GENETIC-VARIABILITY OF CLASSICAL SWINE FEVER VIRUS

The genetic variability of classical swine fever virus was studied by comparative nucleotide sequence analysis of 76 virus isolates, collect ed during a half century from three continents. Parts of the E2 (gp55) and the polymerase gene coding regions of the viral genome were ampli fied by RT-PCR and DNA fragments of 254 and 207 bp, respectively, were sequenced. The comparative sequence analysis of the E2 region reveale d two main phylogenetic groups of CSFV, indicating that the virus appa rently evolved from two ancestor nodes. Group I (represented by Bresci a strain) consisted of old and recent American and Asian viruses, as w ell as old English isolates from the 1950s. This group was subdivided into three subgroups, termed I.A-I.C. Group II (represented by Alfort strain) consisted of relatively recent isolates from Europe, together with strain Osaka, which was isolated in Japan from a pig of European origin. Based on genetic distances the group was divided into subgroup s II.A and II.B. Malaysian isolates were branched into both groups, in dicating multiple origins for contemporaneous outbreaks in that countr y. All ten vaccine strains tested were branched in group I, implying a common ancestor. The Japanese Kanagawa strain, isolated in 1974, and the British Congenital Tremor strain from 1964 were the most distinct variants of CSFV in our collection. The comparison of the nucleotide s equences of the polymerase coding region of 32 European strains distin guished subgroups II.A and II.B which were similar to the correspondin g subgroups of the E2 phylogenetic tree. Thus, the results revealed th at the E2 region and the polymerase coding regions seem to be appropri ate for the grouping of CSFV isolates from all over the world, disting uishing two major groups of the virus. The reliability of these region s for phylogenetic analysis is indicated by the similarity of the resu lts obtained from the two separate parts of the CSFV genome.