Experimental passage of St. Louis encephalitis virus in vivo in mosquitoes and chickens reveals evolutionarily significant virus characteristics.
Experimental passage of St. Louis encephalitis virus in vivo in mosquitoes and chickens reveals evolutionarily significant virus characteristics.
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DOI：
10.1371/journal.pone.0007876
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发表时间：
2009-11-17
期刊：
影响因子：
3.7
通讯作者：
Kramer LD
中科院分区：
文献类型：
--
作者：
Ciota AT;Jia Y;Payne AF;Jerzak G;Davis LJ;Young DS;Ehrbar D;Kramer LD
圣路易斯脑炎病毒（SLEV;黄病毒科，黄病毒）是1999年西尼罗河病毒（WNV）引入之前美国流行性黄病毒脑炎的主要原因。然而，在活动水平和地理分布方面，SLEV的爆发比WNV明显更有限。对这些可变的活性水平的一个可能的解释是，每种病毒适应其宿主周期的潜力存在差异。虫媒病毒需要在不同的宿主中复制，这被认为是对进化和宿主特异性适应的限制。如果循环是在自然界中观察到的遗传稳定性的原因，并且虫媒病毒缺乏宿主特化，那么连续传代应导致突变的积累和更适合在该宿主中复制的特化病毒。以前的研究表明，西尼罗河病毒和SLEV的遗传变化和主机专业化的能力不同，并在成本每个专业化。在试图澄清如何选择压力有助于流行病学模式的WNV和SLEV，我们评估突变体谱的大小，共识遗传变化，并在体内SLEV表型变化后，通过接种在库蚊蚊或鸡20个连续传代。结果表明，遗传变化的能力是大的SLEV和突变谱的大小是主机依赖性使用我们的传代方法。尽管如此，一般缺乏共识的变化，导致通过在任何主机，结果形成鲜明对比的想法，在自然界中的进化的限制，结果从主机循环。结果还表明，一个高水平的适应两个主机已经存在，尽管主机循环。一个菌株显着更具感染性的鸡出现从一个谱系的鸡通道，但其他谱系和所有蚊子通道株没有显示出可测量的主机特定的健身收益。此外，鸡的感染性增加并没有降低蚊子的感染性，这进一步对比了虫媒病毒的适应性权衡的概念。
St. Louis encephalitis virus (SLEV; Flaviviridae, flavivirus) was the major cause of epidemic flaviviral encephalitis in the U.S. prior to the introduction of West Nile virus (WNV) in 1999. However, outbreaks of SLEV have been significantly more limited then WNV in terms of levels of activity and geographic dispersal. One possible explanation for these variable levels of activity is that differences in the potential for each virus to adapt to its host cycle exist. The need for arboviruses to replicate in disparate hosts is thought to result in constraints on both evolution and host-specific adaptation. If cycling is the cause of genetic stability observed in nature and arboviruses lack host specialization, then sequential passage should result in both the accumulation of mutations and specialized viruses better suited for replication in that host. Previous studies suggest that WNV and SLEV differ in capacity for both genetic change and host specialization, and in the costs each accrues from specializing. In an attempt to clarify how selective pressures contribute to epidemiological patterns of WNV and SLEV, we evaluated mutant spectra size, consensus genetic change, and phenotypic changes for SLEV in vivo following 20 sequential passages via inoculation in either Culex pipiens mosquitoes or chickens. Results demonstrate that the capacity for genetic change is large for SLEV and that the size of the mutant spectrum is host-dependent using our passage methodology. Despite this, a general lack of consensus change resulted from passage in either host, a result that contrasts with the idea that constraints on evolution in nature result from host cycling alone. Results also suggest that a high level of adaptation to both hosts already exists, despite host cycling. A strain significantly more infectious in chickens did emerge from one lineage of chicken passage, yet other lineages and all mosquito passage strains did not display measurable host-specific fitness gains. In addition, increased infectivity in chickens did not decrease infectivity in mosquitoes, which further contrasts the concept of fitness trade-offs for arboviruses.
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