In host–parasite co-evolution, parasites are assumed to have an advantage owing to their shorter generation time. Evolution of pathogens within the lifetime of a host individual is implicated as a strong selective force in the evolution of sex and aging in the host. However, this assumption or its testable predictions have not been examined empirically. We classified infectious bacteria and viruses into those that can have continued long-term existence on the host body (group 1) versus those that have only a short-term interaction during an active infection (group 2). We surveyed the literature for age-specific incidence data about infections from both the groups. The age trends of the two groups show contrasting patterns. The incidence of infections by all group 1 pathogens showed a 2.28- to 28-fold increase in older ages. In group 2, 6 out of the 9 pathogens showed a significant declining trend in incidence with age. In both groups, there was greater mortality or morbidity among the infected in the old-age classes. These patterns are better explained by pathogen evolution than by age-related decline in immunity.

中文翻译：

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老年感染：免疫力下降或进化的机会主义者？

在宿主-寄生虫共同进化中，寄生虫被认为具有优势，因为它们的世代时间较短。宿主个体一生中病原体的进化被认为是宿主性别和衰老进化中的强大选择力。然而，这一假设或其可检验的预测尚未经过实证检验。我们将传染性细菌和病毒分为可以在宿主体内持续长期存在的细菌和病毒（第 1 组）和在活动性感染期间仅具有短期相互作用的细菌和病毒（第 2 组）。我们调查了有关两组感染的特定年龄发病率数据的文献。两组的年龄趋势呈现出截然不同的模式。所有第 1 组病原体的感染发生率在年龄较大时增加了 2.28 至 28 倍。在第 2 组中，9种病原体中有6种随着年龄的增长，发病率呈显着下降趋势。在这两组中，老年人群中感染者的死亡率或发病率更高。病原体进化比年龄相关的免疫力下降更好地解释了这些模式。