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).