Abstract
The genotypes and subtypes of 205 HBV isolates collected during 1989-2002 in Estonia and 14 other regions of the former USSR were determined by sequencing and phylogenetic analysis of the S gene. The in Europe prevailing genotypes, A and D, were also circulating in the whole territory of the former USSR including Estonia and accounted for 18.5 and 81% of the strains, respectively. All genotype A strains specified adw2, and a single genotype C strain specified adrq+. Most genotype D strains specified ayw3 and ayw2, although, three strains from Estonia and Siberia specified ayw4. Due to unique substitutions, Ser122 and Ala127, four strains could not be classified according to the subtype. One strain specifying ayw3 encoded Leu143 and Ala145 and was possibly an immune "escape" mutant. At phylogenetic analysis 93% of the Estonian genotype D strains belonged to a cluster specifying mainly ayw3 and were more similar to isolates from Siberia and the Far-East of Russia than to isolates originating from Central Russia which belonged to another cluster of strains specifying mainly ayw2. This pattern might be explained by part of the Estonian population, has roots east of European Russia, based on linguistic evidence. Eight dominant HBV strains represented by identical S gene sequences were identified, one within genotype A and seven within genotype D, three of which included isolates from Estonia and Siberia. Some of these strains were collected over a period of at least 13 years indicating there are genetically stable variants of HBV that remain conserved over decades.
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