Institute for Human Infections and Immunity, Center for Tropical Diseases, and Department of Pathology, University of Texas Medical Branch, Galveston, Texas, USA.
Department of Biochemistry & Molecular Biology and Sealy Center for Structural Biology & Molecular Biophysics, University of Texas Medical Branch, Galveston, Texas, USA.
J Virol. 2014 Aug;88(16):9260-7. doi: 10.1128/JVI.01463-14. Epub 2014 Jun 4.
Western equine encephalitis virus (WEEV) is an arbovirus from the genus Alphavirus, family Togaviridae, which circulates in North America between birds and mosquitoes, occasionally causing disease in humans and equids. In recent decades, human infection has decreased dramatically; the last documented human case in North America occurred in 1994, and the virus has not been detected in mosquito pools since 2008. Because limited information exists regarding the evolution of WEEV, we analyzed the genomic sequences of 33 low-passage-number strains with diverse geographic and temporal distributions and performed comprehensive phylogenetic analyses. Our results indicated that WEEV is a highly conserved alphavirus with only approximately 5% divergence in its most variable genes. We confirmed the presence of the previously determined group A and B lineages and further resolved group B into three sublineages. We also observed an increase in relative genetic diversity during the mid-20th century, which correlates with the emergence and cocirculation of several group B sublineages. The estimated WEEV population size dropped in the 1990s, with only the group B3 lineage being sampled in the past 20 years. Structural mapping showed that the majority of substitutions in the envelope glycoproteins occurred at the E2-E2 interface. We hypothesize that an event occurred in the mid-20th century that resulted in the increased genetic diversity of WEEV in North America, followed by genetic constriction due to either competitive displacement by the B3 sublineage or stochastic events resulting from a population decline.
Western equine encephalitis virus (WEEV) has caused several epidemics that resulted in the deaths of thousands of humans and hundreds of thousands of equids during the past century. During recent decades, human infection decreased drastically and the virus has not been found in mosquito pools since 2008. Because limited information exists regarding the evolution of WEEV, we analyzed 33 complete genome sequences and conducted comprehensive phylogenetic analyses. We confirmed the presence of two major lineages, one of which diverged into three sublineages. Currently, only one of those sublineages is found circulating in nature. Understanding the evolution of WEEV over the past century provides a unique opportunity to observe an arbovirus that is in decline and to better understand what factors can cause said decline.
西方马脑炎病毒（WEEV）是一种黄病毒属、披膜病毒科的虫媒病毒，在北美洲的鸟类和蚊子之间循环，偶尔会导致人类和马科动物患病。近几十年来，人类感染病例急剧减少；北美最后一例有记录的人类病例发生在 1994 年，自 2008 年以来，蚊子池中未检测到该病毒。由于有关 WEEV 进化的信息有限，我们分析了 33 株具有不同地理和时间分布的低传代数量的毒株的基因组序列，并进行了全面的系统发育分析。我们的结果表明，WEEV 是一种高度保守的黄病毒，其最可变基因的差异约为 5%。我们证实了先前确定的 A 组和 B 组谱系的存在，并进一步将 B 组分为三个亚谱系。我们还观察到 20 世纪中叶遗传多样性增加，这与几个 B 组亚谱系的出现和共同循环有关。WEEV 种群数量在 20 世纪 90 年代下降，在过去的 20 年中只检测到 B 组 3 亚谱系。结构映射显示，包膜糖蛋白中的大多数替换发生在 E2-E2 界面。我们假设 20 世纪中期发生了一件事，导致北美 WEEV 的遗传多样性增加，随后由于 B 组 3 亚谱系的竞争替代或种群减少导致遗传收缩。
西方马脑炎病毒（WEEV）在过去一个世纪中引发了几次流行，导致数千人死亡，数万人和数十万匹马死亡。近几十年来，人类感染病例急剧减少，自 2008 年以来，蚊子池中未发现该病毒。由于有关 WEEV 进化的信息有限，我们分析了 33 个完整的基因组序列，并进行了全面的系统发育分析。我们证实了两种主要谱系的存在，其中一种分化为三个亚谱系。目前，只有一个亚谱系在自然界中循环。了解 WEEV 在过去一个世纪中的进化为观察一种正在衰落的虫媒病毒提供了一个独特的机会，并更好地了解是什么因素导致了这种衰落。
