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PubMed1991

Transmission of Angiostrongylus cantonensis through the giant African snail Achatina fulica: an experimental study.

Observations on transmission of the rat lung worm, Angiostrongylus cantonensis, from rats to the snail intermediate host. Achatina fulica, in a vacant lot in Bangkok are described. The prevalence of A. cantonensis increased with snail age until 200 days of age when it attained a plateau of 50-60%. The overall prevalence was 53%. The worm burden slowly rose with age until 200 days of age beyond which it remained relatively constant. The highest mean worm burden of 5,478 was observed in the oldest age group. The parasite distribution in the snail population was highly aggregated both within each age class and in the overall population. Experiments on susceptibility of snails to laboratory infection revealed that worm recovery was dependent on dose of first stage larval infection but was independent of snail size in the range of 4-8 cm. The percent worm recovery of third stage larvae was negatively correlated with dose of infection, and no density-dependent effects of worm burden on worm size were observed.

Analysis of Variance↗

PubMed1991

Laboratory studies on host-parasite relationship of Bithynia snails and the liver fluke, Opisthorchis viverrini.

The infection rate of Bithynia snails to Opisthorchis viverrini eggs was studied in relation to exposure intensity, age and species of host. It was found that 50 miracidial eggs per snail yielded the highest percentage of living surviving positive snails. Bithynia funiculata and Bithynia siamensis siamensis were highly susceptible to O. viverrini, about four to seven times higher than Bithynia siamensis goniomphalos. Young snails, 1-3 months old, appeared more susceptible than old snails.

Animals↗

PubMed1989

Schistosomiasis on Bohol Island, Philippines, with special emphasis on the successful discovery of new habitats of the vector snail, Oncomelania quadrasi, and area-wide mollusciciding.

In the endemic area of schistosomiasis on Bohol Island, we succeeded in locating seven new colonies of the vector snail, Oncomelania quadrasi, four in Trinidad and three in Talibon, in addition to six locations from which the snails were previously recorded. We were led by the proximity of the snail habitat to the residence of the infected individuals. In northern Bohol the continuous wet season would appear to make the major differences between the places that do and those that do not support O. quadrasi. Twice-yearly weed clearance and applying chemical molluscicides (niclosamide and phebrol) for the control of O. quadrasi have been extensively in effect over the snail colonies, since July 1986. Although it has not yet yielded satisfactory results in certain colonies, snails have been eliminated from six habitats in a period of two and a half years.

Animals↗

PubMed1989

Biological control of Biomphalaria glabrata and B. straminea by the competitor snail Thiara tuberculata in a transmission site of schistosomiasis in Martinique, French West Indies.

In Martinique, intestinal schistosomiasis was discovered at the beginning of this century. The intermediate host snail, Biomphalaria glabrata, was considered in the past as a common species in the different habitats of the island, but during the last decade it has been found only in water-cress beds. Several of these water-cress cultures contained mixed populations of B. glabrata and B. straminea. Moreover, these habitats also constituted transmission sites for Schistosoma mansoni infection. In 1979 the thiarid snail Thiara ( = Melanoides) tuberculata was discovered in Madame river, Fort-de-France, and in the following years at other sites. In 1983 a programme of biological control using this snail was started in two groups of water-cress beds. In 1981-1982 the study site, Roxelane valley, sheltered important populations of B. glabrata (45-256 individuals/m2) and of B. straminea (2-30 ind./m2). In January 1983 the competitor T. tuberculata was introduced into the two groups of water-cress beds (1.3 and 1.7 ind./m2 respectively) and during subsequent years snail population sampling was carried out. The results showed rapid colonization by the competitor snail, whose densities reached 178 and 325 ind./m2 in November 1983 and a maximum of 9941 and 13,388 ind./m2 in October 1984. During that time, B. glabrata populations declined: 153 and 41 ind./m2 in November 1983, 4 and 0 ind./m2 in October 1984, and 0 ind./m2 in the two groups of water-cress beds in October 1985. A similar phenomenon was observed for B. straminea. Since October 1985 neither planorbid species has been found by exhaustive sampling of the habitats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1985

The lungfish Protopterus annectans (Owen) as a biocontrol agent against schistosome vector snails.

