PCR products using (A) primer set FP9orf176 showing 240 bp expected band, whereby lanes (1) Negative control; (2) Positive control from original stock; (3) First CEF passage of WT FWPV infection; (4) Second CEF passage of WT FWPV infection; (5) Third CEF passage of WT FWPV infection; (6) First CEF passage of rFWPV-H5 infection; (7) Second CEF passage of rFWPV-H5; (8) Third CEF passage of rFWPV-H5; and (B) primer set H5 showing 1.7 kb expected band, whereby lanes (1) First CEF passage of rFWPV-H5 infection; (2) Second CEF passage of rFWPV-H5 infection; (3) Third CEF passage of rFWPV-H5 infection; M are ExactMark 100 bp or 1 kb DNA ladder marker, respectively (Base Asia). The DNA bands were observed in 1% (w/v) agarose gel.