Transmission electron micrograph (TEM) depicting a peritoneal mesothelial cell from a mouse that had been experimentally infected intra-peritoneally with Orientia tsutsugamushi rickettsial micro-organisms. In this image, an organism was photographically captured as it was budding from the luminal cell surface, while still covered by a third layer consisting of the host cell's plasma membrane. Formerly known as Rickettsia tsutsugamushi, O. tsutsugamushi is the pathogen responsible for causing the febrile disease known as scrub typhus (aka 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. This image has been colorized.