Laboratory and small-scale field experiments have been carried out to study the malacophagous capabilities of the lungfish Protopterus annectans. When individual fish were offered a range of aquatic fauna in aquaria in the laboratory only snails and dragonfly larvae were consumed. When offered a choice, the fish appeared to prefer snails, with larger individuals (up to 300 mm) capable of consuming up to 200 snails per day. The introduction of five P. annectans into a small concrete pond (diameter 5 m) with an established fauna and flora resulted in a reduction in the snail population of over 90% within 2 weeks. This reduction was maintained over a 4-month observation period suggesting that in habitats in which the lungfish can survive, there is a possibility of significant snail control.

Animals↗

PubMed1982

Peroxidase-positive blood cells in snails.

The present study deals with phagocytic blood cells of 3 species of freshwater snails and one terrestrial snail species. Histochemical tests on peroxidase indicate that the blood cells of the freshwater snails have high peroxidase contents, whereas those of the terrestrial snail do not contain this enzyme. Peroxidases were not only present in the lysosomal system but also in the RER and Golgi apparatus. It appears that the phagocytic blood cells of freshwater snails are able to synthesize peroxidase.

Animals↗

PubMed1995

Thin-layer chromatographic and histochemical analyses of neutral lipids in the intramolluscan stages of Leucochloridium variae (Digenea, Leucochloridiidae) and the snail host, Succinea ovalis.

Thin-layer chromatographic and histochemical analyses were used to analyze neutral lipids in the intramolluscan larval stages of Leucochloridium variae and in tissues of the snail host Succinea ovalis. Thin-layer chromatography showed that the major neutral lipids in uninfected snails were triacylglycerols and free sterols. The major neutral lipids in brood sacs minus their encysted metacercariae and in sporocysts were triacylglycerols and free sterols. Encysted metacercariae showed a significant free fatty acid fraction in addition to triacylglycerols and free sterols. Residual snail tissue (mainly head, foot, and visceral mass) from infected snails from which parasites were removed showed only a free sterol fraction. Histochemical staining of tissues with oil red O (ORO) showed the presence of neutral lipid droplets in the brood sac and sporocyst walls and mainly in the suckers, parenchyma, and excretory system of the encysted metacercariae. The residual snail tissue was ORO negative.

Animals↗

PubMedDate not supplied

[The role of glucose in facilitating defensive reactions during feeding in the edible snail Helix lucorum].

The glucose role in a regulation of defense responses during feeding behaviour was studied in the snail Helix lucorum. It was found that 15-20 min after the beginning of the food intake the foot withdrawal response evoked by a train of electrical pulses was facilitated up to 20-30%. At the same time glucose concentration in the haemolymph increased from 0.5 +/- 0.1 mM in the starved molluscs to 0.9 +/- 0.5 mM in the snails at 20-25 min of eating. In the food satiated snails and 30-90 min after the food intake the glucose level in the haemolymph was 1.6 +/- 0.5 mM. It was shown that 0.5 ml glucose solution (5 mM) injected into the mantle cavity also facilitated the foot withdrawal defense response in the fastened snail, whereas injection of 2.5 mM or 10 mM glucose solutions were ineffective. These data support a supposition that glucose in one of the endogenous factors involved in regulation of defense behaviour during feeding in snails.

Animals↗

PubMed1997

[Fluke invasion and the immune system of the snail].

This is a review article concerning an influence of trematodes infections on a defence system of snails. Changes in: snails' plasma composition, a number of hemocytes, size of a hemopoietic organ, molecules secreted by hemocytes and defence cells activities caused by the infections are discussed in detail. The differences in humoral and cellular response between susceptible and resistant strains of snails as well as between young and old snails are also presented in the article. Finally, the problem of an existence of the specific immunological memory in snails is analyzed.

Animals↗

PubMedDate not supplied

[The neuronal mechanisms of site-specific nociceptive sensitization in the snail Helix lucorum].

