Title : Host immune responses and parasitological dynamics in schistosome-infected snails
Abstract:
Schistosomiasis is classified as a neglected tropical disease and is transmitted through freshwater snails that serve as intermediate hosts. Within the mollusc–trematode interaction, schistosome miracidia actively locate and are chemically attracted to specific snail species in aquatic environments. Following attachment, the miracidia penetrate the snail’s integument and transform into sporocysts. These invasive sporocysts release a range of excretory secretory products that enable them to persist within the host and evade the snail’s immune defenses. Through successive development, sporocysts give rise to cercariae, the next larval stage responsible for transmission to the definitive host.
The presence and development of schistosome larval stages within snail tissues induce substantial biological, physiological, biochemical, and immunological alterations in the intermediate host. In many cases, infected snails experience impaired reproduction, including reduced or complete cessation of egg laying, as a consequence of ovotestis damage caused by parasite development. The interaction between snails and schistosomes is governed by a dynamic immune response involving multiple defense mechanisms, such as nitric oxide production, lysozyme activity, phagocytosis, lectin-mediated recognition, and phenoloxidase activation.
To successfully establish infection, schistosomes have evolved sophisticated strategies to overcome or suppress these host immune responses. These include the secretion of potent proteolytic enzymes, the formation of a highly resistant outer tegument, molecular mimicry of host antigens, and the regulated release of immunomodulatory molecules that alter immune cell function. This review focuses on elucidating these immune evasion strategies to enhance understanding of the molecular and immunological determinants underlying snail– schistosome interactions and to support the development of alternative approaches for schistosomiasis control.
