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      Radix natalensis: the effect of Fasciola hepatica infection on the reproductive activity of the snail Translated title: Radix natalensis : effet d’une infestation par Fasciola hepatica sur l’activité reproductrice du mollusque

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          Experimental infections of Egyptian Radix natalensis (shell height at miracidial exposure: 4 mm) with a French isolate of Fasciola hepatica were carried out under laboratory conditions at 22 °C to specify the characteristics and follow the dynamics of their egg-laying. Controls constituted unexposed R. natalensis of the same size. No significant difference between controls and the uninfected snails of the exposed group was noted, whatever the parameter considered. In controls and exposed snails, the dates of the first egg masses were close to each other (56.4–65.3 days). In contrast, the life span of snails and the length of the egg-laying period were significantly shorter and egg production was significantly lower in infected R. natalensis than in controls and uninfected snails. In infected R. natalensis, but without cercarial shedding (NCS snails), egg production was irregular throughout the egg-laying period. In cercarial-shedding (CS) snails, the first egg masses were laid before the first cercarial emergence (at a mean of 56 days and 67 days, respectively). Thereafter, egg mass production of CS snails was irregular up to day 72 of the experiment, stopped during the following two weeks and started again after day 88 for a single snail. In conclusion, the F. hepatica infection of R. natalensis reduced the reproductive activity in both NCS and CS snails. The pattern noted for egg production in infected R. natalensis seems to be species-specific because of the high shell size of this lymnaeid and its role as an atypical intermediate host in the life cycle of the parasite.

          Translated abstract

          Des infestations expérimentales de Radix natalensis provenant d’Égypte (hauteur de la coquille lors de l’exposition miracidienne, 4 mm) avec un isolat français de Fasciola hepatica ont été réalisées dans les conditions du laboratoire à 22 °C afin de préciser les caractéristiques des pontes et suivre leur dynamique. Des témoins ont été constitués avec des R. natalensis de même taille, mais non exposés au parasite. Aucune différence significative entre les témoins et les mollusques non infestés du groupe exposé n’a été relevée, quel que soit le paramètre considéré. Chez les témoins et les mollusques exposés, les dates des premières pontes sont proches les unes des autres (56,4–65,3 jours). Par contre, la durée de vie des limnées, la durée de la période de ponte et la production des œufs sont significativement plus faibles chez les R. natalensis infestés que chez les témoins et les mollusques non infestés. Chez les R. natalensis infestés mais sans émission cercariennes (limnées NEC), la production des œufs est irrégulière tout au long de la période de ponte. Chez les mollusques émettant des cercaires (limnées EC), les premières pontes ont été déposées avant les premières émissions cercariennes (respectivement au 56 ème jour et au 67 ème en moyenne). Par la suite, la production des pontes est irrégulière jusqu’au 72 ème jour de l’expérience avant de s’arrêter pendant les deux semaines suivantes et de reprendre au 88 ème jour chez un seul mollusque. En conclusion, l’infestation de R. natalensis par F. hepatica réduit l’activité reproductrice des limnées EC et NEC. La distribution des pontes chez les R. natalensis infestés semble être spécifique à l’espèce à cause de la grande hauteur de la coquille de cette limnée et de son rôle comme hôte intermédiaire atypique dans le cycle de vie du parasite.

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          Most cited references 6

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          The effects of Fasciola hepatica on Lymnaea truncatula.

           J Hodasi (1972)
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            Oviposition of Lymnaea truncatula infected by Fasciola hepatica under experimental conditions.

            Experimental infections of Lymnaea truncatula by Fasciola hepatica (one, two, or three miracidia per snail) were carried out under laboratory conditions to analyze the oviposition of infected snails and determine the characteristics of their egg masses. In the infected snails from the three groups, egg-laying steadily decreased until week 4 postexposure and stopped afterward until the end of the experiment, except for the cercaria-shedding snails from the one-miracidium group, for which low numbers of egg masses were noted between weeks 9 and 12. In uninfected snails the number of egg masses decreased until week 4 and remained low during subsequent weeks. At weeks 11 and 12 postexposure the natality rate was 98.9% in controls, 56% in the cercaria-shedding snails from the one-miracidium group, and 59.2-68.5% in uninfected snails. In the cercaria-shedding snails from the one-miracidium group the restoration of reproduction activity after week 8 may be explained by a lower parasite burden in these snails than in those from the two- and three-miracidium groups.
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              The development of rediae of Fasciola hepatica in Radix natalensis subjected twice to bimiracidial exposures.

              Experimental infections of Egyptian Radix natalensis with a French isolate of Fasciola hepatica (each snail was subjected twice to a bimiracidial exposure) were carried out to determine how many sporocysts grew in these snails and to study the developmental patterns of redial generations. Single-sporocyst infections were found in 69.3% (34/49) of infected snails, with equivalent numbers of normal and abnormal patterns. Snails with two- and three-sporocyst infections were 24.4% and 6.1%, respectively. In single- and two-sporocyst infections at days 42 and 56 post-exposure, the total redial burden was significantly higher in snails with a normal redial development. In two- and three-sporocyst infections, the overall maturity of rediae was delayed at days 42 and 56. The high frequency of abnormal patterns in R. natalensis (53.1% of all infected snails showed degeneration of a first mother redia) might be due to incomplete adaptation between the snail population and the parasite. The delayed redial maturity in two- and three-sporocyst infections can mainly be explained by the volume of the snail body, which would be insufficient to allow the simultaneous differentiation of most rediae over time.

                Author and article information

                EDP Sciences
                29 May 2014
                : 21
                : ( publisher-idID: parasite/2014/01 )
                [1 ] Department of Zoology, Faculty of Science, University of Tanta 31111 Tanta Egypt
                [2 ] INSERM 1094, Faculties of Medicine and Pharmacy 87025 Limoges France
                Author notes
                parasite140006 10.1051/parasite/2014026
                © Y. Dar et al., published by EDP Sciences, 2014

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                Page count
                Figures: 3, Tables: 1, Equations: 0, References: 17, Pages: 6
                Research Article


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