Comparison of replication and cytopathic effect in MDCK cells. (A) MDCK cells were infected with H5N1 viruses at MOI 1, and the copy numbers of viral RNA in the medium were measured by real-time PCR 24, 48, and 72 hours p.i. (B) Cytopathic effect on MDCK cells 24 hours p.i. Mock-infected cells were used as the negative control. (C) Plaques on MDCK cells infected with SP83 and KAN353 72 hours p.i.