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PubMed1995

Field studies on the transmission and survival of Cyclocoelum mutabile (Digenea) infections in natural snail populations in southern Manitoba, Canada.

The transmission of Cyclocoelum mutabile to snails was examined under natural conditions by sampling the snail communities of 4 natural ponds that had been exposed experimentally to infection by laboratory-infected coots (Fulica americana). Five of 6 snail species in the ponds, Physa jennessi, Promenetus exacuous, Armiger crista, Gyraulus parvus, and Stagnicola elodes, became infected. No natural infections were found in the few Helisoma trivolvis examined. The second most abundant species Promenetus exacuous was infected most often, whereas Physa jennessi, the most abundant species present, was rarely infected. The temporal pattern of infections in the snail community suggests the transmission window of this parasite in southern Manitoba is limited by both the 14 C hatching threshold of the fluke eggs and the seasonality of ovigerous infections in the coot host. No naturally overwintering infections were found in snails from these ponds, which were examined the following spring. None of the 1,120 laboratory-infected snails placed in cages and held overwinter in the ponds survived, whereas 14 of the 1,120 uninfected control snails kept in the same cages survived. These results are consistent with the hypothesis that C. mutabile must be reestablished in northern waterfowl breeding areas each spring.

Animals↗

PubMed1993

Trematode community structure in the pulmonate snail Physa gyrina.

Trematode community structure was examined in the pulmonate snail Physa gyrina over a 12-mo period. A total of 1,181 snails was collected from Charlie's Pond, North Carolina, and was found to be parasitized by 6 trematode species. Infracommunities were relatively species rich when compared to previous studies, with 18.4% of infected snails having multi-species infections. Halipegus eccentricus was found in 88.4% of multiple infections, usually with 1 of 2 other autogenic, egg-transmitted species (Haematoloechus complexus and Glypthelmins quieta). Neither negative interspecific interactions nor a dominance hierarchy were apparent among the trematodes. These factors, along with high snail vagility and the temporal heterogeneity of infective stages in the environment, are suggested to have contributed to the high number of multiple infections. Halipegus eccentricus was also the most prevalent parasite throughout the study, occurring in nearly 50% of all snails during May, June, and July. Apparent parasite-induced host mortality caused by this trematode species contributed to increasing species diversity in larger snails. The component community was also affected by the continuous recruitment of new snails into the host population and by changes in the number of infective stages present over time.

Animals↗

PubMed1996

Asthma after consumption of snails in house-dust-mite-allergic patients: a case of IgE cross-reactivity.

A group of 28 patients from Italy was studied who had asthma after consumption of snail. All patients also had asthma and/or rhinitis caused by house-dust mite. RAST analyses confirmed the combined sensitization to snail and mite. In a few sera, IgE antibodies reactive with other foods of invertebrate origin (mussel and shrimp) were detected. RAST inhibition showed that most IgE antibodies against snail were cross-reactive with house-dust mite. In contrast, the mite RAST was not significantly inhibited by snail. This indicates that house-dust mite was the sensitizing agent. Immunoblot analyses revealed multiple bands in snail extract recognized by IgE. In contrast to what has been described for cross-reactivity between shrimp and mite, tropomyosin played only a minor role as a cross-reactive allergen in these patients. The observations in this study indicate that snail consumption can cause severe asthmatic symptoms in house-dust-mite-allergic patients. It might, therefore, be advisable to screen mite-allergic asthma patients for allergy to snail and other invertebrate animal foods.

Adult↗

PubMed1995

Experimental infection of five subspecies of Oncomelania snails with Angiostrongylus cantonensis.

Five subspecies of Oncomelania snails, Oncomelania hupensis nosophora, O.h. hupensis, O.h.chiui, O.h.formosana and O.h.quadrasi, were experimentally exposed to the first stage larvae of Angiostrongylus cantonesis. The presence of third stage larvae was observed in all of the five subspecies of Oncomelania snails 20 days after infection. Infection rates of the third stage larvae of the parasite in Oncomelania snails were 38.0-40.0%. There were no differences in preferences among Oncomelania snails. The third stage larvae in Oncomelania snails almost distributed in kidney and intestine region, and most of the larvae were active and free in tissues. The distribution pattern of the larvae in Oncomelania snails was quite different from that in Achatina fulica and Ampullarium sp. These third stage larvae were ingested by rats, and developed to adults. These data suggest that Oncomelania snails may play important role when A. cantonensis will spread, and indicate the possibility of human infection with A. cantonensis.

