Japanese Spotted Fever

Japanese spotted fever (JSF) is a tick borne rickettsiosis caused by Rickettsia japonica, endemic in Japan and South Korea (also China, Philippines, Thailand).

• Vectors: Haemaphysalis flava, Dermacentor taiwanensis, and Ixodes ovatus.
• Peak season from April to October. Incubation 2 to 8 days.
• Mortality 1 to 10%, higher in the elderly and with delayed doxycycline (especially in Japan).
• Severe cases: DIC, multiorgan failure, and meningoencephalitis.

• Triad of high fever, rash, and eschar at the tick bite site (about 90%).
• Rash: erythematous maculopapules on the extremities, including palms and soles, spreading to trunk.
• Headache, malaise, myalgia, and thrombocytopenia.
• Complications: shock, renal failure, ARDS, DIC, and encephalopathy.

• PCR of blood or eschar swab, and paired serology (IFA IgG fourfold rise, or indirect IgM).
• Blood: thrombocytopenia, elevated liver enzymes, CRP, and LDH.
• Exclude scrub typhus (Orientia tsutsugamushi), severe fever with thrombocytopenia syndrome (SFTS), Lyme disease, and RMSF.
• Do not delay empiric treatment for confirmation.

• Doxycycline 100 mg orally or IV twice daily for 7 to 10 days (2.2 mg/kg twice daily in children under 45 kg); minocycline 100 mg twice daily is an alternative.
• Add a fluoroquinolone (ciprofloxacin 400 mg IV every 12 hours or levofloxacin) with tetracycline in severe disease (Japanese practice), although macrolides (azithromycin) have been used in pregnancy.
• Supportive care in ICU for shock, DIC, and respiratory failure.
• Co-infection with SFTS should be considered in East Asia (no specific therapy; favipiravir is under study).
• Tick avoidance with protective clothing, repellents, and prompt removal.