Spatial microhabitat selection by Biomphalaria pfeifferi in a small perennial river in Tanzania

A study was carried out in the Mlali river in south-central Tanzania with two aims. First, to determine microhabitat availability in two sites (A and B) with respect to water depth, water velocity and dominant substratum type. Second, to assess microhabitat use by Biomphalaria pfeifferi, the intermediate host snail of intestinal schistosomiasis and to investigate whether these snails show preferences for certain microhabitats. The two sites differed significantly with respect to width, water depth, water velocity and substratum composition. It is suggested that the absence of B. pfeifferi from site B is mainly associated with the high water velocities at that site, where 62% of the measurements exceeded30 cm s^-1. In site A, the microhabitat use by 327 B. pfeifferi snails was assessed by means of direct observation. No significant relationships were found between snail size and the habitat variables investigated, indicating that snail size appeared to be of no importance in spatial microhabitat selection. B. pfeifferi snails showed statistically significant preferences for shallow water (depth: 2–7 cm) and the preferred water velocities ranged between 12 and 21 cm s^-1 with an estimated optimum at13.3 cm s^-1. No statistically significant preferences for substratum type were found. This revised version was published online in August 2006 with corrections to the Cover Date.     

Biological control of the zebra mussel Dreissena polymorpha and the snail Biomphalaria glabrata, using Gramicidin S and D and molluscicidal strains of Bacillus

Applications of Final Whole Culture (FWC) or primary powder material from strains of each of four Bacillus species (B. alvei, B. brevis, B. circulans, B. laterosporus) used singly, as well as the antibiotics Gramicidin S (GS) and Gramicidin D (GD) used singly, were found to be molluscicidal against several life cycle stages of the zebra mussel Dreissena polymorpha. Combinations of the bacterial material with either GS or GD were either additive (for GS) or antagonistic (for GD). The smaller the life cycle stage of the animal, the more sensitive it was to either the bacterial or antibiotic agent. The veliger stage was particularly sensitive to each agent, with the molluscicidal effect being more rapid in the veliger (5 h) than in the adult (6 days). The molluscicidal effects of these agents (at 1–100 μ g ml⁻¹) against the veliger stages of the zebra mussel were comparable to the activity of B. thuringiensis and B. sphaericus against their target organisms. These agents used singly were also active against small adult Biomphalaria glabrata, the snail vector of schistosomiasis (eg at tenths of μ g ml⁻¹ of GS). Received 09 July 1996/ Accepted in revised form 06 November 1996     

Control of Schistosoma mansoni transmission: Strategy for using molluscicides on St. Lucia

Control of Schistosoma mansoni transmission: strategy for using molluscicides on St. Lucia. International Journal for Parasitology 3: 795–801. A simplified model, based on previous field studies, is described to summarize the transmission of Schistosoma mansoni on the West Indian Island of St. Lucia by the snail Biomphalaria glabrata. Snail populations in static habitats play little part in transmission but form a reservoir of snails which invade flowing habitats in the dry season. These flowing habitat populations account for most of the transmission: preventing their establishment should greatly reduce transmission. The reasons why a single molluscicide treatment of the static habitat populations is unlikely to achieve this result are discussed and an alternative, practical strategy is suggested. An initial intensive mollusciciding followed by surveillance, coupled with focal mollusciciding of surviving snail colonies, should suppress the static habitat populations sufficiently to prevent the invasion of the flowing habitats. This practical strategy should have a reasonable chance of reducing S. mansoni transmission judging by the results of similar control schemes using molluscicides.     

Lipid levels in Biomphalaria glabrata infected with different doses of Echinostoma paraensei miracidia

The effect of experimental exposure of Biomphalaria glabrata to different doses (5 and 50) of Echinostoma paraensei miracidia on the total levels of cholesterol and triglycerides circulating in the hemolymph and the neutral lipids in the digestive gland–gonad (DGG) complex were studied. The snails were dissected one, two, three and four weeks after infection to collect the hemolymph and DGG tissue, to measure the levels of cholesterol and triglycerides in the hemolymph and neutral lipids in the tissue. The results for the hemolymph showed a similar order of variation for both substrates tested in the first week after infection. The reduced levels of these lipids in the infected snails indicate intense use of these substrates both by the intermediate host and the parasite, suggesting its probable participation in the energy metabolism and structural construction of the developing larval stages. Alterations in the profile of neutral lipids in the DGG were also found. The results obtained indicate that in this model, the lipid metabolism depends on the miracidial dose used.     

