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At least 19 recordsLinked to original sources
PubMed1989

Identification of snails infected with schistosomes by ELISA employing monoclonal antibodies: Schistosoma mansoni in laboratory snails (Biomphalaria glabrata) and in field snails (Biomphalaria pfeifferi) from Kenya.

An enzyme-linked immunosorbent assay (ELISA) employing monoclonal antibodies was used for detecting Schistosoma mansoni antigens in hemolymph of laboratory snails (Biomphalaria glabrata) in Kenya. Infected laboratory snails shedding cercariae were differentially identified by ELISA from uninfected snails with 100% sensitivity and specificity. Prepatent infections were detected by ELISA from 2 weeks after exposure to miracidia. Thus, ELISA revealed infection 3 weeks before maximal patency was reached (5-6 weeks post-exposure). Infected field snails (B. pfeifferi) shedding cercariae were differentially identified by ELISA, with 100% sensitivity and specificity, from uninfected field snails and from snails naturally infected with other trematodes (echinostomes and strigeids). Prepatent infections with S. mansoni were readily identified by ELISA in field snails. A case is demonstrated where infection rate, as determined by shedding test alone, was 9.8%, whereas the combined figure of prepatent and patent infection rates was 22.9%

Animals↗
PubMed2003

Correlation between snails and fish in fish ponds of World Fish Center (ICLARM) with special reference to snail vectors of schistosomiasis and fascioliasis.

The abundance of snail species in earthen fish ponds, irrigation and drainage canals at World Fish Center (ICLARM) in descending order was Bellamya unicolor (50.89%) > Physa acuta (18.94%) > Cleopatra bulimoides (7.6%) > Lanistes carinatus (6.73%) > Bulinus truncatus (5.19%) > Melanoides tuberculata (4.83%) > Lymnaea natalensis (3.14%) > Gabbiella senaariensis (0.9%) > Biomphalaria alexandrina (0.55%) > Lym naea truncatula (0.4%) > Planorbis planorbis and Succinea cleopatra (0.33%) > Ferrissia isseli (0.18%). Dead snails constituted about 5.19% of all the collected specimens. There were dramatic decrease in the total number of pulmonates in fish ponds which contained only Tilapia sp., and a very small number of cat fish, whereas the numbers of prosobranchia snails were much higher in these ponds. In fish ponds which accommodated a variety of fish species, the most dominant snail was B. unicolor followed by L. carinatus. However, pulmonate snails were absent in these ponds. B. truncatus was the only snail species found in concrete tank which contained only young tilapias with a very small size (5-8 cm in standard length). In irrigation canals, the number of snails and diversity was much higher than those in fish ponds. Out of 191 snails collected from inlet irrigation canal, 71 were dead, but in the outside irrigation canals, seven out of 564 snails were dead. P. acuta was absent in all examined fish ponds, but it was alive and in a high number (497 snails) in the outside irrigation canals. The number of snails collected from Bahnasawy drain was remarkably low (128 snails), however the diversity of snails was much higher compared to those in fish ponds and irrigation canals. Snail populations were stable with constant recruitment of young to adult snails for all the studied species.

Animals↗
PubMed1992

Snail predation by larvae of Sepedon scapularis Adams (Diptera: Sciomyzidae), a potential biocontrol agent of snail intermediate hosts of schistosomiasis in South Africa.

