Genetic recombination plays a pivotal role in the appearance of human norovirus recombinants that cause global epidemics. However, the factors responsible for the appearance of these recombinants remains largely unknown. In this study, we revealed a selective pressure that restricts parental combinations leading to the emergence of norovirus recombinants. To investigate traces of emerging novel recombinants and their parents in the human population, we isolated mass nucleotide sequence clones of human norovirus genogroups I and II in sewage-affected waters over a 4-year sampling period. Fourteen different phylogenetic combinations of recombinants and their parents were defined from the dozens of phylogenetic lineages circulating in the human population. To evaluate the probability of these combinations, parental lineages of each recombinant were categorized into two groups as HP (relatively higher-competitiveness parents) and LP (relatively lower-competitiveness parents), according to their relative detection frequency. Strong categorization of HP and LP was confirmed by tests with modified data and additional variables. An algorithm that was developed in this study to visualize the chance of mixed infection between parents revealed that HP lineages have a higher chance of mixed infection than LP lineages in the human population. Three parental pairing types in recombinants were defined: HP-HP, HP-LP, and LP-LP. Among these, most recombinants were identified as HP-LP, despite the prediction of dominant emergence of HP-HP-type recombinants. These results suggest that nature favors recombinants of human norovirus that originate from parental pairing of heterogeneous competitiveness.

中文翻译：

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父母诺如病毒与不平等竞争能力的配对为后代重组子的出现提供了明显的优势

遗传重组在引起全球流行的人类诺如病毒重组体的出现中起着关键作用。然而，造成这些重组体出现的因素在很大程度上仍然未知。在这项研究中，我们揭示了限制亲本组合的选择性压力，导致诺如病毒重组体的出现。为了调查人口中新兴的新型重组体及其亲本的痕迹，我们在4年的采样期内分离了受污水影响的水中人类诺如病毒基因组I和II的大量核苷酸序列克隆。从人口中循环的数十个系统发育谱系中定义了十四种不同的重组体及其亲本的系统发育组合。为了评估这些组合的可能性，根据其相对检测频率，将每个重组体的亲本谱系分为HP（相对较高竞争性亲本）和LP（相对较低竞争性亲本）两类。通过对修改后的数据和其他变量进行的测试，证实了HP和LP的强分类。在这项研究中开发的一种算法可以可视化父母之间混合感染的机会，该算法表明，在人类群体中，HP谱系比LP谱系具有更高的混合感染几率。定义了重组体中的三种亲本配对类型：HP-HP，HP-LP和LP-LP。在这些重组子中，尽管预测到HP-HP型重组子将主要出现，但大多数重组子仍被鉴定为HP-LP。