Kao Rowland R
Department of Zoology, University of Oxford, South Parks Rd., OX1 3PS, UK.
J Theor Biol. 2006 Oct 7;242(3):634-42. doi: 10.1016/j.jtbi.2006.04.003. Epub 2006 Apr 25.
Maximization of the basic reproduction ratio or R(0) is widely believed to drive the emergence of novel pathogens. The presence of exploitable heterogeneities in a population, such as high variance in the number of potentially infectious contacts, increases R(0) and thus pathogens that can exploit heterogeneities in the contact structure have an advantage over those that do not. However, exploitation of heterogeneities results in a more rapid depletion of the potentially susceptible neighbourhood for an infected host. Here a simple model of pathogen evolution in a heterogeneous environment is developed and placed in the context of HIV transmission. In this model, it is shown that pathogens may evolve towards lower R(0), even if this results in pathogen extinction. For sufficiently high transmissibility, two locally stable strategies exist for an evolving pathogen, one that exploits heterogeneities and results in higher R(0), and one that does not, and results in lower R(0). While the low R(0) strategy is never evolutionarily stable, invading strains with higher R(0) will also converge to the low R(0) strategy if not sufficiently different from the resident strain. Heterogenous transmission is increasingly recognized as fundamental to epidemiological dynamics and the evolution of pathogens; here, it is shown that the ability to exploit heterogeneity is a strategy that can itself evolve.
普遍认为，基本繁殖数R(0)的最大化会推动新型病原体的出现。人群中存在可利用的异质性，例如潜在感染接触数量的高方差，会增加R(0)，因此能够利用接触结构异质性的病原体比不能利用的病原体具有优势。然而，利用异质性会导致感染宿主的潜在易感邻域更快耗尽。本文建立了一个异质环境中病原体进化的简单模型，并将其置于HIV传播的背景下。在这个模型中，研究表明病原体可能会朝着更低的R(0)进化，即使这会导致病原体灭绝。对于足够高的传播性，进化中的病原体存在两种局部稳定策略，一种利用异质性并导致更高的R(0)，另一种不利用异质性并导致更低的R(0)。虽然低R(0)策略在进化上永远不稳定，但如果入侵菌株与驻留菌株的差异不够大，具有较高R(0)的入侵菌株也会收敛到低R(0)策略。异质传播越来越被认为是流行病学动态和病原体进化的基础；本文表明，利用异质性的能力本身就是一种可以进化的策略。