Malacophagous larvae of the fly Sepedon scapularis Adams were shown experimentally to be effective predators of three species of aquatic pulmonate snails tested as prey: Bulinus africanus (Krauss) an important intermediate host of Schistosoma haematobium (Bilharz), Bulinus tropicus (Krauss) and the invasive species Physa acuta Draparnaud. Survival of S. scapularis larvae from instar to instar was negatively affected by the size of prey snails, since larvae tended to be asphyxiated by the mucous secretions of the snails, or by the larval hydrofuge hairs becoming entangled in snail faeces. In experiments to test the choice of S.scapularis larvae for different species and sizes of snails, B.africanus was significantly disfavoured compared with the other two snail species. Small snails (< 3 mm) were more frequently killed by all three larval instars of S.scapularis. First instars killed few, if any, large snails (> 7 mm), whereas second and third instars preyed effectively on all sizes of snails. Third instars killed significantly more snails than younger instars. For larvae offered only one species of snail as prey, the mean total number of snails killed per larva during its entire development was 49 B.africanus, 45 B.tropicus or 34 P.acuta. It is concluded that S.scapularis is potentially useful as a biological control agent for use against indigenous Bulinus and exotic Physa snails.

Analysis of Variance↗
PubMed1991

Trichobilharzia ocellata: influence of infection on the fecundity of its intermediate snail host Lymnaea stagnalis and cercarial induction of the release of schistosomin, a snail neuropeptide antagonizing female gonadotropic hormones.

Subadult and adult specimens of the pond snail Lymnaea stagnalis were infected with the schistosome Trichobilharzia ocellata. Egg production and growth of the snails were monitored over an 8-week period post-infection (p.i.). Snail haemolymph was collected and analysed for the presence of schistosomin, a neuropeptide which antagonizes the action of the snails' female gonadotropic hormones. Snails infected as subadults showed an increase in fecundity during the first 4 weeks p.i. compared with non-infected controls. The possibility is discussed that this increase is caused by an accelerated maturation of the female sex organs due to elevated levels of Dorsal Body Hormone, a female gonadotropic hormone. No difference in fecundity was found between snails infected as adults and control snails during the first 4 weeks p.i. Snails infected as subadults and as adults showed a decrease in fecundity from week 5 p.i. and onwards. This decrease coincided with the appearance of schistosomin in the haemolymph of the snails and with that of differentiating cercariae in the daughter sporocysts. Cercariae are probably involved in the induction of schistosomin release from the snails' CNS into the haemolymph. Snails infected as subadults or as adults grew at approximately the same rate as uninfected snails.

Animals↗
PubMed1997

[Effects of heavy metals on snail development. Use of snails as bio-indicators of heavy metal pollution for the preservation of human health].

The use of snails as biological indicators is particularly appropriate for metals, which they accumulate in their organs. The aim of the present experiment was to carry out a rigorous experimentation in the laboratory and in the wild in order to develop a methodology for the use of snails at a known stage of growth that would give precise information on the toxicity of heavy metals for different concentrations and durations of exposure. We have developed a test of toxicity based on the effects of a noxious and carcinogenic element, cadmium, on the land-snail Helix aspersa aspersa (H.a.a) of one month of age. Five concentrations (50 to 800 micrograms/g), were selected to estimate the concentrations causing 50% inhibition of growth (EC 50) at 14 days: 190 micrograms/g and at 28 days: 180 micrograms/g. A soil matrix contaminated with metals (soil including 800 micrograms/g Cr, 20 micrograms/g Cd, 800 micrograms/g Pb and 2000 micrograms/g Zn) was incorporated into the food at 50 and 75%, it too inhibited the growth of juvenile snails compared to incorporation of control soil. An accurate and rapid (2 to 4 weeks) method is therefore available for the evaluation of the toxicity of pollutants by ingestion. The first trials of this method in the wild consisted of placing batches of 2-month-old snails, identical to those used in the first lab tests, in locations that were either polluted or not. Differences in growth were observed depending on the locations; analysis of the levels of metal in the organs of the snails should enable us to check if there is a correlation between these levels and the growth rates. The results obtained with cadmium compared to those of other authors working with earthworms and soil arthropods show that snails give responses to concentrations comparable to those of earthworms and much more rapidly and with more sensitivity than those of collembolla for example. The ease of handling snails and the perfect control of their breeding are essential factors in carrying out reliable bioassays in toxicology and in ecotoxicology.

