Orientia tsutsugamushi str. Ikeda

Orientia tsutsugamushi (previously called Rickettsia tsutsugamushi) is an obligate intracellular rickettsia living in the salivary glands of trombiculid mites. The bacterium is maternally inherited in mites and is transmitted to humans during larval feeding. Orientia tsutsugamushi is the causative agent of scrub typhus, a disease characterized by fever, rash, eschar, pneumonitis meningitis and disseminated intravascular coagulation. If left untreated, it can lead to sever multiple organ failure. The mortality rate from scrub typhus in untreated patients ranges from 1% to 40%. During World War II, Allied forces suffered more fatalities due to this disease than as a direct consequence of the fighting in South-East Asia. Scrub typhus is restricted to a well-defined area that extends from Eastern Russia and Northern Japan in the north and Northern Australia in the south to Pakistan and Afghanistan in the west. Orientia tsutsugamushi (strain Boryong) was isolated from a Korean patient. Its genome is made up of a single circular chromosome of 2,127,051 base pairs and is the largest among the genomes of Rickettsiales sequenced to date. A unique feature of Orientia tsutsugamushi is the presence of 4197 identical repeats of more than 200 bp, which represents 37% of the genome. In total, 1146 mobile genetic elements, representing 40% of the genome, were identified. Exceptional is also the presence of 359 tra genes for conjugative Type IV Secretion Systems compared to the 4 tra genes of R. felis and to the unique tra gene of R. bellii. Located within or in the immediate vicinity of the tra clusters are more than 200 genes encoding paralogous proteins putatively involved signaling and host-cell interaction processes. 414 transposases were identified, that belong to 5 families, approximately 86% of which are pseudogenes. (HAMAP: ORITB)