“Emergence of serotype III in Miamiensis avidus: molecular identification and virulence in olive flounder (7297)”

Emergence of serotype III in Miamiensis avidus: molecular identification and virulence in olive flounder

Introduction: Miamiensis avidus is a highly pathogenic ciliate responsible for scuticociliatosis in olive flounder (Paralichthys olivaceus) in Korea and Japan. Current vaccines targeting serotypes I and II have shown limited effectiveness, probably due to the presence of uncharacterized serotypes.

Methodology: In this study, the BB19 strain was isolated from diseased olive flounder and identified as M. avidus via phylogenetic analysis of the cytochrome c oxidase subunit 1 (cox1) gene. Serotype-specific PCR, agglutination assays, indirect ELISA, and western blot analyses were performed to determine serotype and antigenic properties. Virulence was assessed through intraperitoneal challenge in olive flounder at different ciliate concentrations.

Results and Conclusions: BB19 was classified as cox1 genotype IV and identified as serotype III based on PCR results. Agglutination and ELISA confirmed that BB19 reacted exclusively with anti-serotype III sera (Mie0301 and BB19), without cross-reactivity to other serotypes. Western blotting revealed a unique 34 kDa antigenic protein in BB19, distinguishing it from the 30 kDa and 38 kDa proteins observed in other serotypes. In challenge tests, BB19 induced 65% cumulative mortality at a dose of 1 × 10⁵ cells/fish, similar to other virulent strains, confirming its high pathogenicity. This study reports the first isolation and characterization of serotype III of M. avidus in Korea. The distinct antigenicity and high virulence of the BB19 strain indicate that existing vaccines may not confer cross-protection. These findings highlight the need for continuous surveillance of emerging serotypes and support the development of multivalent vaccines for effective control of scuticociliatosis in olive flounder aquaculture.

1. JUNG, SUNG-JU, COONNAM NATIONAL UNIVERSITY, Presenter
2. KIM, JIN-YOUNG, CHONNAM NATIONAL UNIVERSITY, Author
3. KIM, JEONG-HOON, CHONNAM NATIONAL UNIVERSITY, Author