tsutsugamushi

Orientia tsutsugamushi, commonly referred to as tsutsugamushi in the context of scrub typhus, is a Gram-negative, obligate intracellular bacterium that causes scrub typhus. It is transmitted to humans by the larval stage of trombiculid mites (chiggers) during feeding. The organism is endemic to the Asia-Pacific region, including parts of Southeast Asia, the Indian subcontinent, and northern Australia, with outbreaks linked to rural, scrub-covered environments.

Infection begins when a chigger bite introduces the bacterium. The organism infects endothelial cells, causing widespread vasculitis and organ involvement. Clinically, onset is abrupt with fever, headache, myalgia, and malaise; an eschar appears at the bite site in a subset of patients. Regional lymphadenopathy and a maculopapular rash may occur. Severe disease can involve the lungs, liver, kidneys, or central nervous system.

Diagnosis relies on exposure history or residence in endemic areas. Indirect immunofluorescence assay is the reference serologic test, with rapid immunochromatographic tests used for screening. PCR can detect Orientia tsutsugamushi DNA during acute illness. Cross-reactivity with other rickettsial diseases can complicate interpretation.

Treatment focuses on prompt antibiotic therapy. Doxycycline is first-line, typically given for 7 days or until 3 days after fever resolves. Alternatives include azithromycin (notably in pregnancy or doxycycline intolerance), rifampin in selected settings, and, in resource-limited contexts, chloramphenicol, though with safety concerns. Timely therapy markedly reduces mortality.

Prevention centers on reducing exposure to chiggers through protective clothing, insect repellents, and avoiding scrubby vegetation. There is no widely used vaccine. Control measures are limited by the ecology of mite vectors and rodent hosts.