Omphiscola Glabra Research Articles

Changes in the Populations of Two Lymnaeidae and Their Infection by Fasciola hepatica and/or Calicophoron daubneyi over the Past 30 Years in Central France.

Field investigations were carried out during three periods (from 1976 to 1997, in 2013-2014, and in 2020-2021) on 39 cattle-raising farms on acidic soils to track changes in the populations of two Lymnaeidae (Galba truncatula and Omphiscola glabra) and their infection with Fasciola hepatica and/or Calicophoron daubneyi. Compared to the survey between 1976 and 1997 on these farms, there was a significant decrease in the number of the two lymnaeid populations and the size of the G. truncatula populations in both 2013-2014 and 2020-2021. This decline was significantly faster in the last nine years than it was before 2013. The area of habitats colonized by G. truncatula showed no significant variation over the years, while that of habitats with O. glabra significantly decreased in the period covered by the three surveys. The prevalence of F. hepatica infection in snails significantly decreased over the years, while C. daubneyi infection increased over time in both lymnaeid species. These changes are due to the use of triclabendazole to treat fasciolosis in ruminants since the 1990s, and are probably a consequence of the successive heatwaves that have occurred since 2018 in the region.

Decline in the number and size of populations of two Lymnaeidae living in central France over the last decade

Field investigations in 2013–2014 on acid soils and in 2016–2017 on sedimentary soils showed that populations of two lymnaeids had decreased in number in central France since 1998. As several heat waves occurred in this region in 2018, 2019 and 2020, it was useful to check whether this decline had further increased in recent years. Surveys in 56 farms in the north-west and west of the Haute Vienne department (acid soils) and 37 farms in the south of Indre (sedimentary soils) were therefore carried out in 2020 and 2021 and the results obtained were compared with those recorded by our team in the same farms in 2013–2014 and 2016–2017. On acid soils, the overall number of populations decreased by 34.7% forGalba truncatula(out of 813 populations in 2013–2014) and 22% forOmphiscola glabra(out of 550), while it decreased by 25% forG. truncatula(out of 361 in 2016–2017) and 15.2% forO. glabra(out of 205) on sedimentary soils. Similarly, the overall density of overwintering snails significantly decreased by 80.7% forG. truncatulaand 70.2% forO. glabraon acid soils, while it significantly decreased by 64.1% and 38.3%, respectively, on sedimentarym soils. In both cases, these decreases were more marked on acid soils than on sedimentary soils. In contrast, the habitats ofG. truncatulaand most of those colonized byO. glabrashowed no significant variation in their area between the two periods of study. The decline in the number of these lymnaeid populations, observed since 1998, is still continuing today in central France and may be due in part to heatwave episodes s that occurred in 2018, 2019 and 2020 in this region.

Linking Macroinvertebrates and Physicochemical Parameters for Water Quality Assessment in the Lower Basin of the Volta River in Ghana

The health of the lower basin of the Volta River in Ghana was evaluated in January–February and May–June 2016 using physicochemical parameters and benthic macroinvertebrates sampled at 10 locations. Selected environmental variables were compared to accepted environmental water quality standard values where applicable. Principal component analysis (PCA) and redundancy analysis (RDA) were used to analyse the association between the benthic macroinvertebrates distribution and physicochemical variables. Pesticide concentrations were generally below the limit of detection 0.01 and 0.005 µg/L for organophosphate/synthetic pyrethroid and organochlorines respectively. Nutrient levels were also generally low; however, significant differences existed between the values of physicochemical parameters at the different sampling sites and seasons (Monte Carlo permutation test; p = 0.002), as well as between the abundance of macroinvertebrates at the different sites and seasons (p = 0.002). The environmental variables dissolved oxygen (DO), phosphate, pH, substratum (p < 0.05), turbidity, conductivity, total dissolved solids, total solids and nitrate (0.05 < p < 0.10) significantly explained the variation in macroinvertebrate composition between sampling stations in the Volta River. Polypedilum fuscipenne, was positively correlated with turbidity and DO concentrations; Physa sp., Centroptilum sp., Centroptiloides sp., Phaon iridipennis and juvenile fish were positively correlated with nitrate concentration and pH and negatively correlated with turbidity and DO. Polluted sites were dominated by the snail Lymnaea glabra. This demonstrates that physicochemical parameters and macroinvertebrates could be applied to describe the water quality and improve the biomonitoring for water resources management and the environmental protection in the Lower Volta River.

