Molecular characteristics and pathogenicity of porcine epidemic diarrhea virus in some areas of China from 2015 to 2018

Abstract Background Since 2010, porcine epidemic diarrhea virus (PEDV) has caused severe diarrhea disease in piglets, which has led to large economic losses in China. To understand the genetic characteristics of PEDV strains that have been circulating in some provinces of China from 2015 to 2018, 362 feces and small intestine samples in pigs were collected and tested. Methods The S gene of PEDV in collected samples were amplified by RT-PCR. A phylogenetic tree was constructed using MEGA6.0 software with the neighbor-joining method to analyze the evolutionary relationship. Nucleotide and deduced amino acid (AA) sequences of S were aligned using the MegAlign program of DNASTAR7.1 software to determine sequence homology. PEDV GDgh16 strain isolation, IFA identification and titer detection were performed in Vero cells. Six 4-day-old healthy colostrum deprived suckling piglets were used for challenging experiment of PEDV GDgh16 strain. Virus copies from the small intestine were detected by RT-qPCR. The other section was stained with the anti-N protein McAb at 1:1000 dilution for immunohistochemical (IHC) examinations. Results The results showed that 160 samples tested positive and the PEDV-positive prevalence was 44.20%. Phylogenetic tree analysis of entire S genes showed that these strains were clustered into four subgroups, G1-b, G1-c, G2-a and G2-b, and that the G2-b strains had become dominant in recent years. Compared with previous strains, these strains had multiple variations in the SP and S1-NTD domains and in the neutralizing epitope of the S protein. Furthermore, we successfully isolated and identified a new virulent G2-b strain, GDgh16, which was well adapted to Vero cells and had a high mortality rate in piglets through challenge experiments. Conclusions Our study provides full insights into the genetic characteristics of prevalent PEDV strains in parts of China, suggesting that the development of novel effective vaccines is necessary and urgent.