Sensitivity test results of the PCR (A) and SYBR Green I RT-qPCR (B). M: DL2000 marker, 1: 2.78×107 copies; 2: 2.78×106 copies; 3: 2.78×105 copies; 4: 2.78×104 copies; 5: 2.78×103 copies; 6: 2.78×102 copies; 7: 2.78×101 copies; 8: 2.78×100 copies.