Pathogenicity and Immunogenicity of a Serially Passaged Attenuated Genotype 2c Porcine Epidemic Diarrhea Virus Cultured in Suspended Vero Cells

Isolation, pathogenicity, and an infectious cDNA clone of the prevalent G2c variant of porcine epidemic diarrhea virus in China

Porcine epidemic diarrhea virus (PEDV) is a major enteric coronavirus causing diarrhea in piglets, and the recent prevalence of its G2c variant poses a significant threat to the pig industry in China. In this study, we successfully isolated a G2c variant strain (designated EHuB4) from a pig farm experiencing an outbreak of severe diarrhea in China, and constructed its full-length cDNA infectious clone using CRISPR/Cas9 technology. The parental EHuB4 strain and its rescued virus, rEHuB4, exhibited similar biological characteristics in Vero cells, including rapid cytopathic effects and the formation of large syncytia, suggesting strong cell fusion ability and replication efficiency. Pathogenicity experiments in piglets demonstrated that both EHuB4 and rEHuB4 caused severe diarrhea and mortality, further confirming that the prevalence of the G2c variant may be the primary reason for the current high incidence of PED outbreaks. We also analyzed the mutation frequency and variation tendency in the amino acids encoded by the EHuB4 Spike (S) gene and identified multiple high-frequency mutation sites located not only in the S1 subunit but also in the intermediate region between heptad repeat 1 (HR1) and HR2. Furthermore, these mutations have persisted since 2011 and may be closely related to virus prevalence, host adaptation, and pathogenicity. In summary, this study not only characterizes the genetic evolution and pathogenicity of the prevalent G2c strain but also provides a valuable molecular tool for developing novel vaccines through the established full-length cDNA infectious clone.

Overview of the recent advances in porcine epidemic diarrhea vaccines

Vaccination is the most effective means of preventing and controlling porcine epidemic diarrhea (PED). Conventional vaccines developed from porcine epidemic diarrhea virus (PEDV) GI-a subtypes (CV777 and SM98) have played a vital role in preventing classical PED. However, with the emergence of PEDV mutants in 2010, conventional PEDV GI-a subtype-targeting vaccines no longer provide adequate protection against PEDV GII mutants, thereby making novel-type PED vaccine development an urgent concern to be addressed. Novel vaccines, including nucleic acid vaccines, genetically engineered subunit vaccines, and live vector vaccines, are associated with several advantages, such as high safety and stability, clear targeting, high yield, low cost, and convenient usage. These vaccines can be combined with corresponding ELISA kits to differentiate infected from vaccinated animals, which is beneficial for disease confirmation. This review provides a detailed overview of the recent advancements in PED vaccines, emphasizing on the research and application evaluation of novel PED vaccines. It also considers the future directions and challenges in advancing these vaccines to widespread use in clinics.

Genetic signatures associated with the virulence of porcine epidemic diarrhea virus AH2012/12

IMPORTANCE

Porcine epidemic diarrhea (PED) caused by PED virus (PEDV) remains a big threat to the swine industry worldwide. Vaccination with live attenuated vaccine is a promising method to prevent and control PED, because it can elicit a more protective immunity than the killed vaccine, subunit vaccine, and so on. In this study, we found two obvious deletions in the genome of a high passage of AH2012/12. We further confirmed the second deletion which contains seven amino acids at the carboxy-terminus of the S2 gene and the start codon of ORF3 can reduce its pathogenicity in vivo. Animal experiments indicated that the recombinant PEDV with deleted carboxy-terminus of S gene showed higher IgG, IgA, neutralization antibodies, and protection effects against virus challenge than the killed vaccine. These data reveal that the engineering of the carboxy-terminus of the S2 gene may be a promising method to develop live attenuated vaccine candidates of PEDV.

Isolation, identification, and pathogenicity of porcine epidemic diarrhea virus

Porcine epidemic diarrhea (PED) is an enterophilic infectious disease caused by the porcine epidemic diarrhea virus (PEDV), which can lead to dehydration-like diarrhea in piglets with a mortality rate of up to 100%, causing huge economic losses to the global pig industry. In this study, we isolated two PEDV strains, FS202201 and JY202201, from diarrheal samples collected from two new PED outbreak farms in 2022. We performed phylogenetic analysis of the S gene and whole gene sequence. The effects of the different mutations on viral pathogenicity were investigated using piglet challenge experiments. The results showed that both strains belong to the G2c subtype, a widely prevalent virulent strain. Compared with FS202201, JY202201 harbored substitution and deletion mutations in nsp1. Both FS202201 and JY202201 infected piglets showed severe diarrhea and significant intestinal tissue lesions at an infection dose of 104 TCID50/mL, with a mortality rate of 50%; however, JY202201 required an additional day to reach mortality stabilization. An infection dose of 103 TCID50/mL reduced diarrhea and intestinal tissue lesions in piglets, with mortality rates of the two strains at 16.7% and 0%, respectively. In addition, PEDV was detected in the heart, liver, spleen, lungs, kidneys, mesenteric lymph nodes, stomach, large intestine, duodenum, jejunum, and ileum, with the highest levels in the intestinal tissues. In conclusion, this study enriches the epidemiology of PEDV and provides a theoretical basis for the study of its pathogenic mechanism and prevention through virus isolation, identification, and pathogenicity research on newly identified PED in the main transmission hub area of PEDV in China (Guangdong).