Salt Treatment Confers Protection Against Acute Carp Edema Virus Reinfection While Promoting Viral Persistence

Area of Science:

• Aquatic animal health
• Virology
• Immunology

Background:

• Carp edema virus (CEV) causes koi sleepy disease (KSD) in common carp, leading to severe physiological distress.
• Salt treatment can restore osmoregulation and save affected fish, but the long-term immune status and viral shedding post-treatment remain unknown.
• Understanding the immune response is crucial for managing CEV in aquaculture and international trade.

Purpose of the Study:

• To investigate the physiological and immunological responses to Carp edema virus (CEV) in both naive and previously infected common carp.
• To determine if salt treatment confers immunity and to assess viral shedding in immunized fish.
• To evaluate the effectiveness of a primary infection followed by salt treatment as an immunization strategy against CEV.

Main Methods:

• Comparative analysis of physiological and immunological markers in naive and CEV-exposed carp.
• Histological examination of gill tissues to assess inflammation and leukocyte infiltration.
• Assessment of T and B lymphocyte responses, type I interferon activation, and antibody production.
• Monitoring of viral shedding in immunized fish after CEV challenge.

Main Results:

• Primary CEV infection causes gill inflammation and immunosuppression, impairing T and B lymphocyte responses.
• Salt treatment following primary infection mitigates pro-inflammatory responses and immunosuppression during reinfection.
• Immunization induces lymphocyte activation, differentiation, and antibody production, indicating an adaptive immune response.
• Despite adaptive immunity, immunized carp do not fully clear CEV, leading to prolonged viral shedding.

Conclusions:

• A primary CEV infection followed by salt treatment can establish a degree of protective immunity in common carp.
• Immunized fish mount an adaptive immune response but remain persistently infected and capable of shedding infectious CEV particles.
• The potential for viral shedding in immunized fish raises concerns for biosecurity in carp aquaculture and global fish trade.