Fig.3 Result of mRNA RT-PCR amplification. A: 2PCV2b; B: 2PCV2b-6M; C: 2PCV2d; D: 2PCV2b-6M; M: DL 2000 Marker.
The real-time quantitative PCR result showed that the viral load of 2PCV2b group was similar to that of 2PCV2b-6M. However, the viral load of 2PCV2d-6M group was higher than that of 2PCV2d group, with significant difference (P <0.05). Similarly, 2PCV2b and 2PCV2b-6M are significantly higher than 2PCV2d (P <0.01) (Fig.4).The infectious titers for each virus at different time points were determined by IFA. The infectious titers increased from 24 to 72h but decreased from 72 to 84h for three viruses. By 72h post-infection, they have the highest viral titer. And the viral titer of mutant virus 2PCV2b and 2PCV2b-6M are highest of four viruses at 72h after infection (Fig.5).