Two hantavirus strains, MF43 and MF113, isolated from Microtus fortis trapped in the Khabarovsk region of far-eastern Russia, were analysed by direct nucleotide sequencing of PCR generated fragments of the M and S segments, by immunofluorescence and by focus reduction neutralization tests (FRNT). The nucleotide sequences revealed that the two isolates were closely related to each other but distinct from all other hantaviruses. Phylogenetic analysis of the M and S segments showed that the MF strains form a separate branch in the Hantavirus tree, positioned between the branches of Prospect Hill and Puumala viruses. The strains were shown to be serologically distinct from the other hantavirus serotypes by FRNT using immune rabbit sera. Puumala virus was the closest relative, both genetically and serologically. We propose that this new hantavirus serotype should be named Khabarovsk (KBR).

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The antigenic relationships among 71 hantavirus strains, isolated from rodent species or humans in several geographic regions, were examined by immunofluorescence assay (IFA) using human patient sera and a panel of 22 monoclonal antibodies prepared against Hantaan, Seoul, and Puumala viruses. The study included virus strains, mainly from the former USSR, for which little or no serological data were available. Fifty-nine of the 71 isolates could be placed into five antigenic groups of hantaviruses, Hantaan (HTN), Puumala (PUU), Seoul (SEO), Prospect Hill (PH), Dobrava/Belgrade (DOB). Twelve isolates were found antigenically closely related to, but distinct from, HTN (2 strains), PUU (4 strains) and PH (6 strains), respectively. The antigenic characteristics of these 12 isolates suggested two supplementary antigenic subgroups of HTN, one of PUU, and two of PH. The two antigenic subgroups of HTN included strains isolated in the Far-East of Russia. The PUU subgroup included strains isolated in European Russia as well as strains isolated in Far-Eastern Russia. The PH group comprised two subgroups, both represented by strains isolated from M. fortis in Far-Eastern Russia. The results showed that the PUU and PH antigenic groups are more complex than previously known and that PH-like virus strains isolated in Russia are antigenically more closely related to PUU virus when compared to prototype PH virus isolated in the USA.