(See also Overview of Rickettsial and Related Infections Overview of Rickettsial and Related Infections Rickettsial diseases (rickettsioses) and related diseases (anaplasmosis, ehrlichiosis, Q fever, scrub typhus) are caused by a group of gram-negative, obligately intracellular coccobacilli. All... read more .)
Scrub typhus is related to rickettsial diseases.
O. tsutsugamushi is transmitted by trombiculid mite larvae (chiggers), which feed on forest and rural rodents, including rats, voles, and field mice. Human infection also follows a chigger bite. The mites are both the vector and the natural reservoir for O. tsutsugamushi.
Scrub typhus is endemic in an area of Asia-Pacific bounded by Japan, Korea, China, India, and northern Australia.
After an incubation period of 6 to 21 days (mean 10 to 12 days), symptoms of scrub typhus start suddenly and include fever, chills, headache, and generalized lymphadenopathy. At onset of fever, an eschar 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 week, 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 week of fever, and pneumonitis may develop during the 2nd week.
In severe cases, pulse rate increases; blood pressure 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 weeks, then falls gradually over several days. With therapy, defervescence usually begins within 36 hours. Recovery is prompt and uneventful.
Manifestations of scrub typhus are similar to those of Rocky Mountain spotted fever and epidemic typhus. However, scrub typhus occurs in different geographic areas (Asia-Pacific area bounded by Japan, Korea, China, India, and northern Australia), and frequently, an eschar develops with satellite adenopathy.
Primary treatment of scrub typhus is doxycycline 200 mg orally once followed by 100 mg twice a day in adults until the patient improves, has been afebrile for 48 hours, and has received treatment for at least 7 days.
Chloramphenicol 500 mg orally or IV 4 times a day for 7 days is 2nd-line treatment. Oral chloramphenicol is not available in the US and its use is associated with adverse hematologic effects, which requires monitoring of blood indices.
Scrub typhus, endemic in Asia-Pacific, is transmitted by the bite of chiggers (mite larvae).
Fever (often accompanied by an eschar at the bite site), chills, severe headache, and generalized lymphadenopathy start suddenly; a rash develops and spreads.
Treat with doxycycline, which results in rapid improvement even in severe cases.