Evolution of acute infections and the invasion-persistence trade-off.
Evolution of acute infections and the invasion-persistence trade-off.
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DOI：
10.1086/597217
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发表时间：
2009-04
期刊：
影响因子：
--
通讯作者：
Bjørnstad ON
中科院分区：
文献类型：
--
作者：
King AA;Shrestha S;Harvill ET;Bjørnstad ON
我们试图了解有利于急性、高度传染性感染演变的条件。大多数关于病原体生活史进化的工作都集中在传播和毒力之间的权衡上。在这里，我们关注的是一种明显的权衡，即使在无毒的病原体之间，病原体的入侵速度和它在有限宿主群体中持续存在的能力之间也是如此。其他作者已经展示了这种入侵-持久性的权衡如何导致中等病原体攻击率，但只有通过在病原体的传播性和感染期的持续时间之间进行权衡才能做到这一点。在这里，我们通过将宿主内病原体动力学的模型-其中病原体的生活史参数直接显示-与种群水平的流行病学模型联系起来进行更深入的研究。我们发现，进化轨迹的一个关键决定因素是将宿主内病原体负载与宿主间传播联系起来的剂量-反应曲线的形状。特别是，在通常的比例假设下，我们发现病原体往往进化到自身灭绝的边缘。在更现实的假设下，存在一个关键的寄主种群规模，超过这个数量，高度急性的病原体将被缓冲，使其免于灭绝。我们的研究是由于百日咳杆菌和副百日咳杆菌这两种人类病原体的敏感度的出现，这两种病原体是从一种以野生动物慢性(非急性)感染为特征的祖先--支气管败血博德氏菌独立进化而来的。与预测更大或更密集种群中更具侵袭性的病原体进化的过多模型不同，入侵与持久性之间的权衡也适用于频率依赖的病原体。
We seek to understand the conditions favoring the evolution of acute, highly transmissible infections. Most work on the life-history evolution of pathogens has focused on the transmission-virulence trade-off. Here we focus on a distinct trade-off that operates, even among avirulent pathogens, between a pathogen’s speed of invasion and its ability to persist in a finite host population. Other authors have shown how this invasion-persistence trade-off can lead to intermediate pathogen attack rates but have done so only by imposing trade-offs between the pathogen’s transmissibility and the duration of the infectious period. Here we delve deeper, by linking a model of within-host pathogen dynamics—in which pathogen life-history parameters figure directly—to an epidemiological model at the population level. We find that a key determinant of the evolutionary trajectory is the shape of the dose-response curve that relates within-host pathogen load to between-host transmission. In particular, under the usual assumption of proportionality we find that pathogens tend to evolve to the edge of their own extinction. Under more realistic assumptions, a critical host population size exists, above which highly acute pathogens are buffered from extinction. Our study is motivated by the emergence of acuteness in two human pathogens, Bordetella pertussis and Bordetella parapertussis, which independently evolved from an ancestor, Bordetella bronchiseptica, characterized by chronic (nonacute) infection of wildlife. In contrast to the plethora of models that predict evolution of more aggressive pathogens in larger or denser populations, the invasion-persistence trade-off also operates for frequency-dependent pathogens.
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