Figure 4

Vaccination and challenge strategies. A At 0 dpv, 4-week-old healthy pigs were inoculated with chimeric PRRSV rGD-SX-5U2 or with DMEM as a mock vaccination control. Then, the piglets immunized with rGD-SX-5U2 or DMEM were subjected to HP-PRRSV SD-YL1712 or NADC30-like PRRSV SX-YL1806 challenge at 42 dpv. Sera were collected at the indicated time points. All the piglets were euthanized at 63 dpv. B–G Temperature, average daily gain rate (ADG), PRRSV-N antibody level, virus-neutralizing antibody titre and virus load of the animal experiment. (B) Rectal temperature of pigs recorded every day. C Average daily gain rate of piglets measured weekly. D PRRSV-N protein-specific antibodies were measured weekly by a Porcine Reproductive and Respiratory Syndrome Virus AB Elisa Kit (JNT, China) according to the manufacturer’s instructions. E Viral neutralization properties of immune sera from 42 dpv. IFA was used to confirm the CPE induced by PRRSV. The absence of CPE at a 1:8 dilution was considered positive for the presence of PRRSV neutralization. Real-time qPCR was used to determine the viral load in the lung tissue (G) and serum (F). A recombinant plasmid containing the ORF7 gene of PRRSV was used to construct a standard curve. The number of PRRSV RNA copies was calculated according to the standard curve.