Intermediate host recognition abilities of Fasciola hepatica miracidia

Fasciola hepatica, the causative agent of fascioliasis in sheep and cattle, requires a compatible snail intermediate host to complete its life cycle. The aquatic larval stage of this parasite is well-adapted for host-finding, with chemotactic abilities that enable it to sense potential host biomolecules. The extent of intermediate host recognition, particularly at the species level, and the downstream correlation with successful attachment has not been explored. This study investigated the ability of F. hepatica miracidia to distinguish between native and invasive host and non-host freshwater snail species during the host-finding and host-attachment phases.

Quantitative and qualitative measurements of miracidial behaviour were compared pre- and post-exposure with snail-conditioned water (SCW) from both native and invasive host snails (lymnaeids Austropeplea cf. brazieri and Pseudosuccinea columella) and non-host snails (the lymnaeid Bullastra lessoni and the physid Physa acuta). Miracidia were also exposed to live snails of each representative species to ascertain whether host-finding correlates with successful miracidial host-attachment.

Miracidia displayed clear shifts in movement profiles post-exposure to SCW, with no qualitative or quantitative differences observed in the behavioural response to different snail species. When exposed to live snails, miracidia were more likely to attach to both host and non-host native species (A. cf. brazieri and B. lessoni) compared with invasive snail species (P. columella and P. acuta). Among invasive snails, miracidia had a higher rate of successful attachment with P. columella (host) than with P. acuta (non-host).

The miracidia of F. hepatica exhibit analogous host-finding responses post-exposure to SCW, regardless of which snail species they are exposed to. Host-finding responses do not correlate with miracidial ability to attach to the snail tissue or with the established host status of the respective snail species. These results provide an insight into host-finding preferences of F. hepatica within the Australian context and lay an important foundation for further exploration into intermediate host-parasite interactions and their mechanisms of action.