| Summary: | 博士 === 國立成功大學 === 基礎醫學研究所 === 100 === RNA viruses likely emergent with high genetic flexibility to facilitate their adaption in contact with limited environment for effective spread between various hosts. In recent years, re-emergent enterovirus 71 (EV71) has been a cause of numerous outbreaks of hand-foot-and-mouth disease with severe neurological complications in the Asia-Pacific region. This study focused on the genetic and antigenic evolution as well as mouse adaption of EV71. In Taiwan, the reemergence of EV71 genotype B5 in 2008 resulted in the largest outbreak of EV71 in the past fourteen years. Phylogenetic analyses revealed dominant genotypic changes from B to C or C to B for at least three times between 1986 and 2008. Furthermore, antigenic cartography of EV71 by using neutralization tests revealed that the reemerging EV71 genotype B5 strains formed a separate cluster distinct from the B1/B4 and C genotypes. Moreover, analyses of full-length genomic sequences of EV71 circulating in Taiwan during this period showed the occurrence of intra- and inter-serotypic recombination. Continuous surveillance of EV71 including the monitoring of genetic evolution and antigenic changes is recommended. In the mouse model, we investigated the effects of infectivity determinants of EV71 on mouse lethality in vivo. We demonstrated mouse-adapted strain increases infectivity, resulting 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 apoptic effect in Neuro-2a cells. 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. VP2149M and VP1145E mutations thus cooperatively promote viral binding and RNA accumulation of EV71, contributing to viral infectivity in vitro and mouse lethality in vivo.
|
|---|
