The S Gene Is Necessary but Not Sufficient for the Virulence of Porcine Epidemic Diarrhea Virus Novel Variant Strain BJ2011C

Abstract

The recently emerged highly virulent variants of porcine epidemic diarrhea virus (PEDV) have caused colossal economic losses to the worldwide swine industry. In this study, we investigated the viral virulence determinants by constructing a series of chimeric mutants between the highly virulent strain BJ2011C and the avirulent strain CHM2013. When tested in the 2-day-old piglet model, wild-type (WT) BJ2011C caused severe diarrhea and death of the piglets within 72 h. In contrast, its chimeric derivative carrying the S gene from CHM2013 (BJ2011C-S) was avirulent to the piglets. Moreover, reciprocal substitution of the BJ2011C S gene (CHM2013-S) did not enable CHM2013 to gain any virulence. However, when the whole structural protein-coding region of BJ2011C (CHM2013-SP) was swapped, CHM2013 started to gain the ability to efficiently colonize the intestinal tract and caused diarrhea in piglets. A further gain of virulence required additional acquisition of the 3' untranslated region (UTR) of BJ2011C, and the resultant virus (CHM2013-SP + 3UTR) caused more severe diarrhea and death of piglets. Together, our findings suggest that the virulence of PEDV epidemic strains is a multigenic event and that the S gene is only one of the necessary determinants. The recently emerged highly virulent PEDV variants are the major cause of the global porcine epidemic diarrhea (PED) pandemic. The S gene of the variants undergoes remarkable variations and has been thought to be the virulence determinant for the enhanced pathogenesis. Our studies here showed that the S gene is only part of the story and that full virulence requires cooperation from other genes. Our findings provide insight into the pathogenic mechanism of the highly virulent PEDV variants and have implications for future vaccine development.

Isolation and characterization of a variant subgroup GII-a porcine epidemic diarrhea virus strain in China

“…These data suggest that Chinese PEDV subgroups GII-a strains have undergone genetic variations, forming potential novel clades. The pathogenicity of different PEDV subgroups has been widely investigated and many reports have confirmed that the PEDV strains of the subgroups GII-a and GII-b are highly pathogenic to suckling piglets, with infection manifesting as severe clinical symptoms with watery diarrhea, vomiting, and dehydration, high viral loads shed in the stool, severe lesions within the intestine, as evidenced by thin-transparent intestinal walls and intestinal villus atrophy or shedding, loss of bodyweight, and rapid death [19,20,29,31,32]. In the present study, PEDV strain HM2017 of subgroup GII-a was strongly virulent to suckling piglets, similar to that of the PEDV strains of subgroups GII-a and GII-b [5,33].…”

“…The piglet body temperatures and weights were recorded before inoculation (−12 hpi) and then every 12 h until death. All piglets were evaluated twice daily for clinical signs of lethargy and diarrhea [29]. The clinical mental state of all piglets was scored according to the following criteria: 0 = normal; 1 = mild lethargy (slow to move, head down); 2 = moderate lethargy (able to stand, but tended to lie down); 3 = heavier lethargy (tended to lie down, but occasionally stood); 4 = severe lethargy (recumbent, moribund).…”

Rapid manipulation of the porcine epidemic diarrhea virus genome by CRISPR/Cas9 technology

“…Using a similar strategy, Fan et al developed an infectious cDNA clone for a Chinese PEDV variant strain, AH2012/12 (Fan et al, 2017). Li et al developed a reverse genetics system for two Chinese PEDV strains with differing virulence by ligation of cDNA fragments into BACs one by one (Li et al, some PEDV proteins, such as S protein and ORF3, in modulating PEDV pathogenicity have been examined (Beall et al, 2016;Hou et al, 2017Hou et al, , 2019Kaewborisuth et al, 2018;Wang et al, 2018). Several recombinant PEDV vaccine candidates have also been generated using reverse genetics systems (Hou et al, 2019;Kao et al, 2018;Wang et al, 2018).…”

“…Li et al developed a reverse genetics system for two Chinese PEDV strains with differing virulence by ligation of cDNA fragments into BACs one by one (Li et al, some PEDV proteins, such as S protein and ORF3, in modulating PEDV pathogenicity have been examined (Beall et al, 2016;Hou et al, 2017Hou et al, , 2019Kaewborisuth et al, 2018;Wang et al, 2018). Several recombinant PEDV vaccine candidates have also been generated using reverse genetics systems (Hou et al, 2019;Kao et al, 2018;Wang et al, 2018). Although infectious clone systems for PEDV using various strategies (Teeravechyan et al, 2016) have become established, approaches to generate a new mutant PEDVs with defined genetic changes using infectious clones remains a tedious process, usually requiring constructing and ligating a set of contiguous cDNA fragments.…”

Attenuation and characterization of porcine enteric alphacoronavirus strain GDS04 via serial cell passage

“…7), indicating a potential relationship between these differences of S protein and pathogenicity of PEAV. It was reported that the S protein is necessary but not sufficient for the virulence of PEDV (Wang et al, 2018). M protein plays an important role in the process of virus assembly by interacting with S and N proteins (de Haan et al, 1999;Nguyen and Hogue, 1997).…”