Figure 1. Detection of porcine circovirus 1 (PCV1), porcine circovirus 2 (PCV2), and porcine parvovirus (PPV) in formalin-fixed, paraffin-embedded lymph-node tissue by multiplex nested polymerase chain reaction (PCR). Lane M: 100 base-pair (bp) DNA ladder; lane 1: positive control for PCV1; lane 2: positive control for PCV2; lane 3: positive control for PPV; lane 4: negative control; lane 5: positive results for the 3 viruses in tissues from pigs experimentally co-infected with the 3 viruses; lane 6: positive results for the 3 viruses in tissues from pigs naturally co-infected with the 3 viruses.