A comparison of the glycolipid compositions of cercarial and adult Schistosoma mansoni and their associated hosts

Glycolipid patterns of cercarial and adult Schistosoma mansoni were determined and compared with those of Biomphalaria glabrata snails and mouse (BALB/c strain) red blood cells by high-performance thin-layer chromatography. Differences in glycolipid content were found between cercariae and adult worms and between these stages and their respective host tissues.     

Effects of diet on the lipid composition of the digestive gland-gonad complex of Biomphalaria Glabrata (Gastropoda) infected with larval Echinostoma Caproni (Trematoda)

This study examined the effects of a larval Echinostoma caproni infection on the neutral lipid composition of the digestive gland-gonad complex (DGG) of Biomphalaria glabrata snails fed hen's egg yolk supplemented with lettuce (Y-L) or lettuce supplemented with Tetramin (L-T). Snails were experimentally infected with the miracidial stage of this echinostome, and their DGGs containing daughter rediae were analyzed for neutral lipids five weeks post-infection by qualitative and quantitative thin-layer chromatography. Light microscopy using Oil Red O (ORO) staining and transmission electron microscopy (TEM) were used to localize neutral lipids in the rediae. The DGGs of infected snails maintained on the Y-L diet showed a significant increase in free sterols and a significant decrease in triacylglycerols compared to uninfected snails maintained on the Y-L diet. The DGGs of infected snails maintained on the L-T diet showed no significant difference in free sterols or triacylglycerols compared to uninfected snails maintained on the L-T diet. ORO staining and TEM showed the presence of lipid droplets in rediae from snails on the Y-L diet. The significant decrease in triacylglycerols in the DGGs of infected snails maintained on the Y-L diet suggests that triacylglycerols were utilized by the rediae.     

Structure of the extracellular hemoglobin of Biomphalaria glabrata

The hemoglobin of Biomphalaria glabrata was purified to homogeneity by gel filtration column followed by anion exchange chromatography. The dissociation products were analyzed by a 5–15% gradient polyacrylamide gel electrophoresis containing sodium dodecyl sulfate (SDS-PAGE) giving a band of 270 kDa and a band of 180 kDa after reduction with β-mercaptoethanol. The same profile was obtained in a 3.5% agarose gel electrophoresis containing SDS (SDS-AGE) but showed additional bands of higher molecular weight. These bands were proposed to be monomers, dimers and trimers, since they showed a good correlation in a plot of R_f versus log M_r. After partial reduction in a two-dimensional SDS-AGE, the proposed monomers and dimers produced two and four bands, respectively, likely indicating one to four chains crosslinked by disulfide bridges. Digestion with four different proteases yielded several equivalent fragments with molecular weights multiples of its minimum molecular weight (17.7 kDa). The circular dichroism spectrum of the protein showed a characteristic high α-helix content (70%). It was proposed that this hemoglobin is a pentamer with a molecular weight of aproximately 1.8×10³ kDa, assembled by five 360-kDa subunits, each formed by two 180-kDa chains linked in pairs by disulfide bridges and each of these chains, in turn, comprised by ten heme binding domains linked in tandem. These data are compared to the published information for other planorbid extracellular hemoglobins.     

Changes in the reproductive biology of Biomphalaria glabrata experimentally infected with the nematode Angiostrongylus cantonensis

This study showed for the first time changes in the reproductive biology of Biomphalaria glabrata experimentally infected with Angiostrongylus cantonensis. The values of all the parameters analyzed (total number of eggs, number of egg masses, number of eggs/mass, number of eggs/snail, percentage of viable eggs and galactogen content in albumen gland) changed with progressive infection. The results indicate the occurrence of partial parasitic castration of B. glabrata by A. cantonensis larvae, probably in response to the depletion of energy reserves, with no injuries to the gonadal tissues.