TBEV Subtyping in Terms of Genetic Distance

Abstract

Currently, the lowest formal taxon in virus classification is species; however, unofficial lower-level units are commonly used in everyday work. <i>Tick-borne encephalitis virus</i> (<i>TBEV</i>) is a species of mammalian tick-borne flaviviruses that may cause encephalitis. Many known representatives of <i>TBEV</i> are grouped into subtypes, mostly according to their phylogenetic relationship. However, the emergence of novel sequences could dissolve this phylogenetic grouping; in the absence of strict quantitative criterion, it may be hard to define the borders of the first TBEV taxonomic unit below the species level. In this study, the nucleotide/amino-acid space of all known TBEV sequences was analyzed. Amino-acid sequence <i>p</i>-distances could not reliably distinguish TBEV subtypes. Viruses that differed by less than 10% of nucleotides in the polyprotein-coding gene belonged to the same subtype. At the same time, more divergent viruses were representatives of different subtypes. According to this distance criterion, <i>TBEV</i> species may be divided into seven subtypes: TBEV-Eur, TBEV-Sib, TBEV-FE, TBEV-2871 (TBEV-Ob), TBEV-Him, TBEV-178-79 (TBEV-Bkl-1), and TBEV-886-84 (TBEV-Bkl-2).