Department of Ecology and Evolutionary Biology, Princeton University, Princeton, NJ 08544, USA.
Biol Lett. 2010 Aug 23;6(4):505-8. doi: 10.1098/rsbl.2009.1019. Epub 2010 Feb 10.
Most models of virulence evolution assume that transmission and virulence are constant during an infection. In many viral (HIV and influenza), bacterial (TB) and prion (BSE and CWD) systems, disease-induced mortality occurs long after the host becomes infectious. Therefore, we constructed a model with two infected classes that differ in transmission rate and virulence in order to understand how the evolutionarily stable strategy (ESS) depends on the relative difference in transmission and virulence between classes, on the transition rate between classes and on the recovery rate from the second class. We find that ESS virulence decreases when expressed early in the infection or when transmission occurs late in an infection. When virulence occurred relatively equally in each class and there was disease recovery, ESS virulence increased with increased transition rate. In contrast, ESS virulence first increased and then decreased with transition rate when there was little virulence early in the infection and a rapid recovery rate. This model predicts that ESS virulence is highly dependent on the timing of transmission and pathology after infection; thus, pathogen evolution may either increase or decrease virulence after emergence in a new host.
大多数毒力进化模型都假设在感染过程中传播和毒力是恒定的。在许多病毒（HIV 和流感）、细菌（TB）和朊病毒（BSE 和 CWD）系统中，宿主具有传染性后很久才会因疾病而死亡。因此，我们构建了一个具有两个感染类别的模型，这两个类别在传播率和毒力方面存在差异，以便了解进化稳定策略（ESS）如何取决于类别之间的传播和毒力的相对差异、类别之间的转变率以及从第二类恢复的速率。我们发现，当感染早期表达毒力或感染后期传播时，ESS 毒力会降低。当每个类别中的毒力相对相等并且存在疾病恢复时，ESS 毒力随转变率的增加而增加。相比之下，当感染早期毒力较低且恢复速率较快时，ESS 毒力随转变率先增加后减少。该模型预测 ESS 毒力高度依赖于感染后传播和发病的时间；因此，病原体进化在新宿主中出现后可能会增加或降低毒力。
