Epidemic strain YC2014 of porcine epidemic diarrhea virus could provide piglets against homologous challenge

Huixing Lin, Lei Chen, Lu Gao, Xiaomin Yuan, Zhe Ma, Hongjie Fan

Porcine epidemic diarrhea virus (PEDV) is the main causative agent of porcine epidemic diarrhea (PED). Since December 2010, a large-scale outbreak of diarrhea has been observed in swine farms in China. Accumulated evidence indicates that this large-scale outbreak of diarrhea were caused by highly virulent PEDV variants. A PEDV strain, YC2014, was isolated from intestinal samples of suckling piglets with acute diarrhea in 2014. The complete genomic sequence of YC2014 and the nucleotide sequence of S gene were aligned with sequences of published isolates using MEGA 5.1 software. The immune protective efficiency of YC2014 were determined by testing PEDV neutralizing antibodies in sera, the colostrum and the milk on 7th day after farrowing of the immunized sows. The diarrhea symptoms of piglets after challenge were also observed. Phylogenetic analysis of the complete genomic sequence of YC2014 and the nucleotide sequence of S gene demonstrated that the YC2014 PEDV strain was clustered with the PEDV epidemic strains, with >99 % nucleotide identity to these PEDV strains. The S gene sequence of YC2014 shared only 93.9 % ~ 94.4 % identities with classical CV777, DR13 and JS2008 strains, with 15 nucleotide insertion in three sites and three nucleotide deletion in one site. The amino acid (AA) sequence of S gene of YC2014 shared only 92.8 % ~ 93.4 % identities with classical CV777, DR13 and JS2008 strains, with 5 AA insertion in two sites and 1 AA deletion in one site. In the immune protective efficiency tests, the neutralizing antibody titers in sera, the colostrum and the milk on 7th day after farrowing of the inactivated YC2014 PEDV strain immunized group were significantly higher than the inactivated CV777 immunized group and the inactivated DR13 immunized group (P < 0.05). The traditional inactivated PEDV vaccines made from CV777 or DR13 could not protect piglets from YC2014 challenge, while inactivated YC2014 could provide piglets with 100 % protection against YC2014 challenge. The results showed that, great antigenicity variation had occurred to this YC2014 PEDV strain. The YC2014 PEDV strain could provide piglets against homologous challenge. It is critical for future pathogenic and antigenic studies, as well as for the development of effective preventive and control vaccines against PEDV.