Overview

Gram-negative obligately intracellular bacteria

Spotted fever group

• Rocky Mountain Spotted fever, Rickettia rickettsii, Tick

• African tick bite fever: Rickettsia africae, Tick

• Mediterranean spotted fever: Rickettsia conorii, Tick

• Japanese spotted fever (JSF): Rickettsia japonica, Tick

• Others: Austrailian tick typhus (Rickettsia australis), Flea-bourne spotted fever (Rickettsia felis)

Scrub typhus group

• Scrub typhus (ST): Orientia tsutsugamushi (different strains/serotypes), Leptotrombidum mite

Typhus group

• Epidemic typhus, Rickettsia prowazekii, Lice

• Endemic typhus, murine typhus, Rickettsia typhi, Flea ()

Geography

Rickettsia endemic to Japan

• JSF (April-October)

• ST (Nov-Dec)

Reference: Distinguishing Japanese Spotted Fever and Scrub Typhus, Central Japan, 2004-2015

Clinical

• Fever

• Rash (non-specific, macular popular)

• Eschar: most pathognomonic sign of scrub typhus is the presence of an eschar, which is variously described as a black-crusted lesion or a cigarette burn-like lesion or a black necrotic lesion. The eschar represents the site of inoculation, where initial multiplication occurs before widespread dissemination

• Breathing difficulty (low O2, ARDS)

• CNS (meningitis)

• Multi-organ failure

Differential Diagnosis

• Dengue

• Typhoid

• Meiliod

• Pneumonia?

Diagnosis

Challenging (gold standard IFA + PCR?)

• Antibody: Immunofluorescent assay (IFA) and others Enzyme-linked immunosorbent assay (ELISA) (e.g. InBios IgM detection combined 3 antigens Kato, Gilliam, TA763), Weil Felix reaction (low sens/spec)

• Nucleic acid detection: PCR (conventional, nested, real-time) Loop-mediated isothermal amplification (LAMP) PCR of eschar tissue

• Antigen detection: culture requires BSL3, PCR

• Isolation: Cell culture, Mouse inoculation

Treatment

• Antibiotics: Doxycycline

• Antipyretic