Pathogenicity of Hantaan virus in newborn mice: Genetic reassortant study demonstrating that a single amino acid change in glycoprotein G1 is relatedto virulence

Two Hantaan virus strains, clone 1 (cl-1), which is virulent in newborn mic e, and its attenuated mutant (mul1E10), were used to examine the pathogenes is of Hantaan virus infection in a mouse model and identify virus factors r elating to virulence. After subcutaneous inoculation of newborn BALB/c mice , cl-1 caused fatal disease with high viral multiplication in peripheral or gans, but mul1E10 produced nonfatal infection with a low level of virus mul tiplication. Intracerebral inoculation of either strain caused fatal diseas e. Histopathological changes in the dead animals were prominent in the brai n, indicating that the brain is the target organ and produces the fatal out come. These results indicate that mul1E10 has a generally less virulent phe notype, and because of decreased multiplication in peripheral tissues, neur oinvasiveness is also decreased. An experiment with genetic reassortant vir uses showed that in newborn mice the M segment is the most related to virul ence and the L segment is partly related. Sequence comparison detected a si ngle deduced amino acid change (cl-l Ile to mul1E10 Thr) at amino acid numb er 515 in glycoprotein G1. One nucleotide change, but no amino acid substit ution, was observed in the noncoding region of the L segment. In mouse brai n microvascular endothelial cells in vitro, viruses possessing a cl-1-deriv ed M segment grew more rapidly than viruses containing a mul1E10 derived M segment. These results suggest that the single amino acid change in the gly coprotein alters peripheral growth, which affects invasion of the central n ervous system in mice.