Data from: A longitudinal study of age-related changes in Haemoproteus infection in a passerine bird

Blood parasites such as malaria and related haemosporidians commonly infect vertebrate species including birds. Understanding age-specific patterns of parasite infections is crucial for quantifying the fitness consequences of parasitism for hosts and for understanding parasite transmission dynamics. We analyzed longitudinal and cross-sectional infection data in house martins (Delichon urbica), a migratory bird suffering from intense haemosporidian infection. We separated within- from among-individual effects of age on prevalence. Our results showed that the probability of blood parasite infection increased as individual house martins aged. We also showed that the prevalence of infection decreased with age at last reproduction when controlling for age, showing a selective disappearance of infected birds from the population (i.e., selection). The estimated effect of age on prevalence was underestimated two- to three-fold if not accounting for such selection. This study highlights the importance of taking among-individual heterogeneity in the capacity to fight a disease into account because such heterogeneity can mask age-related patterns of infection. These findings emphasize the relevance of considering within- and among-individual patterns of infection in order to understand parasite-induced mortality and the potential for parasite transmission.以疟疾及相关血孢子虫（haemosporidians）为代表的血液寄生虫，普遍寄生于包括鸟类在内的脊椎动物类群。解析寄生虫感染的年龄特异性模式，对于量化寄生作用对宿主适合度的影响、阐明寄生虫的传播动态均具有关键意义。本研究针对受重度血孢子虫感染的迁徙鸟类——毛脚燕（Delichon urbica）的纵向与横断面感染数据展开分析，分离了年龄对感染率的个体内效应与个体间效应。研究结果显示，毛脚燕个体的血液寄生虫感染概率随年龄增长而升高。在控制年龄变量的前提下，感染率随末次繁殖年龄的增加而降低，这表明受感染个体从种群中发生选择性消失（即选择作用）。若未考虑此类选择效应，年龄对感染率的估计效应会被低估2至3倍。本研究强调了考量宿主对抗疾病的个体间异质性的重要性——此类异质性可能掩盖感染的年龄相关模式。本研究结果亦凸显了同时分析感染的个体内与个体间模式，对于理解寄生虫诱导的死亡及寄生虫传播潜力的必要性。