Scrub Typhus Clinical Presentation

Updated: Sep 29, 2023
  • Author: David J Cennimo, MD, FAAP, FACP, FIDSA, AAHIVS; Chief Editor: Russell W Steele, MD  more...
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Patients with scrub typhus may present early or later in the course of their disease. In the United States, a history of travel to the endemic area must be sought, specifically probing for exposures in rural areas and contact with vegetation or the ground. [3, 6, 13]

Inoculation through the chigger bite is often painless and unnoticed. The incubation period lasts 6-20 days (average, 10 days). After incubation, persons may experience headaches, shaking chills, lymphadenopathy, conjunctival infection, fever, anorexia, and general apathy. The fever usually reaches 40-40.5°C (104-105°F).

A small painless papule initially appears at the site of infection and enlarges gradually. An area of central necrosis develops and is followed by eschar formation. The eschar (if present) is well developed at the initiation of the fevers, which may drive the patient to seek medical attention. [3, 4, 11, 41, 42]

Diagnosing scrub typhus early in its course can be difficult because many conditions can present with a high fever; however, the presentation of the rash, a history of exposure to endemic areas, and the presentation of the sore caused by the bite can be diagnostic.


Physical Examination

The site of infection is marked by a chigger bite. Approximately 50% of patients with primary infection and 30% of patients with recurrent infection develop an eschar at the inoculation site (see the images below). Given the appropriate history, the eschar is often pathognomonic, but it may be missed by an inexperienced observer.

Typical eschar. Typical eschar.
Eschar on neck. Eschar on neck.
Eschar on scrotum. Eschar on scrotum.

In prospective studies, trained investigators were able to locate an eschar on 68-87% of patients. [8, 41] In adults, the eschar is often truncal, whereas children may have lesions in the perineum. [43] The incidence of an eschar on head, face or neck is estimated to be approximately 5%. [44] Multiple eschars may be present. [4] The eschar may also abrade, leaving an ulcer reminiscent of primary syphilis.

The presence or absence of eschar was thoroughly examined in a study of 176 Korean patients with scrub typhus confirmed by immunofluorescent assay. [43] In this study, 162 (92%) cases had eschar, with 128 (79.5%) on the front of the body. In men, eschars were detected within 30 cm below the umbilicus (19 patients; 35.8%), on the lower extremities (12 patients; 22.6%) and on the chest above the umbilicus (11 patients; 20.8%). In women, the most prevalent area was the chest above the umbilicus (44 patients; 40.7%).

Patients experience abrupt onset of high fever (40-40.5°C [104-105°F]), headache, malaise, and myalgia approximately 10 days after infection. At that time, the eschar (if present) is well formed. Fever is the most commonly reported complaint, occurring more than 98% of the time. [3, 11] Tender regional or generalized lymphadenopathy may provide a clue to diagnosis and is reported in 40-97% of cases. Less frequently, ocular pain, wet cough, malaise, and injected conjunctiva are present. [4, 8, 41, 11, 45]

Toward the end of the first week, approximately 35% (reported range, 15-93%) of patients develop a centrifugal macular rash on the trunk. The rash may progress to become papular (see the image below). [4, 11, 42] It may be transient and easily missed. [3] Additional symptoms at this time may include enlargement of the spleen, cough, and delirium. Pneumonitis or encephalitis may develop during the second week.

Maculopapular rash. Maculopapular rash.

Some patients may have central nervous system (CNS) involvement with tremors, nervousness, slurred speech, nuchal rigidity, or deafness during the second week of the disease. However, results from cerebrospinal fluid (CSF) analysis are either normal or indicate a low number of monocytes. Severe CNS involvement (eg, seizure or coma) is rare. If acute hearing loss is present (as may be the case in as many as one third of patients, according to some reports), it strongly points toward scrub typhus. [3, 6]

Some evidence of pulmonary involvement (eg, cough, tachypnea, or pulmonary infiltrates) is often present. [41] Respiratory compromise may progress to acute respiratory distress syndrome (ARDS), especially in the elderly. [35]

Cardiac involvement is often minor and rare; however, cases of fatal myocarditis have been reported. [46] Infection with O tsutsugamushi may cause a relative bradycardia, [47] which, when combined with rash, may raise concern for typhoid fever. [8]

Scrub typhus may rarely cause acute renal failure, shock, and disseminated intravascular coagulation (DIC). [3]

If the patient does not receive treatment, symptoms may last for more than 2 weeks; with treatment, the patient recovers within 36 hours.