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

Infectious salmon anaemia virus (ISAV) was isolated from farmed Atlantic salmon (Salmo salar) associated with an outbreak of haemorrhagic 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 confirmed as ISAV by an indirect fluorescent antibody test and by reverse transcriptase polymerase chain reaction. Atlantic salmon parr injected with ISAV from the SHK-1 line experienced significant reductions in haematocrits as early as 5 days 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 high mortality occurred in salmon parr injected with 10-fold dilutions of supernatant from ISAV-infected SHK-1 cultures. The ISAV was reisolated from 8 randomly selected salmon that died after experimental infection. Microscopic pathological changes among infected fish included congestion and necrosis, 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 pyloric caeca. The absence of microscopic lesions in the remaining experimentally infected fish could not be explained..