Center for Vector-borne Disease Research and Department of Pathology, Microbiology and Immunology, School of Veterinary Medicine, University of California, Davis, CA 95616, USA.
Division of Vector-Borne Diseases, Centers for Disease Control and Prevention (CDC), Fort Collins, CO 80521, USA.
J Gen Virol. 2012 Jan;93(Pt 1):39-49. doi: 10.1099/vir.0.033159-0. Epub 2011 Sep 21.
Despite utilizing the same avian hosts and mosquito vectors, St Louis encephalitis virus (SLEV) and West Nile virus (WNV) display dissimilar vector-infectivity and vertebrate-pathogenic phenotypes. SLEV exhibits a low oral infection threshold for Culex mosquito vectors and is avirulent in avian hosts, producing low-magnitude viraemias. In contrast, WNV is less orally infective to mosquitoes and elicits high-magnitude viraemias in a wide range of avian species. In order to identify the genetic determinants of these different phenotypes and to assess the utility of mosquito and vertebrate cell lines for recapitulating in vivo differences observed between these viruses, reciprocal WNV and SLEV pre-membrane and envelope protein (prME) chimeric viruses were generated and growth of these mutant viruses was characterized in mammalian (Vero), avian (duck) and mosquito [Aedes (C6/36) and Culex (CT)] cells. In both vertebrate lines, WNV grew to 100-fold higher titres than SLEV, and growth and cytopathogenicity phenotypes, determined by chimeric phenotypes, were modulated by genetic elements outside the prME gene region. Both chimeras exhibited distinctive growth patterns from those of SLEV in C6/36 cells, indicating the role of both structural and non-structural gene regions for growth in this cell line. In contrast, growth of chimeric viruses was indistinguishable from that of virus containing homologous prME genes in CT cells, indicating that structural genetic elements could specifically dictate growth differences of these viruses in relevant vectors. These data provide genetic insight into divergent enzootic maintenance strategies that could also be useful for the assessment of emergence mechanisms of closely related flaviviruses.
尽管使用了相同的禽类宿主和蚊子媒介，但圣路易斯脑炎病毒（SLEV）和西尼罗河病毒（WNV）表现出不同的媒介感染性和脊椎动物致病性表型。SLEV 对库蚊媒介的口服感染阈值较低，在禽类宿主中无致病性，产生低幅度的病毒血症。相比之下，WNV 对蚊子的口服感染性较低，在多种禽类物种中引起高幅度的病毒血症。为了确定这些不同表型的遗传决定因素，并评估蚊子和脊椎动物细胞系在再现这些病毒之间体内差异的实用性，生成了 SLEV 和 WNV 包膜前膜和包膜蛋白（prME）嵌合病毒，并在哺乳动物（Vero）、禽类（鸭）和蚊子 [埃及伊蚊（Aedes（C6/36）和库蚊（CT）]细胞中对这些突变病毒的生长进行了特征描述。在两种脊椎动物系中，WNV 的生长滴度比 SLEV 高 100 倍，并且由嵌合表型确定的生长和细胞病变表型受 prME 基因区域以外的遗传元件调节。两种嵌合体在 C6/36 细胞中的生长模式都与 SLEV 明显不同，这表明结构和非结构基因区域都对该细胞系的生长起作用。相比之下，在 CT 细胞中，嵌合病毒的生长与含有同源 prME 基因的病毒无法区分，这表明结构遗传元件可以特异性决定这些病毒在相关媒介中的生长差异。这些数据为不同的地方性维持策略提供了遗传见解，这对于评估密切相关的黄病毒的出现机制也可能有用。