Animals↗
PubMed1976

The use of a molluscicide, in conjunction with chemotherapy, to control Schistosoma haematobium at the Barombi Lake foci in Cameroon. I. The attack on the snail hosts, using N-tritylmorpholine, and the effect on transmission from snail to man.

The background and strategy of a campaign to control the transmission of Schistosoma haematobium at the isolated crater-lake villages of Barombi Mbo and Barombi Kotto are outlined. A two-pronged attack was envisaged, using N-tritylmorpholine (Frescon) to control the snail host, and niridazole (Ambilhar) to control the parasite in man. The lake villages and their environs are described. Observations, relevant to control, are recorded on the biology of Bulinus rohlfsi and B. camerunensis. Snail populations were sampled by hand picking, and by the use of basket traps baited with dead leaves. Some experiments on the susceptibility of both snails to S. haematobium are described, together with observations on the strains of schistosome developing in monkeys exposed to cercariae from naturally-infected snails from the lakes. Frescon was applied through a tube to the bottom layers at the edge of the lakes, where the snails lived. Concentrations of 2 ppm down to 0.5 ppm N-tritylmorpholine proved necessary for adequate kills. Intervals of 6 weeks between treatments sufficed to control B. rohlfsi, but applications every 2 weeks were needed for B. camerunensis. The numbers of egg-masses, of snails, and of infective snails of both species were recorded before, during and after Frescon/Ambilhar control; and snail transmission rates and indices have been calculated. Control operations reduced transmission by R. rohlfsi to 2.4% of the pre-control level, or to below the detectable threshold. They were most effective at Mbo, where B. rohlfsi was the only intermediate host. At Kotto, despite excellent B. rohlfsi control, transmission of the residual infections in the human population by B. camerunensis persisted during control operations, until the intervals between Frescon applications were cut to 2 weeks.

Animals↗
PubMed1997

Laboratory experiments on snail predation by Sargochromis codringtoni, a candidate for biological control of the snails that transmit schistosomiasis.

The potential efficacy of Sargochromis codringtoni, a species of cichlid fish, in the biological control of snails carrying the Schistosoma spp. infecting man has long been recognized. A laboratory study to produce much-needed data on the malacophagous characteristics of this fish was conducted, to see if field studies on its possible role as a biological agent for snail control in Zimbabwe were likely to be worthwhile. The fish can consume large numbers of snails within a short period: a single fish, provided with trout pellets as an alternative food, not only chose to eat the snails but also consumed > 800 within 3 weeks. Addition of macrophytes to the aquaria used appeared to offer the snails no protection from predation. For fish measuring 15-18 cm in length, there was no size preference among snails measuring up to 12 mm in shell height nor was any species preference observed in experiments involving Bulinus globosus, B. tropicus and Melanoides tuberculata. The fish crushed B. globosus which were > 3.0 mm in shell height in their pharynges but swallowed smaller snails of this species whole. Before field trials are conducted, further laboratory studies, in which field conditions are simulated, should be carried out.

Animals↗
PubMed2002

Biological studies on the snail intermediate hosts of schistosomiasis with a special emphasis on using larval echinostomes as biocontrol agent against larval schistosomes and snails.

The present investigation deals with the infectivity of the two snail intermediate hosts of schistosomiasis, Biomphalaria alexandrina and Bulinus truncatus collected from nine drains in Sharkia Governorate, Egypt. The rate of infection among the snails was general low being 0% in many drains. Regarding B. alexandrina, the rate of infection ranged from 4-16%, and in B. truncatus ranged from 4-8%. Infection with larval echinostomes was dominant over larval schistosomes in the two snail vectors. The distribution of larval schistosomes was restricted to the hepatopancreas of the two snail vectors, while larval echinostomes were distributed in head, foot, kidney, haemocoelic cavity, hepatopancreas...etc. The predation of larval schistosomes by larval echinostomes and the severe histopathological effects induced by larval ecbinostomes strongly enhances using them as biocontrol agent. The physico-chemical parameters and pollution condition in the drains seem to have no effect on the process of snails infectivity. It is concluded that larval echinostomes can resist the polluting conditions in the drain. The two snail vectors exhibit very minimal or rare host response against larval echinostomes. Probably, the toxicants and pollutants in the drain may act as stressor that makes the snails much more susceptible to infection by larval trematodes.

