Therapeutic potential of CpG-ODN 1668 against scuticociliatosis in olive flounder (Paralichthys olivaceus)

•Therapeutic potential of CpG-ODN 1668 against scuticociliatosis was evaluated.•Early treatment with CpG-ODN 1668 clearly increased survival rates of fish.•Therapy with CpG-ODN 1668 against scuticociliatosis was firstly demonstrated.

Scuticociliatosis caused by Miamiensis avidus is one of the major diseases in cultured olive flounder (Paralichthys olivaceus) in Korea. However, until recently, no effective chemotherapy or vaccine has been developed. Oligodeoxynucleotides containing unmethylated deoxycytidyl-deoxyguanosine motifs (CpG-ODNs) have been shown to be effective in enhancing innate immune responses and preventing infectious diseases in fish. However, it has not been experimented whether CpG-ODNs can be used as a therapeutic tool against infectious diseases in fish. In the present study, we evaluated the therapeutic potential of CpG-ODN 1668 against scuticociliatosis in olive flounder for the first time. The group of fish administered CpG-ODN 1668 at 3 days after the infection showed clearly higher survival rates than the groups of fish administered GpC-ODN 1720 or PBS, indicating a high therapeutic potential of CpG-ODN 1668 against scuticociliatosis. However, the treatment efficacy of CpG-ODN 1668 was diminished when administered at 6 days post-infection, and no treatment effect was found when administered at 9 days after the infection. These results suggest that early diagnosis through continuous monitoring and early treatment with CpG-ODN 1668 are essential for increase of treatment efficacy. In conclusion, the present study demonstrated for the first time the possible use of CpG-ODN 1668 in treatment of scuticociliatosis in olive flounder.