Molecular characterization of Urosporidium tapetis sp. nov., a haplosporidian hyperparasite infecting metacercariae of Parvatrema duboisi (Dollfus 1923), a trematode parasite of Manila clam Ruditapes philippinarum on the west coast of Korea

Recently, a putative new hyperparasitic haplosporidian in the genus Urosporidium was identified from metacercariae of the trematode Parvatrema duboisi infecting Manila clam Ruditapes philippinarum on the west coast of Korea. In this study, we applied small subunit ribosomal DNA (SSU rDNA) sequences as a marker to substantiate the phylogenetic relationship of the unidentified Urosporidium within the Order Haplosporida. In our phylogenetic analysis, the 1890 bp of SSU rDNA sequences obtained were closely related to a haplosporidian parasite forming a sister clade to Urosporidium group, although the gene sequences were only 89.22-89.70% similar to Urosporidium spp. Such molecular phylogenetic distance within the genus suggested that the unidentified Urosporidium is a new member of the genus. Accordingly, we report the unidentified haplosporidian hyperparasite as Urosporidium tapetis sp. nov.

First report of Urosporidium sp., a haplosporidian hyperparasite infecting digenean trematode Parvatrema duboisi in Manila clam, Ruditapes philippinarum on the west coast of Korea

In this study, we first report on the occurrence of Urosporidium sp., a haplosporidian hyperparasite infecting the trematode, Parvatrema duboisi, which parasitizes Manila clams, Ruditapes philippinarum on the west and south coasts of Korea. The larval P. duboisi infected by the sporocyst stage of Urosporidium sp. demonstrated numerous small yellowish spores in their tissues. The heavily infected metacercariae exhibited degenerate bodies and the larvae were often motionless. Clams heavily infected by the metacercariae of P. duboisi also displayed abnormal golden spots on the mantle tissue. In histology, different life stages of Urosporidium sp. could be identified, including the uni-nucleate, plasmodial, sporogonic stages and the acid fast mature spores released from the cyst. In scanning electron microscopy (SEM), the mature spore exhibited a semi-circular rim around the apical end and the orifice was covered internally with a flap. Loop-like filaments ornamentation was also identified from Urosporidium sp. in SEM, suggesting that Urosporidium sp. found in this study is a new member in the genus. Prevalence of Urosporidium sp.-infected trematodes in this study ranged from 2.5% to 24.0% in April 2010 and the infection was observed from 8 sampling sites out of the 26 sites surveyed on the west and south coasts.