Evolution of enterovirus 70 in nature: all isolates were recently derived from a common ancestor

The data of large RNase T1-resistant oligonucleotide mapping of enterovirus 70 (EV 70) previously reported (Takeda et al., Virology 134, 375-388, 1984) were subjected to further genetical analysis to estimate the evolutionary rate of genome RNA of EV 70 and to clarify the phylogenetic relationship among isolates. A proportion of common spots between strains decreased as the year elapsed and eventually, only seven spots were common to all the 16 isolates tested, indicating that the substitution is scattered throughout the genome. On the other hand, some specific sets of spots were conserved among geographically or epidemiologically related strains. Base sequence variation of the isolates was deduced according to Aaronson et al. (Nucleic Acids Res. 10, 237-246, 1982) from pariwise comparison of the common spots and used as a genetic distance between them. The base substitution rate of virus genome was estimated by regression analysis of the genetic distance of the isolates against the sampling time. A fairly constant and rapid rate was obtained; it was 1.83 X 10(-3)/base/year. Based on the substitution rate, genetic distance and sampling time of the strains, the phylogenetic tree of EV 70 was constructed using Unweighted Pair Group Method Using Arithmetic Averages (UPGMA) (Nei, Molecular Population Genetics and Evolution, North Holland, Amsterdam, 1975). The tree supports the previous hypothesis that evolution of EV 70 started from a single common ancestor. The time of its emergence was estimated to be 1967 +/- 15 months. The virus branched into many strains early during the first pandemic and has evolved in a divergent fashion, yielding genetically polymorphic viruses in the world.