Zika virus (ZIKV) has the unusual capacity to circumvent natural alternating mosquito-human transmission and be directly transmitted human-to-human via sexual and vertical routes. The impact of direct transmission on ZIKV evolution and adaptation to vertebrate hosts is unknown. Here we show that molecularly barcoded ZIKV rapidly adapted to a mammalian host during direct transmission chains in mice, coincident with the emergence of an amino acid substitution previously shown to enhance virulence. In contrast, little to no adaptation of ZIKV to mice was observed following chains of direct transmission in mosquitoes or alternating host transmission. Detailed genetic analyses revealed that ZIKV evolution in mice was generally more convergent and subjected to more relaxed purifying selection than in mosquitoes or alternate passages. These findings suggest that prevention of direct human transmission chains may be paramount to resist gains in ZIKV virulence.

中文翻译：

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直接脊椎动物传播链中增强的寨卡病毒毒力的快速进化

寨卡病毒（ZIKV）具有规避自然交替的蚊虫-人类传播并通过性和垂直途径直接在人与人之间传播的非凡能力。直接传播对ZIKV进化和适应脊椎动物宿主的影响尚不清楚。在这里，我们显示分子条形码化的ZIKV在小鼠的直接传播链中迅速适应了哺乳动物宿主，这与先前显示的可增强毒力的氨基酸取代的出现相吻合。相反，在蚊子中直接传播或交替宿主传播后，几乎没有ZIKV对小鼠的适应。详细的遗传分析显示，与蚊子或其他传代相比，小鼠中的ZIKV进化通常更趋于收敛，并且纯化选择更为轻松。