Angiostrongylus cantonensis↗

PubMed1997

Development and validation of a satellites based geographic information system (GIS) model for epidemiology of Schistosoma risk assessment on snail level in Kafr El-Sheikh Governorate.

The aim of the present study was to test the accuracy of Advanced Very High Resolution Radiometer (AVHRR) satellite derived temperature difference (dT) maps as a guide for the suitability of the environment for local snail hosts and Schistosoma development-transmission at the village level. The study provided field validation data from 13 villages in Kafr El Sheikh in the Nile Delta that sites present in wet zones of low dT value have more abundant snail populations than that present in the drier zones with high dT values. Results suggest that lower dT values were associated with wetter hydrologic regimes related to the level of underground water table and that this is reflected in the abundance of snail populations and Schistosoma snail infection rates at the village level. Water quality parameters on pH salinity and dissolved oxygen were not correlated with presence of Schistosoma infected snails. Results indicate that abundance of snails and S. mansoni prevalence are related to thermal-hydrology domains associated with surface water, that habitat suitability is related to depth to water table and that regional hydrology characteristics that affect snail host habitat suitability (ie. wet, moist, dry or very dry) can be evaluated using AVHRR dT maps.

Animals↗

PubMed1998

Effect of six non-target snails on Schistosoma mansoni miracidial host finding and infection of Biomphalaria alexandrina under laboratory conditions.

Six snail species naturally associated with Biomphalaria alexandrina, the snail host of Schistosoma mansoni in Egypt, were tested under standard laboratory conditions, for impact on miracidial host findings and infection of the snail host. These snails are the prosobranchs Melanoides tuberculata, Cleopatra bulimoides, Bellamys unicolor and Lanistes carinatus, the pulmonates Planorbis planorbis and Physa acuta. The tested snail ssp. reduced considerably the infection rate of Biomphalaria with S. mansoni especially at a ratio of 10 decoy snails to one Biomphalaria snail. The prosobranchs Melanoides, Cleopatra and Lanistes exhibited more reducing effect on Biomphalaria infection than Bellamya and the pulmonates Physa and Planorbis being 65.2%, 78.8%, 62.9%, 33.3%, 30.3% and 46.9%, respectively.

Animals↗

PubMed1991

Physiologic studies of snail-schistosome interactions and potential for improvement of in vitro culture of schistosomes.

Despite extensive efforts to develop suitable media for rearing the intramolluscan stages of schistosomes, successful in vitro culture of these parasites remains elusive. Recent 31P NMR studies demonstrated that the levels of free phospholipids, particularly phosphatidylcholine, in the digestive gland of the snail, Biomphalaria glabrata, were dramatically reduced when the host was infected with Schistosoma mansoni. It was speculated that absorption of host phosphatides may be an important source of membrane phospholipid precursors and fatty acids for developing sporocysts and cercariae. During the present investigations, B. glabrata was maintained on a high fat diet of egg yolk, and the lipid composition of control uninfected and infected snails examined by 31P and 13C NMR. In addition, the levels of host hemolymph metabolites, including glucose and urea, considered as indicators of parasite nutrient uptake, were monitored. The lipid level of snails fed egg yolk was greatly increased, and hosts developed patient infections in approximately half the time of infected snails maintained on lettuce. The composition of the free phospholipids accumulated in the tissues of B. glabrata fed egg yolk were the same as those previously reported in the cercarial stage of S. mansoni. Moreover, the fatty acids of S. mansoni and those reported here in the neutral lipids and free phosphatides in the host tissues were similar. Uninfected snails maintained on lettuce had higher hemolymph levels of glucose than those reared on egg yolk, and infected hosts on egg yolk had significantly lower levels of hemolymph urea. Beta-hydroxybutyrate was the principal hemolymph metabolite in snails fed egg yolk, but was not detected in snails maintained on lettuce.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗

PubMed1997

Paramphistomum daubneyi: the development of redial generations in the snail Lymnaea truncatula.