Electrophysiological effects of site-specific sensitization after application of strong quinine solution onto snail head or snail mantle were studied in Helix lucorum LPl1 and RPl1 interneurons. Sensitizing stimulation (strong quinine solution) applied onto the snail head or mantle produced synapse-specific facilitation of neural responses evoked by tactile stimulation: synaptic facilitation was more expressed in neural responses evoked by tactile stimulation of the sensitized body site. Synaptic facilitation of the neural responses evoked by tactile stimulation of the snail head was observed 1 hour after corresponding sensitizing stimulation. Two definite phases were separated in the synaptic facilitation. The first phase persisted for 1 hour and was characterized by a "peak-shaped" increase of the EPSP square, in the second phase the EPSP facilitation was maintained at a relatively constant level for more than 3 hours. The synaptic facilitation of the neural responses to tactile stimulation of the snail mantle began 40-60 min later than that of the responses to the stimulation of the head and was characterized by the absence of the first phase. It was suggested that specific character of synaptic facilitation in a command interneuron is determined by peculiarities of genetical regulation of different neural inputs.

Animals↗

PubMed2000

Toxicity of Euphorbia milii latex and niclosamide to snails and nontarget aquatic species.

The toxicity of Euphorbia milii molluscicidal latex and niclosamide (NCL) to target snails (Biomphalaria glabrata and Biomphalaria tenagophila) and nontarget aquatic organisms is evaluated. Planorbidae snails were killed by very low concentrations of lyophilized latex (48-h LC(50), mg/L: B. glabrata, 0.12; B. tenagophila, 0.09; Helisoma duryi, 0.10). Latex was less toxic (48-h LC(50) or EC(50), mg/L) to oligochaeta (Tubifex tubifex, 0.31), planktonic crustacea (Daphnia similis, 0.38; C. dubia, 1.07; Artemia sp., 0.93), and fishes (Danio rerio, 0.96; Poecilia reticulata, 1. 39), and considerably less toxic to Ampullariidae snails (Pomacea sp. , 10.55) and frog tadpoles (Rana catesbeiana, 7.50). Latex (up to 100 mg/L) was not toxic to bacteria (P. putida and V. fischeri), algae (Selenastrum capricornutum and Chlorella vulgaris), and mosquito larvae (Anopheles albitarsis, Aedes aegypti, Aedes fluviatilis). NCL was very toxic (48-h LC(50) or EC(50), mg/L) to Planorbidae snails (B. glabrata, 0.15, B. tenagophila, 0.13; H. duryi, 0.10), T. tubifex (0.11), crustacea (D. similis, 0.19; Ceriodaphnia dubia, 0.47; Artemia sp. 0.18), fishes (D. rerio, 0.25; P. reticulata, 0.29), R. catesbeiana (0.16), and Pomacea sp. (0.76). NCL was toxic to bacteria, algae (96-h IC(50), mg/L: S. capricornutum, 0.34; C. vulgaris, 1.23) and slightly toxic to mosquito larvae. In conclusion, E. milii latex, as compared with the reference molluscicide niclosamide, presents a higher degree of selectivity toward snails which are intermediate hosts of Schistosoma trematodes.

Animals↗

PubMed2000

Snail host finding by Fasciola hepatica and Trichobilharzia ocellata: compound analysis of "miracidia-attracting glycoproteins".

The glycoconjugates from snail-conditioned water of Lymnaea truncatula and L. stagnalis which elicit typical host finding behavior in miracidia of Fasciola hepatica and Trichobilharzia ocellata were separated by anion-exchange chromatography and a two-step size-exclusion chromatography. We obtained fractions attractive for the parasites with MW of about 10(6) Da in both snail species. These fractions still contained species-specific information since miracidia responded only to molecules from their respective host snail. Analysis of the amino acid composition from the protein backbone revealed a similar composition in the effective fractions of both snails. Amounts of serine and threonine were higher than 30 mol %, which is typical for mucin-type glycoproteins. The carbohydrate moieties consisted mainly of galactose and fucose, but nine different other monosaccharides also were identified in smaller amounts. The heterogeneity of the molecules was also confirmed by the binding of six different lectins. Because of these characteristics, the effective molecules were termed "miracidia-attracting glycoproteins" (MAGs). MAGs may play an important role for parasite transmission, as they may increase the chance of an encounter between parasite and host and enable the miracidia to discriminate between their specific intermediate host and other unsuitable snail species.

