Project description:Infectious diseases among fish present an important economic burden for the aquaculture and fisheries industries around the world. For example, the infectious salmon anemia virus (ISAV) is known to infect farmed Atlantic salmon (Salmo salar), and results in millions of dollars of lost revenue to salmon farmers. Although improved management and husbandry practices over the last few years have minimized the losses and the number of outbreaks, the risk of new virulent isolates emerging is still a looming threat to the viability and sustainability of this industry. An understanding of the host-pathogen interactions at the molecular level during the course of an infection thus remains of strategic importance for the development of molecular tools and efficient vaccines capable of minimizing losses in the eventual case of a new outbreak. Using a 32 k cDNA microarray platform (cGRASP), we have studied various signaling pathways and immune regulated genes, activated or repressed, in Atlantic salmon head-kidney during the course of an ISAV infection. Gene expressions were measured at 5 different time-points: 6h, 24h, 3d, 7d and 16d post infection to get an overall view of changes as they occurred in time. The earliest time points showed only a few differentially expressed genes in infected fish, relative to controls, although as time progressed, many additional genes involved in key defense pathways were up-regulated including MHC type I, beta-2 microglobulin, TRIM 25 and CC-chemokine 19. During the latest stage of the infection process, many genes related to oxygen transportation were under-expressed, which correlates well with the anemia observed prior to death in Atlantic salmon infected with virulent strains of ISAV. Atlantic salmon smolts from 2 families of Atlantic salmon were IP injected with either 0.1mL of 10e5 TCID50 mL-1 of virus or 0.1mL of sham solution (L15 culture medium) and divided equally in four 1000 L tanks: 2 duplicate tanks containing ISAV injected fish and 2 duplicate control tanks containing sham solution injected fish. Four fish per family were sampled immediately prior to injection. An additional two fish per family per tank (four fish per family total) were sampled at 6h, 24h, 3d, 7d and 16d post injection. Head-kidney was dissected from each fish and used for microarray analysis. ISAV infected Atlantic salmon were compared to non-infected Atlantic salmon for each time-point.

Project description:Seventeen percent of aquaculture Atlantic salmon in Norway die after transfer from freshwater to seawater facilities, many from infectious disease. The degree to which these deaths are attributable to unseen weakness in smolt preparation is therefore an important concern. Strong evidence in mammals and supporting evidence in other teleosts show that the light environment shapes the immune response via entrainment of the circadian clock. These data are alarming as most smoltification protocols use constant light, which does not entrain the circadian clock and is associated with negative survival outcomes to disease challenge in other species. The goal of our study was to establish how different light environments affected the anti-viral immunity of Atlantic salmon smolts. To achieve this goal, we measured the transcriptional response of select type I and type II interferons and major histocompatibility complexes in the heart and head kidney following an intraperitoneal SAV3 viral challenge delivered under different lighting conditions. We began with two hypotheses. First, that compared with a regular light-dark cycle (long photoperiod; LP), constant light (LL) would have a weaker resistance to viral challenge in Atlantic salmon smolts. Second, that Atlantic salmon smolts kept in a regular light-dark cycle would have altered immune sensitivity between the light and dark phases. To test our first hypothesis, we photostimulated smoltification in parr through exposure to either LP or LL conditions for 6 weeks then challenged them by SAV3 infection. LP and LL groups showed indistinguishable measurements in classical smolt characteristics and comparable levels of SAV3 mRNA in the heart after 8 and 14 days post infection. They also showed comparable transcriptional responses of select type I interferons (IFNa, IFNb, IFNc) and both class I and class II major histocompatibility complexes (MHC I and MHC II) in both heart and head kidney tissue. IFNγ induction in the heart, however, was marked higher in the LL compared to the LP group. While this data suggests a heightened sensitivity of the LL group to SAV3 viral challenge, the consistent induction of MHC II, a key target gene of IFNγ signaling, to SAV3 infection in both LL and LP groups indicates that photoperiod may only have a minor impact on interferon regulation, rather than a more general influence on the viral immune response. To test our second hypothesis, we compared the transcriptomic response in the heart to SAV3 infection delivered either at the mid-light or mid-dark phase in the LP group. Both mid-light and mid-dark groups showed an upregulation of immune related genes and down-regulation of structural genes of mitochondria, but an analysis of the interaction between infection and time of day identified no differentially regulated genes. This second experiment suggests that, unlike in mammals, daily timing of viral infection may not play a major role in the immune response of Atlantic salmon.

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Salmo salar

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