Japanese spotted fever
Patients typically present with the triad of fever (100%), a diffuse rash (100%), and an eschar (71%–94%). Other symptoms include myalgias, headache (80%), meningoencephalitis, and, in severe cases, multiorgan failure. Only around a third of patients recall a tick bite. Mortality rate overall is about 2%, but those who present late in illness (6 or more days) have an increased rate for complications including multiorgan failure, disseminated intravascular coagulopathy, and death. Laboratory findings associated with increased severity include elevated WBC, elevated creatine kinase, low platelets, elevated fibrin degradation products (FDP), and elevated C-reactive protein (CRP).
Risk factors for exposure are living in or visiting an endemic area, contact with vegetation including both crops and forested areas (early cases were associated with bamboo shoots), and older age (60-70 years on average).
A seasonal variation in incidence has been noted with most cases presenting during the warmer months of April through November. The presumed incubation period is 7 days, like other rickettsioses; however, it has not been well-defined.
Patients who are older and/or have diabetes mellitus may be at increased risk for severe infections.
A77.8 – Other spotted fevers
186771002 – Spotted fever group rickettsial disease
Differential Diagnosis & Pitfalls
- Scrub typhus – Patients with scrub typhus often present with lymphadenopathy, but this finding is rare in JSF patients; JSF patients are more likely to present with a skin rash that includes palmar erythema. Patients with scrub typhus will defervesce within 24 hours, while patients with JSF will often take 3-4 days to defervesce, after appropriate therapy has been initiated.
- Murine typhus – Unlike JSF patients, murine typhus patients present with a diffuse rash in fewer than 20% of cases, and they do not present with an eschar.
- Dengue fever
- Leptospirosis – Laboratory values and outdoor exposure may be similar, but leptospirosis patients rarely have a rash (except in cases of hemorrhage / late-stage disease).
- Severe fever with thrombocytopenia syndrome (SFTS) – A tick-borne viral infection with similar geographical and seasonal characteristics to JSF, is less likely to present with a rash, and patients are more likely to have nausea and diarrhea. SFTS tends to present with WBCs of less than 4000 m/L, and patients are more prone to altered mental status.
- Viral exanthem