Safeguarding Atlantic salmon: A non-invasive approach to assess viral disease dynamics, surveillance methods and effect of control measures

Viruses that spread through water represent a major threat to fish health. For many viruses, understanding the interplay between viruses, host and environment presents a major hurdle for the spreading. Infectious salmon anemia virus (ISAV) and Salmonid alphavirus (SAV) both cause notifiable diseases that cause serious losses to the Norwegian salmon industry. Both viruses can infect and cause disease in farmed salmonids in seawater. During infection, the viruses are excreted from infected fish to the water. The project SAFEGUARD have established new tools which can be used for disease surveillance, as well as to study how these viruses can spread in Atlantic salmon farms. Method: The study is carried out by taking seawater samples from Atlantic salmon farms, concentrating the seawater by means of adsorption to and elution from charged filters, and then analyze the concentrate for the presence of the virus that cause disease, using quantitative RT-qPCR. Results: With funding from the Research Council of Norway (SAFEGUARD project), we have developed an alternative method for detecting these two important pathogenic viruses (ISAV and SAV) directly in water samples taken in facilities holding infected fish. This simple and effective method has been optimized in laboratory studies, infection trials and field trials, and has now been published in five international scientific journals. It is gratifying to experience that the idea could be realized. We hope that the results will provide important information that is relevant for the development of improved monitoring methods, infection models and control strategies for infectious diseases, all of which are important tools in the work for better fish health. Another success of this research work is that it will lead to a reduction and replacement of sacrificing live fish for the purpose of examination of the presence of the virus during disease surveillance, as only seawater from the fish farms will be used.

The study has resulted in the development of alternative test strategies, which employs the concept of 3R; replace, reduce and refine, and this will have significant impact on the use of fish for validation of new procedures/test in future.

Disease surveillance, transmission models for spread of infections, and disease control strategies are important tools in fish health management. The SAFEGUARD project aims at developing novel approaches for assessing the impact of viral disease dynamics, transmission and spread in Atlantic salmon farms, which can replace the unfortunate use of live fish, thus satisfying the 3R requirements relating to experimental animals: replace, reduce and refine. SAFEGUARD will follow three mutually supporting lines of work. The first will study infectious disease dynamics and spread within and between fish populations, entirely by-passing the need for fish (non-invasive strategies). The second will use the non-invasive strategiy to distinguish between "live" and "dead" viruses for the purpose of improving the surveillance of farms for specific viral agents. The third line will assess the impact and effectiveness of control strategies and methods, such as cleaning and disinfection routines, and the effect of fallowing of farm sites after disease outbreaks. Application of non-invasive strategies will help fish health management in two ways. First, it will provide tools for fish disease control and fish welfare; and contribute to SAFEGUARD and strengthen the Atlantic salmon industry. Secondly, it will reduce or eliminate the use of live fish for the purpose of testing for virus detection. SAFEGUARD will focus on two important fish viruses, Infectious salmon anaemia virus (ISAV) and Salmonid alphavirus (SAV), which are both notifiable pathogens and are known to Norwegian Atlantic salmon farms. For each of the pathogens, mode of disease dynamics, virus transmission and spread in fish farms are not very well understood, partly due to limitations in reliable study tools. By developing new approach for assessing the impact of viral disease dynamics, transmission and spread in Atlantic salmon, SAFEGUARD will provide early warning systems and contribute to providing sustainable fish hea