Experimental infection with salmonid Alphavirus (SAV) usually induces no mortality in Atlantic salmon and the development and registration of PD vaccines has been hampered by the lack of a reproducible challenge model for PD. Intraperitoneal injection (IP) of pre-smolts with new virulent SAV isolates has induced severe histopathological lesions in heart tissue.
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| Severe epicarditis and myocardial necrosis (Score 4) @ 3 weeks post challenge |
A challenge model using three different test parameters post challenge with IP injection of this SAV3 isolate has been developed. The methods used are detection of live virus (titration in cell culture and specific verification by ELISA), viral RNA in serum (real time PCR) and examination and scoring of histopathological lesions in heart tissue (Figure 1). Efficacy testing of inactivated whole virus vaccine showed a significantly lower concentration of live virus and viral RNA in serum 1 week post challenge for the vaccinated group compared with the non-vaccinated group. No PD-related histopathological lesions were detected in heart tissue 3 weeks post challenge (wpc) for the vaccinated group while severe lesions were observed in the non-vaccinated group. This model can now be used to optimise potential PD vaccines. A wide ranging programme covering advances in knowledge of IPN, VHS, ISA, Ranaviruses and Cyprinid herpes virus was presented.
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