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PubMed1967

The susceptibility of Biomphalaria glabrata throughout its life-history to N-tritylmorpholine.

This study was undertaken as part of a detailed investigation of the molluscicidal properties of N-tritylmorpholine (Frescon, WL 8008). It is shown that the stage of development of Biomphalaria glabrata has a pronounced influence on its susceptibility to N-tritylmorpholine. As the snails grow from hatching to a diameter of 3 mm, the LC(50) falls from 0.04 ppm to 0.02 ppm, but further growth results in a progressive increase in LC(50) until, at a shell diameter of 20 mm, it is 0.17 ppm. N-Tritylmorpholine is much less toxic to snail eggs when used in short exposures. However, young embryos in capsules treated with 5 ppm for 24 hours developed abnormally and died without hatching. Older embryos developed normally but died after hatching. This delayed effect is attributed to contact, during hatching, with N-tritylmorpholine which is associated with the jelly. The difference in susceptibility between snails and eggs is attributed to a slow rate of penetration of the egg membrane.

Animals↗
PubMed1970

Cercarial production from Biomphalaria alexandrina infected with Schistosoma mansoni.

The present paper deals with longitudinal and cross-sectional methods of counting cercariae shed from Biomphalaria alexandrina in Egypt, both experimentally and naturally infected with schistosomes. By the longitudinal method, the daily output of cercariae was counted from the first shedding from experimentally infected snails and from the day of collection from naturally infected ones. The results show that the size of the snails at the time of shedding exerts a very large effect on the output of cercariae and that the numbers obtained in the laboratory are not representative of cercarial output in the field. By the cross-sectional method, the cercarial output in the first 24 hours from infected snails collected in different months from the field was counted. The results show that output is size-specific. When the size-specific output is adjusted to the size-composition of infected snails taken from the field, it is estimated that the daily output from infected snails in the field may be 957.7 cercariae. However, this number may vary with the season.

Egypt↗
PubMed1970

Susceptibility of the small Biomphalaria alexandrina alexandrina from the UAR and the Sudan to infection with a strain of Schistosoma mansoni from Tanzania.

A series of laboratory experiments was carried out to determine the susceptibility of Biomphalaria alexandrina alexandrina, the snail vector of schistosomiasis in the United Arab Republic and the Sudan, to a strain of Schistosoma mansoni from Mwanza, Tanzania. The objective of the investigation was to determine whether or not B. alexandrina is refractory or partially refractory to infection with strains of S. mansoni other than the Egyptian strain.In one series of 5 exposures, snails from a colony originating in Alexandria, UAR, showed a mean infection rate 4 times that observed when snails from the same colony were exposed to the local strain of S. mansoni.

Animals↗
PubMed1993

Schistosoma mansoni: analysis of an unusual infection phenotype in the intermediate host snail Biomphalaria glabrata.

Snails from a B. glabrata stock, selected for nonsusceptibility to the NMRI strain of S. mansoni, exhibited unusual schistosome infections, with multiple sporocysts prominent in the head-foot (foot-sporocysts). When F1 progeny from numerous crosses between well-defined susceptible (S) and resistant (R) parental snails were exposed, 60% of the infected snails also exhibited this unusual phenotype. F1 progeny from S x S snail crosses developed normal infections. Foot-sporocysts usually developed much later than secondary sporocysts of normal infections and before 12 weeks postexposure the tissue reaction surrounding foot-sporocysts was less intense than reactions to sporocysts in other tissues of the body. Cercariae were seen emerging directly from foot-sporocysts. Infection of S x R hybrid progeny by three other strains of S. mansoni also resulted in the production of foot-sporocysts. Development of the foot-sporocyst infection phenotype in progeny from many snail crosses suggests that this phenotype is more common than previously recognized. Over 50% of the F1 progeny from S x R parental crosses developed patent infections, a fact relevant to the possible biological control of schistosomiasis by the introduction of refractory snails into endemic areas.

Animals↗
PubMed1998

Biomphalaria spp: identification of the intermediate snail hosts of Schistosoma mansoni by polymerase chain reaction amplification and restriction enzyme digestion of the ribosomal RNA gene intergenic spacer.

