Scrub typhus is a mite-borne disease caused by Orientia tsutsugamushi (formerly Rickettsia tsutsugamushi). Symptoms are fever, a primary lesion, a macular rash, and lymphadenopathy.
O. tsutsugamushi is transmitted by trombiculid mites, which feed on forest and rural rodents, including rats, voles, and field mice. Human infection follows a chigger (mite larva) bite.
After an incubation period of 6 to 21 days (mean 10 to 12 days), fever, chills, headache, and generalized lymphadenopathy start suddenly. At onset of fever, an eschar often develops at the site of the chigger bite. The typical lesion, common in whites but rare in Asians, begins as a red, indurated lesion about 1 cm in diameter; it eventually vesiculates, ruptures, and becomes covered with a black scab. Regional lymph nodes enlarge. Fever rises during the 1st wk, often to 40 to 40.5° C. Headache is severe and common, as is conjunctival injection. A macular rash develops on the trunk during the 5th to 8th day of fever, often extending to the arms and legs. It may disappear rapidly or become maculopapular and intensely colored. Cough is present during the 1st wk of fever, and pneumonitis may develop during the 2nd wk.
In severe cases, pulse rate increases; BP drops; and delirium, stupor, and muscular twitching develop. Splenomegaly may be present, and interstitial myocarditis is more common than in other rickettsial diseases. In untreated patients, high fever may persist ≥ 2 wk, then falls gradually over several days. With therapy, defervescence usually begins within 36 h. Recovery is prompt and uneventful.
For details of diagnosis, see Rickettsiae and Related Organisms: Diagnosis.
Primary treatment is doxycycline 200 mg po once followed by 100 mg bid until the patient improves, has been afebrile for 24 to 48 h, and has received treatment for at least 7 days. Chloramphenicol 500 mg po or IV qid for 7 days is 2nd-line treatment.
Clearing brush and spraying infested areas with residual insecticides eliminate or decrease mite populations. Insect repellents (eg, diethyltoluamide [DEET]) should be used when exposure is likely.
Last full review/revision November 2012 by William A. Petri, Jr., MD, PhD