Figure 1

Virulence of two strains of influenza A virus on mice. BALB/c mice were intranasally infected with 5 × 10⁵ p.f.u. dose of A/Beijing/501/2009 (H1N1) and A/PR/8/34 (H1N1) viruses. (A) Survival data and (B) Weight loss (C) Viral growth in the lung at different time points. Viral loads were determined in homogenates prepared from lungs at certain time points post-infection by real time RT-PCR test, and were expressed as viral RNA copies per miligram lung tissue. Mean viral load is representative of 5–6 mice lungs per time point group, and I bars indicated the standard deviations. The dotted lines were the control level. $ p < 0.05, compared among different time-points within BJ501 viruses infection, # compared among different time-points within PR8 viruses infection, *p < 0.05 and **p < 0.01, compared between BJ501 and PR8 infections at the same time-point.