This 1976 transmission electron microscopic (TEM) image depicted a hypertrophic peritoneal mesothelial cell from a mouse that had been experimentally infected with Orientia tsutsugamushi rickettsial micro-organisms. This micrograph showed one organism, as it was in the process of budding from the cell’s luminal cell surface, still covered by a third layer, consisting of the host cell's plasma membrane. Other O. tsutsugamushi were visible living freely within the host 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.