SEARCH · PubMed Health

Results for “Snails”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 937 records · Page 52Linked to original sources

PubMed1997

Development of the statocyst in the freshwater snail Biomphalaria glabrata (Pulmonata, Basommatophora).

The development of the statocyst of the freshwater snail Biomphalaria glabrata has been examined from embryo to adult. Special emphasis was put on the growth of the statoconia in the statocysts. In the statocysts of embryonic snails (90-120 h after oviposition) there is not a single statolith but an average of 40-50 statoconia per statocyst. The number of statoconia increases to 385-400 when the snails reach a shell diameter of 4 mm and remains relatively constant thereafter, irrespective of shell size. Small statoconia are found in supporting cells, which suggests that the statoconia are produced within these cells. The average diameter of statoconia and the total mass of statoconia increase with increasing shell diameter. The average number of large statoconia (diameter > 7 microm) per statocyst continues to increase from 2 to 10 mm animals while the number of small ones (diameter < 4 microm) initially rises and then decreases after 4 mm. These results demonstrate continuous growth of the statoconia in the cyst lumen of Biomphalaria. The single statoconia vibrate in a regular pattern in vivo, indicating beating of the statocyst cilia. The statoconia sink under the influence of gravity to load and stimulate receptor cells which are at the bottom. The length of cilia and the size of statocyst gradually increase as the animal grows. However, the increase in the volume of the statocyst is relatively small compared with the increase in body weight during normal development.

Animals↗

PubMed1990

Effects of infection with Angiostrongylus cantonensis on the circulating haemocyte population and the haematopoietic organ of the host snail M-line Biomphalaria glabrata.

The number of circulating haemocytes, the size of the haematopoietic organ, and the size of haemocyte capsules around the parasite were studied in M-line Biomphalaria glabrata snails exposed to 100 or 400 first-stage larvae of Angiostrongylus cantonensis. The number of haemocytes in exposed snails increased significantly at 1 day post-exposure, decreased to control value, and then increased again. The decrease in number of circulating haemocytes is probably due to the removal of cells from the circulation to participate in encapsulation of larvae. The majority of circulating haemocytes in M-line B. glabrata are fully-spread granulocytes, which increase significantly in number in snails following exposure to A. cantonensis larvae. However, populations of partially-spread granulocytes, round cells, hyalinocytes and miscellaneous haemocytes were relatively constant. The size of capsules around the parasite increased during the 42-day interval of the experiment. The haematopoietic organ increased in size in response to infection.

Angiostrongylus↗

PubMed1992

Effect of the organophosphorous insecticide, chlorpyrifos (Dursban), on growth, fecundity and mortality of Biomphalaria alexandrina and on the production of Schistosoma mansoni cercariae in the snail.

Exposure of Biomphalaria alexandrina to sublethal concentrations (0.125, 0.25 and 0.05 ppm) of the organophosphorous insecticide, chlorpyrifos (Dursban), induced a reduction in egg production and egg hatchability. Exposure of Schistosoma mansoni miracidia to the insecticide (60 min, 0.50 ppm) prior to infection of B. alexandrina did not affect the subsequent production of cercariae. However, exposure of S. mansoni-infected snails to the insecticide until day 55, from day 20 to day 62 and from day 35 to 62 following infection resulted in blockage of cercarial shedding. Cercarial shedding commenced in some snails when the treatment stopped. Exposure to the insecticide in concentrations of 0.125 and 0.25 ppm during the first 20 days following infection did not affect the subsequent production of cercariae, but exposure to 0.5 ppm during the first 20 days affected markedly the production of cercariae due to a high snail mortality. The findings indicate that the cercaria is the target stage for the activity of chlorpyrifos on the intramolluscan larval development. It is suggested that S. mansoni cercarial production in B. alexandrina may be a useful system for monitoring the effect of low concentrations of pesticides on the aquatic environment, and that the ability by chemical means to interrupt the cercarial production might be a useful tool in further analyses of important aspects of the snail/parasite relationship.

Animals↗

PubMed1976

A demonstration of the presence of anti-snail antibodies in individuals infected with Schistosoma haematobium.

An extract of the snail Bulinus (Physopsis) africanus, the intermediate host of Schistosoma haematobium, was used as the antigen in haemagglutination tests in a survey of the prevalence of anti-snail antibodies in various population groups. It was found that sera from known bilharzia-infected individuals and randomly selected individuals from bilharzia endemic areas had significantly higher incidences as well as higher titres of antibodies to this snail antigen than non-infected individuals and individuals from non-endemic areas.

