Virulence of influenza viruses for C57BL/6 mice.

<p>Mice were infected with 10⁵ PFU of BJx109, HKx31 or PR8. (A) Weight loss. Mice were weighed daily and results expressed as mean percent weight change of each group (± SEM), compared to the weight immediately prior to infection. (B) Titres of virus in the lungs at day 5 post-infection. Lungs were removed and titres of infectious virus were determined in clarified homogenates by standard plaque assay. Data represent mean virus titres ± 1 SEM. The detection limit for the assay is indicated by the dotted line. Data shown are for groups of 5 mice and are representative of 2 or more independent experiments. * = virus titres from PR8-infected mice were significantly higher than those from HKx31-infected mice (p<0.001, one-way ANOVA).