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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Article: Gastropod immunobiology.[Show abstract] [Hide abstract]
ABSTRACT: Over their 500 million yearhistory, gastropods have radiated into marine, freshwater and terrestrial environments and adopted life styles ranging from herbivory to carnivory to endoparasitism to symbiont-mediated chemoautotrophy. They contend with many pathogens, including several lineages of specialized eukaryotic parasites. Their immunobiology is as yet poorly known, in part because most studies focus on a very small segment of gastropod diversity. Gastropod genome sequences are now forthcoming but synthetic overviews of the gastropod immunome are not yet available. Most immunological studies focus on interactions between gastropods and the larval stages of digenetic trematodes (digeneans) such as the medically important schistosomes. Digeneans elicit demonstrable and relevant snail defense responses and provide insights, augmented by the recently available schistosome genome sequences, for how gastropod responses are subverted. Survival of digeneans in snails depends at least in part on their ability to mimic host glycotopes, to overcome the immediate attack ofreactive oxygen and nitrogen species produced by host hemocytes, and to induce long-term down-regulation of immune functions. Gastropods can mount distinct responses to different categories of pathogens, and can orchestrate effective elevated secondary responses under certain circumstances. Defense responses of at least one gastropod species, Biomphalaria glabrata, involve hemolymph lectins that are diversified by a variety of processes, including somatic diversification. Such observations have played a role in revising our general concept of invertebrate defense to include the possibility of more sophisticated and diversified responses beyond the production of limited repertoires of invariant pattern recognition molecules. The study of gastropod immunobiology is thus of basic interest and has several applied uses as well, including our need to conserve imperiled gastropod diversity.Advances in experimental medicine and biology 01/2010; 708:17-43. · 1.83 Impact Factor
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ABSTRACT: Resistance of the snail Biomphalaria glabrata to the trematode Schistosoma mansoni is correlated with allelic variation at copper-zinc superoxide dismutase (sod1). We tested whether there is a fitness cost associated with carrying the most resistant allele in three outbred laboratory populations of snails. These three populations were derived from the same base population, but differed in average resistance. Under controlled laboratory conditions we found no cost of carrying the most resistant allele in terms of fecundity, and a possible advantage in terms of growth and mortality. These results suggest that it might be possible to drive resistant alleles of sod1 into natural populations of the snail vector for the purpose of controlling transmission of S. mansoni. However, we did observe a strong effect of genetic background on the association between sod1 genotype and resistance. sod1 genotype explained substantial variance in resistance among individuals in the most resistant genetic background, but had little effect in the least resistant genetic background. Thus, epistatic interactions with other loci may be as important a consideration as costs of resistance in the use of sod1 for vector manipulation.PLoS Neglected Tropical Diseases 06/2012; 6(6):e1701. · 4.57 Impact Factor
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ABSTRACT: In 1973 planorbid snails then identified as Biomphalaria straminea were discovered in Hong Kong, China. It was assumed that these snails had been introduced to Hong Kong via the import of tropical fish by air from South America. In 2012 Biomphalaria were found for the first time in Guangdong Province, China. In view of the renewed interest in these invasive snails, a morphological and DNA-sequence based phylogenetic study was undertaken for seven populations of Biomphalaria snails collected in Guangdong. Morphologically and phylogenetically, five of the populations clustered more closely with Biomphalaria kuhniana than with B. straminea. Levels of genetic diversity among the populations were about half those of autochthonous populations in Brazil, the phylogenetic relationships did not correlate with a radiation from any one international port in China, and different lineages appeared associated with different ports. Consequently in explaining the current distribution of the snails, multiple colonization events, each establishing a new local snail population near to maritime international container ports, were considered more likely than the spread of snails from Hong Kong to China. The displacement of B. straminea by B. kuhniana in Guangdong is considered as an explanation for the habitat changes observed among the snails between Hong Kong in the 1980s and the present. The conclusions of the study are that any risk of Schistosoma mansoni transmission in China is more likely to come from parasite importation in the intramolluscan stage, than from transmission by migrant workers from South America or Africa. In addition, although likely to be rare, sporadic outbreaks of imported schistosomiasis (caused by invading infected snails) could be a threat to public health in the vicinity of International container ports (not only in Guangdong Province). Further work is called for to investigate further the presence of B. kuhniana and its potential interactions with B. straminea (the former is thought to be incompatible with S. mansoni), and the responses of Chinese Biomphalaria to potential competitors such as Thiaridae. The current expansion of container ports in Brazil and Venezuela, and the increase in trade with China, is likely to accentuate any current risk of imported schistosomiasis, and surveillance around ports in China, together with further research, are necessary.Acta tropica 05/2014; · 2.79 Impact Factor