Background: Bithynia siamensis goniomphalos is the snail intermediate host of the liver fluke, Opisthorchis viverrini, the
leading cause of cholangiocarcinoma (CCA) in the Greater Mekong sub-region of Thailand. Despite the severe public health
impact of Opisthorchis-induced CCA, knowledge of the molecular interactions occurring between the parasite and its snail
intermediate host is scant. The examination of differences in gene expression profiling between uninfected and O. viverriniinfected
B. siamensis goniomphalos could provide clues on fundamental pathways involved in the regulation of snailparasite
interplay.
Methodology/Principal Findings: Using high-throughput (Illumina) sequencing and extensive bioinformatic analyses, we
characterized the transcriptomes of uninfected and O. viverrini-infected B. siamensis goniomphalos. Comparative analyses of
gene expression profiling allowed the identification of 7,655 differentially expressed genes (DEGs), associated to 43 distinct
biological pathways, including pathways associated with immune defense mechanisms against parasites. Amongst the
DEGs with immune functions, transcripts encoding distinct proteases displayed the highest down-regulation in Bithynia
specimens infected by O. viverrini; conversely, transcription of genes encoding heat-shock proteins and actins was
significantly up-regulated in parasite-infected snails when compared to the uninfected counterparts.
Conclusions/Significance: The present study lays the foundation for functional studies of genes and gene products
potentially involved in immune-molecular mechanisms implicated in the ability of the parasite to successfully colonize its
snail intermediate host. The annotated dataset provided herein represents a ready-to-use molecular resource for the
discovery of molecular pathways underlying susceptibility and resistance mechanisms of B. siamensis goniomphalos to O.
viverrini and for comparative analyses with pulmonate snail intermediate hosts of other platyhelminths including
schistosomes.