Freshwater molluscs fauna of Western Ukraine and its representation in museum collections of Lviv

Based on the literary and personal data, as well as collections of the State Museum of Natural History of the NAS of Ukraine and the Zoological Museum of the Ivan Franko National University of Lviv, the taxonomic composition and peculiarities of the spatial distribution of gastropods and bivalve molluscs in Western Ukraine have been analyzed. Species lists have been drawn up for the Volhynian (Western) Polissia, Volhynian Upland, Male Polissia, Roztochya and Opillya, Western Podillia, Central (Northern) Podillia, Prut-Dnister interfluve, Ciscarpathian, Transcarpathian lowland and mountainous part of the Ukrainian Carpathians. It is established that in the west of Ukraine, 74 autochthonous and 6 adventitious freshwater molluscs with generally recognized species status, belonging to 35 genera and 15 families, can be considered as reliably registered. Adventitious to Western Ukraine are Potamopyrgus antipodarum, Physella acuta, Menetus dilatatus, Dreissena polymorpha, D. bugensis, Sinanodonta woodiana. Additional confirmation requires the presence of Lithoglyphus pyramidatus, Omphiscola glabra, Physella heterostropha, Planorbis carinatus, Pisidium conventus, P. tenuilineatum. Not taking into account the Central Podillia, poorly researched by malacologists, a distinctly pronounced decrease in the species richness of freshwater molluscs is observed only in the mountainous part of the Ukrainian Carpathians (38 species, 17 genera, 8 families), with the presence of some specific components of freshwater molluscs complexes (small gastropods of the genera Bythinella і Paladilhiopsis). The richest taxonomic composition of freshwater molluscs was noted for Volhynian Polissia: 67 species, 29 genera, 15 families. It has been found that most freshwater molluscs are evenly distributed throughout the plain and foothill territories of Western Ukraine. Only few species can be considered as specific components of freshwater malacocomplexes for one of the physical-geographical areas or river basins. A number of species that are not present in the malacological collection of SMNH NASU, as well as the territories poorly represented in it, have been identified. The results obtained will be taken into account when further collecting the museum collection.

Consequences of invasion by Pseudosuccinea columella on the dynamics of native lymnaeids living on the acid soils of central France

ABSTRACTEight road ditches located on granite and colonised by the native lymnaeids Galba truncatula or Omphiscola glabra were studied for 2 years to follow the distribution and density of these species in their habitats when the invasive lymnaeid Pseudosuccinea columella was introduced. Six other ditches populated only by a native lymnaeid or by P. columella were used as controls. The same experiment was also carried out for 3 years in seven water tanks placed in semi-natural conditions. The colonisation of P. columella was more rapid in habitats with G. truncatula than in those with O. glabra. Similarly, this colonisation led to a progressive decrease in the number of native lymnaeids in these ditches and this decrease was also faster for G. truncatula than for O. glabra. A similar decrease of G. truncatula and O. glabra was also noted when P. columella was introduced into water tanks placed in semi-natural conditions. The habitats of G. truncatula or O. glabra on the acid soils of central France can be successfully colonised by P. columella, and the establishment of this invasive species may lead to a decrease of the two native lymnaeids or even the local extinction of one of these (G. truncatula).

