Comparison of the antiviral effect of solid-state copper and silver compounds.

Abstract Antiviral activities of insoluble solid-state and soluble ionic copper and silver compounds were evaluated against influenza A virus (A/PR8/H1N1) possessing a viral envelope and bacteriophage Qβ lacking an envelope. The viral solutions were exposed on glass samples uniformly loaded with copper and silver compounds. Exposure to solid-state cuprous oxide (Cu 2 O) efficiently inactivated both influenza A virus and bacteriophage Qβ, whereas solid-state cupric oxide (CuO) and silver sulfide (Ag 2 S) showed little antiviral activity. Copper ions from copper chloride (CuCl 2 ) had little effect on the activity of bacteriophage Qβ in spite of the fact that copper ions strongly inactivate influenza A in previous studies. Silver ions from silver nitrate (AgNO 3 ) and silver(I) oxide (Ag 2 O) in solution showed strong inactivation of influenza A and weak inactivation of bacteriophage Qβ. We also investigated the influence of the compounds on the function of two influenza viral proteins, hemagglutinin and neuraminidase. Silver ions from AgNO 3 and Ag 2 O remarkably decreased enzymatic activity of neuraminidase through the breakage of disulfide (S S) bonds, corresponding to the selective inactivation of influenza A virus. By contrast, exposure to Cu 2 O markedly reduced the activity of hemagglutinin rather than neuraminidase. These findings suggest that solid-state Cu 2 O disrupts host cell recognition by denaturing protein structures on viral surfaces, leading to the inactivation of viruses regardless of the presence of a viral envelope.