Review of Salmonid Alphavirus: Focus on Viral Survival, Shedding, Detection and Effects of Vaccination

ABSTRACT This review of salmonid alphavirus provides a collection of the most recent knowledge on the factors relevant for the transmission and control of the virus including updates on SAV survival, viral shedding, detection, and effects of vaccination as reported in peer‐reviewed literature, presentations, theses, and annual reports. SAV can survive in all water types, being the longest in colder marine waters without organic loading. The biophysical properties of SAV indicate a moderate to high robustness. The virus is shed from infected salmon in at least faeces and mucus. There is reduced viral shedding in SAV vaccinates compared to unvaccinated fish. Individual heart or mid‐kidney sampling is the fish tissues recommended for screening via RT‐qPCR. SAV can be detected in filtered farm water samples earlier than in monthly fish farm samples. However, detection in water does not necessarily mean that fish will become infected. Genomic surveillance in SAV outbreaks is recommended. Inactivated SAV vaccines have been reported to reduce the number of PD outbreaks, reduce mortalities in a PD outbreak, and reduce the percentage of discarded fish at harvest. DNA‐based vaccines have also shown good efficacy in terms of growth and mortality in natural PD outbreaks.