Data from: A phylogenomic analysis of Marek's disease virus (MDV) reveals independent paths to virulence in Eurasia and North America

Virulence determines the impact a pathogen has on the fitness of its host, yet current understanding of the evolutionary origins and causes of virulence of many pathogens is surprisingly incomplete. Here, we explore the evolution of Marek's disease virus (MDV), a herpesvirus commonly afflicting chickens and rarely other avian species. The history of MDV in the 20th century represents an important case study in the evolution of virulence. The severity of MDV infection in chickens has been rising steadily since the adoption of intensive farming techniques and vaccination programs in the 1950s and 1970s respectively. It has remained uncertain, however, which of these factors is causally more responsible for the observed increase in virulence of circulating viruses. We conducted a phylogenomic study to understand the evolution of MDV in the context of dramatic changes to poultry farming and disease control. Our analysis reveals evidence of geographical structuring of MDV strains, with reconstructions supporting the emergence of virulent viruses independently in North America and Eurasia. Of note, the emergence of virulent viruses appears to coincide approximately with the introduction of comprehensive vaccination on both continents. The time-dated phylogeny also indicated that MDV has a mean evolutionary rate of ~1.6 x 10-5 substitutions / site / year. An examination of gene-linked mutations did not identify a strong association between mutational variation and virulence phenotypes, indicating that MDV may evolve readily and rapidly under strong selective pressures, and that multiple genotypic pathways may underlie virulence adaptation in MDV.

毒力决定了病原体对宿主适合度的影响，但目前学界对众多病原体毒力的进化起源与致病机制的认知仍存在出人意料的缺失。本研究聚焦马立克氏病病毒（Marek's disease virus, MDV）的进化过程，该病毒为疱疹病毒科成员，主要感染鸡，极少侵染其他禽类。20世纪马立克氏病病毒的演化史，是研究毒力进化的重要案例。自20世纪50年代、70年代分别推行集约化养殖技术与疫苗接种计划以来，鸡群中马立克氏病的感染严重程度持续攀升。然而，学界始终无法明确，在当前流行毒株毒力增强的现象中，上述两项因素究竟何者发挥了更关键的致病作用。为探究家禽养殖与疫病防控模式剧变背景下马立克氏病病毒的进化规律，本研究开展了系统发育基因组学分析。分析结果显示马立克氏病病毒毒株存在地理分化特征，系统发育重建结果表明，高毒力毒株分别在北美与欧亚大陆独立出现。值得注意的是，高毒力毒株的出现时间，与两大洲全面推行疫苗接种的时间大致吻合。时间标定系统发育树分析还显示，马立克氏病病毒的平均进化速率约为1.6×10^-5 替换/位点/年。对基因关联突变的分析并未发现突变变异与毒力表型间存在显著关联，这提示马立克氏病病毒可在强选择压力下快速且易变地进化，且其毒力适应性可能存在多种基因型通路。