Molecular genetic characteristics of the envelope glycoprotein (E2) gene of classical swine fever viruses isolated in Thailand

Thirteen classical swine fever virus (CSFV) isolates collected from field outbreaks in various locations of Thailand during 2001�2009 which had been identified by RTPCR were genetically analyzed by partial nucleotide sequencing of the envelope glycoprotein (E2) gene. These sequence data were then phylogenetically analyzed along with the sequences previously submitted to GenBank, as well as those from representatives of the different CSFV subgroups. The sequence and phylogenetic analyses of the E2 gene demonstrated that the thirteen isolates of this study were separated into three different groups. The first group consisted of 4 isolates sharing 98.9�100% and 96.8�100% homology among them in nucleotide and amin o acid sequences, respectively, and belonged to subgroup 1.1. The second group consisted of 5 isolates sharing 97.3�100% and 93.6� 100% homology in nucleotide and amino acid sequences, respectively, and belonged to subgroup 2.1. The last group consisted of 4 isolates sharing 91.5�100% and 92.0�96.8% homology in nucleotide and amino acid sequences, respectively, and belonged to subgroup 2.2. In addition, the isolates in the first group had 97.3�98.4% nucleotid e sequence and 93.6�96.8% amino acid sequence similarities with the CSFV Cstrain, whereas those in the second group had 88.3�89.9% nucleotide sequence and 95.2�96.8% amino acid sequence similariti es with the Italy strain, and those in the last group had 92.0�92.5% nucleotide sequence and 92.0�96. 8% amino acid sequence similarities with the GSJCstrain. These data help to understand the dynamics of Thai CSF virus subgroup evolution and support epidemiological observations.