To gain further insight into the molecular epidemiology of Hantaan virus (HTNV) in Guizhou, China, rodents were captured in this region in 2004 and 2005. In addition, serum samples were collected from four patients. Ten hantaviruses were isolated successfully in cell culture from four humans, two Apodemus agrarius, three Rattus norvegicus and one Rattus nitidus. The nucleotide sequences for their small (S), medium (M) and partial large (L) segments were determined. Phylogenetic analysis of the S and M segment sequences revealed that all of these isolates belong to the species HTNV, suggesting a spillover of HTNV from A. agrarius to Rattus rats. All available isolates from Guizhou were divided into four distinct groups either in the S segment tree or in the M segment tree. The clustering pattern of these isolates in the S segment tree was not in agreement with that in the M or L segment tree, showing that genetic reassortment between HTNV had occurred naturally. Analysis of the S segment sequences from available HTNV strains indicated that they formed three clades. The first clade, which comprised only viruses from Guizhou, was the outgroup of clades II and III. The viruses in the second clade were found in Guizhou and mainly in the far-east Asian region, including China. However, the viruses in the third clade were found in most areas of China, including Guizhou, in which haemorrhagic fever with renal syndrome (HFRS) is endemic. Our results reveal that the highest genetic diversity of HTNV is in a limited geographical region of Guizhou, and suggest that Guizhou might be a radiation centre of the present form of HTNV.
INTRODUCTIONHaemorrhagic fever with renal syndrome (HFRS) is an important human disease; 60 000 to 100 000 cases requiring hospitalization are reported annually worldwide, with the majority occurring in China (Johnson, 1999;Zhang et al., 2004). The disease is caused by hantaviruses, members of the genus Hantavirus in the family Bunyaviridae (Nichol et al., 2005). The virus genome consists of three separate segments of negative-stranded RNA referred to as small (S), medium (M), and large (L) segments, which encode nucleocapsid protein (NP), two envelope glycoproteins (Gn and Gc) and viral RNA-dependent RNA polymerase (RdRP), respectively (Plyusnin et al., 1996). In contrast to other genera of the Bunyaviridae, hantaviruses are not transmitted by arthropods (Schmaljohn & Hjelle, 1997). They establish a chronic infection that causes no apparent harm to rodents of the Muridae family, which are their natural hosts (Childs et al., 1989; Hutchinson et al., 2000;Kurata et al., 1983;Li et al., 1995;Netski et al., 1999). Currently, at least 22 distinct hantavirus species have been identified worldwide; all of these hantaviruses except Thottapalayam virus (TPMV) are carried by rodents (Nichol et al., 2005). Each rodent-borne hantavirus species appears to be associated primarily with one (or a few closely related) rodent species (Nichol et al., 2005; Plyusnin GenBank accession numbers of the S, M and L segment...