Transmission Electron Micrograph (TEM) depicting peritoneal mesothelial cells from a mouse that had been experimentally infected intraperitoneally with Orientia tsutsugamushi rickettsial micro-organisms. This TEM revealed that the extracellular organisms were covered with a distinct third outer membrane of probable host cell origin. Scrub typhus is an acute febrile disease caused by Orientia tsutsugamushi. The disease occurs mainly in the large triangular region extending from Japan in the north, to Australia in the southwest, and the South Pacific Islands in the southeast. Humans are infected by the bite of the larva of the trombiculid mite harboring O. tsutsugamushi. This pathogen attacks endothelial cells resulting in vasculitis. The clinical manifestations are characterized by a papular rash, headache, fever, chills, and an eschar at the site of the chigger bite. Magnification: unknown.