Enterovirus 71 (EV71) is a major cause of hand-foot-and-mouth disease. EV71 infection occasionally associates with severe neurological sequelae such as brainstem encephalitis or poliovirus-like paralysis. We demonstrated that mouse-adapted strain increases infectivity, resulting in higher cytotoxicity of neuron cells and mortality to neonatal mice than a non-adapted strain. Results pointed to EV71 capsid region determining viral infectivity and mouse lethality. Mutant virus with lysine to methionine substitution at VP2149 (VP2149M) or glutamine to glutamic acid substitution at VP1145 (VP1145E) showed greater viral titers and apoptosis. Synergistic effect of VP2149M and VP1145E double mutations enhanced viral binding and RNA accumulation in infected Neuro-2a cells. The dual substitution mutants markedly reduced value of 50% lethal dose in neonatal mice infection, indicating they raised mouse lethality in vivo. In sum, VP2149M and VP1145E mutations cooperatively promote viral binding and RNA accumulation of EV71, contributing to viral infectivity in vitro and mouse lethality in vivo.
