To obtain standard curves for absolute quantification, the PCR product of HBoV was cloned into a plasmid vector pGEM®-T Easy Vector (Promega, Madison, WI, USA), purified using a QIAprep mini prep kit (Qiagen Inc., Valencia, CA, USA), and quantified using UV spectroscopy (1 genomic copy = 5 × 10 -12 µg). Serial 10-fold dilutions of the cloned plasmid were prepared to generate the standard curves.