Emergence of a classical variant of porcine epidemic diarrhea virus novel to Thailand responsible for the milder clinical disease in a herd previously infected with a pandemic variant

In 2014, porcine epidemic diarrhea (PED) outbreaks characterized by mild clinical disease and low pre-weaning mortality increased in frequency in Thailand. An outbreak investigation, based on the detection of the classical variant and the allowance of the herd owners, was conducted in 5 swine herds and 25 intestinal samples were submitted from herds with outbreaks of diarrhea for sequencing analysis. PEDV isolation and complete nucleotide sequences of the spike (S) glycoprotein were determined. The PEDV isolate EAS1 was identified. Phylogenetic analysis based on the full-length spike gene demonstrated that EAS1 belonged to the classical variant group with high nucleotide and amino acid identity (98.4-99.0% and 96.6-97.9%) with LZC and SM98, which are the Chinese and Korean classical variant PEDVs, respectively. The results suggest the emergence of a classical variant PEDV responsible for the mild clinical disease in Thailand. The introduction could have been due to the use of illegally imported modified live vaccines from other countries.