Babesia is an apicomplexan parasite of significance that causes the disease known as babesiosis in domestic and wild animals and in humans worldwide. Babesia infects vertebrate hosts and reproduces asexually by a form of binary fission within erythrocytes/red blood cells (RBCs), yielding a complex pleomorphic population of intraerythrocytic parasites. Seven of them, clearly visible in human RBCs infected with Babesia divergens, are considered the main forms and named single, double, and quadruple trophozoites, paired and double paired pyriforms, tetrad or Maltese Cross, and multiparasite stage. However, these main intraerythrocytic forms coexist with RBCs infected with transient parasite combinations of unclear origin and development. In fact, little is understood about how Babesia builds this complex population during its asexual life cycle. By combining cryo-soft X-ray tomography and video microscopy, main and transitory parasites were characterized in a native whole cellular context and at nanometric resolution. The architecture and kinetics of the parasite population was observed in detail and provide additional data to the previous B. divergens asexual life cycle model that was built on light microscopy. Importantly, the process of multiplication by binary fission, involving budding, was visualized in live parasites for the first time, revealing that fundamental changes in cell shape and continuous rounds of multiplication occur as the parasites go through their asexual multiplication cycle. A four-dimensional asexual life cycle model was built highlighting the origin of several transient morphological forms that, surprisingly, intersperse in a chronological order between one main stage and the next in the cycle.

中文翻译：

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巴贝虫无性生命周期的四维特征，从滋养体到多寄生虫阶段

巴贝斯虫是一种重要的顶端复合体寄生虫，可在全世界的家养和野生动物以及人类中引起称为巴贝虫病的疾病。巴贝虫感染脊椎动物宿主并通过红细胞/红细胞 (RBC) 内的二元裂变形式无性繁殖，产生复杂的多形性红细胞内寄生虫种群。其中七个，在感染巴贝虫的人类红细胞中清晰可见, 被认为是主要形式，并命名为单、双和四倍滋养体、成对和双对梨形、四分体或马耳他杂交体和多寄生虫阶段。然而，这些主要的红细胞内形式与感染了不明来源和发育的瞬时寄生虫组合的红细胞共存。事实上，人们对巴贝虫在其无性生命周期中如何构建这个复杂的种群知之甚少。通过结合低温软 X 射线断层扫描和视频显微镜，主要和暂时的寄生虫在原生全细胞环境和纳米分辨率下进行了表征。详细观察了寄生虫种群的结构和动力学，并为之前的B. divergens提供了额外的数据建立在光学显微镜上的无性生命周期模型。重要的是，首次在活的寄生虫中观察到了涉及出芽的二元裂变繁殖过程，揭示了当寄生虫经历其无性繁殖周期时，细胞形状和连续轮次繁殖发生了根本性变化。建立了一个四维无性生命周期模型，突出了几种瞬态形态的起源，令人惊讶的是，这些形态以时间顺序散布在周期的一个主要阶段和下一个阶段之间。