Rediae of Paramphistomum daubneyi were counted and measured in Lymnaea truncatula to elucidate the variability in the numbers of free rediae and cercariae occurring between naturally infected snails and experimental single-miracidium infections. Experiments were performed using one miracidium per snail and snail raising was carried out at 20 degrees C. Two redial generations succeeded each other in the snail until day 49. A mean of 8-10 rediae differentiated in the sporocyst at days 7 and 14; the remaining germ balls and redial embryos decreased in number after day 21. First-generation rediae became free in the snail's body starting at day 14 and their number increased to a mean of 7.5 at day 49, with a maximum of 10 rediae being detected in 1 snail. They produced second-generation rediae, which exited from the body starting at day 28, and then cercariae, which exited from day 42 onward. The count of second-generation rediae was 6-6.2/snail at day 49, with a maximum of 12 being detected in 1 snail; they produced only cercariae.

Animals↗

PubMed1986

Echinostoma paraensei: hemocytes of Biomphalaria glabrata as targets of echinostome mediated interference with host snail resistance to Schistosoma mansoni.

Earlier in vivo work by Lie et al. (1977) indicated that the innate resistance of the 10R2 strain of Biomphalaria glabrata to PR1 Schistosoma mansoni could be interfered with if the snails were infected previously with another trematode, Echinostoma paraensei. We have studied this interference phenomenon using in vitro methods in an attempt to understand its mechanistic basis. Hemolymph, derived from 10R2 snails infected with E. paraensei for 14-28 days, killed 25% of S. mansoni sporocysts in vitro, significantly less (P less than 0.001) than the 90% killing rate observed with hemolymph from uninfected, control 10R2 snails. Hemolymph from the infected 10R2 snails and from schistosome susceptible M line snails did not differ significantly (P greater than 0.1) in their relative inability to kill S. mansoni sporocysts in vitro. The defect in sporocyst killing exhibited by echinostome infected 10R2 snails was traced to the cellular, rather than the humoral, component of the hemolymph. Preparations containing uninfected 10R2 snail hemolymph and echinostome daughter rediae exhibited significantly less (P less than 0.001) killing of S. mansoni sporocysts than did controls containing only 10R2 hemolymph and S. mansoni sporocysts. Our results suggest that echinostome larvae release factors that interfere with the ability of B. glabrata hemocytes to kill S. mansoni sporocysts.

Animals↗

PubMedDate not supplied

Control of Schistosoma mansoni in the Blue Nile Valley of western Ethiopia by mass chemotherapy and focal snail control: a primary health care experience.

A simplified combination of human mass treatment with oxamniquine and focal snail control has been applied in a local Schistosoma mansoni control programme in a primary health care setting in the Dalati and Agallu Metti areas of the Ethiopian Blue Nile Valley. Teams of local health personnel and farmers did the daily work under intermittent supervision. Monthly snail surveys near the major villages disclosed a seasonal pattern with many infected snails during the dry season in upper stagnant sections of tributary rivers (1000-1200 m altitude) with favourable temperatures, and few snails in the rainy season. The highest prevalences and intensities of human infection were found in the 15-19 year age group living in the lower altitudes around 700 m. 5067 individuals (50-80% of the local population) were treated with 20-40 mg oxamniquine per kg body weight during the rainy seasons of 1985 (Dalati) and 1986 (Agallu Metti). In the Dalati area cross sectional surveys in 1985 and 1986, before and after the mass treatment, showed a reduction in prevalence from 42.4% to 11.4%, while in the Agallu Metti area a stratified random sample showed a prevalence reduction from 65.4% in 1986 to 7.8% in 1987 and a reduction in the prevalence of moderate to heavy infection (greater than 100 eggs per gram of stool) from 36.9% to 1.4%. Beginning in 1986 niclosamide was applied focally wherever infected snails were found and the monthly snail surveillance continued until 1989. As a result of this combined approach overall snail infection rates were reduced from 11.2% (Dalati) and 32% (Agallu Metti) to zero and 2% respectively. In 1989 the human prevalence was still only 8.6% in Agallu Metti. This programme has shown that it is feasible to control S. mansoni in these very remote localities through the primary health care system.

