Synergistic effects of koi herpesvirus infection and nanoplastic exposure on the physiological and immune responses of koi carp.

Abstract

Polystyrene nanoparticles (PS-NPs), increasingly detected in freshwater environments, are emerging aquatic pollutants that may aggravate viral infections and pose risks to aquatic animal health. This study examined how PS-NPs interact with koi herpesvirus (KHV) to affect the physiology and immunity of koi carp (Cyprinus carpio), using both in vitro Cyprinid carp brain (CCB) cells and in vivo exposure. The results demonstrated that koi ingested PS-NPs in a dose-dependent manner. PS-NPs significantly enhanced KHV replication in both CCB cells and koi carp, increasing viral protein levels by 3-5-fold and viral gene expression by up to 8-10-fold compared with no PS-NPs. Key physiological indicators were altered: superoxide dismutase (SOD) activity and interleukin-1β (IL-1β) gene expression increased, type-I interferon (IFN-I) expression decreased, acid phosphatase (ACP) activity declined, and alkaline phosphatase (AKP) activity increased. These responses indicate that PS-NPs and KHV synergistically intensified oxidative stress, inflammation, and immune dysregulation. Additional changes in reactive oxygen species (ROS)-related and immune markers supported this effect. PS-NPs also disrupted gut microbiota composition, leading to dysbiosis that further weakened host immunity and facilitated viral infection. Overall, this study demonstrates that PS-NPs amplify the pathogenic effects of KHV and highlights their ecological risks to freshwater fish health.