Rickettsial Infections: Key Features
- Transmission: Vector-borne (ticks, lice, fleas) or aerosolized (e.g., Coxiella burnetii).
- Pathogenesis: Obligate intracellular bacteria; disrupt endothelial cells, causing vasculitis.
- Clinical Spectrum:
- R. rickettsii (Rocky Mountain Spotted Fever): Fever, rash, multiorgan failure (high mortality).
- R. prowazekii (Epidemic Typhus): Fever, rash, delirium (high mortality if untreated).
- O. tsutsugamushi (Scrub Typhus): Eschar, lymphadenopathy, pneumonia.
- R. typhi (Murine Typhus): Fever, rash, no eschar (mild course).
- Diagnosis:
- Serology: Indirect immunofluorescence assay (IFA) for acute/ convalescent titers (4-fold rise).
- PCR: Detects rickettsial DNA in blood, tissue (sensitive for early diagnosis).
- Skin Biopsy: Immunofluorescence for rickettsial antigen in eschars.
- Treatment:
- Doxycycline (100 mg bid) is first-line for all severe cases (Rationale: inhibits protein synthesis, effective against intracellular pathogens).
- Chloramphenicol (alternative for pregnant women, though not FDA-approved for rickettsiae).
- Prevention:
- Vector control (insecticides, protective clothing).
- Vaccines: Limited availability (e.g., Q-fever vaccine for at-risk groups).