The intermediate hosts of S. mansoni in South America, B. glabrata, B. tenagophila, and B. straminea, were identified by restriction fragment length polymorphism (RFLP) analysis of the internal transcribed spacer region of the rRNA gene. The restriction patterns obtained with DdeI were the most informative of the eight enzymes that were tried. The RFLP profiles obtained using this enzyme are highly distinctive and exhibit low levels of intraspecific polymorphism even between specimens collected from diverse regions of Brazil, Argentine, Paraguay, and Uruguay. The method proved useful for the identification of DNA extracted from eggs, permitting species identification while preserving the living adult specimens for further studies.

Animals↗
PubMed1978

Degradation of the radula in the snails Biomphalaria glabrata Say and Limnaea stagnalis L. (Gastropoda, Pulmonata).

The radula of snails is formed at the posterior end of the radular gland or pocket, and degraded at the same rate at its anterior end. Degradation is due to different secretory activities of the inferior epithelium of the radular gland. Its secretions seem to degrade enzymatically the matrix of the radular membrane and basal plates of teeth, leaving only chitin containing microfibres and degradation products. The sclerotized parts of the teeth remain unchanged, but as they are now only loosely connected with the radular membrane. they are torn off easily during feeding movements. The rest of the degraded and frayed radular membrane and the subradular membrane are also lost by abrasion during feeding. The cells of the inferior epithelium are connected with each other by septate desmosomes and an elaborate system of deep lateral interdigitation which may provide tensil strength. Extrusion of degraded cells of the inferior epithelium into the subradular membrane takes place, although the thick basal lamina forms a continuous sheath which is closely adjoined to the basal parts of the inferior epithelium. Nerve fibres containing vesicles with electron dense neurosecretory material (deduced from the diameter of 200--250 nm) are attached to this sheath or penetrate into it; they may be involved in the regulation of production and degradation processes during radula replacement. Problems of the forward transport of radula and inferior epithelium are discussed.

Animals↗
PubMed1990

Comparative glucose tolerance studies in the freshwater snail Biomphalaria glabrata: influence of starvation and infection with the trematode Schistosoma mansoni.

The dynamic reactions of B. glabrata on intravasal loads of 20-1000 micrograms glucose.g live fresh wt-1 were studied in standard fed snails (SFS). Starved snails (SS) and snails infected with S. mansoni (IS) were given 100-500 micrograms glucose.g fresh live wt-1. Mean hemolymph glucose level was 12.1 mg.100 ml-1 in SFS. It was not significantly lower in SS (10.7 mg.100 ml-1), but significantly reduced in IS (8.5 mg.100 ml-1). Since hemolymph volumes were significantly increased in SS, the amount of circulating glucose (pool) did not change (75 micrograms.g body weight-1) compared to SFS (62 micrograms.g-1). It was, however, reduced to 41 micrograms.g-1 in IS. In SFS the circulating glucose pool had to be doubled to induce significantly elimination of the injected glucose. Tripled pools were eliminated with half-times of 45 min, whereas lower and higher glucose loads were eliminated significantly slower (half-times: 80-105 min). Glucose tolerance of SS was reduced: half-times were doubled, and metabolization of injected glucose was reduced. Since tissue fresh weights were lowered by 40%, absolute incorporation of 14C from labeled glucose was lowered, but specific incorporation (per mg) was higher than in SFS and IS. Glucose tolerance of IS was increased: metabolic clearance rates rose by 70% and half-times were shortened by 30%, though absolute and specific rates of 14C incorporation were lowered. However, IS lost 25% of the label to the water, whereas SFS lost 12% and SS only lost 8%. Using the antimetabolite 2-deoxyglucose, 80% of the losses proved to be glucose in IS, and 50% in SFS. The present results suggest the existence of a glucostatic regulation in B. glabrata with lower sensitivity and capacity than in mammals. As to glucose tolerance, the often reported parallelism in metabolic shifts induced by starvation and parasitic infection was not confirmed.

Animals↗
PubMed1995

Biosynthesis of the storage polysaccharide from the snail Biomphalaria glabrata, identification and specificity of a branching beta 1-->6 galactosyltransferase.

