|Description:||This 1976 transmission electron microscopic (TEM) image depicted a hypertrophic peritoneal mesothelial cell of mouse that had been experimentally infected intraperitoneally with Orientia tsutsugamushi rickettsial micro-organisms. In this photomicrograph there were several organisms visible free within the mesothelial cell's cytoplasm.|
Formerly known as Rickettsia tsutsugamushi, Orientia tsutsugamushi is the pathogen responsible for causing the febrile disease known as "scrub" typhus, which is also known as "river", or "flood" typhus. The disease is transmitted to humans through the bite of larval trombiculid mites, i.e., chiggers that had fed on infected rodents. The disease is characterized by the formation of a cutaneous ulcerative lesion at the site of the mite bite, which evolves into a blackened eschar known as "tache noire". The initial ulcer is followed by localized lymphadenopathy, fever, and a generalized maculopapular rash.