Animals↗
PubMed1977

Temperature relations of aerial and aquatic respiration in six littoral snails in respiration in six littoral snails in relation to their vertical zonation.

Aerial and aquatic rates of oxygen consumption were determined over a range of 5 degrees to 45 degrees C at 5 degrees C intervals for six species of marine littoral snails: including the sublittoral species, Acmaea testudinalis, Mitrella lunata, and Lacuna vincta; and the truly intertidal species, Littorina obtusata, L. littorea, and L. saxatilis. Polarographic oxygen electrodes were used with normally active snails collected from populations on Nobska and Manomet Points, Massachusetts. Three subtidal species, A. testudinalis, Lacuna vincta, and M. lunata, do not display any metabolic adjustment to increasing temperature, with thermal limits reached at 30 degrees to 35 degrees C. Aerial respiration in A. testudinalis is similar to aquatic O2 uptake, but rates average only 36.4% of aquatic rates. The intertidal congeners, Littorina obtusata, L. littorea and L. saxatilis, have varying degrees of aerial and aquatic metabolic regulation with increasing temperature. L. obtusata, a low intertidal snail exposed to air for 15% to 45% of the tidal cycle, displays a respiratory pattern of "passive endurance" to high temperatures both in air and in water. L. littorea, the dominant snail of the midlittoral region, remains active when exposed to air (30% to 75% of the tidal cycle) and has a zone of metabolic regulation between 20 degrees C and 30 degrees C. Over this, the normal ambient temperature range, the Q10 closely approximates one, and nearly equivalent O2 uptake rates occur in air and in water. L. saxatilis from the upper littoral region is exposed to air for 70% to 95% of the tidal cycle and is characterized by reduced aerial and aquatic O2 uptake rates above 25 degrees C, representing a reversible torpor up to its thermal maximum at 44 degrees C. For these six snail species, respiratory responses to increasing temperature are thus directly related to the pattern of vertical distribution in the intertidal environment. Discussion of this relationship stresses that the evolution of other nearterrestrial structures and functions in littoral snails has proceeded in a discontinuous fashion. Despite this, the temperature responses in respiration parallel the functional morphology of the pallial structures and the physiological patterns of response to low oxygen stress, as well as adaptive features of reproduction, larval development, water-control, and nitrogenous excretion.

Acclimatization↗
PubMed1986

Population studies on Oncomelania quadrasi, the snail intermediate host of Schistosoma japonicum, in the Philippines. 5. Quantitative analysis on successful snail control by land reclamation.

For the control of Oncomelania quadrasi, environmental modifications, i.e., clearing of vegetation, leveling of swampy depression and draining of stagnant water by channeling and excavation were carried out at 3 areas in Leyte, Philippines from 1974 to 1977. The change of snail population resulted in the land reclamation was evaluated by the methods previously developed by the population studies on this snail. As a result of statistical analysis based on y = log(x + 0.01) transformation and the antilogarithmic mean density A-y = (antilog -y) -0.01, the reduction of snail population was observed at 13 out of 18 sites studied at 3 project areas and the significant reduction was statistically confirmed at 9 sites of them. Particularly at Dagami area, which was a wide and heavily snail-infested land adjacent to Dagami Poblacion, the reduction rate of snail density reached 87.7% to 99.2% and some wet depressions have been converted into good rice fields with little snail infestation at the last survey.

