Mother-to-child transmission of hepatitis B virus (HBV) is the main route of transmission in Asia, and characterization of HBV quasispecies is needed to further understand virus evolution and adaptation. To understand changes in HBV during mother-to-child transmission, we enrolled nine pairs of mothers and children in the study, including a set of twins. Three groups were infected with HBV genotype C, and six groups were infected with HBV genotype B. The full-length HBV genome was amplified by PCR from serum samples before antiviral treatment, the whole viral genomes from each pair were sequenced, and the complexity and diversity of the quasispecies were analyzed. The entropy of transmitted HBV in children was found to be lower than their mothers, suggesting that there was a bottleneck effect during HBV transmission from the mother to the child. Selective evolution was shown by calculating πN and πS in the whole genomes, and the highest values were obtained for the X gene, which plays a role in viral replication and immune escape. All genotype C patients and only one genotype B pair had a πN/πS greater than 1 ratio, indicating that positive selection had occurred. In addition, quasispecies were found to be different between the twin children despite having the same mother, indicating that virus evolution is host-specific.

中文翻译：

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母婴传播期间乙型肝炎病毒的宿主内部多样性：X基因可能在传播后的儿童病毒存活中发挥关键作用。

乙型肝炎病毒（HBV）的母婴传播是亚洲的主要传播途径，需要对HBV准种进行鉴定，以进一步了解病毒的进化和适应性。为了了解母婴传播期间HBV的变化，我们在研究中招募了9对母亲和儿童，包括一对双胞胎。三组感染了HBV基因型C，六组感染了HBV基因型B。在进行抗病毒治疗之前，通过PCR从血清样品中扩增了全长HBV基因组，对每对的整个病毒基因组进行了测序，其复杂性和分析了准种的多样性。发现儿童中传播的HBV的熵低于母亲，这表明在HBV从母亲传播给儿童的过程中存在瓶颈效应。通过计算整个基因组中的πN和πS可以显示选择性进化，并且X基因获得了最高值，该X基因在病毒复制和免疫逃逸中起作用。所有基因型C患者和只有一对基因型B对的πN/πS大于1的比率，表明发生了阳性选择。此外，尽管双胞胎母亲的母亲相同，但准种却有所不同，这表明病毒的进化是宿主特异性的。