Isolation and characterization of Chinese porcine epidemic diarrhea virus with novel mutations and deletions in the S gene.

Porcine epidemic diarrhea (PEDV) has raised growing concerns in the pig-breeding industry because it has caused significant economic losses. To better understand the molecular epidemiology and genetic diversity of PEDV field isolates, in this study, the complete spike (S) and ORF3 genes of 17 PEDV variants in Zhejiang, China during 2014 to 2017, were characterized and analyzed. Phylogenetic analysis based on the S gene and ORF3 gene of these 17 novel PEDV strains and PEDV reference strains indicated that all the PEDV strains fell into two groups designated G1 and G2. Notably, the strains identified in 2014-2015 were in G2, while the other five strains identified from 2016 to 2017 were in G1. Sequencing and phylogenetic analyses showed that recently prevalent Chinese PEDV field strains shared higher identities with United States strains than with South Korean strains. Compared with classical vaccine strains, a series of deletions and frequently occurring mutations were observed in the receptor binding domains of our PEDV strains. Besides, we successfully isolated and reported the genetic characterization two novel PEDV strains, PEDV-LA1 and PEDV-LY4-98, found on the Chinese mainland, which had significant variations in the S gene. Meanwhile, the virulence of the new mutants may be changed, the PEDV-LY4-98 strain, which has multiple mutations in the signal peptide-encoding fragment of the S gene showed delayed cytopathic effects and smaller plaque size compared with strain PEDV-LA1, which lacks these mutations. Three unique amino acid substitutions (L7, G8, and V9) were identified in the SP-encoding fragment of the S1 N-terminal domain of the PEDV-LY4-98 S protein compared with the S proteins of all the previous PEDV strains. The animal experiment revealed that these two novel strains were high pathogenic to neonatal pigs. Whether these amino acids substitutions and the N-glycosylation site substitutions influence the antigenicity and pathogenicity of PEDV remains to be investigated. Meanwhile, amino acid substitutions in the neutralizing epitopes may have conferred the capacity for immune evasion in these PEDV field strains. This study improves our understanding of ongoing PEDV outbreaks in China, and it will guide further efforts to develop effective measures to control this virus.

The viral non-structural protein 1 alpha (Nsp1α) inhibits p53 apoptosis activity by increasing murine double minute 2 (mdm2) expression in porcine reproductive and respiratory syndrome virus (PRRSV) early-infected cells.

Apoptosis is one of the most important mechanisms of pathogenesis in porcine reproductive and respiratory syndrome virus (PRRSV)-infected cells. The tumor suppressor p53 plays a critical role in apoptotic induction in viral infections. In the present study, we found that p53 activity was inhibited at the early stage of PRRSV infection in both the highly pathogenic (HP) and lowly pathogenic (LP) PRRSV isolates. Bax expression showed a similar change pattern to that of p53. Murine double minute 2 (mdm2) expressed higher in PRRSV-infected cells than in uninfected cells at the early stage of infection and promoted p53 degradation. We show for the first time that the non-structural protein 1 alpha (Nsp1α) of PRRSV is a negative regulator of p53 activity through increasing mdm2 expression and p53 ubiquitination, while p53 is inhibitory to PRRSV replication at the early stage of infection. We conclude that PRRSV manipulates the host factors mdm2 and p53 via its Nsp1α for increased replication at the early stage of infection. These provide a novel perspective to understand the interaction between apoptosis and replication of PRRSV.