Sequence analysis and genetic classification of tick-borne encephalitis viruses from Europe and Asia

The epidemiology of tick-borne encephalitis virus was investigated by compa rative sequence analysis of virus strains isolated in endemic areas of Euro pe and Asia. Phylogenetic relationships were determined from the nucleotide and amino acid sequences of the major envelope (E) protein of 16 newly seq uenced strains and nine previously published sequences. Three genetic linea ges could be clearly distinguished, corresponding to a European, a Far East ern and a Siberian subtype. Amino acids characteristic for each of the subt ypes ('signature' amino acids) were identified and their location in the at omic structure of protein E was determined. The degree of variation between strains within subtypes was low and exhibited a maximum of only 2.2% at th e amino acid level. A maximum difference of 5.6% was found between the thre e subtypes, which is in the range of variation reported for other flaviviru ses.