Snail Galba Truncatula Research Articles

Assessing the microbiota of the snail intermediate host of trematodes, Galba truncatula

BackgroundThe microbiome is known to play key roles in health and disease, including host susceptibility to parasite infections. The freshwater snail Galba truncatula is the intermediate host for many trematode species, including the liver and rumen flukes Fasciola hepatica and Calicophoron daubneyi, respectively. The snail-parasite system has previously been investigated. However, the specific interaction between the snail-associated microbiota and intra-snail developmental stages of trematodes has yet to be explored.MethodsGalba truncatula snails were collected from farms in Northern Ireland and trematode infection was diagnosed using PCR. High-throughput sequencing analysis of the bacterial 16S ribosomal DNA V3-V4 hypervariable regions was subsequently applied to characterise the microbiota of both uninfected and infected snails.Results We first showed that the snail harboured microbiota that was distinct for its environment. The microbiota of infected snails was found to differ significantly from that of uninfected snails. In particular, the bacterial genera Mycoplasma and Methylotenera were significantly more abundant in infected snails, while genera Sphingomonas and Nocardioides were predominantly associated with uninfected snails. ConclusionThese findings pave the way to future studies on the functional roles of bacteria in host-parasite relationships.Graphical

Fasciolosis-An Increasing Challenge in the Sheep Industry.

Simple SummaryFasciolosis caused by Fasciola hepatica is a serious disease and a huge challenge in the sheep industry. The disease has several clinical manifestations including acute death, anemia, ill-thrift and loss of body condition. Climate change with milder temperatures and heavier rainfall will increase the risk of fasciolosis. Grazing management and treatment with flukicide are at present the only options to restrain F. hepatica infection. However, control possibilities are challenging, and resistance to flukicide drugs is increasing. Diagnostic improvements, targeted treatment and vaccines will hopefully increase animal health and welfare on fluke infested pastures in the future.The liver fluke Fasciola hepatica may cause severe infection in several mammalian species, including sheep and humans. Fasciolosis is a parasitic disease occurring worldwide in temperate climates and involves intermediate lymnaeid snails as vectors, in Europe the pond snail Galba truncatula in particular. In the sheep industry, the disease is a serious welfare and health problem. Fasciolosis is usually classified as acute, subacute or chronic according to the number and stage of flukes present in the liver, but with a considerable overlap. Acute disease, associated with a large number of migrating larvae, often results in sudden death due to acute and massive hemorrhage, while chronic fasciolosis is characterized by anemia, hypoalbuminaemia and weight loss. The management of fasciolosis is an increasing challenge in the sheep industry. Early diagnostic tests are limited. Protective immunity against liver flukes in sheep is low or lacking, and vaccines are not yet available. Treatment and control possibilities are challenging, and resistance to flukicide drugs is increasing. In addition, climate change with warmer and more humid weather will have a substantial effect on the establishment of both flukes and snails and will most likely increase the future distribution of F. hepatica.

Endemic occurrence of Fasciola hepatica in an alpine ecosystem, Pyrenees, Northeastern Spain.

Fasciola hepatica is a liver parasite of ruminants whose distribution is determined by its intermediate host, the freshwater snail Galba truncatula. In Europe, F.hepatica is mostly associated with lowlands. Infection from sympatric domestic reservoirs is rarely reported in wild mountain ungulates. This study explores F.hepatica in a multi-host system in a European alpine area. Serum samples (n=1,209) from Pyrenean chamois (Rupicapra p. pyrenaica), European mouflon (Ovis aries musimon), domestic sheep (Ovis aries) and domestic cattle (Bos taurus) were collected in the National Game Reserve of Freser-Setcases (NGRFS) in Catalonia, Northeastern Spain, from 2008 to 2019, and tested for antibodies against F.hepatica. During the same period, the livers of 214 chamois hunted in the NGRFS were inspected for F.hepatica and associated pathological changes. Finally, 907 freshwater snails were collected in summer 2016 between 1559 and 2,224 metres above sea level (asl) in the NGRFS, and F.hepatica DNA sought by PCR. Antibodies against F.hepatica were detected in all four species, with a higher prevalence in cattle and sheep than in chamois. Fasciola hepatica and hepatic lesions were concurrently observed in 13/214 of the chamois livers inspected (6.1%, CI95 2.9%-9.3%). Fasciola hepatica DNA was detected in one out of the 907 snails (0.1%, Cl95 0.1% - 0.3%; Ct value 33.3) and collected at 2054m asl. Fasciola hepatica was consistently detected in a high mountain multi-host system, suggesting that its life cycle is completed and that it occurs endemically at the highest elevation reported in Europe. Transhumant livestock are the likely source in this alpine ecosystem, which according to rare occurrence of F.hepatica DNA in G.truncatula is still a suboptimal habitat for F.hepatica life cycle. Studying parasites at their highest distribution range can be useful to monitor climate change in seasonal mountain environments.

