Arthropod-borne and Infectious Diseases Laboratory, Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, Colorado, United States of America.
PLoS One. 2013;8(3):e60427. doi: 10.1371/journal.pone.0060427. Epub 2013 Mar 27.
Western equine encephalitis virus (WEEV) is a naturally occurring recombinant virus derived from ancestral Sindbis and Eastern equine encephalitis viruses. We previously showed that infection by WEEV isolates McMillan (McM) and IMP-181 (IMP) results in high (∼90-100%) and low (0%) mortality, respectively, in outbred CD-1 mice when virus is delivered by either subcutaneous or aerosol routes. However, relatively little is known about specific virulence determinants of WEEV. We previously observed that IMP infected Culex tarsalis mosquitoes at a high rate (app. 80%) following ingestion of an infected bloodmeal but these mosquitoes were infected by McM at a much lower rate (10%). To understand the viral role in these phenotypic differences, we characterized the pathogenic phenotypes of McM/IMP chimeras. Chimeras encoding the E2 of McM on an IMP backbone (or the reciprocal) had the most significant effect on infection phenotypes in mice or mosquitoes. Furthermore, exchanging the arginine, present on IMP E2 glycoprotein at position 214, for the glutamine present at the same position on McM, ablated mouse mortality. Curiously, the reciprocal exchange did not confer mouse virulence to the IMP virus. Mosquito infectivity was also determined and significantly, one of the important loci was the same as the mouse virulence determinant identified above. Replacing either IMP E2 amino acid 181 or 214 with the corresponding McM amino acid lowered mosquito infection rates to McM-like levels. As with the mouse neurovirulence, reciprocal exchange of amino acids did not confer mosquito infectivity. The identification of WEEV E2 amino acid 214 as necessary for both IMP mosquito infectivity and McM mouse virulence indicates that they are mutually exclusive phenotypes and suggests an explanation for the lack of human or equine WEE cases even in the presence of active transmission.
西方马脑炎病毒（WEEV）是一种天然重组病毒，源自祖先辛德毕斯病毒和东部马脑炎病毒。我们之前曾表明，当病毒通过皮下或气溶胶途径感染时，源自 McMillan（McM）和 IMP-181（IMP）的 WEEV 分离株分别导致近交系 CD-1 小鼠的高（约 90-100%）和低（0%）死亡率。然而，对于 WEEV 的特定毒力决定因素知之甚少。我们之前观察到，在摄入受感染的血餐之后，IMP 可高效（约 80%）感染库蚊，但 McM 的感染率则低得多（10%）。为了了解病毒在这些表型差异中的作用，我们对 McM/IMP 嵌合体的致病表型进行了特征描述。编码 McM E2 的嵌合体在 IMP 骨架上（或相反）对小鼠或蚊子的感染表型具有最显著的影响。此外，将 IMP E2 糖蛋白第 214 位的精氨酸替换为 McM 中相同位置的谷氨酰胺，可消除小鼠死亡率。奇怪的是，这种相反的替换并未赋予 IMP 病毒对小鼠的毒力。蚊子感染性也得到了确定，而且非常重要的一个基因座与我们之前确定的小鼠毒力决定因素相同。用 McM 相应的氨基酸替换 IMP E2 的氨基酸 181 或 214，会将蚊子的感染率降低到类似于 McM 的水平。与小鼠神经毒力一样，氨基酸的相互替换并未赋予蚊子感染性。WEEV E2 氨基酸 214 对于 IMP 蚊子感染性和 McM 小鼠毒力都是必需的，这表明它们是相互排斥的表型，这也解释了为什么即使存在活跃的传播，也没有人类或马感染 WEE 病毒的病例。