Galba truncatula and Omphiscola glabra (Gastropoda, Lymnaeidae): present decline in populations living on sedimentary soils in central France

Field investigations in habitats colonized by Galba truncatula or Omphiscola glabra were carried out to determine if the number of habitats, their area and the number of overwintering snails had not changed over the past 20 years. These habitats were studied in 57 cattle- or sheep-breeding farms located in three French natural regions on sedimentary soils. Compared to the numbers of snail habitats recorded before 1998, the values observed in 2016–2017 were significantly lower, with an overall decline rate of 30% for G. truncatula and 38% for O. glabra. Variations in this decline rate were noted with the type of snail habitat and the largest decreases were observed for vernal pools in meadows. Significantly lower areas in 2016–2017 were noted in two habitat types (drainage furrows, road ditches) for G. truncatula and two other habitat types (drainage furrows, pond banks) for O. glabra. Significantly lower densities of overwintering snails were observed in 2016–2017 in G. truncatula habitats located in drainage furrows and road ditches, while no significant difference was noted for O. glabra, whatever the habitat type. Several causes were at the origin of this population decline and the most important were the present development of mechanical cleaning in road ditches, that of subsurface drainage in meadows and regular gyro-crushing of vegetation around pools in meadows. The data reported in this study confirm the decline that several authors have already noted for O. glabra in Western Europe. The results obtained for G. truncatula require reviewing the biogeographical status of this species and taking possible measures to ensure its conservation while taking into account its role as intermediate host in the F. hepatica cycle.

Galba truncatula and Fasciola hepatica: Genetic costructures and interactions with intermediate host dispersal

Antagonistic interactions between hosts and parasites are key structuring forces in natural populations. Demographic factors like extinction, migration and the effective population size shape host-parasite metapopulational dynamics. Therefore, to understand the evolution of host-parasite systems it is necessary to study the distribution of the genetic variation of both entities simultaneously. In this paper, we investigate the population genetics co-structure of parasites and hosts within a metapopulation of the liver fluke, Fasciola hepatica, and two of its intermediate hosts, the main intermediate host in Europe, Galba truncatula, and a new intermediate host, Omphiscola glabra, in Central France. Our results reveal an absence of specificity of flukes as regard to the two alternative hosts though O. glabra shows higher prevalence of F. hepatica. Host and parasites displayed contrasting population genetics structure with very small, highly inbred (selfing) and strongly isolated G. truncatula populations and much bigger, panmictic and more dispersive F. hepatica. This could indicate a local adaptation of the parasite and a local maladaptation of the host. We also unveil a parasite-mediated biased population genetics structure suggesting that infected G. truncatula disperse more; have higher dispersal survival than uninfected snails or, more likely, that immigrant snails are infected more often than local snails (local parasites are less adapted to local hosts). Finally, an absence, or at least an ambiguous signature of isolation by distance was observed in both host and parasite population. A very weak migration rate for G. truncatula provides a reasonable explanation for this ambiguous result. Alternatively, smaller sample sizes combined with modest migration rates might explain the difficulties to unveil the signal in F. hepatica.

Insights into the reproductive activity ofOmphiscola (Lymnaea) glabra(Gastropoda: Lymnaeidae) in relation to soil geology in Central France

Transplantations of Omphiscola glabra from granite to marl, or vice versa, between farms known for cases of fasciolosis have shown differences in the maximum shell height of adult snails. To determine whether these differences were due to parasitism, soil geology, or a combination of both factors, four snail populations living on marl or granite were investigated over 12 months to specify the characteristics of egg-laying in spring, and to follow the shell growth of both snail generations. In both types of habitats, the number of egg-masses per adult snail and their size significantly decreased during the 7 weeks of snail egg-laying. During this period, each adult snail on marl laid a mean of 6.4 masses and 93.3 eggs. On granite, the mean values were 5.7 masses and 69.1 eggs, respectively. Two annual generations, the first in spring and the other in autumn, were noted in these habitats. The maximum shell height of adults was different: a mean of 19.8 and 20.5 mm on marl compared with 17.2 and 18.2 mm on granite. Soil geology thus plays a role in the egg-laying and shell growth of O. glabra .