Amino Acids↗

PubMed1985

Search for shared antigens in the schistosome-snail combination Trichobilharzia ocellata-Lymnaea stagnalis.

Mother and daughter sporocysts of Tricholbilharzia ocellata, developing in the snail host Lymnaea stagnalis, were searched for substances with antigenic similarities to the snail's haemolymph. Antisera to cell-free snail haemolymph and fractions thereof were used in three different immunocytochemical staining methods, applied on sections of parasitized snails. Snail tissue was consistently stained; cercariae were stained, indicating that the applied methods were successful. Most sections through mother and daughter sporocysts were completely unstained. It is concluded that neither mother nor daughter sporocysts are masked by the antigens studied or substances mimicking these. The relevance of the present observations is discussed.

Animals↗

PubMed2002

Serine protease and phenoloxidase activities in hemocytes of Biomphalaria glabrata snails with varying susceptibility to infection with the parasite Schistosoma mansoni.

The snail Biomphalaria glabrata possesses hemocytes, which are supposed to interact with the larval stages of the human parasite Schistosoma mansoni. We describe trypsin-like serine protease(s) and phenoloxidase activities in lysates from these hemocytes. Both enzymes have activity optima around pH 9.5. The serine protease was inhibited by EDTA, PMSF, antipain and aprotinin, and the phenoloxidase activity by diethydithiocarbamate. By comparison, the serine protease activity in secretions of S. mansoni cercariae also had an alkaline pH optimum around 10.5 and was sensitive to the same inhibitors. In addition, serine protease activities from snails and cercariae had the same molecular mass of 28 kDa. However, the K(m) value of the serine protease(s) and the K(i) values of different inhibitors were generally lower for the snail enzyme than for the cercarial enzyme. The serine protease activity varied among individual snails but activity in hemocyte lysates and hemolymph correlated strongly. There was no detectable difference in the levels of activity between snails which are susceptible or resistant to schistosome infection.

Animals↗

PubMed1997

Miracidial host-finding in Fasciola hepatica and Trichobilharzia ocellata is stimulated by species-specific glycoconjugates released from the host snails.

The miracidia of Fasciola hepatica and Trichobilharzia ocellata approach their host snails Lymnaea truncatula and L. stagnalis by increasing their rate of change of direction (RCD) in increasing gradients of snail-conditioned water (SCW), and they perform a turnback swimming in decreasing gradients. Both hostfinding responses in both species were induced by glycoconjugates with a molecular weight of > 30 kDa that were sensitive to hydrolysis with pronase E and oxidation with NaIO4. Alkaline cleavage revealed that they contained carbohydrates linked O-glycosidically via serine and N-acetylgalactosamine. Miracidia clearly preferred SCW from their specific host snail versus other sympatric snail species and did not respond to water conditioned with fish, tadpoles, or leeches. Differences in the chemical characteristics of SCW from the intermediate hosts L. truncatula and L. stagnalis could be shown by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, blotting, and subsequent carbohydrate detection. The first step of purification of the effective signaling SCW components from both snail species was achieved by ion-exchange chromatography.

Animals↗

PubMed1989

The use of Phytolacca dodecandra berries in the control of trematode-transmitting snails in Zimbabwe.

Phytolacca dodecandra, a plant with berries of a known molluscicidal potency, was cultivated in Chiweshe. Studies on the snail population density of Bulinus globosus and Lymnaea natalensis as well as schistosome infection rates in the former were carried out in two streams, in one of which a water extract of P. dodecandra berries was applied in late April and May 1987. Snail sampling was carried out twice a month from April 1986 to April 1988, that is for 12 months prior to and after the mollusciciding exercise. B. globosus snails obtained from both streams were examined for infection by cercarial shedding before they were returned to their sites of collection. The 8-h water extract of P. dodecandra was applied to human watercontact points. The two applications were aimed at achieving a concentration of 50 mg/l. No snails were recovered from the experimental sites for a period of 7 months after the mollusciciding exercise. Snails were recovered in the treated sites only after the onset of the rainy season.

