Fig 1.

Reduced clinical illness in H1N1pdm-infected newly weaned ferrets. Clinical signs of A/Mexico/4108/2009 (10⁶ EID₅₀)-infected young ferrets (n = 23, 5 to 8 weeks old) and adult ferrets (n = 18, 4 to 6 months old) were measured daily over 14 days p.i. Temperature (A) and weight (B) were recorded daily until the last day and are expressed as a percentage relative to the average preinfection level calculated from the values on days 0 and −1. As a control, the body weights of uninfected newly weaned ferrets (n = 13, 5 to 8 weeks old) were monitored for 15 days and represented as a percentage relative to the average baseline level calculated from the values for the first 2 days of observation after they were weaned from their mothers. (B) The inset x axis is defined as days postinfection/post-weaning day and the y axis as percent baseline weight (%). (C) Animals were evaluated daily for nasal discharge, sneezing, and inactivity level, and the highest percentages (and fractions [number of ferrets displaying symptoms/total number of ferrets tested]) of infected ferrets displaying symptoms are shown. The physical inactivity index measures the degree to which ferrets respond to environmental stimuli, with the basal level being 1.000. Error bars represent standard errors of the means. *, P < 0.05 by Student's t test comparing infected adult to infected young ferrets; **, P < 0.05 by Student's t test comparing uninfected to infected young ferrets.