Adult↗

PubMed1977

Interference with Fasciola hepatica snail finding by various aquatic organisms.

Previous studies using radioactive miracidia have shown that a number of non-host snails and bivalves, interposed as 'decoys' in linear test channels, may interfere with the capacity of Fasciola hepatica miracidia to infect Lymnaea truncatula. Applying similar experimental principles, the role of several other potential interferents have been analysed in the present study. Daphnia pulex (Cladocera) and larvae of Corethra sp. (Diptera) exercised significant interfering effects by protecting 'target' snails from infection. Evidence suggested that this effect was a result of their normal predatory behaviour. Other organisms including Herpobdella testacea and Helobdella stagnalis (Hirudinea), Acellus aquaticus (Isopoda), Planaria lugubris (Turbellaria) and L. truncatula egg clusters failed to interfere with miracidial host-finding. Nor did P. lugubris and L. truncatula 'conditioned water' interfere with the capacity of the miracidia to infect their host snail.

Animals↗

PubMed1992

Modulation of the activity of the internal defence system of the pond snail Lymnaea stagnalis by the avian schistosome Trichobilharzia ocellata.

Effects of infection with the avian schistosome Trichobilharzia ocellata on the activity of the internal defence system of the intermediate snail host Lymnaea stagnalis were studied, utilizing an in vitro phagocytosis assay for determining haemocyte activity. A distinction was made between plasma- and cell-associated effects. The period immediately after penetration of the parasite into the snail host (1.5-72 h post-exposure (p.e.)) was extensively studied. In addition, several time-points coinciding with the later-successive-stages of parasite development (2, 4, 6, 8 and 10 weeks p.e.) were investigated. Plasma-associated enhancement of defence activity was found between 1.5 and 6 h p.e., followed by plasma-associated suppression between 12 and 72 h p.e. A cell-associated activation was found between 1.5 and 6 h p.e. and also at 8 and 10 weeks p.e. How these effects on the defence system may be related to phenomena observed in infected snails at these time-points is discussed.

Analysis of Variance↗

PubMed1994

Observations on the effects of different chemotherapy strategies on the transmission of Schistosoma mansoni in Machakos District, Kenya, measured by long-term snail sampling and cercariometry.

Transmission of Schistosoma mansoni was monitored by routine snail sampling for Biomphalaria pfeifferi and by supplementary cercariometric measurements in 4 neighbouring study areas in Machakos District, Kenya. After 1 year, extensive, population-based chemotherapy with a single dose of praziquantel was given in 3 areas, but only minimal treatment in the fourth. In the year preceding treatment, seasonal transmission of S. mansoni and other non-human trematodes occurred in all 4 areas, despite some ecological differences and the effects of earlier treatment campaigns in 1 of the study areas. After treatment of all infected subjects in one area in which there had been earlier chemotherapy campaigns, S. mansoni transmission remained very low. It was reduced for at least 2 years after chemotherapy targeted at either all heavily infected subjects or all infected school children, but it was unaffected in an area where treatment was restricted to those few very heavily infected cases at risk of developing disease. Nowhere was transmission entirely eliminated by chemotherapy and that of non-human trematodes continued unabated. The snail data correspond well with the human, parasitological data. Targeting school children was as effective as more extensive campaigns, but chemotherapy alone never stopped S. mansoni transmission: reinfection was inevitable, at rates determined by ecological factors affecting snail populations.

Animals↗

PubMed2001

Compatibility and sex in a snail-schistosome system.

Knowledge of the genetics underlying resistance to parasitic infection has important repercussions for our understanding of infection dynamics and the mechanisms of host-parasite co-evolution. The aim here was to determine for a Biomphalaria glabrato-Schistosoma mansoni system whether (1) resistance is dominant over susceptibility, (2) it is possible to crossbreed snails to be simultaneously resistant and/or susceptible to more than one parasite strain and (3) compatibility genotype affects reproductive strategy. Using replicate snail strains artificially selected for either resistance or susceptibility to single replicate parasite strains, individual snails from each line were paired with a selected partner of matched or non-matched compatibility status and cross-breeding was identified by RAPD-PCR. The resulting compatibility phenotype of all offspring was determined. Support for all 3 hypotheses were obtained. The results are discussed in terms of their applied and theoretical implications.

