Scrub Typhus

After an incubation period of approximately ≥ 7 days (symptoms usually occur within 7 to 10 days and last 14 to 21 days) (1), symptoms of scrub typhus start suddenly and include fever, chills, headache, and generalized lymphadenopathy.

Chigger Bite (Vesicle)

Image

This photo shows a person's skin 24 hours after being bitten by a chigger (mite larvae). Note the vesicle at the bite site was caused by the bite of a larval harvest mite of the genus Trombicula.

CDC

At the onset of fever, an eschar often develops at the site of the chigger bite. The typical lesion begins as an erythematous, indurated lesion about 1 cm in diameter; it eventually vesiculates, ruptures, and becomes covered with a black scab. Whether different strains of O. tsutsugamushi can cause an eschar varies, and an eschar is easier to detect in people with light skin. A macular rash develops on the trunk during days 5 to 8 of fever in 25 to 50% of patients, often extending to the arms and legs (1). It may disappear rapidly or become maculopapular and intensely colored. Regional lymph nodes enlarge.

Scrub Typhus Eschar

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This photo shows a scrub typhus eschar on a person's leg.

DR P. MARAZZI/SCIENCE PHOTO LIBRARY

Fever rises during the first week, often to 40 to 40.5° C. Headache is severe and common, as is conjunctival injection. Cough is present during the first week of fever, and pneumonitis may develop during the second 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.

Scrub Typhus

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Scrub typhus (tsutsugamushi disease) manifests as an eschar at the site of a chigger bite (top). A diffuse macular rash follows the appearance of the eschar (bottom).

Images courtesy of Yoshiki Taniguchi, MD. From Taniguchi, Y: Eschar, fever, and rash in a 43-year-old man. Dermatology Online Journal 3(2), 1997.

• History and physical examination

• Molecular diagnostic testing (polymerase chain reaction [PCR]) of infected tissue or blood specimens

• Biopsy of tissue with immunohistochemistry to detect organisms

• Acute and convalescent serologic testing (serologic testing not useful acutely)

The diagnosis of scrub typhus relies on timely identification of clinical signs such as fever, rash, and eschar with satellite lymphadenopathy in the appropriate epidemiologic context. Manifestations of scrub typhus are similar to those of Rocky Mountain spotted fever and epidemic typhus. However, scrub typhus usually occurs in different geographic areas.

Laboratory confirmation is primarily through indirect immunofluorescence assay serology showing increased titers between acute and convalescent samples (1). Weil-Felix OX-K agglutination assays are not recommended because of low sensitivity and specificity (1).

PCR testing on skin biopsies or an eschar swab may allow earlier diagnosis, and immunohistochemistry on formalin-fixed tissue biopsy is an adjunctive method.

Because scrub typhus is not common in the United States, serologic and molecular assays are not typically available at regional health departments but may be performed at the United States Centers for Disease Control and Prevention (CDC).

For further details, see Diagnosis of Rickettsial and Related Infections.

• DoxycyclineDoxycycline

• Sometimes other tetracyclines or azithromycinSometimes other tetracyclines or azithromycin

Antibiotics are most effective if given soon after symptoms begin.

Doxycycline is the first-line treatment of scrub typhus. This medication is administered until the patient improves, has been afebrile for 48 hours, and has received treatment for at least 7 days. Doxycycline is the first-line treatment of scrub typhus. This medication is administered until the patient improves, has been afebrile for 48 hours, and has received treatment for at least 7 days.

For patients who are pregnant or who have severe doxycycline allergy, azithromycin has been shown to be a safe and effective alternative to allergy, azithromycin has been shown to be a safe and effective alternative todoxycycline (1).

In patients who are not pregnant, azithromycin and other tetracyclines may be alternatives to In patients who are not pregnant, azithromycin and other tetracyclines may be alternatives todoxycycline; however, the certainty of evidence is low (2). 

Chloramphenicol is also an alternative treatment. Chloramphenicol is also an alternative treatment.Chloramphenicol can cause adverse hematologic effects, which require monitoring of blood indices, and, in neonates, gray baby syndrome.

Although some tetracyclines can cause tooth staining in children < 8 years of age, the United States Centers for Disease Control and Prevention (CDC) advises that a course of doxycycline is warranted (Although some tetracyclines can cause tooth staining in children doxycycline is warranted (3), given for 5 days for mild illness and for 10 days for high-risk children. Research indicates that short courses of doxycycline (5 to 10 days, as used for rickettsial disease) can be used in children without causing tooth staining or weakening of tooth enamel (4).

Eliminating or decreasing mite populations by clearing brush and spraying infested areas with residual insecticides helps prevent scrub typhus.

Insect repellents (eg, diethyltoluamide [DEET], picaridin, IR3535, oil of Lemon eucalyptus (OLE), para-menthane-diol (PMD), or 2-undecanone) should be used on skin surfaces when exposure is likely.Insect repellents (eg, diethyltoluamide [DEET], picaridin, IR3535, oil of Lemon eucalyptus (OLE), para-menthane-diol (PMD), or 2-undecanone) should be used on skin surfaces when exposure is likely.