Chitosan-selenium nanoparticles suppress infectious spleen and kidney necrosis virus through immune modulation and viral replication inhibition in zebrafish (Danio rerio).

Infectious spleen and kidney necrosis virus (ISKNV) is one of the most challenging diseases causing substantial financial losses in global aquaculture. However, effective strategies for controlling ISKNV infections in ornamental fish are lacking. In this study, chitosan-selenium nanoparticles (CTS-SeNPs) were synthesized and evaluated as potential strategies for controlling ISKNV infection. The characterization of CTS-SeNPs confirmed the conjugation of chitosan with SeNPs, resulting in the formation of spherical particles with an average size of 51.73 nm and exhibiting moderate stability. Furthermore, the morphology and stability were retained for 24 h in the freshwater environment. The CTS-SeNPs exhibited viral suppression efficacy at 40 μg/mL, downregulating major capsid protein gene expression in ISKNV-infected dwarf gourami fin (DGF) cells. The inhibition rates at 48 and 72 hpi in the DGF cells were 94.02 ± 0.39 % and 91.82 ± 3.84 %, respectively. During the ISKNV replication cycle, CTS-SeNPs were found to affect the attachment and replication stage. In zebrafish, the viral suppression efficacy of CTS-SeNPs was evaluated by two different administration methods: intraperitoneal injection (IP) and immersion administration (IM). At safe concentrations (1 μg/mL for IP and 40 μg/mL for IM), CTS-SeNPs demonstrated improved survival rates of 53.33 ± 9.42 % (IP) and 50.00 ± 8.16 % (IM). Additionally, viral loads in survivors were lower than those in ISKNV-infected fish. In terms of immune gene expression, CTS-SeNPs upregulated interferon-inducible genes. Moreover, after ISKNV infection following CTS-SeNPs administration, type I interferon induction (interferon φ2 and interferon φ3) was identified, suggesting that CTS-SeNPs enhance viral suppression through immune modulation, indicating their potential as effective anti-ISKNV agents.