Animals↗
PubMed1982

Population studies on Oncomelania quadrasi, the snail intermediate host of Schistosoma japonicum, in the Philippines. 3. Data transformation for significance test of snail density.

For the comparative study of densities of Oncomelania quadrasi, the snail intermediate host of Schistosoma japonicum in the Philippines, the survey data should be transformed to stabilize the variance in determining the significant difference of densities among populations and to evaluate control measures by the difference, since the snail is distributed unevenly in the field. Comparison was made for the efficiency of stabilizing variance among 7 transformation formulas so far reported, and 2 new additional formulas in the present study. As a result, a simple transformation by y=log (x+0.01) was found to be most reliable. This nonparametric transformation can be applied to any snail population irrespective of the type of distribution and the degree of clumping. By this formula, there is no need to discard snail-free samples which are important to evaluate control measures. Using this transformation, snail survey data were analyzed in the areas where control measures were undertaken during the past several years. And significant reduction of snail densities was proven using the t-test.

Animals↗
PubMed1981

Population studies on Oncomelania quadrasi, the snail intermediate host of Schistosoma japonicum, in the Philippines. I. Distribution pattern of the snail in the field.

Distribution of Oncomelania quadrasi, the snail intermediate host of Schistosoma japonicum, was studied in Leyte, Philippines for the type of distribution based upon a large number of survey data. Among four distribution models examined, three uneven distribution models, i.e., the double Poisson, Neyman type A and negative binomial fitted well in this order but the Poisson model showed the poorest fitness. This indicates that the snails are distributed unevenly over the field and that the population mostly consists of small clusters of individual snails. Elucidation of the snail distribution pattern is necessary for determination of sample size in snail survey and for data transformation in significance test of the snail density comparison.

Animals↗
PubMed2002

Characterisation of two snail genes in the gastropod mollusc Patella vulgata. Implications for understanding the ancestral function of the snail-related genes in Bilateria.

Snail genes have been found to play a role in mesoderm formation in two of the three clades of bilaterians, deuterostomes (comprising the chordates) and ecdysozoans (comprising the arthropods). No clear data are available on the role these genes play in development of the mesoderm in the third clade, that of lophotrochozoans (comprising annelids and molluscs). We identified two new members of the snail gene family in the gastropod mollusc Patella vulgata. Phylogenetic analysis showed that the two genes clearly belong to the snail sub-family. Their expression patterns do not indicate a role during early mesoderm formation. In fact, contrary to expectations, the snail genes of Patella were mostly expressed in the ectoderm. In view of the location of their expression sites, we suggest that these genes could be involved in regulating epithelial-mesenchymal transitions (EMT) and cell motility, as has recently been demonstrated for snail genes in vertebrates. This may well correspond to the ancestral function of these genes. The results are discussed in the light of the evolutionary origin of the mesoderm. Electronic supplementary material to this paper can be obtained by using the Springer LINK server located at http://dx.doi.org/10.1007/s00427-002-0228-1.

Amino Acid Sequence↗
PubMedDate not supplied

Snails and snail farming: an introduction for the veterinary profession.

In the past veterinary interest in snails has been confined to their role in the transmission of disease; nowadays the trend to keep these animals in captivity--for food, for study, as 'companion animals'--means that the profession is increasingly likely to be consulted about their health, welfare or conservation. An understanding of the biology of snails is an important prerequisite to work with them. Land snails are hermaphrodite and have a complex reproductive system; other organs also show special adaptations. Management methods vary considerably and farmed snails can be maintained under extensive or intensive conditions. Methods for handling and transporting them are important considerations. There is little published information on the diseases and pathology of snails but suboptimum environment, poisons, nutritional deficiencies, predators and parasites are known to cause, or contribute, to their mortality.

Animal Husbandry↗
PubMed2003

Comparative studies on the internal defense system of schistosome-resistant and -susceptible amphibious snail Oncomelania nosophora 1. Comparative morphological and functional studies on hemocytes from both snails.

