Electron microscopic observations of the embryo Leptotrombidium (Leptotrombidium) pallidum naturally infected with Rickettsia tsutsugamushi.

Embryos of Leptotrombidium (Leptotrombidium) pallidum mites naturally infected with Rickettsia tsutsugamushi were examined by electron microscopy. Rickettsiae were not found in eggs just after oviposition, but were easily detected in cells at the various parts of the embryos just before hatching, indicating that the rickettsiae are surely vertically transmitted from infected adult mites to the larvae through embryos, and the rickettsiae may multiply in situ during the developing process of the embryo.