FIG 2.
Serially egg-passaged M41-CK lineages are attenuated in vivo. Viral pathogenicity was assessed in a series of three separate animal studies. Assessment of lineages A and C was performed in separate investigations, while lineages A1 and D were assessed in a joint study. For each group (n = 12), 8-day-old SPF chicks were inoculated with 1 × 105 PFU of each virus via the ocular and nasal routes. Clinical signs, including snicks per bird per minute (A) and rales (B), were recorded daily from days 3 to 7 postinfection. (C) Ciliary activity was assessed by observation of 10 tracheal cross sections (rings) from three randomly selected birds per group on days 4 and 6 postinfection. The mean ciliary activity of these three birds is plotted, with SEM plotted as error bars. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ****, P < 0.0001. (D) Detection of IBV in trachea by using PCR or qPCR methods.