FIGURE 4.

Acquisition of the internal gene constellation of H7N9 virus resulted in enhanced pathogenicity and replication of H9N2 virus in mouse. Mice were intranasally inoculated with a single dose of 10⁶ EID₅₀ of the parental H9N2 CK/F98 virus or the CK/F98-4664Int virus with the six internal genes derived from H7N9 SH/4664 virus. (A) Weight loss during a 14-day observation period. (B) Survival curve during a 14-day-observation period. Mice that lost >25% of their pre-inoculated weight were regarded as dead and euthanized. (C) Virus titers in animal lungs, as determined by EID50 using MDCK cells. (D) Virus titers in animal nasal turbinates, as determined by EID50 using MDCK cells. n = 3 for each group. Data are expressed as mean ± SEM. P < 0.05, **P < 0.01, and ***P < 0.001 by one-way ANOVA.