Proliferation of kuchijirosho causative agent in a fugu-derived cell line

Area of Science:

• Aquaculture
• Virology
• Fish Pathology

Background:

• Kuchijirosho is a fatal disease affecting farmed fugu (Takifugu rubripes).
• The infectious agent, though suspected to be a virus, remained unidentified due to the lack of a suitable cell line.
• Previous research indicated a filtrable agent, suggesting a viral etiology.

Purpose of the Study:

• To identify the causative agent of Kuchijirosho.
• To establish a permissive cell line for the Kuchijirosho-causing agent (KCA).
• To determine the genomic nature (RNA or DNA) of the KCA.

Main Methods:

• Inoculation of fugu brain extract onto a fugu eye cell line.
• Observation of cytopathic effects and confirmation of infectivity in fugu.
• Sodium iottalamate density gradient centrifugation to determine agent density.
• Application of nucleotide synthesis inhibitors (5-Fluorouracil, IUdR) to assess KCA genome type.

Main Results:

• Cytopathic effects were observed in fugu eye cells 7 days post-inoculation.
• Inoculated fugu developed Kuchijirosho, confirming the fugu eye cell line's ability to proliferate the KCA.
• The infectious fraction exhibited a density of 1.15 g/mL.
• 5-Fluorouracil, but not IUdR, inhibited KCA yield in a dose-dependent manner, indicating an RNA genome.

Conclusions:

• The fugu eye cell line is permissive to the Kuchijirosho-causing agent (KCA).
• The KCA is confirmed to be an RNA virus.
• This study provides the first identification and characterization of the KCA, crucial for understanding and managing Kuchijirosho in aquaculture.