Tao Hui, Li Lian, White Maria C, Steel John, Lowen Anice C
Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, USA.
Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, Georgia, USA
J Virol. 2015 Aug;89(16):8453-61. doi: 10.1128/JVI.01162-15. Epub 2015 Jun 3.
The reassortment of gene segments between influenza viruses increases genomic diversity and plays an important role in viral evolution. We have shown previously that this process is highly efficient within a coinfected cell and, given synchronous coinfection at moderate or high doses, can give rise to ~60 to 70% of progeny shed from an animal host. Conversely, reassortment in vivo can be rendered undetectable by lowering viral doses or extending the time between infections. One might also predict that seeding of transmitted viruses into different sites within the target tissue could limit subsequent reassortment. Given the potential for stochastic factors to restrict reassortment during natural infection, we sought to determine its efficiency in a host coinfected through transmission. Two scenarios were tested in a guinea pig model, using influenza A/Panama/2007/99 (H3N2) virus (wt) and a silently mutated variant (var) thereof as parental virus strains. In the first, coinfection was achieved by exposing a naive guinea pig to two cagemates, one infected with wt and the other with var virus. When such exposure led to coinfection, robust reassortment was typically seen, with 50 to 100% of isolates carrying reassortant genomes at one or more time points. In the second scenario, naive guinea pigs were exposed to a cagemate that had been coinoculated with wt and var viruses. Here, reassortment occurred in the coinoculated donor host, multiple variants were transmitted, and reassortants were prevalent in the recipient host. Together, these results demonstrate the immense potential for reassortment to generate viral diversity in nature.
Influenza viruses evolve rapidly under selection due to the generation of viral diversity through two mechanisms. The first is the introduction of random errors into the genome by the viral polymerase, which occurs with a frequency of approximately 10(-5) errors/nucleotide replicated. The second is reassortment, or the exchange of gene segments between viruses. Reassortment is known to occur readily under well-controlled laboratory conditions, but its frequency in nature is not clear. Here, we tested the hypothesis that reassortment efficiency following coinfection through transmission would be reduced compared to that seen with coinoculation. Contrary to this hypothesis, our results indicate that coinfection achieved through transmission supports high levels of reassortment. These results suggest that reassortment is not exquisitely sensitive to stochastic effects associated with transmission and likely occurs in nature whenever a host is infected productively with more than one influenza A virus.
流感病毒之间基因片段的重配增加了基因组多样性，并在病毒进化中发挥重要作用。我们之前已经表明，在共感染细胞内这个过程非常高效，并且在中等或高剂量同步共感染的情况下，可产生约60%至70%从动物宿主排出的子代病毒。相反，通过降低病毒剂量或延长感染之间的时间，体内重配可能变得无法检测到。人们还可能预测，将传播的病毒接种到靶组织内的不同部位可能会限制随后的重配。鉴于随机因素在自然感染期间限制重配的可能性，我们试图确定其在通过传播共感染的宿主中的效率。在豚鼠模型中测试了两种情况，使用甲型流感病毒/巴拿马/2007/99（H3N2）病毒（野生型）及其沉默突变变体（变体）作为亲本病毒株。在第一种情况中，通过将一只未感染的豚鼠暴露于两只同笼饲养的动物来实现共感染，其中一只感染野生型病毒，另一只感染变体病毒。当这种暴露导致共感染时，通常会看到强烈的重配，在一个或多个时间点，50%至100%的分离株携带重配基因组。在第二种情况中，将未感染的豚鼠暴露于一只已同时接种野生型和变体病毒的同笼饲养动物。在这里，重配发生在同时接种的供体宿主中，多个变体被传播，并且重配体在受体宿主中普遍存在。总之，这些结果证明了重配在自然界中产生病毒多样性的巨大潜力。
由于通过两种机制产生病毒多样性，流感病毒在选择压力下迅速进化。第一种是病毒聚合酶将随机错误引入基因组，其发生频率约为每复制核苷酸10^(-5)个错误。第二种是重配，即病毒之间基因片段的交换。已知在严格控制的实验室条件下重配很容易发生，但在自然界中的频率尚不清楚。在这里，我们测试了一个假设，即与同时接种相比，通过传播共感染后的重配效率会降低。与这个假设相反，我们的结果表明通过传播实现的共感染支持高水平的重配。这些结果表明，重配对与传播相关的随机效应不是非常敏感，并且只要宿主被一种以上甲型流感病毒有效感染，重配很可能在自然界中发生。