Rapid detection of Galba truncatula in water sources on pasture-land using loop-mediated isothermal amplification for control of trematode infections

BackgroundFascioliasis caused by the trematodes Fasciola hepatica and F. gigantica, is a global neglected zoonotic disease estimated to cost the livestock industry over €2.5 billion annually. Farm management measures and sustainable use of anthelmintics can, in principle, effectively control trematode infection in livestock and reduce the rate of developing anthelmintic resistance. Previously, we designed an environmental DNA (eDNA) assay to identify a common trematode intermediate host, the freshwater snail Galba truncatula, in water sources to measure specific trematode infection risk areas on pasture-land. To improve this procedure, we now report a loop-mediated isothermal amplification (LAMP) assay to identify G. truncatula eDNA.MethodsA LAMP assay was designed and optimised (e.g. temperature, time duration and primer concentration) to identify G. truncatula DNA. The ability of the LAMP assay to target G. truncatula DNA was identified, and LAMP assay limit of detection was investigated in comparison to conventional PCR. In the field, 48 water samples were collected from stream, ditch and water pool habitats in four locations at two Aberystwyth University farms over a seven week period to investigate the applicability of the LAMP assay for use on eDNA samples, in comparison to conventional PCR.ResultsThe LAMP assay delivered detectable results in 30 min at 63 °C. The assay discriminated between G. truncatula DNA and non-target DNA, presenting a level of DNA detection comparable to conventional PCR. No significant difference was found between the ability of the LAMP and PCR assay to identify G. truncatula eDNA in water samples. Kappa coefficient analysis revealed a moderate level of agreement between LAMP and PCR assays.ConclusionsThis study demonstrated that the LAMP assay can detect G. truncatula eDNA in a simple and rapid manner. The LAMP assay may become a valuable tool to determine optimum pasture management for trematode parasite control.

Spatial patterns of Fasciola hepatica and Calicophoron daubneyi infections in ruminants in Ireland and modelling of C. daubneyi infection

BackgroundFasciola hepatica has always represented a threat to Irish livestock because the Irish climate is highly suitable for the main local intermediate host of the parasite, the snail Galba truncatula. The recent clinical emergence of infections due to Calicophoron daubneyi has raised the question of whether the two parasites, which share a niche during part of their life-cycles, interact in some way. Here, we used geographical information systems (GIS) to analyse the distribution of both parasites in cattle and sheep. We also developed the first predictive model of paramphistomosis in Ireland.ResultsOur results indicated that, in cattle, liver fluke infection is less common than rumen fluke infection and does not exhibit the same seasonal fluctuations. Overall, we found that cattle had a higher likelihood of being infected with rumen fluke than sheep (OR = 3.134, P < 0.01). In addition, infection with one parasite increased the odds of infection with the other in both host species. Rumen fluke in cattle showed the highest spatial density of infection. Environmental variables such as soil drainage, land cover and habitat appeared to be the most important risk factors for C. daubneyi infection, followed by rainfall and vegetation. Overall the risk of infection with this parasite was predicted to be higher in the west of the country.ConclusionsThis study shows differences between the infection rates and spatial patterns of bovine and ovine infections with F. hepatica and C. daubneyi in Ireland. Whether the reasons for this are due to susceptibility, exposure and/or management factors is yet to be determined. Furthermore, the rumen fluke model indicates distinct risk factors and predicted distribution to those of F. hepatica, suggesting potential biological differences between both parasite species.

Recovery of Fascioloides magna (Digenea) population in spite of treatment programme? Screening of Galba truncatula (Gastropoda, Lymnaeidae) from Lower Austria

During the past decade, Fascioloides magna, the large American liver fluke, has spread within free-living deer in wetlands of the Danube in Lower Austria. The aim of this study was to determine the current infection rates with F. magna and other digenean parasites in the intermediate host snail Galba truncatula from risk areas in Lower Austria. A total of 3444 G. truncatula were collected and examined microscopically for the presence of digenean trematodes. A set of randomly selected snails and isolated trematode stages were also investigated molecular biologically by PCR and sequencing. Digenean parasites were detected with a prevalence of 2.41% (1.83% Paramphistomoidea; 0.46% Echinostomatoidea; 0.09% Strigeida; 0.06% Plagiorchiida). F. magna was found with an overall prevalence of 0.23%, which may indicate a recovery of the parasite population in spite of an ongoing triclabendazole treatment programme. Moreover, high risk areas and a seasonality of infections were observed.

