曼氏血吸虫尾蚴利用弹性流体动力学耦合高效游动
Schistosoma mansoni cercariae exploit an elastohydrodynamic coupling to swim efficiently
摘要：
许多寄生虫的运动性对于其宿主的感染过程至关重要，例如血吸虫曼氏血吸虫的传播周期。在人类感染阶段，未成熟的亚毫米级寄生虫（称为尾蚴）在淡水中游动，通过穿透皮肤感染人类。这种感染导致血吸虫病，这是一种寄生虫病，其全球社会经济影响与疟疾相当。由于尾蚴不进食，因此其寿命有限，约为12小时，有效的运动对于寄生虫的生存和血吸虫病的传播至关重要。然而，缺乏对尾蚴如何游动的第一原理的理解。通过结合实验，理论和机器人为基础的方法，我们证明，尾蚴推动自己对重力利用一个独特的弹性流体动力学耦合。我们发现，尾蚴击败他们的尾巴在一个周期性的方式，同时保持一个固定的灵活性附近的后端和前端。在这些区域中的柔性允许流体阻力和弯曲阻力之间的相互作用：弹性流体动力学耦合，以自然地打破时间反演对称性，并使运动在小的长度尺度。我们提出了一个理论模型，一个“T-游泳者”，它捕捉了尾蚴的关键游泳表型。我们进一步验证了我们的研究结果，通过宏观尺度的机器人实现的“T-游泳者”，解释了独特的叉尾几何形状的尾蚴。最后，我们发现，尾蚴保持灵活性，在其后端和前端在一个最佳的制度，有效的游泳，我们的理论模型预测。我们期望我们的工作为将S.曼氏尾蚴对疾病传播的影响，并能够探索预防血吸虫病的新策略。
英文摘要：
The motility of many parasites is critical for the infection process of their host, as exemplified by the transmission cycle of the blood fluke Schistosoma mansoni. In their human infectious stage, immature, submillimetre-scale forms of the parasite known as cercariae swim in freshwater and infect humans by penetrating through the skin. This infection causes Schistosomiasis, a parasitic disease that is comparable to malaria in its global socio-economic impact. Given that cercariae do not feed and hence have a finite lifetime of around 12 hours, efficient motility is crucial for the parasite's survival and transmission of Schistosomiasis. However, a first-principles understanding of how cercariae swim is lacking. Via a combined experimental, theoretical and robotics based approach, we demonstrate that cercariae propel themselves against gravity by exploiting a unique elastohydrodynamic coupling. We show that cercariae beat their tail in a periodic fashion while maintaining a fixed flexibility near their posterior and anterior ends. The flexibility in these regions allows an interaction between the fluid drag and bending resistance: an elastohydrodynamic coupling, to naturally break time-reversal symmetry and enable locomotion at small length-scales. We present a theoretical model, a 'T-swimmer', which captures the key swimming phenotype of cercariae. We further validate our results experimentally through a macro-scale robotic realization of the 'T-swimmer', explaining the unique forked-tail geometry of cercariae. Finally, we find that cercariae maintain the flexibility at their posterior and anterior ends at an optimal regime for efficient swimming, as predicted by our theoretical model. We anticipate that our work sets the ground for linking the swimming of S. mansoni cercariae to disease transmission and enables explorations of novel strategies for Schistosomiasis prevention.
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