Infectious salmon anemia (ISA) caused by the infectious salmon anemia virus (ISAV) leads to disease outbreaks that entails considerable economic and welfare complications for Atlantic salmon farming .
This study examined the impact of vaccination and selective breeding on mortality and load of virus by assessing the susceptibility to ISA of two genetics groups (high and low resistant against ISAV ) of S. salar vaccinated with a commercial ISAV vaccine. Groups injected with a vaccine without the ISAV component, were included as a negative control. The fish were challenged by intraperitoneal (IP) injection or cohabitation . The evaluation of protection was assessed based on differences in specific accumulated mortality and viral loads between vaccinated and control groups and the different genetic groups.
The groups vaccinated with the ISAV component resulted in reduced mortality compared to the groups vaccinated without the ISAV component in both infection models , from above 72% mortality in groups vaccinated without the ISAV component to below 16% mortality in groups vaccinated with the ISAV component . There was a significant difference between the genetic groups vaccinated without the ISA component from the IP challenge (p-value = 0.001) , and an indication but not a significant contrast between groups from the cohabitation challenge (p-value = 0.085) . Based on the result comparisons of mortality in the different groups , additional analysis was performed to assess the viral load between groups using qPCR. There were significantly lower viral loads in the high-resistant genetic group compared to the low- resistant genetic group, both vaccinated with th e ISAV component, from the cohabitation challenge (p-value = 0.020).
The use of an ISAV component in vaccines for Atlantic salmon reduced mortality after challenge. The results also indicate that selective breeding for increas ed ISAV resistance leads to reduced mortality, and significantly reduced viral loads. Vaccination, as well as selective breeding leads to reduced mortality and viral loads, which could reduce viral shedding to the surroundings .