Transmission routes and infection dynamics of salmonid alphavirus (SAV)

PD is an important cause of losses in salmonid aquaculture in Norway and has become a severe threat to the economy of the industry. Little is known about how the causal agent, SAV, is dispersed within and between sites. Knowledge about this will have larg e impact on the choice of strategies for mitigation of PD. Also, there is a need for more thorough studies on transmission routes of SAV. The proposed project will therefore focus on the relative importance of vertical and horizontal transmission, surviva l of the virus, and the dynamics of infection within and between fish populations.Vertical transmission will be investigated in an infection experiment, which was started in 2007. Fertilised eggs from naturally infected brood fish were subjected to differ ent disinfection regimes. Also, eggs and sperm from non-infected fish were bath challenge with SAV 3. Further, the potential for horizontal transmission under natural conditions will be studied. In the first part of this work, laboratory studies to invest igate the survival of SAV 3 under conditions relevant to persistence and spread in non-sterile seawater will be performed. We will also perform an infection experiment to test the potential for horizontal transmission under various conditions. Models of h orizontal transmission are used to explore how an infection spreads within and between sites and describe the driving forces in virus dispersal. Sites suspected to be at high risk of contracting SAV 3 infection will be monitored for SAV 3. A model will be used to increase the accuracy of a stochastic dispersal model. Transmission of SAV between farms will be investigated in a 3D-hydrophysical model developed by NIVA. The established characteristics of SAV survival in seawater in the proposed project will be used to predict how far a ?package of SAV? will reach at different time intervals and with varying environmental conditions.