Isolation and experimental inoculation of an S INDEL strain of porcine epidemic diarrhea virus in Japan

• We isolated and sequenced PEDV strains circulating in Japan.
• One strain contained distinct insertion and deletions in the S gene.
• This S INDEL strain had lower pathogenicity than the NA prototype strain in piglets.
• Excretion of the S INDEL strain in feces from inoculated piglets was delayed.
• Viral dynamics of the S INDEL strain differed from that of the NA prototype strain.

In 2013, porcine epidemic diarrhea (PED) was reported in Japan for the first time in 7 years and caused significant economic losses. In the present study, we isolated PED virus (PEDV) circulating in Japan using Vero cell cultures and analyzed sequences of S1 genes of these PEDV isolates. Sequence analysis revealed that one of these strains contained distinct insertion and deletions in the S gene (i.e., S INDEL). Furthermore, inoculation of PEDV into 1-week-old pigs demonstrated that the S INDEL strain had a lower pathogenicity than the North American (NA) prototype strain. This is the first report comparing pathogenicity of an S INDEL strain with the NA prototype strain following experimental inoculation. Excretion of PEDV in the feces of S INDEL strain-inoculated pigs occurred later than in NA prototype strain-inoculated pigs. Thus, our findings suggested that the S INDEL strain had different viral dynamics than the NA prototype strain.