Animals↗

PubMed1992

Biomphalaria glabrata: influence of calcium, lectins, and plasma factors on in vitro phagocytic behavior of hemocytes of noninfected or Schistosoma mansoni-infected snails.

In vitro phagocytosis of erythrocytes by hemocytes of B. glabrata, intermediate host of S. mansoni, is strongly influenced by calcium, several lectins, and plasma factors. Our results indicate that two different mechanisms of non-self-recognition in B. glabrata may occur: (1) In the presence of calcium, phagocytosis occurs in noninfected and in infected snails without involvement of any other substances, and hemocytes of schistosome resistant as well as those of susceptible snails are able to recognize and phagocytose the target cells. (2) In the absence of calcium, phagocytosis occurs if bridging molecules (heterologous lectins in our assays) were present for which effector and target cells possess binding sites or if target cells were plasma coated prior to the assays. In suspensions in homologous plasma, hemocytes of both snail strains, infected or noninfected, subsequently showed phagocytic activities of about 70-80%. Preincubation of target cells in homologous plasma resulted in similar high phagocytic activities of hemocytes even in the absence of plasma during the standard assay. In these assays, a significantly higher proportion of hemocytes of resistant snails phagocytosed plasma-opsonized erythrocytes, whereas hemocytes of susceptible snails internalized less erythrocytes per cell and needed 60 min to phagocytose at percentages equivalent to that of resistant hemocytes within 10 min. Preincubation of erythrocytes in resistant plasma significantly increased the subsequent phagocytic activity of susceptible hemocytes, whereas preincubation of erythrocytes in susceptible plasma decreased the phagocytosis level of resistant hemocytes.

Animals↗

PubMed1989

Developmental and comparative aspects of nonsynaptic release by the egg-laying controlling caudodorsal cells of basommatophoran snails.

In an immunoelectron microscope study the postembryonic development of the cerebral caudodorsal cells (CDC) in the freshwater snail Lymnaea stagnalis was studied as well as the development of similar neurons in other basommatophoran families. The CDC of adult L. stagnalis control egg-laying and associated behaviors by releasing various peptides, including the ovulation hormone CDCH. The CDC release peptides from neurohemal axon terminals and from nonsynaptic release sites of axon collaterals. During postembryonic development the collateral system develops synchronously with the neurohemal area. The first collaterals appear in the cerebral commissure of juvenile snails (10 mm shell height; S = 10). Up to S = 30 they gradually increase in size and length and eventually run through the entire inner compartment. Secretory granules in both collaterals and neurohemal axon terminals increase in size as well. Immunoelectron microscopy combined with the TARI-method for the demonstration of exocytosis indicates that CDCH-release from collaterals and neurohemal terminals occurs already in S = 10; exocytosis of immunoreactive granule contents takes place from nonsynaptic release sites, unspecialized areas of the axolemma of the collaterals. Release activity in the collaterals gradually increases up to S greater than or equal to 20. Neurohemal release activity shows a similar picture except for a steep increase in adult snails. A distinct glial sheath, separating the neurohemal area from the collateral system, appears around S = 15. Representatives of three families of Basommatophora, viz. the lymnaeid L. ovata, the planorbid Planorbis planorbis, and the bulinid Bulinus truncatus possess a well-developed collateral system showing many signs of exocytosis. A glial sheath separates the collaterals from the neurohemal area. Secretory granules of the CDC in L. ovata stain weakly positive with the anti-CDCH antiserum. Since the other Basommatophora did not show immunoreactivity, the chemical structure of egg laying peptides in Basommatophora seems to be genus specific. Apparently the secretory activity of both the neurohemal area and the collateral system is not only important in the sexually mature animal, being involved in the control of egg laying and egg-laying behavior, but also in the juvenile snail. The finding of a collateral system in representatives of three basommatophoran families strongly indicates the importance of the system for the control of reproduction in basommatophoran snails in general.

Animals↗