Synonymy between Lymnaea bogotensis Pilsbry, 1935 and Lymnaea cousini Jousseaume, 1887 (Gastropoda: Lymnaeidae)

The lymneid snail Lymnaea bogotensis Pilsbry 1935 is synonymized with L. cousini Jousseaume 1887, based on morphological comparisons of the reproductive systems. The shell, renal tube, and reproductive system are described and illustrated from specimens collected in the type locality and the municipality of Paipa, Colombia. Bibliographical records reveal L. columella to be the commonest lymneid in the country. The latter two species can be differentiated based on the morphology of the penial complex.     

First report of Lymnaea cousini Jousseaume, 1887 naturally infected with Fasciola hepatica (Linnaeus, 1758) (Trematoda: Digenea) in Machachi, Ecuador

We report the first finding of Lymnaea cousini naturally infected with Fasciola hepatica in Ecuador. A sample of 70 snails was collected in April 2005 from a wetland located in a valley at approximately 3000 m a.s.l., near the locality of Machachi, Pichincha Province. The prevalence of natural infection in L. cousini was 31.43%, which is the highest value ever recorded for naturally infected lymnaeid species.     

Development of Fasciola hepatica in Lymnaea columella infected with miracidia derived from cattle and marmoset infections

The development of Fasciola hepatica from two species of definitive hosts, i.e. cattle (Bos taurus) and a marmoset (Callithrix penicillata) in the snail Lymnaea columella was determined based on the production of rediae and cercariae and snail survival rate. More rediae and cercariae at 60-74 days post-infection were produced by snails infected by cattle-derived miracidia (cattle group) than by those infected by marmoset-derived miracidia (marmoset group). Among the L. columella parasitized by the marmoset group, the survival rate and the percentage of positive snails were higher than among those parasitized by the cattle group. Eggs of F. hepatica released in cattle faeces were significantly bigger than those released in marmoset faeces. Miracidia originating from parasites that completed their development in cattle were more efficient in infecting the intermediate host. These results suggest that vertebrate-host origin influences the eggs produced by the parasite and the infection rates in the snail host L. columella.     

The effects of the slug biological control agent, Phasmarhabditis hermaphrodita (Nematoda), on non-target aquatic molluscs

The nematode Phasmarhabditis hermaphrodita is used as a commercial biological control agent of slugs in the UK. Although it is known to affect other terrestrial mollusc species, its effects on freshwater molluscs are not known. The present study investigated the effects of P. hermaphrodita on the survival of juvenile Lymnaea stagnalis and Physa fontinalis, two common freshwater snails, at 'spray tank' concentration and a 50% diluted 'spray tank' concentration over a 14-day period. Survival of L. stagnalis was significantly reduced at both application levels but P. fontinalis suffered no mortalities over the experimental period. The possible differential mechanisms of pathology between the two host species are discussed.     

Parasite influences on host life history: Echinostoma revolutum parasitism of Lymnaea elodes snails

Using field surveys and experimental infections, we investigated the influence of a trematode parasite on life history traits of adult Lymnaea elodes snails. We found that parasitism significantly affected the growth, fecundity, and survival of host snails. Within five of the six natural L. elodes populations we sampled, shell length of echinostome-infected hosts was significantly greater than for uninfected conspecifics. Furthermore, we show that gigantism occurs among experimentally infected snails due to an accelerated growth rate and size-selective mortality following an Echinostoma revolutum infection. The fecundity of infected snails sharply decreased beginning at 3 weeks post exposure (PE) and all egg production eventually ceased for most hosts by 5–6 weeks PE. Energy constraints, imposed by parasite development, alter the host energy budget. Early in the infection, parasite depletion of host energy reserves reduces host reproduction, but sufficient resources remain to allow accelerated host growth. Mortality was increased among host snails at two distinct stages: shortly after exposure and several weeks after cercariae were first released. We did not observe tissue degradation in snails during the first 4 weeks after exposure to the parasite, but destruction of host tissues was noted among snails dying later in the infection. Received: 5 September 1997 / Accepted: 19 November 1997     

