Biomphalaria tenagophila: dynamics of populations of resistant and susceptible strains to Schistosoma mansoni, with or without pressure of the parasite.
ABSTRACT 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.
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ABSTRACT: In mice experimentally infected with Schistosoma mansoni, praziquantel (2-cyclohexylcarbonyl-1,3,4,6,7,11b-hexahydro-2H-pyrazino[2,1-a]isoquinoline-4-one), administered orally at the levels of 100 and 50 mg/kg, for 5 consecutive days, produced oogram changes in all animals and a pronounced hepatic shift of schistosomes (97.1 and 89.1, respectively). At lowest levels (12.5 and 6.3 mg/kg), alterations in the oogram could still be detected, although hepatic shift of schistosomes was no more evident. After a single intramuscular injection, the results obtained paralleled those observed with a single-dose oral treatment. The hepatic shift was only moderate at 200 and 100 mg/kg and the percentages of worms retained in the liver, after perfusion, were particularly low. When nasal route in a 1-day regimen was used, the results obtained were slightly less evident as compared with those observed by oral route (5-day schedule).Advances in Parasitology 02/1968; 6:233-90. · 3.78 Impact Factor
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ABSTRACT: Biomphalaria tenagophila is very important for schistosomiasis transmission in Brazil. However its mechanisms of interaction with Schistosoma mansoni are still scantly studied. Since this snail displays strains highly susceptible or completely resistant to the parasite infection, the knowledge of that would be a useful tool to understand the mechanism of snail resistance. Particularly, the Taim strain consistently shows absolute resistance against the trematode, and this resistance is a dominant character. A multidisciplinary research group was created aiming at studying B. tenagophila/S. mansoni interaction. The possibility for applying the knowledge acquired to obtain a biological model for the control of S. mansoni transmission in endemic areas is discussed.Memórias do Instituto Oswaldo Cruz 02/2004; 99(5 Suppl 1):109-11. · 1.36 Impact Factor
- Memorias Do Instituto Oswaldo Cruz - MEM INST OSWALDO CRUZ. 01/1955; 53.