FIG. 9.

Virulence of H3L⁻ mutant virus is attenuated in vivo. BALB/c mice were either mock infected or intranasally infected with WT or H3L⁻ mutant virus doses of 10⁷ PFU (A), 10⁶ PFU (B), and 10⁵ PFU (C) at day 0 as indicated in each graph. Body weight was measured on a daily basis. There were five mice per group. All (100%) of the mice infected with 10⁷ PFU of the WT virus 50% of mice infected with 10⁶ PFU of the WT virus died between 10 to 14 days p.i.