In vivo efficacy of praziquantel against Echinoparyphium aconiatum (Trematoda: Echinostomatidae) parasitizing the great pond snails Lymnaea stagnalis (Gastropoda: Lymnaeidae)

The present study had a practical goal. I aimed to determine whether praziquantel could reduce the production of Echinoparyphium aconiatum (Trematoda: Echinostomatidae) cercariae in infected snails Lymnaea stagnalis (Gastropoda: Lymnaeidae) without killing the hosts. Praziquantel is a broad-spectrum antihelminth agent. It caused a total cessation of cercaria shedding when the praziquantel concentration in the treatment bath was 10 mg/L and the treatment time was 30 h or longer. A next research step which has to be taken before giving detailed recommendations about using praziquantel for ceasing production of E. aconiatum cercariae in parasitized snails is to follow the survivorship and performance of treated snails after a praziquantel exposure for longer than in this medium-term (3 days) experiment.     

Aspects of the maintenance of the life cycle of Fasciola hepatica in Lymnaea columella in Minas Gerais,Brazil

Fascioliasis is a parasitic disease of domestic ruminants that occurs worldwide. The lymnaeid intermediate hosts of Fasciola hepatica include Lymnaea columella, which is widely distributed in Brazil. A colony of L. columella from Belo Horizonte, MG, was reared in our laboratory to be used in studies of the F. hepatica life cycle, the intermediate host-parasite relationship and development of an anti-helminthic vaccine. In the first experiment 1,180 snails were exposed to miracidia of F. hepatica eggs removed from the biliary tracts of cattle from the State of Rio Grande do Sul. In the second and third experiments the snails were exposed to miracidia that had emerged from F. hepatica eggs from Uruguay, maintained in rabbits. The rates of infection in the first, second and third experiments were 0, 42.1 and 0% respectively. Over 15,806 metacercariae were obtained and stored at 4 degrees C. Four rabbits weighing 1.5 kg each were infected with 32-44 metacercariae and two with 200. Three rabbits begin to eliminate eggs of the parasite in the feces from 84 days after infection onwards. The biological cycle of F. hepatica in L. columella and the rabbit was completed within 124 days.     

Paramphistomum daubneyi: characteristics of infection in three lymnaeid species

Experimental infections of two South American lymnaeids (Lymnaea neotropica and L. viatrix var. ventricosa) with Paramphistomum daubneyi were carried out to determine if these snail species could sustain larval development of this digenean and, if so, to specify their potential for cercarial production. A French population of Galba truncatula infected and raised according to the same protocol served as controls. In both experiments, prevalence of P. daubneyi infections in snails did not significantly differ from each other. In snail groups evaluated for cercarial shedding (first experiment), a significantly lower number of shed cercariae was noted for L. neotropica, while those from G. truncatula and L. v. ventricosa did not differ significantly from each other. Dissection of infected snails at day 65 post-exposure at 20 °C (second experiment) found significantly lower burdens of P. daubneyi rediae and cercariae in the bodies of L. neotropica than in those of G. truncatula and L. v. ventricosa. Compared to total cercarial production observed in dissected snails, the percentage of cercariae which exited from snails was 75.6% for G. truncatula, 21.6% for L. neotropica, and 91.4% for L. v. ventricosa. This last species seems to be a good candidate for metacercarial production of P. daubneyi.     

Activity of Euphorbia splendens var. hislopii N.E.B. (Euphorbiaceae) latex against Lymnaea columella (Say, 1817) (Pulmonata: Lymnaeidae), intermediate host of Fasciola hepatica, Linnaeus, 1758 (Trematoda: Fasciolidae). 2: limited field-testing

The molluscicidal evaluation of Euphorbia splendens var. hislopii (Crown of thorns) against Lymnaea columella snails, intermediate host of Fasciola hepatica, in irrigation ditches of the Pisciculture Station at Universidade Federal Rural do Rio de Janeiro, was studied under limited field conditions. An aqueous solution of the latex at 5 mg/l was tested in two irrigation ditches (experimental and control ditches), after initial sampling of the snail population present. Twenty-four hours after application of the product, it was verified that 97.4% of free L. columella snails and 100% of snails of the same species captive in cages and used as sentinels at three points equidistant from the application site in the experimental ditch, died. For Biomphalaria tenagophila and Melanoides tuberculata snails, present in the experimental ditch, the mortality was 100%, for the species Pomacea spp. the mortality was 40%. No mortality was verified in the free mollusks, or in the sentinels in the ditch used as control. E. splendens var. hislopii latex is thus an efficient natural molluscicide, which may be used as an alternative control agent against L. columella.     

