Overview of interactions between parasitic digenea and their molluscan hosts, with special emphasis on the Lymnaeidae

Abstract

Digeneans (Platyhelminthes, Trematoda) are considered as a very ancient and as the most diversified group of internal metazoan parasites of animals. They can have important detrimental effects on human and animal health. They also affect populations dynamics of their hosts, are able to shape the structure of communities, and can act as determinants of ecosystems structure and functioning. Whereas life-cycles are diversified, the fundamental life-cycle of digeneans is characterized by a mollusc as the first intermediate host, where an important asexual multiplication occurs and by a vertebrate as definitive host. The interactions between digeneans and molluscs are complex; they start with the infection of the mollusc by the miracidial larval stage, which implies molecular mechanisms of attraction, recognition, and attachment. Once the penetration successful, an intimate association starts between the mollusc and the digenean, where the mollusc displays an intense immune response and, in turn, the digenean counter-attacks by different mechanisms. All these complex interactions can lead to high reciprocal specializations which can lead to host–parasite specificity. After its installation, the miracidium converts into a sporocyst which develops and starts an intense asexual multiplication, highly detrimental for the molluscan fitness. At the end of several cycles of asexual reproduction, the last larval stages, the cercariae, are emitted and will serve to infect the following host. Taking into account the complexity of mollusc–digenean interactions, their sensitivity to environmental perturbations and their importance in ecological and epidemiological risks, such interactions have to be particularly scrutinized. In this chapter, we review such host–parasite interactions with emphasis on the Lymnaeidae.