Adolescent↗

PubMed1994

Interleukin 1 activity in haemolymph from strains of the snail Biomphalaria glabrata varying in susceptibility to the human blood fluke, Schistosoma mansoni: presence, differential expression, and biological function.

Cytokines control many of the steps in the complex pathways of immune and inflammatory responses in mammals. Recent reports also indicate that some invertebrates may produce cytokines such as interleukin 1 (IL-1). Certain strains of the snail, Biomphalaria glabrata (intermediate host for the human blood fluke, Schistosoma mansoni), possess a soluble plasma factor that stimulates the haemocyte-mediated killing of larval schistosomes, making them resistant to infection. In this study, we have sought to determine whether these snails possessed IL-1 in their plasma, and whether this cytokine was associated with resistance of B. glabrata to S. mansoni. Plasma from susceptible (M-line) and resistant (10-R2, 13-16-R1) strains of B. glabrata that had been unexposed or exposed to S. mansoni were tested for the presence of IL-1-like activity. Experiments employing both a bioassay and an immunoassay indicated that an IL-1-like molecule was present, in varying quantities, among the snail strains. Further, plasma IL-1 levels were significantly affected by exposure to S. mansoni, with levels dropping in M-line and 10-R2 snails, but increasing in the 13-16-R1 strain. However, both resistant strains maintained significantly higher IL-1 levels than M-line snails. Recombinant, human IL-1 (rhIL-1) was shown to prime haemocytes from both resistant snail strains for superoxide production, but had no effect on haemocytes from susceptible B. glabrata. Moreover, the addition of an IL-1 receptor antagonist protein (IRAP) eliminated this priming effect. Priming with rhIL-1 and/or IRAP had no effect on phagocytosis rates in any of the snail strains tested.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed2001

Use of satellite remote sensing and geographic information systems to model the distribution and abundance of snail intermediate hosts in Africa: a preliminary model for Biomphalaria pfeifferi in Ethiopia.

Geographic information system (GIS) risk models for the snail-borne diseases caused by Schistosoma spp. and Fasciola spp. have recently been developed based on climate and satellite-retrieved data on temperature and vegetation coverage. By using these models, it was possible to describe a relationship between vegetation index (Normalized Differences Vegetation Index (NDVI)), land surface temperature (T(max)) and disease prevalence, but little reference was made to the distribution of the corresponding intermediate host snail. Presence of the intermediate host snail is a key factor determining distribution of the disease in sub-Saharan Africa and a good snail distribution mode would probably mirror the endemic area of schistosomiasis. In the present analysis, it was shown that snail distribution data corresponds with schistosomiasis prevalence data in relation to a forecast model based on NDVI and T(max) data derived from the Advanced Very High Resolution Radiometer (AVHRR) onboard the National Oceanic and Atmospheric Administration satellite series. The 'best fit' model included NDVI values from 125 to 145 and a T(max) data range of 10-32 degrees C. This model included 92.3, 90.4 and 94.6% of the positive snail sample sites in GIS query overlay areas extracted from annual, dry season and wet season composite maps, respectively. For other sites in Africa, other NDVI and T(max) ranges may be more appropriate, depending on the species of snail present, a topic that will be examined in further studies.

Africa↗

PubMed2001

Effects of endocrine modulating substances on reproduction in the hermaphroditic snail Lymnaea stagnalis L.