The susceptibility of Lymnaea fuscus to experimental infection with Fasciola hepatica

Three experiments on the infection of Lymnaea fuscus with Fasciola hepatica were carried out to determine if successful infections and maturation of the parasite were dependent on the size of snails at miracidial exposure. The first experiment was performed using 1-4-mm-high snails from 2 populations of L. fuscus and 1 population of Lymnaea palustris. In these snails each subjected to a single bimiracidial exposure, the prevalence of F. hepatica infection at day 35 postexposure ranged from 20.3% to 46.2% in snails measuring 1 mm in height at exposure; it was lower in the 2-mm snails and was 0 in higher size classes. The second experiment was performed by subjecting 1- and 4-mm L. fuscus to 1, 2, and 3 bimiracidial exposures. The prevalence of F. hepatica infection at day 35 postexposure was maximum in the 1-mm snails exposed once to miracidia and decreased with increasing number of exposures. The results were negative in 4-mm snails. Cercarial shedding of F. hepatica was studied in the third experiment using 1- and 2-mm L. fuscus each subjected to a single bimiracidial exposure. The total number of cercariae released from these snails was less than 50. From these results, it can be concluded that L. fuscus showed a partial resistance to F. hepatica infection due to snail age.     

Exposure to Fasciola hepatica miracidia increases the sensitivity of Lymnaea (Fossaria) humilis to high and low pH

Humidity and temperature have been considered important factors affecting the infectivity of Fasciola hepatica to its molluscan host. One hundred and thirty laboratory-reared Lymnaea humilis were exposed for 4 hr to the miracidia of F. hepatica over a pH range from 4.0 to 10.0, and their rates of survival were compared with 130 similarly treated but unexposed control snails. All control snails died within 24 hr at pH 4.0, but they showed better survival at pH 5.0-10.0. Their sensitivity to solutions with high and low pH, however, was increased if kept in the presence of F. hepatica miracidia. Snails exposed at pH 5.0 died within 24 hr, whereas most other pHs also affected survival such that by day 18 only those snails exposed at pH 7.2 remained alive. The increased sensitivity of the snails to pH could be explained by a damage-mediated release of parasite enzymes, because infectivity was highest at pHs associated with the lowest host mortality.     

Planorbidae, Lymnaeidae and Physidae of Ecuador (Mollusca: Basommatophora)

In the course of a trip to Ecuador I had the opportunity of collecting topotypic specimens of the following nominal species of pulmonate molluscs: Biomphalaria cousini Paraense, 1966; Planorbis equatorius Cousin, 1887; P. canonicus Cousin, 1887; Lymnaea cousini Jousseaume, 1887 and P. boetzkesi Miller, 1879. Additional findings were: Helisoma trivolvis (Say, 1817), Biomphalaria peregrina (Orbigny 1835), Drepanotrema anatinum (Orbigny, 1835), D. kermatoides (Orbigny, 1835), D. lucidum (Pfeiffer, 1839), D. surinamense (Clessin, 1884), Lymnaea columella Say, 1817 and Physa acuta Draparnaud, 1805. P. boetzkesi and P. canonicus are considered junior synonyms of Gyraulus hindsianus (Dunker, 1848) and Biomphalaria peregrina (Orbigny, 1835), respectively.     

