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, Puum ala virus (PUUV) is thought to be co-evolving with its natural host, the ba nk vole Clethrionomys glareolus. To gain insight into the evolutionary hist ory 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 votes to Fennoscandia. Full-length sequences of the S RNA segment and partial sequences (nt 2168-2569) of the M segment we re recovered by RT-PCR directly from bank vote tissues collected at three l ocations in Russian Karelia and one location in Denmark. Phylogenetic analy sis 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 clo se relatedness to any of the known PUUV strains and formed a distinct phylo genetic lineage on trees calculated for both S and M segment sequences. Alt hough no direct link between the Danish PUUV strains and those of the south ern Scandinavian lineage was found, within the S segment of Danish PUUV str ains, two regions with higher similarity to either northern Scandinavian or - to a less extent - southern Scandinavian genetic lineages were revealed, suggesting evolutionary connections of their precursors.