Molecular characterization of porcine epidemic diarrhea virus associated with outbreaks in southwest China during 2014-2018

Abstract

Porcine epidemic diarrhea virus (PEDV), which re-emerged in China since 2010, has swept across the whole country leading to tremendous economic losses. In this study, a total of 645 diarrhea samples collected from 156 pig farms in Sichuan and Guizhou province during 2014-2018 were tested for PEDV. We found that samples from 47.66% (84/156) of the farms were positive for PEDV with an overall detection rate of 35.81% (231/645). Fifty-two strains were selected for full-length S gene analyses, and these strains were classified into three subgroups, an S-INDEL subgroup (G1c), and two non-S-INDEL subgroups (G2b, AJ1102-like and G2c), accounting for 15.38% (8/52), 23.08% (12/52) and 59.62% (31/52) of the total analysed strains, respectively. We found these three subgroups of PEDV coexisted in Sichuan province, and the S-INDEL strain was detected in Guizhou. Further antigenic variation analysis of the neutralizing epitopes (S10, COE, SS2, SS6 and 2C10) on the spike protein revealed that the S-INDEL and non-S-INDEL strains shared similar variation features in COE and SS6, but exhibited distinct variation patterns in the S10 domain. Unique variation patterns on N-glycosylation sites in the S protein were also observed for the S-INDEL and non-S-INDEL strains. Moreover, nine strains (three from each subgroup) were subjected to full-genome characterization. Complete genome phylogeny showed an inconsistent tree topology for genotyping, with two G2c strains grouped into the GII-b (AH2012-like) genogroup and the remaining seven strains including three S-INDEL strains grouped into the GII-c genogroup. Further recombination analyses indicated that six of the GII-c strains probably originated from intra-genogroup recombinations. Notably, three newly emerged S-INDEL strains with novel recombination patterns were first identified. Together, our data revealed a new status of PEDV in southwest China, which can increase understanding of the prevalence, genetic characteristics and evolutionary profiles of circulating PEDV strains in China.

Keywords: S-INDEL strain; molecular characterization; phylogenetic analysis; porcine epidemic diarrhea virus; recombination.