FIG. 8.
Virulence of recombinant VN/1203 viruses in chickens. (A and B) Groups of 10 6-week-old chickens were intravenously infected with 104 PFU of the VN/1203-WT, -ESEV, or -RSKV virus. (A) Percentages of birds surviving on days 1 to 3. (B) Calculated intravenous pathogenicity index (IVPI) for each virus. (C and D) Groups of five 6-week-old chickens were infected oronasally with 104 PFU of the WT, ESEV, or RSKV virus. (C) Percentages of chickens surviving during the course of the experiment. (D) Swab samples were collected daily and analyzed for viral RNA by real-time RT-PCR. OS, oropharyngeal swab; CS, cloacal swab. †, real-time RT-PCR results are presented as threshold cycle (CT) values as follows: /, >40; (+), >30 to 40; +, >25 to <30; ++, >20 to <25; +++, <20.