The isolation of infectious salmon anaemia virus (ISAV) from asymptomatic wild fish species including wild salmon, sea trout and eel established that wild fish can be a reservoir of ISAV for farmed Atlantic salmon. This report characterizes the biological properties of ISAV isolated from a disease outbreak in farmed Coho salmon in Chile and compares it with ISAV isolated from farmed Atlantic salmon in Canada and Europe. The virus that was isolated from Coho salmon tissues was initially detected with ISAV-specific RT-PCR (reverse transcription-polymerase chain reaction). The ability of the virus to grow in cell culture was poor, as cytopathology was not always conspicuous and isolation required passage in the presence of trypsin. Virus replication in cell culture was detected by RT-PCR and IFAT (indirect fluorescent antibody test), and the virus morphology was confirmed by positive staining electron microscopy. Further analysis of the Chilean virus revealed similarities to Canadian ISAV isolates in their ability to grow in the CHSE-214 cell line and in viral protein profile. Sequence analysis of genome segment 2, which encodes the viral RNA polymerase PB1, and segment 8, which encodes the nonstructural proteins NS1 and NS2, showed the Chilean virus to be very similar to Canadian strains of ISAV. This high sequence similarity of ISAV strains of geographically distinct origins illustrates the highly conserved nature of ISAV proteins PB1, NS1 and NS2 of ISAV. It is noteworthy that ISAV was associated with disease outbreaks in farmed Coho salmon in Chile without corresponding clinical disease in farmed Atlantic salmon. This outbreak, 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 population or a new strain of ISAV. KEY WORDS: ISAV in Coho salmon · ISAV morphology · Immunoprecipitation of ISAV proteins Resale or republication not permitted without written consent of the publisherDis Aquat Org 45: [9][10][11][12][13][14][15][16][17][18] 2001 associated, resulting in focalized infection of the cell monolayer and slow development of CPE. ISAV isolates from Norway and Scotland, similar to the second Canadian group (the CHSE-negative phenotype), do not produce CPE in the CHSE-214 cell line. However, there are significant nucleotide and amino acid sequence differences between the European and Canadian isolates on RNA segments 2 and 8 (Blake et al. 1999), and the European isolates could be differentiated from Canadian isolates by reverse transcriptionpolymerase chain reaction (RT-PCR) and restriction fragment length polymorphism (RFLP) on RNA segment 2 (Kibenge et al. 2000).The present study characterizes an orthomyxo-like virus isolated from farmed Coho salmon Oncorhynchus kisutch in Chile, with clinical disease. While erythrocytic inclusion body syndrome virus (EIBSV) was detected in one fish sample, the orthomyxo-like virus was found in several fish tissue pools from the affected farms. The virus was biologically chara...