Diagnosis of scrub typhus

Abstract

Scrub typhus is an acute febrile illness that, if untreated, can result in considerable morbidity and mortality. One of the primary reasons for delays in the treatment of this potentially fatal infection is the difficulty in diagnosing the condition. Diagnosis is often complicated because of the combination of non-specific symptoms that overlap with other infections commonly found in endemic areas and the poor available diagnostics. In the majority of the endemic settings, diagnosis still relies on the Weil–Felix test, which is neither sensitive nor specific. Other methods of testing have become available, but at this time, these remain insufficient to provide the rapid point-of-care diagnostics that would be necessary to significantly change the management of this infection by providers in endemic areas. This article reviews the currently available diagnostic tools for scrub typhus and their utility in the clinical setting.

Keywords::

• 56-KDa type-specific antigen
• ELISA
• immunofluorescence assay
• Orientia tsutsugamushi
• rapid diagnosis
• scrub typhus

Financial & competing interests disclosure

The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

No writing assistance was utilized in the production of this manuscript.

Key issues

• Scrub typhus is a grossly under-diagnosed disease because of its non-specific clinical presentation and poor available diagnostics.

• Serological testing is still the most common method for diagnosis.

• Immunofluorescent antibody testing remains the gold standard for serologic diagnosis. However, it requires specialized equipments and expertise, which is usually not available in scrub typhus endemic settings.

• Evaluation of currently available rapid diagnostic kits are hampered by the imperfect gold standard and the geographic strain variation.

• Among all the available serological tests, IgM ELISA remains the most useful confirmatory test, which is still an expensive and time-consuming test.

• With no single diagnostic test capable of rapidly detecting this deadly infection, the development of a highly sensitive and specific point-of-care test is of utmost urgency.