Identification and pathogenicity of a variant porcine epidemic diarrhea virus field strain with reduced virulence

Background: Since 2010, a variant Porcine epidemic diarrhea virus (PEDV), which causes an acute, highly contagious, and devastating viral enteric disease with a high mortality rate in suckling pigs, broke out in China and spread rapidly to neighboring countries, even to the North America. This virus gradually became the main subtype of PEDV worldwide. However, there were no reports of mild pathogenicity of a variant porcine epidemic diarrhea virus in China. Findings: In 2013, a PEDV-positive sample from a sow with very mild clinical sign was used to inoculate in Vero cells to isolate the virus. This PEDV field strain, designated FL2013 strain, was successfully propagated and genetically characterized. The phylogenetic trees based upon either the complete genome or S gene showed that the FL2013 strain belongs to the genogroup G2b. The S gene of FL2013 has a 7-aa deletion (FEKVHVQ) in the C-terminus comparison with the other G2 PEDV sequences. Further comparative pathology study indicated that the FL2013 strain had reduced virulence to newborn piglets. Conclusions: A novel variant PEDV strain FL2013 with reduced virulence, as determined by the pathological study, was identified from east China. This strain is closely related to the genogroup-2 PEDV strains prevalent in the U.S. and China currently, but had a short deletion at the 3'-end of the spike gene.