Japanese spotted fever
Alerts and Notices
SynopsisFirst reported in 1984, Japanese spotted fever (JSF) is a tick-borne illness caused by Rickettsia japonica, which is largely limited geographically to Japan's pacific (central and southwestern) coastal regions. Cases have also been reported from the Japanese Sea coastal area along with South Korea and China, and the pathogen has been reported in Taiwan, Thailand, and Laos. The tick vector is Haemaphysalis longicornis. Bites from this species of tick have also been associated with the development of allergy to mammalian meat (see alpha-gal syndrome). Its animal reservoir(s) are still unknown. About 40 cases are reported in Japan each year, and this rickettsia can be of significant pathogenic potential, on par with Rickettsia rickettsii – the agent of Rocky Mountain spotted fever – in older and immunocompromised individuals.
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
Japanese spotted fever