Two morphologically distinct blood cell types (hemocytes), Type I and Type II were found coexisting in hemolymph from two kinds of snails, Oncomelania nosophora strain, viz. from the Nirasaki strain (schistosome-resistant snail) and the Kisarazu strain (schistosome-susceptible snail). Ten min after inoculation of SRBC, the majority of Type I cells from Nirasaki strain flattened and spread over the surface of the glass plate by extending pseudopodia. In the Kisarazu strain, Type I cells adhered to the surface of substrate with spike-like filopodia, but did not form spreading lamellipodia. Type I cell from the Nirasaki strain phagocytosed SRBC but that from the Kisarazu strain did not. The starting time of recognition of foreign materials was slightly different in the Type I hemocytes from the two strains. Type II cells from both strains were round and lymphocyte-like. Ten or sixty min after incubation, Type II cells from neither strain adhered to the surface of substrate or SRBC, and did not phagocytose SRBC. Type II cells from the Nirasaki strain were quite similar to those from the Kisarazu strain. We concluded that Type I cells from the schistosome-resistant snail, Nirasaki strain, possessed higher phagocytic activity than those from the susceptible snail, Kisarazu strain, despite the morphological similarities of the hemocytes from both strains.

Animals↗
PubMed1998

Experimental control of the schistosome-transmitting snail Biomphalaria pfeifferi by the ampullariid snail Pila ovata.

Adults of the African ampullariid snail Pila ovata were examined for their ability to control laboratory populations of the pulmonate snail Biomphalaria pfeifferi, a widespread, intermediate host of the human pathogen Schistosoma mansoni in sub-Saharan Africa. In a 6-week experiment conducted in large (100 x 60 x 60 cm) outdoor tanks containing floating macrophytes (Nymphaea caerula) and initially set up with one adult ampullariid for every three adult pulmonates, the numbers of B. pfeifferi egg masses were always about half those in similar tanks without P. ovata. Although, by week 6, the numbers of B. pfeifferi in the control tanks (without ampullariids) had increased 5-fold, from an initial mean of 30 snails/tank, there was no significant increase in the numbers of B. pfeifferi in the experimental tanks (containing ampullariids). Results of experiments conducted in indoor glass aquaria indicated that adult P. ovata rapidly attacked egg masses or neonates (< 2.5 mm shell diameter) of B. pfeifferi but had no effect on the adults. The adult ampullariids also significantly decreased cover by floating macrophytes over a 6-week period compared with that in similar but ampullariid-free aquaria. This decrease in plant cover is relevant to biological control of the schistosome vectors as macrophytes serve as food, shelter and oviposition sites for pulmonate snails. The present result indicate the ability of P. ovata to inhibit multiplication of B. pfeifferi populations, at least under laboratory conditions, both directly, through predation, and indirectly, by competition for resources. Pila ovata may therefore prove useful in the biological control of medically important, pulmonate snails.

Animals↗
PubMed2000

Variability of Fasciola hepatica infection in Lymnaea ovata in relation to snail population and snail age.

Bimiracidial infections of Lymnaea ovata with Fasciola hepatica were performed under laboratory conditions to determine the susceptibility of snails from six French populations to trematode infection. In five populations of L. ovata the prevalence of infection in the 1-mm groups ranged between 2.7% and 43.7% at day 35 postexposure; it decreased in the 2-mm snails and was zero in larger groups. In the snails from Thenay (periodically polluted brook) the prevalence of F. hepatica infection decreased from the 1-mm group to the 8-mm group (from 23.9% to 1.0%) and was zero in the 10-mm L. ovata. The total number of cercariae shed per snail was 18.3 in the 1-mm group, increasing to 117 in the 8-mm group. The latter findings could be interpreted as a consequence of periodic pollution in the brook of Thenay; pollution might disrupt the defense system of L. ovata and facilitate the subsequent larval development of F. hepatica.

Aging↗