ORIENTIA TSUTSUGAMUSHI. Bacterium Orientia tsutsugamushi budding from its host cell peritoneal mesothelial cell, colorized TEM. This specimen comes from the peritoneal cavity of a mouse infected experimentally to diagnose the infection of a patient. Other bacteria are visible in the cytoplasm. Orientia tsutsugamushi, formerly known as Rickettsia tsutsugamushi, is a bacterium responsible for scrub typhus or Japanese flood ever. It is a Gram negative bacillus, intracellular exclusively, that proli