Various man-made agents like pesticides, industrial chemicals and some natural substances have the potential to alter hormonal pathways that regulate reproductive processes in certain species of wildlife. Until now, only a few investigations have been undertaken to determine the effects of these substances on reproductive capacities (fecundity and fertility) in exposed invertebrate aquatic species. In this study one of the most abundant mollusc of European limnic systems, the hermaphroditic gastropod Lymnaea stagnalis was investigated to determine the effects of endocrine modulating substances on reproductive parameters. Known endocrine modulating substances were tested using the following nominal concentrations; Tributyltin (TBT in ng Sn/l) and beta-sitosterol at 1, 10 and 100 ng/l, respectively, and 4-nonylphenol (4-NP) at 1, 10 and 100 microg/l. In addition, experiments were carried out with 1, 10 and 100 ng/l of t-methyltestosterone. All the testing was carried out on recently matured adults of Lymnaea. Fifteen to twenty snails per treatment were exposed for between 7 and 12 weeks in a semi-static test with a weekly exchange of testwater. Shell height and weight and mortality of the adults, egg production, hatching rate of the eggs, and histopathology of the adult snails were analysed. The same parameters were investigated on F(1) generation snails from exposed parents at two dates (1 week after exposure and at the end of the exposure duration). Treatments with TBT and 4-NP had only slight effects on the egg production of the adults and hatching rate of the eggs. However, increased histopathological changes were observed in epithelial tissues of the adult snails, e.g. lung and foot also characterised by extreme inflammatory processes. While beta-sitosterol and t-methyltestosterone had no effect on the shell height and weight or the mortality of adult snails nor on the egg production or ensuing egg hatching rate, beta-sitosterol treated snails presented a distinct atrophy of the albumen gland and so did t-methyltestosterone, albeit with a lower degree of atrophy. The observed histopathological effects due to exposure to tributyltin or 4-NP are suggested to lead to long-term adverse reproductive effects mediated by an impairment of the fitness of the snails. In the experiments the steroid-dependant (beta-sitosterol and t-methyltestosterone) degeneration of the albumen gland caused no obvious adverse effects on the fecundity nor fertility of the adults or on F(1)-generation. However, the impact on fertility following a prolonged exposure to high concentrations of the phytoestrogen cannot be predicted.

Animals↗

PubMed1999

The identification of markers segregating with resistance to Schistosoma mansoni infection in the snail Biomphalaria glabrata.

Both snail and parasite genes determine the susceptibility of the snail Biomphalaria glabrata to infection with the trematode Schistosoma mansoni. To identify molecular markers associated with resistance to the parasite in the snail host, we performed genetic crosses between parasite-resistant and -susceptible isogenic snails. Because resistance to infection in adult snails is controlled by a single locus, DNA samples from individual F2 and F1 backcross progeny, segregating for either the resistant or susceptible phenotypes, were pooled (bulked segregant). Genotypes for both parents were determined with 205 arbitrary decamer primers by random amplified polymorphic DNA-PCR. Of the 205 primers, 144 were informative, and the relative allele frequencies between the pools for these primers were determined. Two primers, OPM-04 and OPZ-11, produced fragments in the resistant parent of one cross that were inherited in a dominant fashion in the resistant F2 and backcross-bulked segregant progeny. Subsequent typing of DNA samples of individual progeny snails showed that the 1.2-kb marker amplified by primer OPM-04 and the 1.0-kb marker produced by primer OPZ-11 segregated in the same dominant fashion with the resistant phenotype. Sequence analysis of the 1.2-kb marker showed that it corresponds to a repetitive sequence in the snail genome with no homology to existing DNA sequences in the public databases. Analysis of the 1. 0-kb marker showed that it also corresponds to a repetitive sequence in the B. glabrata genome that contains an imperfect ORF, with homology to retrovirus-related group-specific antigens (gag) polyprotein.

Animals↗

PubMed1979

Schistosome infection rates in field snails: Schistosoma mansoni in Biomphalaria pfeifferi from Kenya.

Six collections of Biomphalaria pfeifferi were made in the Nairobi and Machakos areas of Kenya. Individual cercarial shedding (Method A) showed that 6.9% (65/938) of the snails had mature 'patent' Schistosoma mansoni infections (range 3.1--34% in the six collections). Crushing (Method B) about one-third of the remaining snails detected no additional mature infections but yielded 1.4% (four snails from one collection) with secondary sporocysts from immature 'prepatent' infections. Weekly shedding observations for five weeks (Method C) on the remainder of the snails showed that 6.9% (40 snails from four collections--range 1.5--30%) shed cercariae maturing from infections immature at the time of collection. As Method B detected no cercariae, Method A apparently detected all 'patent' infections reliably, despite the stress suffered by the snails before examination. Method C was simpler and more efficient than Method B in the detection of infections which were immature at the time of collection. Judging from the rate at which infections matured in Method C, field snails in heavily endemic areas are subjected to pulses of infection rather than to a continuous flow of miracidia. The 'patent' infection rate was not correlated to the 'prepatent' infection rate. Some of the implications of these findings to mathematical models of schistosome transmission are discussed.

