DNA Vaccination in Farmed Fish with a Focus on Salmonid Alphavirus Infection in Atlantic Salmon (Salmo salar L.) in Norway.

Pancreas disease (PD), caused by Salmonid alphavirus (SAV), is a notifiable disease in Atlantic salmon (Salmo salar L.) in Norway. Conventional inactivated virus vaccines have shown variable effects in mitigating the disease, and a DNA vaccine has been used over the last 7-8 years, which may have resulted in the reduction in the number of reported PD cases. This manuscript provides a comprehensive overview of DNA vaccination in farmed fish, with a focus on the licensed DNA vaccine, Clynav®, against SAV3 infection. It explores the biological underpinnings of SAV infection, immune mechanisms activated by DNA vaccines, and the benefits and limitations of this approach. Although antigen processing and presentation mechanisms following DNA vaccination in fish remain incomplete, studies document robust innate responses and measurable adaptive immunity, including neutralizing antibodies, as seen in Clynav, and transcriptomic studies indicate that cell-mediated immunity is evoked under experimental conditions. Comparative trials demonstrate that DNA vaccination reduces viral load, tissue pathology, and, potentially, viral transmission, outperforming traditional oil-adjuvanted vaccines. Additionally, DNA-vaccinated fish show improved growth performance under field conditions. These findings support DNA vaccination as a promising strategy for controlling PD in salmon aquaculture, with implications for fish health, welfare, and sustainable production.