Metagenomic and Pathogenic Assessments Identify a Pathogenic Porcine Reproductive and Respiratory Syndrome Virus 1 with New Deletions from Adult Slaughter Pig in 2022

Abstract

Since we first reported porcine reproductive and respiratory syndrome virus 1 (PRRSV1) wild type strains in mainland China in 2011, PRRSV1 infection has been detected in more than 20 provinces in China. During the routine investigation of PRRSV1 epidemiology in 2022, we isolated a novel PRRSV1 strain (SD1291) from an adult slaughter pig in Linyi, Shandong Province. The SD1291 could only be isolated with primary alveolar macrophages (PAMs), not with Marc-145 cells. In addition, the 2022 SD1291 isolate has higher in vitro replication efficacy than the 2014 PRRSV1 HLJB1 isolate in PAMs. Due to high genetic variation, the complete genome of SD1291 was determined by metagenomic sequencing, which showed that SD1291 shares the highest genome similarity (88.12%) with the PRRSV1 HeB47 isolate. Sequence alignment results identified a four-amino-acid deletion in nsp2 and a five-amino-acid deletion in the GP3 and GP4 overlap region of SD1291. A complete-genome-based phylogenetic tree showed that SD1291 is grouped with BJEU06-1-like PRRSV1 isolates. A piglets’ challenge study showed that SD1291 can cause high fever (the highest is 41°C), reduced weight gain, mild lung consolidation, and interstitial pneumonia indicating that SD1291 is a pathogenic PRRSV1 isolate. Overall, this study first identified a novel pathogenic PRRSV1 isolate from an adult slaughter pig in China. Our findings also suggested that new PRRSV1 variants could escape the current PRRSV vaccination system and circulate in adult swine herds, which deserve more attention.

A chimeric porcine reproductive and respiratory syndrome virus 1 strain containing synthetic ORF2-6 genes can trigger T follicular helper cell and heterologous neutralizing antibody responses and confer enhanced cross-protection

“…SD1291 is a virulent PRRSV1 strain isolated from Shandong Province in 2022 [ 8 ]. HLJB1 is a low-virulence PRRSV1 strain isolated from Heilongjiang Province, China, in 2014 [ 6 ].…”

“…The sera collected at 0 dpi, 42 dpi (0 days post-challenge (dpc)) and 63 dpi (21 dpc) were also used for virus neutralization tests against HLJB1 and SD1291, as previously described [ 19 , 32 ]. All the pigs were euthanized at 21 dpc, and tissue samples were collected and utilized for histopathological examination [ 8 ]. The gross pathologies of the lungs and lymph nodes were scored in a blinded fashion according to previously described methods [ 33 – 35 ].…”

“…An epidemiological study indicated that the PRRSV1 infection rate reached 24.8% on 50 farms in Guangdong Province [ 7 ]. Currently, PRRSV1 infection has been identified in more than 20 provinces [ 8 ]. The PRRSV1 SC2020-1 isolate was associated with a 15% abortion rate on a farm in Sichuan Province [ 9 ].…”

“…The PRRSV1 SC2020-1 isolate was associated with a 15% abortion rate on a farm in Sichuan Province [ 9 ]. More importantly, recent Chinese PRRSV1 isolates (ZD-1, SD1291 and 181,187-2) have been determined to be virulent [ 8 , 10 , 11 ]. However, no specific PRRSV1 vaccine is available in China [ 12 ].…”

“…All commercial PRRSV-modified live vaccines (MLVs) are developed using Marc-145-adapted PRRSV strains. However, all Chinese PRRSV1 field isolates (in addition to PRRSV1 MLV-derived isolates) can be isolated from PAMs but cannot adapt to Marc-145 cells [ 5 , 6 , 8 , 10 , 11 , 15 ], which represents another obstacle to developing a Chinese PRRSV1-specific vaccine.…”