Data from: Virulence-driven trade-offs in disease transmission: a meta-analysis

The virulence--transmission trade-off hypothesis proposed more than 30 years ago is the cornerstone in the study of host-parasite co-evolution. This hypothesis rests on the premise that virulence is an unavoidable and increasing cost because the parasite uses host resources to replicate. This cost associated with replication ultimately results in a deceleration in transmission rate because increasing within-host replication increases host mortality. Empirical tests of predictions of the hypothesis have found mixed support, which cast doubt about its overall generalizability. To quantitatively address this issue, we conducted a meta-analysis of 30 empirical studies, after reviewing over 4000 published papers, focusing on the four core relationships between (1) virulence and recovery rate, (2) within-host replication rate and virulence, (3) within-host replication and transmission rate, and (4) virulence and transmission rate. We found strong support for an increasing relationship between replication and virulence, and replication and transmission. While the overall mean effect suggests that these relationships decelerate with increasing parasite replication, which theoretically arises from limited host resources to exploit, the effect was uncertain due to high within-study variability. There was insufficient data to quantitatively test the other two core relationships predicted by the theory. Overall, the results suggest that the current empirical evidence provides partial support for the trade-off hypothesis, but more work remains to be done.

三十余年前提出的毒力（virulence）-传播（transmission）权衡假说，是宿主-寄生虫协同进化（host-parasite co-evolution）研究领域的基石理论。该假说的核心前提为：寄生虫利用宿主资源进行增殖时，毒力会随之产生且不断升高，这是无法避免的代价。这种与增殖相关的代价最终会导致传播速率放缓，因为宿主体内增殖水平的提升会升高宿主死亡率。针对该假说预测的实证检验结果喜忧参半，这使得学界对其整体普适性提出了质疑。
为从定量层面解决这一问题，我们在梳理4000余篇已发表文献后，对30项实证研究开展了元分析（meta-analysis），重点关注四大核心关联：（1）毒力与恢复速率；（2）宿主体内增殖速率（within-host replication rate）与毒力；（3）宿主体内增殖（within-host replication）与传播速率；（4）毒力与传播速率。我们发现，增殖与毒力、增殖与传播之间均存在显著的正向关联，这一结论得到了强有力的实证支持。尽管整体平均效应显示，随着寄生虫增殖水平提升，上述关联会呈现放缓趋势——这一现象在理论上源于宿主可利用资源的有限性，但由于单项研究内部存在较高变异性，该效应的可靠性仍有待确认。现有数据不足以支撑对该理论预测的其余两大核心关联开展定量检验。总体而言，现有实证证据仅为该权衡假说提供了部分支持，相关研究仍有进一步拓展的空间。