SELECTIVE PRECIPITATION REACTION: A NOVEL DIAGNOSTIC TEST FOR TISSUE PATHOLOGIY IN ATLANTIC SALMON (Salmo salar) INFECTED WITH SALMONID ALPHAVIRUS (SAV3)

While investigating biomarkers for infection with salmonid alphavirus (SAV), the cause of pancreas disease (PD), a selective precipitation reaction (SPR) has been discovered in serum which could be an on-farm qualitative test and an in-laboratory quantitative assay for health assessments in aquaculture. Mixing serum from Atlantic salmon, Salmo salar, with SAV infection with a sodium acetate buffer caused a visible precipitation which does not occur with serum from healthy salmon. Proteomic examination of the precipitate has revealed that the components are a mix of muscle proteins, for example enolase and aldolase, along with serum protein such as serotransferrin and complement C9. The assay has been optimized for molarity, pH, temperature and wavelength so that the precipitation can be measured as the change in optical density at 340 nm (Δ₃₄₀). Application of the SPR assay to serum samples from a cohabitation trial of SAV infection in salmon showed that the Δ₃₄₀ in infected fish rose from undetectable to a maximum at 6 weeks post-infection correlating with histopathological score of pancreas, heart and muscle damage.

Through manipulation of protein stabilities in aqueous solutions a novel diagnostic tool has been identified in identifying the pathological damage elicited during pancreas disease (PD) in Atlantic salmon. This novel assay destabilises proteins, which during homeostasis are intracellular, from plasma/ serum samples thus serving as a useful non-destructive health screening tool. The assay has potential platforms as a quantitative in lab (Figure 1) and qualitative point of care (Figure 2) test. The cause of this differential precipitation reaction has been found through proteomic investigation to be due to the difference in stabilities to normal circulatory proteins and that of intra-cellular and some immune response proteins. This study details the discovery, optimisation, application, and potential for this novel assay.