Chemotaxis of Miamiensis avidus to hyaluronic acid, a component of fish surface mucus

Miamiensis avidus is a marine parasitic ciliate belonging to the order Scuticociliatida, the members of which are the causal agents of scuticociliatosis. This ciliate has resulted in considerable economic losses to the aquaculture industry in the Republic of Korea and Japan. Nevertheless, the development of vaccines and therapeutics has proven to be challenging, and there are currently no reports of such products commercially available in Korea or Japan. Furthermore, the aetiology and pathogenesis of M. avidus infection in fish remain unknown, as do the underlying reasons for the initial infection. Our goal was to investigate the mechanism of infection by examining the chemotactic response of M. avidus to fish tissues. We found that M. avidus exhibited a high degree of chemotaxis towards the tissues, blood, and surface mucus of the olive flounder (Paralichthys olivaceus) specimens used in the experiment. We analyzed the components of olive flounder surface mucus to determine the degree of chemotaxis induced by each component. Miamiensis avidus exhibited pronounced chemosensitivity to hyaluronic acid, one of the constituents. Given the nature of the surface mucus, it is plausible to suggest that it acts as a potent attractant for initial parasitism by scuticociliates.