Fig. 9.
Repeated IFN treatment strongly inhibits an attenuated variant of R65 in chickens but is ineffective against wild-type R65. (A) Kinetics of disease development in IFN-treated (n = 6) and mock-treated (n = 6) birds following infection with 2 × 106 PFU of mutant virus R65-PR8(123). Animals were examined at 12-h intervals, and clinical scores were assigned as described in Materials and Methods. The graph depicts the median clinical scores of the groups. The asterisks indicate significant differences between groups (comparison of medians by Mann-Whitney U test or Wilcoxon signed-rank test; P < 0.05). (B) Viral titers in brain homogenates of birds infected with R65-PR8(123) at day 5.5 postinfection. (C) Kinetics of disease development in IFN-treated (n = 6) and mock-treated (n = 6) birds following infection with 2 × 106 PFU of R65-wt. The animals were examined at 12-h intervals, and clinical scores were assigned as described in Materials and Methods. The graph depicts the median clinical scores of the groups. The asterisk indicates a significant difference between groups. (D) Viral titers in brain homogenates of birds infected with R65-wt. The animals were killed when severely ill between days 2.5 and 3 postinfection. Each dot represents the result for one animal. The origin of the y axis was set to the detection limit of the titrations (101.9 FFU/brain).