| Summary: | 碩士 === 國立陽明大學 === 醫學生物技術研究所 === 88 === An outbreak associated with enterovirus infection occurred in Taiwan area during the year of 1998. It was reported that there were 129,106 cases of hand-foot-and-mouth disease or herpangina in the outbreak ; among them, 405 patients suffered from severe diseases with complications including encephalitis, aseptic meningitis, pulmonary edema, hemorrhage, acute flaccid paralysis, and myocarditis. Accumulated death toll has been 78 patients ; most of them were five years old or younger.
Enteroviruses belong to the Family Picornaviridae, where the picornaviral genome consists of a single strand of message-active RNA. Presently, it is known that there are 66 types that can infect human, including Polioviruses type 1-3, Coxsackieviruses A group, Coxsackieviruses B group, Echoviruses and Enteroviruses type 68-71. Most of the syndromes caused by enterovirus infections are mild, with few exceptions such as enterovirus 71 (EV71) where severe diseases even death may incur.
It will be challenging to develop vaccines against enteroviruses due to the multiple serotypes. Therefore, an effort has been made to study the protease 2A that plays a major role in viral replication, and may serve as a molecular target for anti-enterovirus therapy. We started by analysis of the protease 2A in 10 EV71 isolates from the 1998 outbreak and 10 Coxsackie B1 (CVB1) strains collected during 1993-1999. Analysis sequences of the DNA nucleotide and protein amino acid showed that the variations among the EV71 are slight whereas those of CVB1 are greater. We further map the cleavage site of the protease 2A in EV71 prototypic strain (BrCr) by molecular cloning followed by site-directed mutagenesis. The cleavage site was confirmed by both prokaryotic and eukaryotic expression systems. As for the study on the CVB1, two clinical isolates, CVB1-8 and CVB1-5, with relatively greater variations in the protease 2A were used for further investigation. It was shown that the rate of viral replication and cytopathic effect is more rapid with the CVB1-8 infection than those with the CVB1-5 in the Vero and GBM cells. This is consistent with the finding that the cleavage of the host protein-eIF4G by protease 2A is more effective with CVB1-8 infection. The data indicate that the variations in the protease 2A regions between these two CVB isolates may account for the differences in their replication and pathogenesis. Experiments to clarify the mechanism are in progress.
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