The detection of snail host habitats in liver fluke infected farms by use of plant indicators

Field investigations in 361 liver fluke infected cattle- or sheep-breeding farms on acid soil were carried out during thirty years in March and April to record indicator plants in relation to the category of site colonized by the intermediate host of liver fluke, the snail Galba truncatula. Seven types of snail zones and six species of indicator plants were recorded in the 7709 positive sites studied. The most frequent habitats were located at the peripheral extremities of open drainage furrows. Juncus acutiflorus, Juncus effusus, Glyceria fluitans, and Agrostis stolonifera were the indicator plants. Plant indicators were highly efficient (38–80% of variance explained) when used with the size of site area within a hydrographical zone. The identification of positive sites for G. truncatula is a key for controlling the intermediate host on pastures through biological control with predatory molluscs. The positive sites may be detected using a two-step method including first categorization of hydrographical zones and then, within a zone, use of one or several indicator plants (frequently J. acutiflorus).

Correlation between parasite prevalence and adult size in a trematode-mollusc system: evidence for evolutionary gigantism in the freshwater snail Galba truncatula?

The snail-trematode host-parasite system has been widely studied, as trematodes are known to greatly influence the fitness of their hosts. Indeed, during their development, the trematodes castrate the snail and one possible consequence of infection is gigantism of the snail. Snail gigantism is usually investigated experimentally by comparing the size of healthy and artificially infected snails. Here, I focused on naturally infected populations in order to investigate if snails submitted to trematode pressure have evolved specific life-history traits to respond to the parasite prevalence in their natural population. To this end, I estimated the correlations between measures of size (obtained from healthy laboratory individuals originating from populations) and the parasite prevalence at the population level. I found that the adult size of populations was positively correlated with population prevalence, an indication that gigantism might be operating. Moreover, I found a positive relation between growth and fecundity in healthy populations, while no such trade off was found in highly parasitized populations, suggesting that there may be a cost in fecundity to this gigantism.

Effects of Selection and Drift on G Matrix Evolution in a Heterogeneous Environment: A MultivariateQst–Fst Test With the Freshwater SnailGalba truncatula

Unraveling the effect of selection vs. drift on the evolution of quantitative traits is commonly achieved by one of two methods. Either one contrasts population differentiation estimates for genetic markers and quantitative traits (the Q(st)-F(st) contrast) or multivariate methods are used to study the covariance between sets of traits. In particular, many studies have focused on the genetic variance-covariance matrix (the G matrix). However, both drift and selection can cause changes in G. To understand their joint effects, we recently combined the two methods into a single test (accompanying article by Martin et al.), which we apply here to a network of 16 natural populations of the freshwater snail Galba truncatula. Using this new neutrality test, extended to hierarchical population structures, we studied the multivariate equivalent of the Q(st)-F(st) contrast for several life-history traits of G. truncatula. We found strong evidence of selection acting on multivariate phenotypes. Selection was homogeneous among populations within each habitat and heterogeneous between habitats. We found that the G matrices were relatively stable within each habitat, with proportionality between the among-populations (D) and the within-populations (G) covariance matrices. The effect of habitat heterogeneity is to break this proportionality because of selection for habitat-dependent optima. Individual-based simulations mimicking our empirical system confirmed that these patterns are expected under the selective regime inferred. We show that homogenizing selection can mimic some effect of drift on the G matrix (G and D almost proportional), but that incorporating information from molecular markers (multivariate Q(st)-F(st)) allows disentangling the two effects.

High quantitative and no molecular differentiation of a freshwater snail (Galba truncatula) between temporary and permanent water habitats

We investigate the variation in quantitative and molecular traits in the freshwater snail Galba truncatula, from permanent and temporary water habitats. Using a common garden experiment, we measured 20 quantitative traits and molecular variation using seven microsatellites in 17 populations belonging to these two habitats. We estimated trait means in each habitat. We also estimated the distributions of overall genetic quantitative variation (QST), and of molecular variation (FST), within and between habitats. Overall, we observed a lack of association between molecular and quantitative variance. Among habitats, we found QST>FST, an indication of selection for different optima. Individuals from temporary water habitat matured older, at a larger size and were less fecund than individuals from permanent water habitat. We discuss these findings in the light of several theories for life-history traits evolution.

Histopathological effects of Thiodan® on the freshwater snail,Galba truncatula (gastropoda, pulmonata)

Histopathological alterations in three tissues, namely, digestive gland, foot and mantle of the freshwater snail Galba truncatula induced by Thiodan 35 EC, a commercial preparation of endosulfan, were studied in the laboratory. The snails were exposed to five sublethal concentrations of Thiodan, two of them higher concentrations at 0.33% and 0.65% in glass jars for short-term exposure (96 h) and three of them lower concentrations at 0.08%, 0.16% and 0.27% for long-term exposure (10, 20 and 30 days). Thiodan caused significant histopathological changes in the tissues of the snail, irrespective of the concentration of the pesticide and its exposure period. The histopathological changes included accumulation of amoebocytes in the hemolymphatic spaces between the tubules of the digestive gland, exudation in the lumen of tubules, expansion of hemolymphatic spaces between the tubules and increase of vacuolation and necrotic changes in the digestive cells. Disruption of columnar muscle fibers and alteration of epithelial layers were detected in the foot and mantle of the treated specimens. The number and size of mucous and protein cells in the foot and mantle also changed.