FIG. 5.
Lethal response and growth of recombinant viruses in mouse lungs. (A) Groups of five BALB/c mice were infected intranasally with 106 PFU each of the indicated recombinant viruses, and survival was monitored for 12 days. (B) Groups of three BALB/c mice were intranasally infected with 5 × 103 PFU of the recombinant viruses, and lungs were collected at 3 dpi for titration of infectious virus by a plaque assay. Values are shown as means with standard deviations, calculated per gram of lung tissue. All the mutants grew to significantly higher levels than the wt (indicated with an asterisk) (P < 0.05; t test).