School of Mathematics and Statistics, University of Sheffield, Sheffield S3 7RH, UK.
Proc Biol Sci. 2012 Aug 22;279(1741):3234-40. doi: 10.1098/rspb.2012.0647. Epub 2012 May 2.
By definition, parasites harm their hosts, but in many infections much of the pathology is driven by the host immune response rather than through direct damage inflicted by parasites. While these immunopathological effects are often well studied and understood mechanistically in individual disease interactions, there remains relatively little understanding of their broader impact on the evolution of parasites and their hosts. Here, we theoretically investigate the implications of immunopathology, broadly defined as additional mortality associated with the host's immune response, on parasite evolution. In particular, we examine how immunopathology acting on different epidemiological traits (namely transmission, virulence and recovery) affects the evolution of disease severity. When immunopathology is costly to parasites, such that it reduces their fitness, for example by decreasing transmission, there is always selection for increased disease severity. However, we highlight a number of host-parasite interactions where the parasite may benefit from immunopathology, and highlight scenarios that may lead to the evolution of slower growing parasites and potentially reduced disease severity. Importantly, we find that conclusions on disease severity are highly dependent on how severity is measured. Finally, we discuss the effect of treatments used to combat disease symptoms caused by immunopathology.
根据定义，寄生虫会伤害它们的宿主，但在许多感染中，大部分病理学是由宿主免疫反应驱动的，而不是寄生虫直接造成的损害。虽然这些免疫病理学效应在个体疾病相互作用中通常得到了很好的研究和机制理解，但对于它们对寄生虫和宿主进化的更广泛影响，人们的理解相对较少。在这里，我们从理论上探讨了免疫病理学（广义上定义为与宿主免疫反应相关的额外死亡率）对寄生虫进化的影响。具体来说，我们研究了免疫病理学作用于不同流行病学特征（即传播、毒力和恢复）如何影响疾病严重程度的进化。当免疫病理学对寄生虫有代价，例如通过降低传播能力而降低其适应性时，总会选择增加疾病的严重程度。然而，我们强调了一些寄生虫可能受益于免疫病理学的宿主-寄生虫相互作用，并强调了可能导致生长缓慢的寄生虫和潜在疾病严重程度降低的情况。重要的是，我们发现关于疾病严重程度的结论高度依赖于如何衡量严重程度。最后，我们讨论了用于对抗免疫病理学引起的疾病症状的治疗方法的影响。
