Levin B R
Emory University, Atlanta, Georgia 30322, USA.
Emerg Infect Dis. 1996 Apr-Jun;2(2):93-102. doi: 10.3201/eid0202.960203.
In recent years, population and evolutionary biologists have questioned the traditional view that parasite-mediated morbidity and mortality¿virulence¿is a primitive character and an artifact of recent associations between parasites and their hosts. A number of hypotheses have been proposed that favor virulence and suggest that it will be maintained by natural selection. According to some of these hypotheses, the pathogenicity of HIV, Vibrio cholerae, Mycobacterium tuberculosis,theShigella,as well as Plasmodium falciparum,and many other microparasites, are not only maintained by natural selection, but their virulence increases or decreases as an evolutionary response to changes in environmental conditions or the density and/or behavior of the human population. Other hypotheses propose that the virulence of microparasites is not directly favored by natural selection; rather, microparasite-mediated morbidity and mortality are either coincidental to parasite-expressed characters (virulence determinants that evolved for other functions) or the product of short-sighted evolution in infected hosts. These hypotheses for the evolution and maintenance of microparasite virulence are critically reviewed, and suggestions are made for testing them experimentally.
近年来，种群生物学家和进化生物学家对传统观点提出了质疑，该传统观点认为寄生虫介导的发病和死亡——即毒力——是一种原始特征，是寄生虫与其宿主近期关联产生的一种假象。人们提出了一些支持毒力的假说，并表明毒力将通过自然选择得以维持。根据其中一些假说，人类免疫缺陷病毒、霍乱弧菌、结核分枝杆菌、志贺氏菌以及恶性疟原虫和许多其他微寄生虫的致病性不仅通过自然选择得以维持，而且其毒力会随着对环境条件变化或人类种群密度和/或行为变化的进化反应而增加或降低。其他假说则提出，微寄生虫的毒力并非直接受到自然选择的青睐；相反，微寄生虫介导的发病和死亡要么与寄生虫表达的特征（为其他功能而进化的毒力决定因素）巧合，要么是受感染宿主中短视进化的产物。本文对这些关于微寄生虫毒力进化和维持的假说进行了批判性综述，并提出了通过实验对其进行检验的建议。