A photoperiod gene regulates vitellogenesis in Lymnaea peregra (Mollusca: Gastropoda: Pulmonata)

Summary

Populations of the fresh-water snail Lymnaea peregra from different localities vary in their capacity to lay eggs, responding either to long day or to short day photoperiods. These responses are genetically determined by a single gene locus with the long day allele dominant over the short day allele. Although previtellogenic stages of oogenesis are not affected by an inhibitory photoperiod, vitellogenesis is essentially shut down. The volumes of the dorsal bodies, which are endocrine organs that mediate vitellogenesis, are significantly smaller in snails maintained in an inhibitory photoperiod. Implantation of cerebral ganglia with attached dorsal bodies, both from egg laying animals and from dormant animals that have the potential to lay eggs in the postoperative photoperiod, into snails that were inhibited by insufficient photoperiod resulted in a significant increase in vitellogenesis in the ovotestes of the hosts. An increase in host dorsal body volume was also observed. The photoperiod gene appears to control some aspect of the cerebral ganglion that activates the dorsal body to produce a hormone that stimulates vitellogenesis in the ovotestes. Photoperiodic control of reproduction may be a factor contributing to the diverse life history strategies observed in this species.     

Cadmium toxicity and snail-digenean interactions in a population of Lymnaea spp

The toxicity of cadmium to a population of Lymnaea peregra and L. stagnalis naturally infected with a range of digeneans and collected from a number of sites in the lower Thames Valley, UK was investigated. Lymnaeid snails were exposed to 100 microg l-1 cadmium and the effects on host survival and emergence of cercariae recorded. Overwintered L. peregra, but not L. stagnalis, showed significantly reduced survival compared to seasonally infected snails, i.e. snails which have acquired an infection during the spring or summer. A significant increase in survival with increasing snail size was demonstrated for L. stagnalis and for seasonally infected L. peregra only. Only L. stagnalis infected with Diplostomum spathaceum and L. peregra infected individually with D. spathaceum, Sanguinicola inermis, Echinoparyphium recurvatum and Notocotylus attenuatus demonstrated a significantly reduced survival compared to laboratory-bred controls. The exposure of L. stagnalis to cadmium resulted in a significant reduction in the emergence of D. spathaceum over a 5-day period but cadmium-exposed L. peregra showed no difference in the emergence of E. recurvatum cercariae over a 3-day exposure period. The mechanisms and importance of metal toxicity to snail-digenean interactions are discussed.     

Interspecific antagonism and virulence in hosts exposed to two parasite species

Co-infection of host organisms by multiple parasite species has evolutionary consequences for all participants in the symbiosis. In this study, we co-exposed aquatic-snails (Biomphalaria glabrata) to two of their trematode parasites, Schistosoma mansoni and Echinostoma caproni. In co-exposed snails, E. caproni prevalence was 63% compared to only 23% for S. mansoni. Co-exposed E. caproni-infected snails exhibited reduced fecundity, higher mortality, and higher parasite reproduction (higher virulence) compared to hosts exposed to echinostomes alone. Conversely, co-exposed S. mansoni-infected snails released fewer parasites and produced greater numbers of eggs compared to hosts exposed to S. mansoni alone. These results suggest that co-exposure not only influences the establishment (presence or absence) of particular parasite species, but also impacts host life history, parasite reproduction, and the virulence of the interaction.     

Effects of diet and<Emphasis Type="Italic"> Echinostoma revolutum</Emphasis> infection on energy allocation patterns in juvenile<Emphasis Type="Italic"> Lymnaea elodes</Emphasis> snails

Resource allocation strategies may be influenced by both biotic and abiotic factors. The purpose of this study was to investigate the effects of both parasitism and diet quality on the growth, reproduction, and survival of the pond snail, Lymnaea elodes. In addition, we assessed parasite growth and reproduction. High-protein (high diet) or low-protein diets (low diet) were fed to juvenile L. elodes snails that were either exposed or sham-exposed to the castrating trematode, Echinostoma revolutum. Host growth was assessed weekly; reproduction and survival were recorded every 2-3 days. We estimated parasite development as the time to parasite release from the host (patency), and parasite reproduction as the number of larvae shed from infected snails at two time points. Diet and infection status had significant effects on snail growth. Infected snails produced few eggs and tended to grow to larger sizes than uninfected snails regardless of diet. In contrast, exposed-uninfected individuals displayed diet-dependent patterns of growth and reproduction. On the high-protein diet, uninfected and exposed-uninfected snails exhibited similar patterns of growth and reproduction, whereas in the low-diet treatment, exposed-uninfected snails exhibited reduced growth and delayed reproduction relative to uninfected individuals. Survival differed among treatments in the latter stages of the study with infected snails exhibiting reduced survival relative to snails from other treatments. Moreover, infected low-diet snails exhibited lower survival than infected high-diet snails. Parasite development and reproduction did not appear to be directly influenced by the quality of host diet. Results from this study suggest that energy allocation patterns are context-dependent in juvenile snails, influenced by parasite exposure and diet quality. Furthermore, parasite reproduction appears to depend more on host size than on the quality of host diet.     

