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Scrub Typhus

Ira Shah

Consultant Pediatrician and Pediatric Infectious Diseases, Nanavati Hospital, Mumbai, India
First Created: 01/02/2013 Last Updated: 02/01/2024

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Introduction

Scrub typhus, also called Tsutsugamushi disease, is an acute infectious disease that is transmitted to humans by certain mites (chiggers). Recent outbreaks have been seen in India. The causative organism is Orientia (formerly Rickettsia) tsutsugamushi. Trombiculid mites (Leptotrombidium delinese & L. Akamushi) serve as both reservoirs and vectors.

Pathology

The basic pathologic process of scrub typhus is a perivasculitis of the small blood vessels analogous to the other rickettsial diseases. In addition, an eschar or necrotic inflammatory lesion develops at the site of the mite bite, with subsequent regional lymphadenopathy. General lymphadenopathy occurs commonly in scrub typhus but rarely or not at all in all other rickettsial diseases.

Presentation

The chigger bite results in a papule, enlarging to a bulla that rapidly sloughs, leaving a shallow ulcer. A black crust surrounded by a 1-2 cm erythematous raised circle then forms (Figure 1). Within 5 days, an unremitting fever to 40 degrees C accompanied by a severe headache is seen in virtually all patients. Generalized lymphadenopathy is the most consistent physical finding, The characteristic rash of scrub typhus is maculopapular & generalized & most prominent on non - exposed skin surfaces. Hepatosplenomegaly and conjunctival injection are common; deafness and tinnitus occur less commonly. Myocarditis and disseminated intravascular coagulation also have been reported.

Figure 1: Rickettsial rash with eschar (arrow)

Diagnosis

The Weil-Felix OX-K strain agglutination reaction may be the only serologic test available in less developed countries. However, it is not very sensitive; OX-K agglutinins develop in only a little more than 50 percent of scrub typhus patients. Moreover, OX-K agglutinins are also produced by relapsing fever. A fourfold rise in agglutinin titres in paired sera or a high cut-off titre (>1:320) in single samples is diagnostic for skin infection. Immunofluorescent tests are much more diagnostic and reliable.

Treatment

Tetracycline is the drug of choice. In younger children, chloramphenicol or quinolone group of antibiotics is used.

References

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