Department of Biology, Center for Infectious Disease Dynamics, The Pennsylvania State University, University Park, PA, USA.
Proc Biol Sci. 2023 Mar 29;290(1995):20230117. doi: 10.1098/rspb.2023.0117.
A common assumption in the evolution of virulence theory literature is that pathogens transmit better when they exploit their host more heavily, but by doing so, they impose a greater risk of killing their host, thus truncating infectious periods and reducing their own opportunities for transmission. Here, I derive an equation for the magnitude of this cost in terms of the infection fatality rate, and in doing so, I show that there are many cases where mortality costs are too small to plausibly constrain increases in host exploitation by pathogens. I propose that pathogen evolution may often be constrained by detection costs, whereby hosts alter their behaviour when infection is detectable, and thus reduce pathogen opportunities for onward transmission. I then derive an inequality to illustrate when mortality costs or detection costs impose stronger constraints on pathogen evolution, and I use empirical data from the literature to demonstrate that detection costs are frequently large in both human and animal populations. Finally, I give examples of how evolutionary predictions can change depending on whether costs of host exploitation are borne out through mortality or detection.
在毒力理论文献的演变中，一个常见的假设是，当病原体更严重地利用宿主时，它们的传播效果更好，但这样做会增加杀死宿主的风险，从而缩短感染期并减少自身传播的机会。在这里，我根据感染死亡率推导出了一个用于衡量这种成本的方程，由此可以看出，在许多情况下，死亡率成本太小，不太可能限制病原体对宿主的利用程度增加。我提出病原体的进化可能经常受到检测成本的限制，即宿主在感染可检测时改变其行为，从而减少病原体继续传播的机会。然后，我推导出一个不等式来说明死亡率成本或检测成本对病原体进化的限制更强，我使用文献中的经验数据来证明在人类和动物群体中，检测成本通常都很大。最后，我给出了一些例子，说明根据宿主利用成本是通过死亡率还是检测来承担，进化预测可能会发生怎样的变化。