Adult snails synthesize in their albumen glands a storage polysaccharide called galactan which is utilized by the developing embryos. With [6-3H]-uridine 5'diphosphogalactose the incorporation of labelled D-galactose into the polysaccharide can be traced in freshly removed glands maintained in a bathing buffer. After centrifugation of homogenized glands, galactosyltransferase activity is only found in the insoluble fraction. Chaps extracts of this material retain almost all of their activity and can be used for comparison of the incorporation rates into different native galactans or in various oligosaccharides. A highly efficient beta-(1-->6) galactosyltransferase was detected when methyl 3-O-(beta-D-galactopyranosyl)-beta-D-galactopyranoside was offered as acceptor. The substitution at the penultimate residue resulted in a branched trisaccharide as demonstrated by 1H-NMR-spectroscopy and permethylation analysis of the reaction product. Comparable results were obtained with various oligosaccharides containing an internal galactose unit glycosidically linked beta 1-->3. Attempts to separate and purify the various enzymes involved resulted in the isolation of a fraction which is able to transfer D-Gal exclusively to native galactan, but not to oligosaccharides. A further fraction was obtained from a different resin with activity for native galactan and 6-O-(beta-D-galactopyranosyl)-D-galactopyranose, but without any for methyl-3-O-(beta-D-galactopyranosyl)-beta-D-galactopyranose. It is thus concluded that at least three different enzymes are involved in the biosynthesis of this snail galactan.

Animals↗
PubMed1977

[Microcalorimetric investigations of the host-parasite relationship between Biomphalaria glabrata and Schistosoma mansoni (author's transl)].

1. The ratio of dry weight to wet weight of infected snails (5.5 +/- 2.2%) is significantly smaller than that of uninfected animals (8.3 +/- 1.0%). 2. The specific values of oxygen consumption and heat-production per dry weight are significantly higher for infected snails (2.41 +/- 0.44 microliter O2/h/mg; 12.63 +/- 1.24 muW/mg) than for uninfected ones (1.88 +/- 0.24 microliter O2/h/mg, 8.94 +/- 0.91 muW/mg). 3. The rate of oxygen consumption always suffices to explain the measured heat flows for aerobic catabolism of carbohydrates or fats and proteins, respectively. Neither for infected nor for uninfected snails is it necessary to assume an anaerobic energy metabolism. 4. Structures in the calorimetrically obtained heat production curves are discussed.

Animals↗
PubMed1978

An automatic method for recording the emergence of cercariae of Schistosoma mansoni from the snail Biomphalaria glabrata.

In order to study the pattern of emergence of trematode larvae from the snail hosts (S. mansoni from B. glabrata) an automatic apparatus was developed. This apparatus allows the snails, each suspended by a thread, to be transported at intervals of at least half an hour into different beakers into which the cercariae are shed. This "eclosion clock" is essentially a carriage driven on perlon wheels along steel bars.

Animals↗
PubMed1980

Experimental epidemiology of schistosomiasis. I. The prepatent period and cercarial production of Schistosoma mansoni in Biomphalaria snails at various constant temperatures.

Laboratory experiments have permitted the quantification of the developmental times (prepatent periods) of Schistosoma mansoni in the snail over the whole possible range of constant temperatures. The basis relationship is satisfactorily described by a hyperbola of the formula y = 268/(x-14.2), y being the minimum time from miracidial infection to cercariae shedding (in days) x the mean temperature, and 14.2 the theoretical temperature threshold (in degrees C). Cercariae production takes place within the limits of +16 degrees C and 35 degrees C, the number of cercariae being low and the mortality of snails high at the extreme values. Long-term alternations between two temperature levels resulted in prepatent periods corresponding exactly to the proportional time-temperature products. However, slight accelerations of up to 7% and more could be observed when the prepatency began in a period of high temperature. The number of cercariae each snail shed during a period of one hour exposure per week decreased from about 1,500 at 18 degrees C to about 250 at 16 degrees C. Shedding ceased completely after 1-2 weeks at 15 degrees C.

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