Molecular pathology in ISAV infection

The current understanding on the pathogenesis and the mechanism of persistence of ISAV in fish is limited. Three permissive fish cell lines SHK-1, CHSE-214 and TO were used to determine if the cytopathic effect (CPE) observed in ISAV isolate NBISA01 and U5575-1 infection is due to apoptosis or necrosis. Apoptosis was observed only in SHK-1 and CHSE-214 infected cells with both isolates. TO cells infected by both isolates did not undergo apoptosis but showed damage characteristic of necrosis. These findings suggest that the mechanism of cell death during ISAV infection is dependent on the cell type. The TO cells were used to study the gene expression of ISAV using New Brunswick isolate-RPC-01-0593-01, Nova Scotia isolate-U5575-1 and Norwegian isolate 810/9/99 and in situ hybridization with ISAV segments 7 and 8 riboprobes. The difference in the frequency of hybridization signals between U5575-1 and the other two isolates was statistically significant (P=0.004), indicating that the pathology associated with ISAV infection in vivo may depend not only on infected cell types but also on the infecting ISAV isolate..