Animals↗

PubMed2001

Seasonality in the transmission of schistosomiasis and in populations of its snail intermediate hosts in and around a sugar irrigation scheme at Richard Toll, Senegal.

Irrigation for intensive sugar cultivation started in the early 1980s at Richard Toll, some 100 km from the mouth of the Senegal River. Infections with Schistosoma mansoni were first seen in late 1988. This study records quantitative snail surveys for over 3 years from 1992 at sites representing different habitats in and around the irrigation scheme. Populations of both Biomphalaria pfeifferi (the intermediate host of S. mansoni) and Bulinus spp. (mainly B. truncatus, the local host of S. boris) peaked in late 'spring' or early 'summer', depending on the habitat, and then remained low until the following spring', B. pfeifferi favoured smaller, man-made habitats with most transmission between May and August each year. The less abundant Bulinus spp. favoured larger natural and man-made habitats with most S. bovis transmission between April and July. S. mansoni infections were more, but S. bovis infections were less abundant than other trematodes in their respective snail hosts. Ecological changes in the early 1980s due to sugar irrigation pre-dated similar, more widespread changes in the late 1980s when the completion of dams across the Senegal River prevented seasonal rain fed floods and sea water intrusion. S. mansoni has since spread rapidly around Richard Toll. The incompatibility of the local S. haematobium strains with the dominant bulinid snails has so far prevented an epidemic of urinary schistosomiasis at Richard Toll, but the invasion of similar downstream habitats by susceptible B. globosus is worrying. The principal control measure, chemotherapy, given in the 'winter' would minimise the rate of reinfection. It could be reinforced by judicious mollusciciding within the sugar irrigation scheme but not elsewhere.

Animals↗

PubMed2005

An expressed sequence tag survey of gene expression in the pond snail Lymnaea stagnalis, an intermediate vector of trematodes [corrected].

The pond snail Lymnaea stagnalis is an intermediate vector for the liver fluke Fasciola hepatica, a common parasite of ruminants and humans. Yet, despite being a disease of medical and economic importance, as well as a potentially useful comparative tool, the genetics of the relationship between Lymnaea and Fasciola has barely been investigated. As a complement to forthcoming F. hepatica expressed sequence tags (ESTs), we generated 1320 ESTs from L. stagnalis central nervous system (CNS) libraries. We estimate that these sequences derive from 771 different genes, of which 374 showed significant similarity to proteins in public databases, and 169 were similar to ESTs from the snail vector Biomphalaria glabrata. These L. stagnalis ESTs will provide insight into the function of the snail CNS, as well as the molecular components of behaviour and response to parasitism. In the future, the comparative analysis of Lymnaea/Fasciola with Biomphalaria/Schistosoma will help to understand both conserved and divergent aspects of the host-parasite relationship. The L. stagnalis ESTs will also assist gene prediction in the forthcoming B. glabrata genome sequence. The dataset is available for searching on the world-wide web at http://zeldia.cap.ed.ac.uk/mollusca.html.

Amino Acid Sequence↗

PubMed2000

Functional recovery of respiratory behavior during axonal regeneration in snails (Lymnaea stagnalis) is experience dependent.

This study investigated the role of experience in recovery of pulmonary respiration during axonal regeneration in Lymnaea stagnalis. Pulmonary respiration occurs when snails break the water surface and open the lung orifice, the pneumostome. It was shown that axotomy of all the axons innervating the pneumostome and surrounding area prevents the occurrence of lung respiration in 69% of snails. In the remaining 31%, lung respiration persisted, indicating that peripheral components alone are capable of initiating pneumostome openings and closures. Five weeks postsurgery, all snails with previous nerve crushes showed opening of the pneumostome with normal latency after breaking the water surface. However, prevention of pulmonary respiration during the recovery period dramatically changed the recovered behavior. Thus, experience in pulmonary respiration during axonal regeneration plays a role in the recovery of this behavior.

Animals↗

PubMed2004

Biomphalaria tenagophila: genetic variability within intermediate snail hosts susceptible and resistant to Schistosoma mansoni infection.

