Figure 2: Respiratory droplet transmission of influenza virus between ferrets.

Four donor ferrets were infected with a total of 10⁴ PFU of a mixture of two viruses that differed by a single synonymous change at nucleotide 318 (A or U) in PB2 gene in the ratio 90% genotype A1:10% genotype A2. Four RD sentinel animals were exposed day 1 to day 12 by housing in cages adjacent to donor ferrets. Infectivity in nasal washes obtained on each day after infection of donor animals was titrated by plaque assay in MDCK cells and is plotted on left hand side y axis. Percent genotype A1 (red bars) or A2 (blue bars) was established by pyrosequencing RNA extracted from nasal wash and is plotted on right hand side y axis. The dotted lines indicate the limit of detection of pure genotype for the pyrosequencing assay, established as the mean minus 1.96 standard deviation of the mean of four independent measurements of pure genotype A1 or A2 virus.