A Novel Attenuated NADC30-Like PRRSV Vaccine Candidate Provides Cross-Protection Against Homologous and Heterologous...

Porcine reproductive and respiratory syndrome (PRRS) virus (PRRSV) is one of the major pathogens threatening the global swine industry and causes enormous economic losses annually. Vaccination remains one of the most important strategies for the prevention and control of PRRSV infection. In this study, a novel genotype 2 NADC30-like PRRSV strain, designated AHFY, was isolated and characterized from eastern China. Phylogenetic analysis revealed that strain AHFY belonged to sublineage 1.8. An attenuated strain, AHFY-F140, was obtained through 140 serial passages in MARC-145 cells. Genomic sequence comparison between AHFY-F140 and the parental strain AHFY-F1 identified two discontinuous amino acid (aa) deletions in the nonstructural protein 2 (NSP2) gene, spanning residues 355-364 and 391-583, which were first detected at passage 90 and persisted through passage 140. The viral titer gradually increased with passaging, rising from 10^4.3 TCID₅₀/mL for the parental strain AHFY-F1 to 10^8.7 TCID₅₀/mL for AHFY-F140. A pathogenicity evaluation was conducted in 4-week-old PRRSV-free New American Line piglets using AHFY-F1 and AHFY-F140. Piglets inoculated with AHFY-F1 developed persistent fever and obvious respiratory clinical signs, accompanied by severe and typical histopathological lung lesions. In contrast, piglets inoculated with AHFY-F140 showed no fever or other clinical signs. PRRSV-specific antibodies became positive at 11 days postinoculation (dpi) in AHFY-F140-inoculated piglets, which was later than the 7 dpi observed in AHFY-F1-inoculated piglets. Furthermore, immunization with AHFY-F140 provided robust protection against subsequent challenge with either the parental strain AHFY-F1 or the highly pathogenic PRRSV (HP-PRRSV) strain JXA1 (lineage 8). Collectively, these findings demonstrate that the attenuated strain AHFY-F140 represents a promising vaccine candidate against both NADC30-like and JXA1-like PRRSV infections.