First reported in 1984, Japanese spotted fever (JSF), or oriental spotted fever, is a tick-borne rickettsial illness caused by Rickettsia japonica, which is limited geographically to Japan (central and southwestern coastal regions). 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 elderly and immunocompromised patients.
Patients present with fever (100%), a diffuse rash (100%), an eschar (71%–94%), myalgias, headache (80%), meningoencephalitis, and, in severe cases, multiorgan failure. 29% of patients recall a tick bite. Patients frequently have thrombocytopenia (28%), elevated creatine kinase (64%), and elevated fibrin degradation products (57%). Mortality rate overall is ~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. Lab findings associated with increased severity include elevated WBC, elevated creatine kinase, low platelets, elevated fibrin degradation products, and elevated C-reactive protein.
Risk factors for exposure that have been cited are residence in Japan, contact with vegetation (especially bamboo shoots), and older age (60-70 years on average).
A seasonal variation in incidence has been noted: May / June in northeastern Japan, and November / December in southwestern Japan.
The presumed incubation period is 7 days, like other rickettsioses; however, it has not been well defined.
Patients who are elderly and/or have diabetes mellitus may be at increased risk for severe infections.
Tick bites from some Haemaphysalis species may be associated with the subsequent development of allergies to mammalian meat (eg, beef, pork) in a small number of patients. It is thought that the allergy is mediated by induced IgE antibodies to alpha-gal (galactose-alpha-1,3-galactose), a mammalian oligosaccharide. Individuals with elevated IgE titers to alpha-gal have experienced urticaria, angioedema, and anaphylaxis symptoms either immediately or 3-6 hours (delayed onset) after ingesting mammalian meat (alpha-gal syndrome). Exactly how the tick bite leads to development of this allergy is unclear. Implicated tick bites have been noted to itch for 2 or more weeks.
Codes
ICD10CM: A77.8 – Other spotted fevers
SNOMEDCT: 186771002 – Spotted fevers
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Differential Diagnosis & Pitfalls
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. In addition, scrub typhus patients often present with lymphadenopathy, and this finding is rare in JSF patients; JSF patients have palmar erythema, and scrub typhus patients do not.
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.
Leptospirosis – Laboratory values and outdoor exposure may be similar, but leptospirosis patients rarely have a rash (except in cases of hemorrhage / late stage disease).
