Sequence analysis of the ORF 7 region of transmissible gastroenteritis viruses isolated in Korea

Three (KT2, 133, and DAE) transmissible gastroenteritis viruses (TGEVs) were isolated from pigs suspected of having TGE in Korea. One, KT2 (KT2-L), was passaged 128 times (KT2-H) in swine testicular cells. The open reading frame 7 (ORF 7) gene from each of the four TGEVs (KT2-L, KT2-H, 133, and DAE), which is located at the 3' end of the TGEV genome, was amplified by reverse transcriptase-polymerase chain reaction (RT-PCR). Amplified PCR products were cloned, sequenced, and compared with published sequences of non-Korean TGEV strains. Differences in replication and cytopathic effect (CPE) between the KT2-L and KT2-H strains in swine testicular cells were investigated. Korean TGEV field strains had 94.8-99.6% nucleotide and 92.1-98.7% amino acid sequence similarity with each other, and 87.8-100.0% nucleotide and 84.2-100.0% amino acid sequence similarity with non-Korean TGEV strains. Compared to the original KT2-L strain, the KT2-H strain differed by 2.2 and 3.9% in nucleotide and amino acid sequences, respectively. Specifically, the KT2-H had six nucleotide and two amino acid deletions compared to the original KT2-L strain. In phylogenetic analysis of the ORF 7 gene, Korean TGEV strains were clustered into two groups. One group (KT2-L, KT2-H, 133) was related to TGEV strains isolated in Japan. Another Korean TGEV isolate (DAE) was related to a strain from China and one from the USA. The Korean TGEV isolates appear to have evolved from a separate lineage of TGEV strain. Differences in growth rate and CPE between the KT2-L and KT2-H strains were discovered in swine testicular cells (STCs). The KT2-H strain exhibited a higher replication rate than KT2-L and produced a CPE distinctly different from that of the KT2-L strain.