Salmonid alphavirus infection in Atlantic salmon : viral properties and host responses to infection

• Main Author: Guo, Tz-Chun
• Other Authors: Evensen, Øystein, Haugland, Øyvind
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Norwegian University of Life Science, Ås 2017
• Subjects: Atlantic salmon
• Online Access: http://hdl.handle.net/11250/2447783

Pancreas disease (PD) is a contagious viral disease in salmonid aquaculture in Europe and North America. PD is caused by salmon pancreas disease virus also referred to as salmonid alphavirus (SAV), which belongs to the genus alphavirus within the family Togaviridae. Up to now, at least six subtypes of SAV have been reported. In Norway SAV3 was the only subtype detected in PD diseased fish, but from 2010, a marine variant of subtype 2 has been on an increase, particularly in the Møre and Romsdal and Sør-Trøndelag counties. A better understanding of host-pathogen interactions will provide the basis for improved disease control and vaccine development. Currently, there is one commercial vaccine licensed in Norway and UK/Ireland against PD, based on inactivated whole virus. The efficacy of the vaccine under field conditions has been questioned. In this thesis, the focus was first on the elicited immune response induced by SAV3 infection both in vivo and in vitro. Fish challenged in lab-experiments with SAV3 developed classical, pathological changes as seen under a natural infection. The sequence of pathological changes in the primary target organs, pancreas and subsequently heart, coincides with virus replication levels. Despite a strong innate immune response was detected in the affected organs, the virus infection progressed. The same phenomenon was observed when SAV3 was inoculated onto susceptible cell lines. However, when cells were pre-treated with recombinant IFN-α from 24 to 4 hours prior to infection, viral replication was halted, suggesting the timing of initiation of IFN system is imperative for the antiviral activity. The work was followed by the development of an infectious SAV3 cDNA clone by use of reverse genetics. The constructed cDNA clone containing the full-length genome can be manipulated by deletion, insertion or substitution via genetic engineering. This constitutes a powerful tool for studying viral pathogenesis and developing nucleic acid based vaccines. The recovery of recombinant SAV3 was ...