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ABSTRACT: The 17D-204 vaccine manufactured in South Africa (17D-204-SA) and a large plaque variant (17D-LP) derived from it were highly virulent in adult mice. The LD50 of 17D-LP virus was 0-2 p.f.u. for mice following intracerebral inoculation. In comparison, a medium plaque variant derived from 17D-LP, termed 17D-MP virus, was found to be attenuated in adult mice following the same route of inoculation (> 10(4) p.f.u./LD50). Replication of 17D-MP virus was decreased in infected mouse brains compared to 17D-LP virus. Also, 17D-MP virus was slightly temperature sensitive at 39.5 degrees C. Compared to its parent viruses, 17D-204-SA and 17D-LP, 17D-MP virus had one unique mutation at nt 8045 in the genome which resulted in a single amino acid substitution (Pro --> Ser) at residue 137 of the NS5 protein and appeared to be the mutation responsible for the attenuation of 17D-MP virus. This is the first time that altered virulence of a flavivirus caused by mutation in a non-structural protein gene, other than NS1, has been reported.
Journal of General Virology 08/1998; 79 ( Pt 8):1895-9. · 3.36 Impact Factor
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ABSTRACT: The heterogeneous nature of the yellow fever (YF) 17D-204 vaccine virus population was exploited in this study to isolate virus variants able to escape neutralization by the 17D-204 vaccine-specific MAb 864. The conformational change on the virus surface that resulted in the loss of the MAb 864-defined epitope was effected in each variant by a single amino acid mutation in the envelope (E) protein at either position E-305 or E-325. Interestingly, both positions were mutated during attenuation of the 17D-204 vaccine substrain from the wildtype Asibi strain. The mutations in several of the variants represented reversion to the wildtype Asibi virus sequence consistent with loss of a 17D-204 substrain-specific epitope. The majority of the variant viruses were shown to have altered mouse neurovirulence phenotypes, ranging from complete avirulence through to increased virulence. The avirulent variants are the first flavivirus MAb-neutralization-resistant variants to be attenuated for neurovirulence in the adult mouse model. Overall, the results indicate that the E protein epitope recognized by MAb 864 defines a functionally important region that encodes major molecular determinants of YF virus pathogenesis in vivo.
Virology 05/1998; 244(1):59-65. · 3.35 Impact Factor
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ABSTRACT: The live-attenuated yellow fever (YF) vaccine virus, strain 17D-204, has long been known to consist of a heterologous population of virions. Gould et al. (J. Gen. Virol. 70, 1889-1894 (1989)) previously demonstrated that variant viruses exhibiting a YF wild-type-specific envelope (E) protein epitope are present at low frequency in the vaccine pool and were able to isolate representative virus variants with and without this epitope, designated 17D(+wt) and 17D(-wt), respectively. These variants were employed here in an investigation of YF virus pathogenesis in the mouse model. Both the 17D-204 parent and the 17D(+wt) variant viruses were lethal for adult outbred mice by the intracerebral route of inoculation. However, the 17D(-wt) variant was significantly attenuated (18% mortality rate) and replicated to much lower titer in the brains of infected mice. A single amino acid substitution in the envelope (E) protein at E-240 (Ala-->Val) was identified as responsible for the restricted replication of the 17D(-wt) variant in vivo. The 17D(+wt) variant has an additional second-site mutation, believed to encode a reversion to the neurovirulence phenotype of the 17D-204 parent virus. The amino acid substitution in the E protein at E-173 (Thr-->Ile) of the 17D(+wt) variant which results in the appearance of the wild-type-specific epitope or nucleotide changes in the 5' and 3' noncoding regions of the virus are proposed as a candidates.
Virology 04/1997; 230(2):376-80. · 3.35 Impact Factor
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ABSTRACT: Of four wild-type strains (Nakayama-original, SA14, 826309 and Beijing-1) of Japanese encephalitis (JE) virus that were passaged six times in HeLa cells (HeLa p6), two (Nakayama-original and 826309) became attenuated for mice. In the case of strain Nakayama-original, the virulence for mice was markedly reduced and attenuation was retained on passage in primary chicken embryo fibroblast, LLC-MK2 and C6/36 cells. The binding of non-HeLa-passaged Nakayama virus to mouse brain membrane receptor preparations could be differentiated from binding by Nakayama HeLa p6 virus, suggesting that the envelope (E) protein is involved in the attenuated phenotype. Both of the attenuated viruses can be distinguished from the virulent non-HeLa-passaged parental viruses by examination with E protein reactive vaccine and wild-type-specific monoclonal antibodies (MAbs). The vaccine-specific MAb V23, which is only reactive with the SA14 series of live vaccine viruses, recognized the HeLa cell-attenuated Nakayama-original and 826309 viruses, whereas two wild-type-specific MAbs (MAbs K13 and K39) lost reactivity. Comparison of the nucleotide sequences of the structural protein genes of the 826309 and Nakayama-original virulent parent and attenuated HeLa p6 viruses revealed that the viruses differed by 37 and 46 nucleotides coding for eight and nine amino acid mutations, respectively. However, other than one amino acid in the E protein, the membrane and E protein amino acid sequences of the two attenuated HeLa p6 viruses were identical.
Journal of General Virology 12/1995; 76 ( Pt 11):2757-64. · 3.36 Impact Factor
