Figure 5. Replication of influenza viruses in vivo. To evaluate pathogenicity in mice, 6- to 8-week-old BALB/c mice (n = 11 mice/group/experiment) were infected with 105 50% tissue culture infectious dose (TCID50) units of the indicated viruses and weight loss was monitored for 14 days postinfection (dpi) (A). At 3 dpi and 6 dpi, lungs (B) and nasal washes (C) were collected from 3 mice/group and viral titers were determined by TCID50 analysis. Data are presented as mean ± SEM. *p<0.05 versus sw/Chile virus.