BARBOSA, F. S. & BARBOSA, C. S. The Bioecology of Snail Vectors for Schistosomiasis inBrazil. Cad. Saude Publ., Rio de Janeiro, 10 (2): 200-209, Apr/Jun, 1994.This paper describes the ecology of two species of Biomphalaria: B.glabrata and B. straminea.These species have been intensively studied in Brazil and in other countries since the 1950s. Theliterature in this area can be broadly subdivided into three categories, linked to three distinct historicalperiods: 1) an accumulated store of early studies carried out in the laboratory and in the field; 2) thedevelopment of quantitative ecological models; and 3) the development of an alternative methodologyfor breeding snails under seminatural conditions.Key words: Snail Ecology; Biomphalaria sp.; SchistosomiasisINTRODUCTIONInvestigations into the ecology of freshwatersnails have shown that the populationdynamics of these animals depend on thephysical geography of a given region. Landcontours, soil composition, hydrography, andclimate all have a significant effect on snailpopulation dynamics.Further factors that effect the distributionand abundance (biogeography) of snails, andthat will be addressed at a secondary level inthis paper, include: the biotic and non-bioticenvironment, behavior, reproduction,genetics, interactions within and betweenspecies, and human influences. Therelationship between the snail host and itsparasites will not be discussed.Although any physical, chemical, orbiological factor can have a significant effecton population dynamics, a few factors –especially those related to climate

The Bioecology of Snail Vectors for Schitosomiasis in Brazil Bioecologia dos Caramujos Vetores da Esquistossomose no Brasil

This paper describes the ecology of two species of Biomphalaria: B.glabrata and B. straminea. These species have been intensively studied in Brazil and in other countries since the 1950s. The literature in this area can be broadly subdivided into three categories, linked to three distinct historical periods: 1) an accumulated store of early studies carried out in the laboratory and in the field; 2) the development of quantitative ecological models; and 3) the development of an alternative methodology for breeding snails under seminatural conditions.

http://www.scielo.br/pdf/csp/v10n2/v10n2a07.pdf

The bioecology of snail vectors for schitosomiasis in Brazil

Specimens of Biomphalaria tenagophila exposed to miracidia of Schistosoma mansoni were submitted to different desiccation periods as follows: group I: 24 h after exposure, desiccated for 28 days; group II: after cercariae elimination, desiccated for 7 days; group III: 21 days after exposure, desiccated for 7 days; group IV: 14 days after exposure, desiccated for 14 days; group V: 7 days after exposure, desiccated for 21 days. From the obtained data it was verified that desiccation was not capable of interrupting the development of larvae of S. mansoni in mollusks. A delay in the development of S. mansoni larvae in groups I, III, IV and V was observed. A pause was verified in the development of S. mansoni larvae in groups II, III, IV and V. Some larvae, in groups I, III, IV and V, did not suffer as a result of desiccation and continued their development. Larvae in the cercariae stage were shown to be more sensitive to desiccation. It was possible to obtain clearing of mollusks infected by sporocysts II and cercariae using a period of 7 days of desiccation.

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Effects of the desiccation on Biomphalaria tenagophila (Orbigny, 1835) (Mollusca) infected by Schistosoma mansoni Sambon, 1907

Experiments were carried out to test the susceptibility of Biomphalaria tenagophila to the infection with strain SJ of Schistosoma mansoni in the F1, F2 and non-selected parental generation. The potential adaptation of B. tenagophila to desiccation, in healthy mollusks and those exposed to the larvae of S. mansoni of the F1, F2 and non-selected parental generations was also studied. The presence of mucus and soil, at the shell opening, protected the snails against desiccation, favoring survival. The healthy mollusks performed more attempts against desiccation than those exposed to the larvae of the parasite. The mortality rate, during desiccation, was higher among mollusks that remained buried and with the shell opening unobstructed. During the desiccation period the stage of development of the parasite was influenced by the weight loss and the survival of the snails. The longer the period of desiccation, the greater was the weight loss observed, abbreviating survival. The non-selected parental generation was more sensitive to desiccation than the F1 and F2 generations, both in healthy mollusks and in those exposed to S. mansoni larvae. Healthy mollusks were more resistant to desiccation than those exposed to the larvae of the S. mansoni. Desiccation did not interrupt the development of S. mansoni larvae in mollusks, causing a delay in the cercariae elimination. The susceptibility of B. tenagophila to the SJ strain of S. mansoni, in mollusks maintained in water during the larvae incubation period, was similar in all three generations.

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Biomphalaria tenagophila (Orbigny, 1835) (Mollusca): adaptation to desiccation and susceptibility to infection with Schistosoma mansoni Sambon, 1907

Paleoecological studies of continental gastropods give valuable information about the depositional environment of the fossil assemblages. In South America, these assemblages from the Late C...

Continental Late Cretaceous gastropod assemblages from Uruguay. Paleoecology, age, and the oldest record of two families and a genus

The authors confirmed in laboratory conditions the occurrence of burrowing in the behavioral repertoire of Biomphalaria glabrata. They observed that the burried snails recovered, after a 20 days' desiccation period, better than others that had remained on the soil surface. More detailed work is necessary to determine the epidemiological importance of such behavior.

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Estudos sobre o comportamento dos planorbídeos: II - enterramento de Biomphalaria glabrata (Say, 1818) como meio de proteção contra a dessecação

A technique involving time-lapse cinematography was developed for studying the behavioral repertoire of planorbids in laboratory conditions. Observations were carried out within a chamber with controlled light and temperature; recording was done by single frame shooting at 10 second intervals, with synchronized strobed flash. This technique has allowed accurate measurements of different aspects of the activity of Biomphalaria glabrata (Say, 1818), and can be useful in analysing the level of response of planorbids to molluscicides, in experimental tests, as well as their protective behavior under general adverse conditions.

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Jorge S. Raymundo

Papers

Estudos sobre o comportamento dos planorbídeos: II - enterramento de Biomphalaria glabrata (Say, 1818) como meio de proteção contra a dessecação

Estudos sobre o comportamento dos Planorbídeos: I - uma técnica de observação e registro comportamental por cinematografia