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

Porcine epidemic diarrhea virus (PEDV) is a highly pathogenic swine coronavirus causing severe diarrhea and high mortality to piglets. PEDV strain AH2012/12 isolated from a diarrheal piglet has been passaged in vitro for over 102 passages. Viral infection assay revealed that PEDV AH2012/12-P102 (the 102nd passage of AH2012/12) showed an enhanced fusogenicity than the wild-type AH2012/12. Animal experiments demonstrated that AH2012/12-P102 is an attenuated PEDV strain as shown by the evidence of no mortality, extremely low virus shedding, and no sign of diarrhea in the AH2012/12-P102 challenged piglets. Compared with AH2012/12, AH2012/12-P102 had two obvious deletions in the genome, one deletion is in the S1 gene and the second deletion contains the carboxy-terminus of the S2 gene and the start codon of ORF3. Using the reverse genetic system of PEDV, we generated a series of recombinant PEDVs with deletions based on the deletion in the genome of AH2012/12-P102. Viral infection assays indicated that the second deletion could enhance the fusogenicity of PEDV AH2012/12. Animal experiments showed that the first deletion could reduce the virulence but not fully attenuate AH2012/12, but the second deletion could attenuate PEDV AH2012/12 in vivo . Further animal experiments indicated that the recombinant PEDV with deleted carboxy-terminus of S gene induced higher IgG, IgA, neutralization antibodies, and protection effects against virus challenge than the killed vaccine. Collectively, our data demonstrated two genetic features associated with the virulence of PEDV AH2012/12 and provided a promising method for the development of attenuated vaccine candidates for PEDV. 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.