Molecular evolution of Puumala hantavirus in Fennoscandia: phylogenetic analysis of strains from two recolonization routes, Karelia and Denmark

Like other members of the genus Hantavirus in the family Bunyaviridae, Puumala virus (PUUV) is thought to be co-evolving with its natural host, the bank vole Clethrionomys glareolus. To gain insight into the evolutionary history of PUUV in northern Europe during the last post-glacial period, we have studied wild-type PUUV strains originating from areas along two postulated immigration routes of bank voles to Fennoscandia. Full-length sequences of the S RNA segment and partial sequences (nt 2168–2569) of the M segment were recovered by RT–PCR directly from bank vole tissues collected at three locations in Russian Karelia and one location in Denmark. Phylogenetic analysis showed that strains from Karelia and Finland belong to the same genetic lineage, supporting the hypothesis that PUUV spread to present Finland via a Karelian land-bridge. The Danish PUUV strains showed no particularly close relatedness to any of the known PUUV strains and formed a distinct phylogenetic lineage on trees calculated for both S and M segment sequences. Although no direct link between the Danish PUUV strains and those of the southern Scandinavian lineage was found, within the S segment of Danish PUUV strains, two regions with higher similarity to either northern Scandinavian or – to a less extent – southern Scandinavian genetic lineage