Orientia tsutsugamushi

• Chigger-borne rickettsial infection caused by the intracellular Gram-negative bacterium Orientia tsutsugamushi that causes scrub typhus

Background

Life Cycle

• The entire life cycle is maintained within Leptotrombidium mites by vertical/transovarial transmission
• Leptotrombidium larvae (called chiggers) normally feed on rodents, and occasionally humans, who are dead-end hosts

Epidemiology

• Most common in rural Asia and western Australia, as well as other parts of eastern Asia, including Russia and India

Clinical Manifestations

• Fever, headache, myalgia, lymphadenopathy, and an eschar
  • Lymphadenopathy sometimes grouped near the eschar
  • Should almost always be able to find the eschar if you look hard enough
• Transient pale macular rash
• May have cough
• May have mental status changes and hepatosplenomegaly
• In severe cases, may progress to multiorgan failure and hemorrhage
• After treatment, may relapse
• Infection also decreases HIV viral load and can lead to immune reconstitution

Diagnosis

• Four-fold rise in immunofluorescence serology
• PCR on eschar, blood, or lymph node biopsy

Management

• Doxycycline 100 mg po bid for 7 days
• Alternative: azithromycin 500 mg p.o. daily for 1-3 days
• For severe disease, combination doxycycline and azithromycin for 7 days
  • Dosing may be unusual: doxycycline 200 mg bid x2 followed by 100 mg bid; azithromycin 500 mg bid x2 followed by 500 mg daily