Virulence and pathogenicity of infectious salmon anemia virus isolated from farmed salmon in Atlantic Canada

Infectious salmon anemia virus (ISAV) was isolated from farmed Atlantic sal mon Salmo salar associated with an outbreak of hemorrhagic kidney syndrome in the Bay of Fundy, Canada. The virus induced cytopathic effects in salmon head kidney cell line SHK-1 from Atlantic salmon and was positively confir med as ISAV by an indirect fluorescent antibody test and by reverse transcr iptase polymerase chain reaction. Atlantic salmon parr injected with ISAV f rom the SHK-1 line experienced significant reductions in hematocrits as ear ly as 5 d postinfection (DPI). Mortality began 17 DPI and reached 76% by 24 DPI at a water temperature of 11 degrees C. In a second trial, similarly h igh mortality occurred in salmon parr injected with 10-fold dilutions of su pernatant from ISAV-infected SHK-1 cultures. The ISAV was reisolated from e ight randomly selected salmon that died after experimental infection. Micro scopic pathological changes among infected fish included congestion and nec rosis; seen in the livers from 7 of 19 samples and in the kidney from 1 of 18 salmon examined. Other tissues affected included gill, intestine, and py loric caeca. The absence of microscopic lesions in the remaining experiment ally infected fish could not be explained. Further studies are therefore ne eded to better understand the factors contributing to pathological changes after natural or experimental infection.