A dairy farmer presents with 10 days of high fever, severe headache, myalgia, and hepatitis with transaminases three times normal. There is no rash despite marked toxicity. Blood cultures are negative. Which feature most reliably distinguishes the causative agent from other members of the Rickettsiaceae group?
- A It is transmitted by inhalation of infected aerosols rather than an arthropod bite ✓
- B It is an obligate intracellular organism that cannot grow on cell-free media
- C It causes vasculitis by invading vascular endothelium
- D It responds to doxycycline therapy
Correct answer: A. It is transmitted by inhalation of infected aerosols rather than an arthropod bite
Explanation
The vignette describes Q fever due to Coxiella burnetii. Unlike Rickettsia and Orientia species, Coxiella produces no rash because it does not infect vascular endothelium, and it is acquired by inhalation of aerosols from infected animal products, especially placental tissue, not by a tick or mite bite. Options B and D apply to all rickettsiae including Coxiella, and option C applies to spotted fever and typhus group organisms but not to Coxiella.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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