Electron-microscopic observation of mouse spleen tissue infected with Orientia tsutsugamushi isolated from Shandong, China.

Low-virulent Orientia tsutsugamushi (Ot) were successfully isolated from scrub typhus patients in Shandong, China, and the isolates were similar to the Kawasaki type identified by nested polymerase chain reaction (PCR). To identify the morphological characterization of the low-virulent Ot, and elucidate the pathological changes on host cells, mouse spleen tissue infected with the Ot isolated from Shandong was used for the ultrastructural study. Transmission electron microscopy showed that the Ot parasitized in the spleen were different in size, shape and electron density and many significant changes occurred in cytoplasmic organelles of the inoculated mouse spleen cells. Swollen perinuclear cisterna was observed in the nuclear membranes of mononuclear cells and a multivesicular body was found in the intracytoplasm of the macrophage. In the phagosome of the macrophage, many Ot enveloped with an additional membrane were found to push the phagosomal membrane outward from inside. The results indicated that the low-virulent Ot and the spleen cells suffered various damages.