Pathogenesis of infectious salmon anaemia virus (ISAV) in rainbow trout (Oncorhynchus mykiss)

The first objective of this thesis was to detail the pathology of ISAV-induced lesions in rainbow trout (Oncorhynchus mykiss) as compared to Atlantic salmon (Salmo salar) and to quantify the relative susceptibility of rainbow trout to clinical ISA disease. The virus infection in the two species demonstrated different mortality patterns and pathology characteristics. Atlantic salmon showed a typical acute mortality pattern peaking at 8-16 days post-infection (dpi) depending on virus dose, whereas in rainbow trout, only the highest virus dose (107.13-7.8 TCID 50/200mul) showed a similar pattern. The middle (104.13 TCID50/200mul) and lowest virus doses (102.13 TCID50/200mul) in rainbow trout induced only sporadic protracted mortality, lasting up to 46 dpi. Infected rainbow trout that were live-sampled and those that died, demonstrated increased erythrophagia, clusters of cellular degeneration in the haematopoietic portion of the kidney, and occasionally myocarditis. These lesions are very different from the typical necrosis in liver and kidney that occur in infected Atlantic salmon, and were indicative of an antiviral response by a host with some immunity to the ISAV infection.;The third objective of this research was to use an in situ hybridization protocol which had been previously optimized for ISAV-infected Atlantic salmon (Moneke et al., 2003) and apply it to post-challenge rainbow trout tissues to determine the viral target cell and tissue distribution in this more resistant species. This work indicated a comparable tropism in both species, with endothelial cells, subendothelial macrophages and leucocytes being the predominant host cells.;The final objective was to use real time RT-PCR on the tissues of rainbow trout survivors of ISAV experimental infection to assess potential viral persistence and contribute to increasing knowledge of the pathogenesis of ISAV. Samples taken from rainbow trout 63 day after experimental infection with ISAV were found positive by this method, indicating the potential for a prolonged carrier state in rainbow trout.;The second objective was to assess the influence of cell line in the propagation of the viral inoculum. The pilot work had virus grown in the TO cell line, derived from Atlantic salmon head kidneys. It was hypothesized that propagating inoculum in a cell line derived from an Oncorhynchus sp. might increase viral pathogenicity in rainbow trout. Survival analysis failed to demonstrate a cell line influence on viral inoculum virulence.