typhus, any of a group of infectious diseases caused by microorganisms classified between bacteria and viruses, known as rickettsias. Typhus diseases are characterized by high fever and an early onset of rash and headache. They respond to antibiotic treatment with tetracycline and chloramphenicol and can be prevented by vaccination. Epidemic typhus, the most serious in the group, is caused by Rickettsia prowazeki, which is transmitted in the feces of body lice. It occurs in crowded, unsanitary conditions and has historically been a major killer in wartime. It occurs more commonly in cooler climates and seasons. Brill's disease, also called recrudescent typhus, is believed to be a milder recurrence of epidemic typhus. Endemic murine typhus is primarily a disease of rodents and is spread to humans by rat fleas. The symptoms are milder than those of epidemic typhus. Scrub typhus (Tsutsugamushi fever) is carried to humans by infected mites. It occurs primarily in East Asia and the Southeast Pacific islands.