As shown in Figure 1B , the effect of SD/09 viral infection on lung wet:dry weight ratio did not change significantly within 2 days p.i. However, a dramatic increase was observed from day 4 p.i., and reached a peak on day 8 p.i., which was nearly twice that observed in control group lungs (p,0.01). The change in lung wet weight:body weight ratio was similar to the change in lung wet:dry weight ratio ( Figure 1C ). The results indicated that the SD/09 virus could induce acute lung edema in mice.