FIG 6.

Pathogenicity of H9N2 mutant viruses in mice. Five BALB/c mice per group were inoculated with 10⁶ TCID₅₀ of the indicated viruses or mock infected with PBS. (A) Survival rate of mice. Mice that lost >30% of their baseline weight were euthanized. (B) Body weight changes of mice. The values represent the average body weights compared to the baseline weight ± standard deviations from five mice. (C) Hematoxylin- and eosin-stained lung sections from mice infected with the indicated viruses at 5 dpi. Bar, 200 μm.