Basic studies of epithelial responses in the context of gill proliferative disease in Atlantic salmon.

Proliferative gill diseases (PGDs) is a major challenge for the fish farming industry. Different agents are associated with PGD and a main host response is an exaggerated increase of epithelial cells, which cause respiratory distress. Poxvirus has been reported in gills of salmon with PGD and may play a role in the development of the disease. In addition, many agents associated with PGD infect epithelial cells and have not been cultured, making controlled challenge experiments difficult. Therefore, the overall objective of this project is to get basic knowledge about gill epithelial cells with a special emphasis on infectious agents infecting these cells. To comply with this overall goal, we wanted to establish cell lines from salmon gills and investigate functional aspects with regard to permissiveness for virus infections and epithelial cell proliferation. Further, we wanted to identify and characterize the genome from poxvirus of salmon and characterize responses in salmon gills infected with poxvirus. We have now generated two cell lines from salmon gills and both are permissive to a number of virus and may represent important tools to cultivate other agents infecting gills and to generate more knowledge about gill cell biology. Further we have characterized the first genome sequence of a poxvirus infecting fish, namely Atlantic salmon, and demonstrated that the virus is associated with disease not only in all types of smolt farms, but also in salmon months after sea transfer.

Proliferative gill diseases (PGDs) is a major challenge in Atlantic salmon farming. Many microorganisms have been found in diseased gills. The main host response is an overgrowth of the gill surface cells to an extent that cause respiratory difficulties. In other words an important part of the disease problem in PGDs is an inappropriate host response. Research efforts have so far focused on detection of microorganisms and description of disease changes. The main objective of this project is to increase th e understanding of the surface cell host response in PGDs. A laboratory model with the cells in question will be established and characterized. Different growth stimuli and signals suspected to cause the overgrowth will be characterized and tested, also w ith regard to inhibition. This may open up new therapeutic possibilities for modulation of host response to avoid the respiratory difficulties by surface cell overgrowth. The focus is on the basic mechanisms leading to the observed cell overgrowth. Severa l microorganisms associated with PGD have not been isolated in pure culture. This is an important prerequisite for controlled challenge experiments to test the importance of the microorganisms for disease. A subgoal of the project is thus to explore if th e establishment of a cell culture as above also can be used to isolate microorganisms which have not been possible to cultivate so far.