Detection of habitats colonized by Omphiscola glabra (Gastropoda: Lymnaeidae) on acid soils using indicator plants

The lymnaeid Omphiscola glabra is known to be an intermediate host in the life cycle of Fasciola hepatica and knowing its distribution in the field is important to determine that of the parasite. Looking at indicator plants has been proposed by several authors as one of the most practical ways of carrying out a malacological survey in pastures of a farm. Field investigations on 361 French farms breeding cattle or sheep on acid soils were thus carried out for 36 years in March or April to list indicator plant species in seven types of habitats colonized by O. glabra , and determine the characteristics of their habitats (area, snail density) for each indicator plant. Six plant species: Agrostis stolonifera , Dactylis glomerata , Glyceria fluitans , Juncus acutiflorus , Juncus effusus and Lotus uliginosus , were examined in 3137 snail habitats. J. effusus was the best indicator species to detect snail populations in five habitat types, while J. acutiflorus was the best indicator for snail populations living in spring heads. The other four plant species characterized only a few populations. Snail habitats detected with J. acutiflorus , J. effusus or L. uliginosus were significantly larger in area, while the density of overwintering snails was significantly lower in habitats with G. fluitans . These initial results suggest that J. effusus is a good indicator for the detection of O. glabra in the acid soils of central France. However, additional studies are required to test its limitations in the field.

Calicophoron daubneyi and Fasciola hepatica: characteristics of natural and experimental co-infections of these digeneans in the snail Lymnaea glabra.

A retrospective study on different Lymnaea glabra samples collected from central France between 1993 and 2010 was carried out to determine the prevalence of natural co-infections with Calicophoron daubneyi and Fasciola hepatica, and to specify the composition of redial burdens. Experimental infections of L. glabra performed during the same period of time were also analysed to study metacercarial production of each digenean in co-infected snails. Controls were naturally or experimentally co-infected Galba truncatula. In natural co-infections, prevalence was 0.7% in L. glabra (186/25,128) and 0.4% in G. truncatula (137/31,345). Low redial burdens were found in these snails, with F. hepatica rediae significantly more numerous in L. glabra than in G. truncatula (7.5 per snail instead of 5.2). In contrast, the total numbers of C. daubneyi rediae in both lymnaeids were close to each other (4.3 and 3.0 rediae, respectively). In experimentally co-infected groups, prevalence was greater in G. truncatula than in the other lymnaeid (6.3% instead of 3.0%). Significantly shorter patent periods and lower metacercarial production for each digenean were noted in L. glabra than in G. truncatula. However, in both lymnaeids, the two types of cercariae were released during the same shedding waves and several peaks during the patent period were synchronous. In spite of a greater shell height for L. glabra, metacercarial production of both digeneans in co-infected snails was lower than that in G. truncatula, thus indicating a still incomplete adaptation between these French L. glabra and both parasites.

Current decline in the number and size of Galba truncatula and Omphiscola glabra populations, intermediate hosts of Fasciola hepatica, on the acidic soils of Central France.

Field investigations on the habitats colonized by Galba truncatula or Omphiscola glabra were carried out on 162 farms of the Limousin region, Central France, to determine whether there is currently a decline in the number and size of snail populations. Seven types of snail habitats were considered here. Compared to the numbers of snail populations recorded from 1976 to 1992, the values noted from 2013 to 2016 were significantly lower, with a decline rate of 34% for G. truncatula and 23% for O. glabra. Variations in this decline rate with the type of snail habitat were also noted. The greatest decreases in the numbers of snail populations were noted for spring heads located in meadows and for road ditches, while the lowest were noted for open drainage furrows present in meadows. The distribution of these habitats according to their area did not show any significant change over time. In contrast, overwintering snails were significantly less numerous in 2013–2016 in five types of habitats for G. truncatula and in three types only for O. glabra. Several causes underlie this population decline. Among them, the current development of mechanical cleaning in open drainage systems and road ditches, that of subsurface drainage in meadows, and regular gyro-crushing of vegetation around temporary spring heads were the most important.

