Isolation and characterization of a hantavirus from Lemmus sibiricus: Evidence for host switch during hantavirus evolution

A novel hantavirus, first detected in Siberian lemmings (Lemmus sibiricus) collected near the Topografov River in the Taymyr Peninsula, Siberia (A. Pl yusnin et al., Lancet 347:1835-1836, 1996), was isolated in Vero E6 cells a nd in laboratory-bred Norwegian lemmings (Lemmus lemmus). The virus, named Topografov virus (TOP), was most closely related to Khabarovsk virus (KBR) and Puumala viruses (PUU). In a cross focus reduction neutralization Lest, anti-TOP Lemmus antisera showed titers at least fourfold higher with TOP th an with other hantaviruses; however, a rabbit anti-KBR antiserum neutralize d TOP and KBR at the same titer. The TOP M segment showed 77% nucleotide an d 88% amino acid identity with KBR and 76% nucleotide and 82% amino acid id entity with PUU. However, the homology between TOP and the KBR S segment wa s disproportionately higher: 88% at the nucleotide level and 96% at the ami no acid level. The 3' noncoding regions of KBR and the TOP S and;M segments were alignable except for 113- and 58-nucleotide deletions in KBR. The phy logenetic relationships of TOP, KBR, and PUU and their respective rodent ca rriers suggest that an exceptional host switch took place during the evolut ion of these viruses; while TOP and KBR are monophyletic, the respective ro dent host species are only distantly related.