Optimization of PCR using individual tissue DNA with individual multiplex PCR primers. Lanes: 1, 1-kb DNA ladder; 2, ALV-positive cell culture DNA showing an amplicon size of 613 bp with p27 gene primers; 3, MDV-positive cell culture DNA showing an amplicon size of 856 bp with meq gene primers; 4, β-actin gene-specific primers used as internal control showing an amplicon size of 396 bp in CEF cell culture DNA; 5, REV-positive cell culture DNA showing an amplicon size of 204 bp with LTR sequence-specific primers.