Aplexa hypnorum(Gastropoda: Physidae) exerts competition on two lymnaeid species in periodically dried ditches

Samples of adult Aplexa hypnorum were experimentally introduced into periodically dried ditches colonized by Galba truncatula or Omphiscola glabra to monitor the distribution and density of these snail species from 2002 to 2008, and to compare these values with those noted in control sites only frequented by either lymnaeid. The introduction of A. hypnorum into each ditch was followed by the progressive colonization of the entire habitat by the physid and progressive reduction of the portion occupied by the lymnaeid towards the upstream extremity of the ditch. Moreover, the size of the lymnaeid population decreased significantly over the 7-year period, with values noted in 2008 that were significantly lower than those recorded in 2002. In contrast, the mean densities were relatively stable in the sites only occupied by G. truncatula or O. glabra . Laboratory investigations were also carried out by placing juvenile, intermediate or adult physids in aquaria in the presence of juvenile, intermediate or adult G. truncatula (or O. glabra ) for 30 days. The life stage of A. hypnorum had a significant influence on the survival of each lymnaeid. In snail combinations, this survival was significantly lower for adult G. truncatula (or O. glabra ) than for intermediate snails. In contrast, the survival of juveniles was similar to that noted in the corresponding controls. This interspecific competition between the physid and either lymnaeid may not be due to food present in their habitat, but might be due to the toxicity of mucus secreted by intermediate and adult A. hypnorum .

Larval trematode infections inLymnaea glabrapopulations living in the Brenne Regional Natural Park, central France

Lymnaea glabra is known to be a natural intermediate host of two flukes, Calicophoron daubneyi and Fasciola hepatica, in central France. But it can also sustain larval development of other digeneans. Adult snails were thus collected from 206 habitats in 2014 and 2015 to identify parasite species and determine the prevalence of each digenean infection in relation to the five types of snail habitats. Seven digenean species were noted in 321 infected snails (out of 17,647 L. glabra). Snails with F. hepatica or C. daubneyi were found in 14.5% and 12.6% of habitats, respectively. Percentages were lower for snails with Opisthoglyphe ranae (5.8%), Haplometra cylindracea (5.3%) and were less than 5% for those infected with Echinostoma revolutum, Notocotylus sp. or Plagiorchis sp. Prevalence noted for each parasite species varied with the type of habitat. The number of species in L. glabra was lower than that found in G. truncatula from the same region (7 instead of 10). The distribution and prevalence of each digenean species were thus dependent on the type and location of each snail habitat.

Transmission patterns of Fasciola hepatica to ruminants in Sweden

Transmission patterns of Fasciola hepatica were investigated on beef cattle (n=3) and sheep (n=3) farms in Sweden between 2011 and 2012. The dynamics of fluke infection, particularly estimated time of infection, were screened each grazing season by ELISA detection of antibodies in lambs (n=94) and first grazing season calves (n=61). Colostral transfer of F. hepatica antibodies from seropositive ewes was detected in sheep up to 11 weeks of age. In sheep, the estimated time of infection differed significantly between herds and years. Typical ‘winter infection’ was observed on two sheep farms in 2012, but the most prevalent transmission pattern was found to be ‘summer infection’, characterised by infection of animals in late summer by F. hepatica originating from overwintered and/or spring-excreted eggs. In contrast, beef calves were infected mainly in September–October (‘summer infection’). Furthermore, lymnaeid and succineid snails were collected on the pastures used by these animals both in spring and in the autumn each year. In total, 1726, 588, 138, 130, 93 and 42 specimens of Galba truncatula, Lymnaea palustris, Lymnaea glabra, Lymnaea fuscus, Radix peregra and Succinea putris, respectively, were collected and identified. These were subsequently examined for the presence of F. hepatica DNA by species-specific PCR and the findings compared against mean monthly rainfall and temperature data for each farm. The main intermediate host of the liver fluke was G. truncatula, with a prevalence range of F. hepatica infection from 0% to 82%. Only 1 out of 42 terrestrial S. putris tested positive for F. hepatica, casting doubt on the role of this species in transmission of F. hepatica in Sweden. In conclusion, two main peak periods of infection were observed: May–June (from overwintered infected snails=‘winter infection’) and August–September (from metacercariae developed and produced by snails during summer=‘summer infection’). The occurrence and frequency of ‘winter infection’ were dependent on local environmental factors such as snail habitat availability or grazing behaviour of animals, rather than on climatic factors.

