Data from: Variation in relapse frequency and the transmission potential of Plasmodium vivax malaria

There is substantial variation in the relapse frequency of Plasmodium vivax malaria, with fast relapsing strains in tropical areas, and slow relapsing strains in temperate areas with seasonal transmission. We hypothesise that much of the phenotypic diversity in P. vivax relapses arises from selection of relapse frequency to optimise transmission potential in a given environment, in a process similar to the virulence trade-off hypothesis. We develop mathematical models of P. vivax transmission and calculate the basic reproduction number R0 to investigate how transmission potential varies with relapse frequency and seasonality. In tropical zones with year round transmission, transmission potential is optimised at intermediate relapse frequencies of 2-3 months: slower relapsing strains increase the opportunity for onward transmission to mosquitoes, but also increase the risk of being outcompeted by faster relapsing strains. Seasonality is an important driver of relapse frequency for temperate strains, with the time to first relapse predicted to be 6-9 months, coinciding with the duration between seasonal transmission peaks. We predict there is a threshold degree of seasonality, below which fast relapsing tropical strains are selected for, and above which slow relapsing temperate strains dominate, providing an explanation for the observed global distribution of relapse phenotypes.

间日疟原虫（Plasmodium vivax）疟疾的复发频率存在显著差异：热带区域分布快速复发株，而具有季节性传播特征的温带区域则以慢速复发株为主。我们提出假说：间日疟原虫复发的多数表型多样性，源于对复发频率的选择过程，以此优化特定环境下的传播潜力，该过程与毒力权衡假说（virulence trade-off hypothesis）的机制类似。本研究构建了间日疟原虫传播的数学模型，并计算基本再生数R₀，以探究传播潜力随复发频率与季节节律的变化规律。在全年持续传播的热带区域，传播潜力在2-3个月的中等复发频率下达到最优：慢速复发株虽可提升向蚊虫的后续传播概率，但也面临被快速复发株竞争排除的风险。季节节律是驱动温带株复发频率的关键因素，研究预测首次复发的时长为6-9个月，与季节性传播峰值之间的间隔时长相吻合。我们预测存在临界季节节律阈值：当阈值低于该临界值时，自然选择会青睐快速复发的热带株；当阈值高于该临界值时，慢速复发的温带株将占据主导地位，这为全球范围内已观测到的复发表型分布格局提供了合理解释。