Electron Microscopic Observations of Release of Orientia tsutsugamushi by Process of Budding from the Salivary Gland Cell of Infected Leptotrombidium pallidum Larvae.

恙虫病是由立克次体感染的东方体引起的，通过感染立克次体幼虫的叮咬传播给人类。日本爱知县黑线姬鼠自然感染梅毒东方体螨群。每只裸鼠的耳朵内侧只涂有一只自然感染的螨虫。因此，自然感染梅毒螺旋体的钉螺在感染后6h内即可传播给寄主。在电子显微镜下，未摄食梅毒螺旋体幼虫唾液腺细胞内的分泌颗粒散布在细胞质中，里氏立克次体散布在颗粒之间。贴壁后24小时，大量分泌颗粒向腺体细胞顶端移动，细胞底部可见大量典型立克次体。腺体细胞顶面正下方可见少量立克次体，管腔内可见带有寄主细胞膜的立克次体通过萌发从顶面逃逸。Rickettsiae在从腺体细胞逃逸的过程中，位于细胞的自由面，有时通过柄与寄主细胞相连。提示唾液腺细胞中的立克次体通过根尖表面萌发，迁移到唾液腺细胞表面，并从唾液腺细胞中逃逸。在唾液腺细胞的细胞质和顶面也可观察到许多具有东方体样细胞壁的小囊泡。这些小泡可能是在取食蚊类幼虫的过程中通过萌发从唾液腺细胞顶面逸出的。

Scrub typhus or Tsutsugamushi disease is caused by the infection of Orientia tsutsugamushi which is transmitted to man by the bite of larval trombiculid mites infected with the rickettsia. The naturally infected with Orientia tsutsugamushi mite colony of L.pallidum derived from Apodemus spesiosus trapped in Aichi Prefecture, Japan. Only one naturally infected mite was applied to the inside of ear of each nude mouse. Therefore, O.tsutsugamushi was transmitted from naturally infected L.pallidum to the host on and after 6 hours. In the electron micrographs, secretory granules in the salivary gland cell of unfed L.pallidum larva were seen randomly distributed throughout the cytoplasma, and rickettsiae were found scattered among the granules. At 24 hrs after attachment, numerous secretory granules moved toward the apexes of the gland cells, and a large number of typical rickettsiae were observed at the bases of cells. A few rickettsiae could be seen just below the apical surface of the gland cell, and a rickettsia with a host cell membrane escape from the apical surface by budding was recongnized in the lumen. Rickettsiae in the process of escape from the gland cell were located at the free surface of the cell, where occassionally connected to the host cell by a stalk. It is suggested that the rickettsiae in the salivary gland cell migrate to the apical surface and escape from the salivary gland cells by budding through the apical surface. Many small vesicles with Orientia tsutsugamushi-like cell wall were also observed in cytoplasma and apical surface of salivary gland cells. These small vesicles probably escapes from apical surface of salivary gland cells by budding during feeding of larval trombiculid mites.