Lymnaea glabra: progressive increase in susceptibility to Fasciola hepatica through successive generations of experimentally infected snails.

Experimental infections of Lymnaea glabra (two populations) with Fasciola hepatica were carried out during seven successive snail generations, to determine if prevalence and intensity of snail infection increased over time through descendants of snails already infected with F. hepatica. Controls were descendants coming from uninfected parents and infected according to the same protocol. No larval forms were found in the bodies of control snails coming from uninfected parents. In contrast, prevalence and intensity of F. hepatica infection in snails originating from infected parents progressively increased from the F2 or F3 to the F6 generation of L. glabra. In another experiment carried out with the F7 generations of L. glabra and a single generation of Galba truncatula (as controls), the prevalence of F. hepatica infection and the total number of cercariae were lower in L. glabra (without significant differences between both populations). If the number of cercariae shed by infected snails was compared to overall cercarial production noted in snails containing cercariae but dying without emission, the percentage was greater in G. truncatula (69% instead of 52-54% in L. glabra). Even if most characteristics of F. hepatica infection were lower in L. glabra, prevalence and intensity of parasite infection increased with snail generation when tested snails came from infected parents. This mode of snail infection with F. hepatica suggests an explanation for cases of fasciolosis occurring in cattle-breeding farms where paramphistomosis is lacking and G. truncatula is absent.

Рідкісні та маловідомі черевоногі молюски (Gastropoda) рівнинної частини заходу України

The information about the rare and poorly-known molluscs distributed in the western part of Podolian Upland and other flat parts of Western Ukraine were analysed. On the whole, 27 species of the land molluscs and 10 species of the freshwater molluscs among which Granaria frumentum , Chondrina clienta and Plicuteria lubomirskii entered in the Rote List of Ukraine were put into the review. Apparently the presence of Lymnaea glabra entered in the Rote List of Ukraine as L. clavata in the basin of Bug requires of the additional confirmation. The same concerns the presence in the Western Ukraine of the freshwater molluscs Lymnaea turricula , Planorbis carinatus and Gyraulus acronicus . A considerable part of the land molluscs reviewed in the article need a protection on the national-wide level. Particularly, this relates to the semislugs Daudebardia brevipes and D. rufa , majority of the finds of them concentrated near by Lviv, and to the snails Pupilla sterri (relic species), Truncatellina claustralis , Pyramidula pusilla . Some of the mentioned species ( Carpathica calophana , Cellariopsis orientalis, Eucobresia nivalis ) are the usual components of the land mollusc fauna of Ukrainian Carpathians, but they relatively rarely get to the flat part of the Western Ukraine. They can need a protection on the margin of their natural areas. Keywords : molluscs, Gastropoda, protection, Western Ukraine.

Omphiscola glabra(Gastropoda, Lymnaeidae): Changes occurring in natural infections withFasciola hepaticaandParamphistomum daubneyiwhen this snail species is introduced into new areas

Cross-transplantations of Omphiscola glabra between two French departments (Haute-Vienne and Indre) were carried out to study snail settlement in these new sites during six years and to determine if this snail species was well adapted to its local parasites (Fasciola hepatica and Paramphistomum daubneyi). Local snails placed in new sites for each department were used as controls. In Indre furrows, the number of adults per population and the area of each habitat peaked on the third year post-introduction. Similar findings were also noted in the Haute-Vienne furrows occupied by local snails but peaks were only observed on the fourth year. In contrast, in Haute-Vienne sites populated by introduced snails, there was a progressive decrease in snail abundance and habitat area from the second year. The local O. glabra transplanted in Haute-Vienne kept their same degree de susceptibility to F. hepatica and P. daubneyi, thus demonstrating a good adaptation of these snails to their parasites. In other groups of transplanted snails, the first natural infections were only noted from the second or third year post-introduction and their prevalence progressively increased over time. Local adaptation of these latter snails to parasites would be more progressive in time and would stretch over several snail generations.

