Prevalence and phylogenetic analysis of spike gene of porcine epidemic diarrhea virus in Henan province, China in 2015-2019

Porcine epidemic diarrhea virus (PEDV) causes diarrhea, dehydration and a high morbidity and mortality in piglets. To investigate the prevalence and molecular characteristics of the spike (S) gene of the PEDV strains, 575 faecal and intestinal samples were collected from individual pigs with diarrhea in 18 regions in Henan, China from April 2015 to March 2019. The detection results showed that PEDV infection was high up to 51.65% in Henan pigs. The PEDV positive rate in suckling piglets was the highest (60.47%), and it existed widely both in PEDV-vaccine immunized (25.00%) and non-immunized pigs (62.29%). The complete S gene of twenty-two representative PEDV strains were sequenced and analyzed. Phylogenetic analysis based on the S gene sequences revealed that the sixteen of the sequenced PEDV Henan strains were located in the G2-a Glade and more related to the PEDV variant strains. The other six of the sequenced PEDV strains were closely related to S-INDEL strains and grouped within in the G1 -b Glade. The Recombinant Identification Program (RIP) and Simplot analysis showed PEDV Henan strains were evolved from the epidemic variant strains and there existed potential recombinant points in the S genome. Furthermore, the deduced amino acid sequences analysis of the S protein showed that there existed multiple amino acid mutations in the S protein of PEDV Henan strains, including the neutralizing epitope CO-26 K equivalent (COE) and SS6 when compared with the CV777-based vaccine strain. These amino acid mutations in the S protein may change the antigenicity in the PEDV Henan variants, leading to the failure of immunization with the traditional vaccine based on the CV777 strain. These results would support the understanding of the prevalence and evolution characteristics of PEDV in China and promote the development of novel vaccines based on the current prevalence variant strains.