DNA analysis by molecular techniques has significantly expanded the perspectives of the study and understanding of genetic variability in molluscs that are vectors of schistosomiasis. In the present study, the genetic variability of susceptible and resistant B. lenagophila strains to S. mansoni infection was investigated using amplification of their genomic DNA by RAPD-PCR. The products were analyzed by PAGE and stained with silver. The results showed polymorphism between tested strains with four different primers. We found two bands of 1,900 and 3,420 bp that were characteristic of the susceptible strains with primer 2. The primers 9 and 10 identified a single polymorphic band that was also characteristic of (3,136 and 5,041 bp, respectively) susceptible snails. Two polymorphic bands were detected by primer 15: one with 1,800 bp was characteristic of the resistant strain and the other with approximately equal to 1,700 bp in the susceptible one. These results provide additional evidence showing that the RAPD-PCR technique is adequate for the study of polymorphisms in intermediate hosts snails of S. mansoni. The obtained results are expected to expand the knowledge about the genetic variability of the snails and to permit the future identification of genomic sequences specifically related to the resistance/susceptibility of Biomphalaria to the larval forms of S. mansoni.

Animals↗

PubMed2000

Localization and fate of aluminium in the digestive gland of the freshwater snail Lymnaea stagnalis.

The digestive gland of the freshwater snail Lymnaea stagnalis, exposed to water containing an elevated concentration of aluminium at neutral pH for up to 30 days, followed by a 20 day recovery period, was examined by light and electron microscopy and X-ray microanalysis. Aluminium was localized in the yellow granules present in the digestive and excretory cells and in the green and small granules present in the digestive cells. More aluminium, silicon, phosphorus and sulphur were present in all three granule types from aluminium exposed snails. The number of yellow and green granules from the digestive gland of aluminium exposed snails showed a progressive increase over the experimental period compared to controls. The number and aluminium content of the granules is likely to reflect the role of the digestive gland as a 'sink' for accumulated aluminium. We propose that intracellular monomeric silica is involved in the detoxification of aqueous aluminium which at neutral pH is largely in the form of an insoluble polyhydroxide. The increased amounts of sulphur and phosphorus in the granules are likely to be part of a broad response to metal loading but probably do not play a significant role in the storage and detoxification of aluminium.

Aluminum↗

PubMed1975

The influence of stream geology on the distribution of the bilharzia host snails, Biomphalaria pfeifferi and Bulinus (physopsis) sp.

The Gladdespruit and Komati River surveys have shown that similar environmental conditions have developed where the watercourses flowed over particular rock types. In these watercourses a potentially useful association was found between the occurrence of permanent, lentic habitats produced by the weathering of bedrock with a hardness above 5 in Mohs' Scale of Hardness and the longitudinal distribution of persistent populations of the bilharzia intermediate host snails Biomphalaria pfeifferi and Bulinus (Physopsis) sp. Bilharzia transmission follows this pattern in these waterways. Weathering of bedrock with hardness below 5 in Mohs' scale, and/or flow over beds of alluvial sand, produced perpetually lotic (flowing) environments without persistent host snail populations because of the snail's inability to tolerate high current speeds. However a few temporary populations survived in temporarily lentic habitats during the dry winter season.

Africa↗

PubMed1991

Laboratory evaluation of B-2 as a molluscicide in the control of the snail intermediate hosts of schistosomiasis in South Africa.

There is a continuous need for the development and evaluation of new, inexpensive but highly effective molluscides for the control of freshwater snails acting as intermediate hosts of schistomiasis. For this reason B-2 (Hokko Chemical Industry Co. Ltd, Japan), also called Phebrol (sodium 2,5-dichloro-4-bromophenol), was evaluated in our laboratory as a candidate molluscicide for the control of freshwater snails in South Africa. Bulinus africanus and Biomphalaria pfeifferi, intermediate hosts of Schistosoma haematobium and Schistosoma mansoni respectively, were exposed to different B-2 concentrations for 24 and 48 hours. An indigenous fish species, Oreochromis mossambicus, which is common in local schistosomiasis endemic areas, was also exposed to the molluscicide. The calculated values obtained from a probit analysis (LC50, 24 hours: B. africanus = 2.6 mg 1(-1) and B. pfeifferi = 2.9 mg 1(-1), indicated that these species from southern Africa are less sensitive to B-2 than are B. truncatus and B. pfeifferi from northern Africa, which in turn are less sensitive than the Oncomelania spp. from Japan, China and the Philippines. It is expected that molluscicidal levels of B-2 would be harmful to O. mossambicus populations. Although B-2 has a marked potential for snail control in South Africa, niclosamide (Bayluscide) remains the molluscicide of choice.

