Exploring the molecular mechanism of nano-selenium against IHNV in rainbow trout: in vivo and in vitro studies.

Infectious hematopoietic necrosis virus (IHNV) causes devastating losses in salmonid aquaculture. Nano-selenium, a novel nanoscale form of elemental red selenium, has recently attracted significant attention due to its antiviral properties. In this study, we investigated the antiviral activity and molecular mechanisms of nano-selenium against IHNV using an in vitro rainbow trout hepatocyte model and an in vivo rainbow trout infection model. Our results demonstrated that nano-selenium interfered with IHNV adsorption and inhibited viral replication and release. Pre-incubation of hepatocytes with nano-selenium significantly upregulated the expression of selenium-related genes Gpx and Trx, enhancing cellular resistance to IHNV infection. In vivo experiments showed that dietary supplementation with nano-selenium increased the survival rate of rainbow trout following IHNV challenge. Moreover, nano-selenium enhanced the activities of serum antioxidant enzymes Gpx, SOD, CAT, ACP, and AKP, while reducing MDA levels, thereby improving the overall antioxidant capacity of the host. Histopathological analysis revealed that nano-selenium alleviated tissue damage in the head kidney and spleen of infected fish. Gene expression analysis further indicated that IHNV infection significantly induced the expression of interferons (IFN-1a, IFN-1b, IFN-γ1, IFN-γ2) and their downstream interferon-stimulated genes (VIG-1, VIG-2), as well as inflammatory cytokines (TNF-α, IL-1β). Dietary nano-selenium upregulated IFN-related gene expression while suppressing TNF-α and IL-1β expression. In conclusion, our findings suggest that nano-selenium exerts significant antiviral activity against IHNV by enhancing antioxidant defenses and modulating the innate immune response, highlighting its potential as a promising antiviral agent for IHNV control in aquaculture.