Abstract
While coâinfections are common in both wild and cultured fish, knowledge of the interactive effects of multiple pathogens on host physiology, gene expression and immune response is limited. To evaluate the impact of coâinfection on host survival, physiology and gene expression, sockeye salmon Oncorhynchus nerka smolts were infected with the salmon louse Lepeophtheirus salmonis (Vâ/SL+), infectious hematopoietic necrosis virus (IHNV; V+/SLâ), both (V+/SL+), or neither (Vâ/SLâ). Survival in the V+/SL+ group was significantly lower than the Vâ/SLâ and Vâ/SL+ groups (p = 0.024). Coâinfected salmon had elevated osmoregulatory indicators and lowered haematocrit values as compared to the uninfected control. Expression of 12 genes associated with the host immune response was analysed in anterior kidney and skin. The only evidence of L. salmonisâinduced modulation of the host antiviral response was downâregulation of mhc I although the possibility of modulation cannot be ruled out for mxâ1 and rsad2. Coâinfection did not influence the expression of genes associated with the host response to L. salmonis. Therefore, we conclude that the reduced survival in coâinfected sockeye salmon resulted from the osmoregulatory consequences of the sea lice infections which were amplified due to infection with IHNV.
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