Animals↗

PubMed1996

The genetical and environmental determination of phally polymorphism in the freshwater snail Bulinus truncatus.

In some species of self-fertile pulmonate snails, two sexual morphs co-occur in natural populations: regular individuals and aphallic individuals that cannot transmit sperm to other snails. Purely aphallic populations therefore reproduce obligatorily by selfing. Understanding the evolution of aphally and selfing in these snails requires a precise knowledge of phally determination. In this paper, we investigate the genetic and environmental determination of aphally in Bulinus truncatus by a survey of the family (offspring) aphally ratio of 233 individuals originating from seven natural populations and a study of the reaction norm of the family aphally ratio to temperature using 60 individuals from 10 selfed lineages of one population. Our results indicate a high genetic variability for the determination of aphally between populations and within some populations, associated with a high level of genetic determination. Our second experiment indicates a significant temperature and lineage effect though no interaction between these two effects. We discuss our results in the framework of threshold models developed for dimorphic traits with polygenic inheritance. We propose that the sexual morph of an individual at a given temperature is determined by a temperature threshold value depending on both the individual genotype and probabilistic processes.

Animals↗

PubMed1997

The substrate specificity of the snail Lymnaea stagnalis UDP-GlcNAc:GlcNAc beta-R beta 4-N-acetylglucosaminyltransferase reveals a novel variant pathway of complex-type oligosaccharide synthesis.

UDP-GlcNAc:GlcNAc beta-R beta 1-->4-N-acetylglucosaminyltransferase (beta 4-GlcNAcT) of the snail Lymnaea stagnalis is an enzyme with structural resemblance to mammalian beta 4-galactosyltransferases (beta 4-GalT). The enzyme, which is present in the prostate gland of the snail, was expressed in a recombinant form in insect cells using the baculovirus technology. This form was used to determine the enzyme's in vitro substrate specificity in order to assess its possible role in vivo. The enzyme appeared to be a genuine GlcNAcT as no UDP-sugar other than UDP-GlcNAc could serve as an efficient donor substrate. Acceptor specificity studies showed that the enzyme is far more restricted in acceptor usage than beta 4-GalT. Oligomers of beta 4-GlcNAc were relatively poor acceptors, indicating that this enzyme is not involved in the synthesis of chitin-like molecules. Both its polypeptide structure and acceptor specificity suggest that it neither is implicated in the synthesis of the chitobiose core of N-linked glycans. Preferred substrates are those that contain a beta-GlcNAc residue attached to the carbon-6 of Gal or GalNAc residues, as found in vertebrate blood-group I-active and O-linked core 2- and 4-based oligosaccharides, respectively. By contrast, compounds in which GlcNAc is beta 6-linked to Man (as in N-linked glycans) are poor acceptors. Analysis of the products formed in vitro by 1H-NMR spectroscopy and acetolysis showed that the enzyme establishes a GlcNAc beta 1-->4GlcNAc linkage and shows branch specificity with a blood-group I-active trisaccharide substrate. Furthermore, the enzyme differs from beta 4-GalT in that it is not responsive to alpha-lactalbumin. It is proposed that the enzyme functions in a novel, variant pathway of complex-type oligosaccharide synthesis in the snail.

Animals↗

PubMed1993

Definition of the DNA-binding site repertoire for the Drosophila transcription factor SNAIL.

The Drosophila gene snail (sna) which encodes a zinc finger protein is essential for dorsal-ventral pattern formation in the developing embryo. We have defined a repertoire of SNAIL (SNA) binding sites using recombinant SNA proteins to select specific binding sequences from a pool of random sequence nucleotides. The bound sequences which were selected by multiple rounds of gel retardation and amplification by the polymerase chain reaction (PCR) were subsequently cloned and sequenced. The consensus sequence, 5'G/A A/t G/A A CAGGTG C/t A C 3', with a highly conserved core of 6 bases, CAGGTG, shares no significant homology with known binding sequences of other Drosophila zinc finger proteins. However, the CAGGTG core is identical to the core motif of aHLH (helix-loop-helix) binding sites. The strongest SNA binding is obtained with sequences containing this core motif whereas reduced binding is seen for sequences with canonical CANNTG HLH motifs. Interestingly, SNA binding is detected in the promoter region of the snail gene. Transient expression in co-transfection experiments using a SNA binding element (SBE) linked to a heterologous promoter indicates that SNA has the ability to function as a transcription activator.

Animals↗