acute infectious disease in humans that is caused by the parasite Rickettsia tsutsugamushi and is transmitted to humans by the bite of certain kinds of trombiculid mites, or chiggers. The causative agent of scrub typhus, the bacterium R. tsutsugamushi, is primarily a parasite of certain mites, of which two closely related species, Leptotrombidium (Trombicula) akamushi and L. deliens, are the carriers of the disease. During their larval stage, these mites acquire the infection from wild rodents or other small animals. The infection is passed to humans when a mite larva bites a person. Scrub typhus occurs in Southeast Asia and its associated archipelagoes and in Japan, in which latter country the disease was first described (1899) and systematically investigated (1906–32). During World War II scrub typhus killed or incapacitated thousands of troops who were stationed in rural or jungle areas in the Pacific theatre.

A person falls ill with scrub typhus about 10 to 12 days after being bitten by an infected mite. A reddish or pinkish lesion appears at the site of the mite bite, and the person begins to experience headache, fever, chills, and general pains, along with swollen lymph glands. About one week after the fever has started, a pinkish rash develops over the skin of the trunk and may extend to the arms and legs. While the course of the fever may end in two weeks, it is not unusual for it to last three or even four weeks. A more or less extensive pneumonitis is common, and abnormalities in the heart, lungs, and blood may also arise, leading to impairment of heart function and circulatory failure. When untreated, scrub typhus can be fatal, but the course of the disease can now be arrested by the administration of chloramphenicol or the tetracyclines (tetracycline), upon which recovery is prompt and uneventful.