Isolation and identification of infectious salmon anaemia virus (ISAV) from Coho salmon in Chile

The isolation of infectious salmon anaemia virus (ISAV) from asymptomatic w ild fish species including wild salmon, sea trout and eel established that wild fish can be a reservoir of ISAV for farmed Atlantic salmon. This repor t characterizes the biological properties of ISAV isolated from a disease o utbreak in farmed Coho salmon in Chile and compares it with ISAV isolated f rom farmed Atlantic salmon in Canada and Europe. The virus that was isolate d from Coho salmon tissues was initially detected with ISAV-specific RT-PCR (reverse transcription-polymerase chain reaction). The ability of the viru s to grow in cell culture was poor, as cytopathology was not always conspic uous and isolation required passage in the presence of trypsin. Virus repli cation in cell culture was detected by RT-PCR and IFAT (indirect fluorescen t antibody test), and the virus morphology was confirmed by positive staini ng electron microscopy. Further analysis of the Chilean virus revealed simi larities to Canadian ISAV isolates in their ability to grow in the CHSE-214 cell line and in viral protein profile. Sequence analysis of genome segmen t 2, which encodes the viral RNA polymerase PB1, and segment 8, which encod es the nonstructural proteins NS1 and NS2, showed the Chilean virus to be v ery similar to Canadian strains of ISAV. This high sequence similarity of I SAV strains of geographically distinct origins illustrates the highly conse rved nature of ISAV proteins PB1, NS1 and NS2 of ISAV. It is noteworthy tha t: ISAV was associated with disease outbreaks in farmed Coho salmon in Chil e without corresponding clinical disease in farmed Atlantic salmon, This ou tbreak, which produced high mortality in Coho salmon due to ISAV, is unique and may represent the introduction of the virus to a native wild fish popu lation or a new strain of ISAV.