Rickettsia

Three forms of typhus are also caused by rickettsia. Epidemic typhus is caused by R. prowazekii, a bacterium that is transmitted by the human body louse. Consequently, episodes of this disease occur when humans are brought into close contact with each other under unsanitary conditions. Endemic typhus and scrub typhus are caused by R. typhi and R. tsutsugamushi, respectively. Transmitted by rat fleas, endemic typhus is a mild disease of fever, headache, and rash. Scrub typhus, named for its predilection for scrub habitats (although it has since been found to occur in rainforests, savannas, beaches, and deserts as well) is transmitted by chiggers. Unlike endemic typhus, scrub typhus is a serious disease that is fatal if not treated.