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PubMed1976

Studies on resistance in snails. 4. Induction of ventricular capsules and changes in the amebocyte-producing organ during sensitization of Biomphalaria glabrata snails.

Formation of an amebocyte aggregate in the ventricular cavity of Biomphalaria glabrata can be induced 30 hr or more after a single infection by irradiated or (less frequently) by normal Echinostoma lindoense miracidia. The resulting amebocyte mass frequently encapsulated and destroyed the developing E. lindoense sporocysts within the ventricle. The constituent amebocytes of the capsule correspond in vitro and by staining characteristics to circulating amebocytes of uninfected snails, but with additional inclusion bodies, increased mucopolysaccharide, acid phosphatases, and lipid-positive staining reactions. Mitotic activity, rapid growth, and later regression of the amebocyte-producing organ (located between the posterior mantle epithelium and anterior pericardial endothelium) follow the growth and regression sequence of the ventricular capsule. Though peripheral foci of secondary amebocyte production have been found and were previously known, the amebocyte-producing organ appears to be the primary amebocyte source responsible for the snails' rapid intraventricular sporocyst encapsulation.

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PubMed2004

Large-scale, polymerase chain reaction-based surveillance of Schistosoma haematobium DNA in snails from transmission sites in coastal Kenya: a new tool for studying the dynamics of snail infection.

Levels of prepatent Schistosoma haematobium infection were monitored in intermediate host snails (Bulinus nasutus) collected from transmission sites in coastal Kenya, using a polymerase chain reaction (PCR) assay amplifying the Dra I repeated sequence of S. haematobium. The timing and number of prepatent and patent infections were determined for each site and, where the time of first appearance was clear, the minimal prepatent period was estimated to be five weeks. High, persistent, prepatency rates (range = 28-54%), indicated a significant degree of repeated area contamination with parasite ova. In contrast, rates of cercarial shedding proved locally variable, and were either low (range = 0.14-3.4%) or altogether absent, indicating that only a small proportion of infected snails reach the stage of cercarial shedding. Given the apparently strong focal effects of environmental conditions, implications of these new data are discussed regarding the estimation of local force of transmission and the design of control activities.

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PubMed1967

Calcareous septa formed in snail shells by larvae of snail-killing flies.

Larvae of 13 species of Pherbellia and Colobaea that feed in exposed aquatic snails uitilize a product of the Malpighian tubules before they pupate to form a plate-like structure within the shell or to reinforce the anterior end of the puparium. The substance is partly calcium carbonate, and carbonic anhydrase may be involved in its production.

Animals↗
PubMedDate not supplied

Current advances on the study of snail-snail interactions, with special emphasis on competition process.

Field work research on population dynamic of snails from the regions of Belo Horizonte and Lagoa Santa give much information about interactions among two or more species of mollusks: Pomacea haustrum, Biomphalaria glabrata, B. tenagophila, B. straminea and Melanoides tuberculata. Data ranging from two years to several decades ago suggest that the Pampulha reservoir is like a cemetery of B. glabrata and B. straminea, species that coexist for more than 14 years in a small part of a stream, whereas only B. glabrata lives in all the streams of the basin. In the last ten to twenty years B. tenagophila has coexisted with P. haustrum and M. tuberculata in the Serra Verde ponds and in the Pampulha dam. However these species have not settled in any of the brooks, except temporarily. The data suggest that the kind of biotope and the habitat conditions are decisive factors for the permanence of each species in its preferencial biotope. B. glabrata, natural from streams and riverheads, quickly disappears from the reservoirs and ponds where it coexists with other species for a short time, independently of the competitive process. Competition needs to be better studied, since in Central America and Caribean islands this kind of study has favored the biological control of planorbid species.

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PubMed1996

Studying the snail's clock at better than a snail's pace.

The eye of Bulla gouldiana, the cloudy bubble snail, contains a circadian pacemaker that times a nocturnal locomotor rhythm. The eye expresses a circadian rhythm in spontaneous impulse activity that is generated within individual neurons at the base of the retina. There are approximately 100 of these "clock neurons" that are electrically interconnected. The retinal clock can be synchronized by light cycles. Synchronization involves membrane depolarization and calcium influx into pacemaker neurons. While rhythm expression involves an ionic calcium flux, and rhythm expression appears to be mediated by changes in potassium conductance, circadian rhythm generation does not appear to rely on transmembrane fluxes. Rather, the molecular events of transcription and translation appear to be critical players in generating the near twenty-four-hour rhythm in optic nerve activity.

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PubMed1992

Trichobilharzia ocellata infections in its snail host Lymnaea stagnalis: an in vitro study showing direct and indirect effects on the snail internal defence system, via the host central nervous system.

In this in vitro study we investigated whether previously described in vivo plasma-associated effects, that occurred in the period shortly after penetration of Trichobilharzia ocellata into the snail host Lymnaea stagnalis (1.5-72 h post-exposure; p.e.) were direct and/or indirect effects of parasite-derived factor(s). It was investigated whether the effect is mediated by the central nervous system (CNS) of the host. Phagocytic activity of the haemocytes was taken as a parameter for the activity of internal defence of the host. A number of preliminary experiments were performed. When the supernatant of in vitro cultured parasites (33 h; corresponding with their developmental stage in vivo when plasma-associated activation was found) was applied directly to monolayers of haemocytes, it appeared to enhance their phagocytic activity. No direct effect, however, was found with a supernatant of parasites cultured for a longer period of time (72 h; when, in vivo, a plasma-associated suppression was found). In this case, indirect suppression was detected: the parasites appeared to have released a factor that induced the CNS of the host to release material suppressing the activity of the internal defence system of the host. To date the nature of this factor is unknown.

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PubMed1975

Control of snail hosts of bilharziasis in Egypt. 3. Effect of the organophosphorous insecticide, dursban, on carbohydrate metabolism of the snails Biomphalaria alexandria and Bulinus truncatus.

The effects of the organophosphorous insecticide, Dursban, on aerobic oxidation, glycolysis, glucose utilization and gluconeogenesis in snails tissues were determined. Dursban had a biphasic effect on the aerobic oxidation of succinate, glutamate + malate and TMPD + ascorbate while it had only an inhibitory action on pyruvate oxidation. The compound significantly inhibited glycolysis, glucose utilization and gluconeogenesis when used at high concentrations (ten times higher than its LC50). However, it had a slight effect on thepreviously mentioned process when its concentration was equal to or approximated its LC50. The relationship between the metabolic effect of Dursban and its molluscicidal activity is discussed.

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