3.3 Growth characteristics of YNG strain comparing with other variant strains
One-step growth curve experiment, CPE observation, and TCID50 assay were conducted to analyze the growth characteristics of these PRV strains aforementioned in PK15 and Vero cells, with YNG strain as the control. The viral copies were determined according to the standard curve: lg [virus copies] = -0.2293x+9.832, r2=0.9963. As shown in Fig. 3 , YNG strain exhibited a similar growth curve as that of YNP strain both in PK15 and Vero cells. The virus titers of YNG and YNP strains in PK15 and Vero cells at the 36 hpi were 107.14, 106.88 and 106.80, 106.75TCID50/mL, respectively (Fig. 3 ). Likewise, there was no obvious difference of CPEs in PK15 and Vero cells triggered by distinct PRV strains, suggesting that YNG strain should be a PRV variant.