- Scrub typhus or bush typhus is a form of typhus caused by the intracellular parasite Orientia tsutsugamushi, a Gram-negative α-proteobacterium of family Rickettsiaceae first isolated and identified in 1930 in Japan.
- Scrub typhus is transmitted by some species of trombiculid mites ("chiggers", particularly Leptotrombidium deliense), which are found in areas of heavy scrub vegetation. The bite of this mite leaves a characteristic black eschar that is useful to the doctor for making the diagnosis.
- Scrub typhus is endemic to a part of the world known as the tsutsugamushi triangle (after O. tsutsugamushi) This extends from northern Japan and far-eastern Russia in the north, to the territories around the Solomon Sea into northern Australia in the south, and to Pakistan and Afghanistan in the west. It may also be endemic in parts of South America, too.
- It affects females more than males in Korea, but not in Japan, and which may be because sex-differentiated cultural roles have women tending garden plots more often, thus being exposed to vegetation inhabited by chiggers. The incidence is increasing in the southern part of the Indian subcontinent and in northern areas around Darjeeling.
Symptoms and Signs
- Incubation period of 6 to 21 days (mean 10 to 12 days).
- fever, chills, headache, and generalized lymphadenopathy start suddenely.
- muscle pain, cough, and gastrointestinal symptoms.
- Morbilliform rash, eschar, splenomegaly, and lymphadenopathies are typical signs. At onset of fever, an Escher often develops at the site of the chigger bite.
- The typical lesion of scrub typhus, 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 collared. 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.
The cheapest and most easily available serological test is the Weil-Felix test, but this is notoriously unreliable.
Biopsy of rash with fluorescent antibody staining to detect organisms
Acute and convalescent serologic testing (serologic testing not useful acutely)
- Doxycycline: Primary treatment is doxycycline 200 mg po once followed by 100 mg bid until the patient improves, has been afebrile for 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.
No licensed vaccines are available.