Figure 1.
Small plaque variants of Beij/89 show enhanced virulence for mice. (A) Replication of uncloned Beij/89 (Un) and plaque purified L, S or Mo viruses in mouse lung. Data shown represent virus titres in the lungs of 5 mice inoculated 3 days prior with 105 PFU of virus. Data was confirmed with 5 independent clones of L, S and Mo viruses. (B & C) Time course of virus titres recovered from the respiratory tract of mice following intranasal inoculation with 105 PFU of L, S or Mo viruses. Infectious virus present in (B) lung or (C) nasal tissues was determined at various times post-infection by plaque assay on MDCK cell monolayers. Virus titres are shown as the mean ± 1 SD of 5 mice. The dashed line represents the lower limit of detection of virus in each sample (2.1) and for statistical analysis samples with a value below the limit of detection were assigned an arbitrary value of 2.0. * = p < 0.01, Kruskal-Wallis test.