Department of Integrative Biology, University of California, Berkeley, CA 94720, USA.
Mathematical Institute, University of Oxford, Oxford OX2 6GG, UK.
Proc Biol Sci. 2021 Aug 11;288(1956):20210900. doi: 10.1098/rspb.2021.0900.
There is increasing interest in the role that evolution may play in current and future pandemics, but there is often also considerable confusion about the actual evolutionary predictions. This may be, in part, due to a historical separation of evolutionary and medical fields, but there is a large, somewhat nuanced body of evidence-supported theory on the evolution of infectious disease. In this review, we synthesize this evolutionary theory in order to provide a framework for clearer understanding of the key principles. Specifically, we discuss the selection acting on zoonotic pathogens' transmission rates and virulence at spillover and during emergence. We explain how the direction and strength of selection during epidemics of emerging zoonotic disease can be understood by a three Ts framework: trade-offs, transmission, and time scales. Virulence and transmission rate may trade-off, but transmission rate is likely to be favoured by selection early in emergence, particularly if maladapted zoonotic pathogens have 'no-cost' transmission rate improving mutations available to them. Additionally, the optimal virulence and transmission rates can shift with the time scale of the epidemic. Predicting pathogen evolution, therefore, depends on understanding both the trade-offs of transmission-improving mutations and the time scales of selection.
人们对进化在当前和未来的大流行病中可能发挥的作用越来越感兴趣，但人们对实际的进化预测往往也存在相当大的混淆。这可能部分是由于进化和医学领域的历史分离，但在传染病进化方面有大量的、有一定细微差别的证据支持的理论。在这篇综述中，我们综合了这一进化理论，以便为更清晰地理解关键原则提供一个框架。具体来说，我们讨论了在溢出和出现期间，对人畜共患病病原体的传播率和毒力起作用的选择。我们解释了如何通过三 T 框架（权衡、传播和时间尺度）来理解新发人畜共患传染病流行期间的选择方向和强度。毒力和传播率可能存在权衡，但在出现的早期，选择可能更有利于传播率，特别是如果不适应的人畜共患病病原体具有“无成本”的传播率改善突变。此外，最佳的毒力和传播率可以随着流行病的时间尺度而变化。因此，预测病原体的进化取决于对传播率改善突变的权衡以及选择的时间尺度的理解。
