975). Many authors (Corrêa et al 1979, Santos et al 1979, Bezerra et al 1997, 2003, Martins-Souza et al 2003, Rosa et al 2004, 2005, Barbosa et al 2006, Pereira et al 2008 have described the existence of a geographic lineage of B. tenagophila (provided from Ecological Station of Taim, state of Rio Grande do Sul, Brazil) resistant to S. mansoni. This lineage represents an important population in which to study the defence mechanisms of these invertebrate hosts to S. mansoni infection.…”