Animals↗

PubMed1979

Bacterial flora of the schistosome vector snail Biomphalaria glabrata.

The aerobic heterotrophic bacterial flora in over 200 individuals from 10 wild populations and 3 laboratory colonies of the schistosome vector snail Biomphalaria glabrata was examined. Internal bacterial densities were inversely proportional to snail size and were higher in stressed and laboratory-reared snails. The numerically predominant bacterial genera in individual snails included Pseudomonas, Acinetobacter, Aeromonas, Vibrio, and several members of the Enterobacteriaceae. Enterobacteriaceae seldom predominated in laboratory colonies. Our data suggest that Vibrio extorquens and a Pasteurella sp. tend to predominate in high-bacterial-density snails. These snails may be compromised and may harbor opportunistic snail pathogens.

Aerobiosis↗

PubMed2000

Rescue of sporocysts of Schistosoma mansoni in nonsusceptible Biomphalaria by head-foot transplantation into susceptible snails.

To measure the longevity of sporocysts of Schistosoma mansoni in nonsusceptible snails (13-16-R1 and Salvador strains of Biomphalaria glabrata, and Biomphalaria obstructa), the head-foot (HF) of miracidia-exposed snails was transplanted into the hemocoel of a susceptible NIH albino recipient at 1-36 days postexposure (DPE). Recipient snails which were not exposed to miracidia then were monitored for infection transferred by the implant, and infection prevalences in recipients of HF transplants from nonsusceptible donors were compared to those in snails implanted with an HF from NIH albino donors. Transplants from NIH albino snails between 1 to 15 DPE infected 98% of recipients. Similarly, at 1 DPE, 69-85% of transplants from nonsusceptible snails contained viable sporocysts, as shown by resulting patent infections in the recipients. Recipient infection prevalence, and presumably numbers of transplants containing viable sporocysts, declined as a function of DPE, and by 5-9 DPE this decrease was significant for all 3 types of nonsusceptible donors. However, viable sporocysts still occurred in B. obstructa and 13-16-R1 B. glabrata as late as 19 and 20 DPE, respectively, and in Salvador B. glabrata as late as 33 DPE. Thus, sporocysts persist in nonsusceptible snails considerably longer than suggested by results of previous histological studies.

Animals↗

PubMed2005

Multi-species interactions among a commensal (Chaetogaster limnaei limnaei), a parasite (Schistosoma mansoni), and an aquatic snail host (Biomphalaria glabrata).

This study assessed the effects of a commensal, Chaetogaster limnaei limnaei, and a parasitic trematode, Schistosoma mansoni, on infection patterns and life-history responses in the aquatic snail Biomphalaria glabrata. Prevalence of infection was significantly higher in snails that were devoid of C. limnaei limnaei relative to those that were colonized by the commensal, indicating that the oligochaete may protect the host from trematode infection. This finding appeared to be the direct result of the commensal as opposed to indirect stimulation of the immune system, as hemocyte numbers did not differ between C. limnaei limnaei-colonized and noncolonized snails. Snail growth and reproduction were affected by the presence of C. limnaei limnaei and exposure to S. mansoni. Two-way ANOVA revealed a significant effect of both C. limnaei limnaei presence and trematode exposure on B. glabrata growth over the 5-wk study with C. limnaei limnaei-colonized and parasite-infected snails demonstrating the greatest growth. Snails exposed, but uninfected, by S. mansoni demonstrated the lowest growth regardless of commensal colonization. Chaetogaster limnaei limnaei colonization had no effect on egg production, but S. mansoni-infected snails produced significantly more eggs than individuals from other treatment groups. Survival remained over 85% in all treatment groups. The ecological implications of these results are discussed.

Analysis of Variance↗