Q fever as a biological weapon.

Q fever is a bacterial zoonosis caused by Coxiella burnetii, a unique intracellular coccobacillus, adapted to live within the phagolysosomes of macrophages and monocytes. It is highly infectious, with as little as one organism needed to cause clinical infection, making it an attractive organism for use in biowarfare. Despite its high infectivity, it has low virulence, and most patients undergo only asymptomatic seroconversion. Acute clinical manifestations are a nonspecific febrile illness, pneumonia, hepatitis, and neurologic abnormalities ranging from headache to meningoencephalitis. Chronic Q fever can result in endocarditis, hepatitis, or a chronic fatigue syndrome. Diagnosis usually is made by serology because culture of the highly contagious organism is potentially hazardous. Tetracyclines are the antibiotics of choice. When individualized therapy is possible, a 14- to 21-day course of doxycycline usually is used. In a mass casualty situation, a 5- to 7-day course of doxycycline is recommended, both for therapy and prophylaxis. For chronic infections such as endocarditis, 18 months of doxycycline supplemented with hydroxychloroquine is currently the best therapy.