Lymnaea fuscus (Pfeiffer, 1821) as a potential intermediate host of Fascioloides magna in Europe

Experimental infections of two different populations of Lymnaea fuscus in France and Sweden, with a Czech isolate of Fascioloides magna were carried out to determine if this lymnaeid species enables parasite larval development. Species identification of both snail populations was performed using the morphology of the copulatory organ, and also confirmed by sequencing of the internal transcribed spacer 2 (ITS2) region of the snail genomic rDNA. Only juvenile snails measuring less than 3 mm (1–3 weeks of age) were successfully infected (the viable cercariae were recorded) and infection prevalence decreased with age, as documented by increased shell height. In both French and Swedish L. fuscus populations, prevalence ranged between 1.1% and 58.8%. The mean number of metacercariae obtained from cercariae-shedding snails was 13.7 (±11.4), while the total cercarial production noted in snails dissected at day 85 post-exposure was 147.5 (±56.6). Compared to uninfected control snails, we observed reduced growth of infected snails. Despite age-related resistance of snail to the parasite, and limited cercarial production in these experimentally infected snails, F. magna was still able to complete larval development in L. fuscus.     

The effect of cohabitation of Tubifex tubifex (Oligochaeta: Tubificidae) populations on infections to Myxobolus cerebralis (Myxozoa: Myxobolidae)

The competitive interactions between susceptible and resistant Tubifex tubifex (Oligochaeta: Tubificidae) exposed to Myxobolus cerebralis (Myxozoa: Myxobolidae) infections were investigated in two laboratory trials. Competition was assessed by the total parasite production over the course of the trials in mixed and pure cultures of M. cerebralis exposed worms, and by the genetic analyses of worms from the control and experimental groups at the beginning and end of the experiments. Mixed cultures of resistant and susceptible worms showed a 70% reduction in production of parasites released when compared with pure cultures of susceptible worms. In studies with laboratory and field-collected oligochaetes the mixed cultures at the end of the cohabitation experiments were dominated by resistant Tubifex from lineage V (HB strain) this strain of Tubifex has a competitive advantage over worms from other lineages. The results of this study suggest that certain species of Tubifex may be dead-end hosts to M. cerebralis by absorbing or inactivating the parasite and may also show greater survival compared to susceptible oligochaetes in certain whirling disease enzootic habitats.     

Effects of Fasciola gigantica experimental infection on some inorganic elements in the snail host Lymnaea natalensis

Flame atomic absorption spectrometry was performed to determine the alteration in the concentrations of metallic ion Pb, Zn, K, Na, Fe, Cu and Co in the soft parts of the Lymnaea natalensis snails shedding Fasciola gigantica cercariae and to determine the alteration in the concentration of Ca in the soft parts and shells of the same snails. The Co was found to be present at concentration level below the detection limits of the analytical method used. Regarding detected elements, three elements Zn, K and Cu were found to be present at significantly higher concentrations in cercariae-shedding snails compared with uninfected snails. Two elements, Pb and Na, showed significant decrease in cercariae-shedding snails compared to uninfected ones. The concentration of Fe showed non-significant increase. The results showed significant lowering in the calcium content of the shells and soft parts of cercariae-shedding snails relative to the calcium content in the uninfected ones. The obtained results and the hypothesis of hypercalcification in shells of infected snails were discussed.