Lack of phylogenetic evidence that the Shimen strain is the parental strain of the lapinized Chinese strain (C-strain) vaccine against classical swine fever

The Chinese hog cholera lapinized virus (HCLV), also called the “Chinese strain” or “C-strain” of classical swine fever virus (CSFV), was developed in China in the 1950s. There are uncertainties about the genetic heterogeneity and origin of this vaccine virus. The objectives of this study were to investigate the genetic heterogeneity of the C-strain, for which nucleotide sequences have been submitted to GenBank from different laboratories, and to determine whether there is any evidence to support the hypothesis that the C-strain originated from the Shimen strain. Analysis of 150 nearly complete E2 gene sequences revealed that the C-strain clade includes several HCLV vaccine strains, cell-culture-adapted Riems strains, and viruses isolated from diseased pigs. The whole-genome phylogeny indicated that the ancestor of the C-strain was only distantly related to the Shimen strain. Therefore, there was no phylogenetic evidence to support the Shimen-origin hypothesis.