This 1976 transmission electron microscopic (TEM) image depicted a hypertrophic peritoneal mesothelial cell of mouse that had been experimentally infected with Orientia tsutsugamushi rickettsial micro-organisms. In this view, there were several organisms visible free within the mesothelial cell's cytoplasm. Formerly known as Rickettsia tsutsugamushi, O. tsutsugamushi is the pathogen responsible for causing the febrile disease known as scrub typhus. The disease is transmitted to humans through the bite of larval trombiculid mites, i.e., chiggers, that had fed on infected rodents.