Prevalence and intensity of infections in the lymnaeid snail Omphiscola glabra experimentally infected with Fasciola hepatica, Fascioloides magna and Paramphistomum daubneyi

Single and double infections of juvenile Omphiscola glabra (Gastropoda: Lymnaeidae) with Paramphistomum daubneyi and/or Fasciola hepatica were carried out to determine the redial burden and cercarial production in snails dissected at day 60 or at day 75 post-exposure (p.e.) in the laboratory at 20 degrees C. The results were compared with those obtained with single-miracidium infections by Fascioloides magna. Compared to F. hepatica, low values were noted at day 75 p.e. for the prevalence of snail infections with P. daubneyi (4.6-8.3% instead of 23.6-25.9%), the total number of free rediae (10.7-17.9 per snail instead of 26.3-34.7), and that of free cercariae (112.8-136.9 per snail instead of 177.8-248.5). Despite a greater number of free rediae at day 75 p.e. (36.2-45.6 per snail), the prevalences of snail infections with F. magna and cercarial production were similar to those noted for F. hepatica. The results concerning F. hepatica and P. daubneyi might partly be explained by a progressive adaptation of O. glabra to sustain the larval development of these digeneans over the years, as this snail is a natural intermediate host of F. hepatica and P. daubneyi in central France since 1995. Compared with the high number of fully-grown rediae of F. magna in O. glabra, cercarial production seemed limited and this might be explained by the presence of high numbers of rediae which reduced the avaibility of nutrients for cercarial differentiation within the snail.

The presence of uninfected Omphiscola glabra in a breeding of infected Galba truncatula enhanced the characteristics of snail infections with Fasciola hepatica

Experimental infections of Galba truncatula with Fasciola hepatica were carried out under laboratory conditions to determine if the presence of another lymnaeid, Omphiscola glabra, during snail breeding had an indirect effect on the growth of G. truncatula and to analyse consequences on cercarial production. When the two lymnaeids are raised together, the survival of G. truncatula at day 30 post-exposure (PE), the prevalence of snail infections, and the shell height of cercariae-shedding snails at day 45 PE were significantly higher. By contrast, the other parameters characterizing snail infections only showed insignificant variations. The origin of O. glabra (living in a snail community, or monospecific population) used for the breeding of G. truncatula did not have a significant effect on the values of each parameter. Even if variations in the mean numbers of metacercariae were insignificant, the greater survival of G. truncatula at day 30 PE and the higher numbers of cercariae-shedding snails in the groups living with O. glabra allowed to obtain a higher total number of larvae than in alone-raised groups of G. truncatula.

First studies on the susceptibility of Omphiscola glabra (Gastropoda: Lymnaeidae) from central France to Fascioloides magna

Experimental infections of Omphiscola glabra (preadult snails), originating from central France, to a Czech isolate of Fascioloides magna miracidia were carried out to determine if the local populations of O. glabra may ensure the larval development of this parasite and to compare these results with those noted for a natural snail host, Galba truncatula. The presence of experimentally infected snails was noted in the six populations of snails studied. However, only a few snails shed their cercariae (O. glabra 5.3 to 17.1%, G. truncatula 15.1% in the first population, and no shedding in the other). The shell heights of cercariae-shedding (CS) snails were significantly greater than those of other infected snails, for O. glabra as well as for G. truncatula. The number of metacercariae noted in each snail group was low and showed insignificant variations. When experimental infections of O. glabra were performed in relation to the shell height of snails (from 1 to 14 mm) at miracidial exposure, the prevalence of infected snails significantly decreased with increasing shell heights at exposure. However, the presence of CS snails was only noted from the 5-6 to the 9-10 mm groups, and the mean number of metacercariae per group ranged from 27 to 44.2. Despite the high infectivity of the Czech isolate of F. magna miracidia, there was an incomplete adaptation with the French G. truncatula and O. glabra used in this study, as the metacercarial production was low, and cercarial shedding only occurred for snails which showed a strong increase of their shell height during F. magna infections.