Q fever

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Q fever is an acute or chronic disease caused by the rickettsial-like bacillus Coxiella burnetii. Acute disease causes sudden onset of fever, headache, malaise, and interstitial pneumonitis. Chronic disease manifestations reflect the organ system affected. Diagnosis is confirmed by several serologic techniques, isolation of the organism, or polymerase chain reaction (PCR). Treatment is with doxycycline or chloramphenicol .
(See also Overview of Rickettsial and Related Infections.)
Coxiella burnetii is a small, intracellular, pleomorphic bacillus that is no longer classified as Rickettsia. Molecular studies have reclassified it as Proteobacteria in the same group as Legionella species.
Q fever can be

Acute
Chronic

Acute disease causes a febrile illness that often affects the respiratory system, although sometimes the liver is involved. Women infected during pregnancy have an increased risk of spontaneous abortion and preterm delivery.
Chronic Q fever occurs in lt; 5% of patients. It usually manifests as endocarditis or hepatitis; osteomyelitis may occur.
Worldwide in its distribution, Q fever is maintained as an inapparent infection in domestic or farm animals. Sheep, cattle, and goats are the principal reservoirs for human infection. C. burnetii persists in stool, urine, milk, and tissues (especially the placenta), so that fomites and infective aerosols form easily. C. burnetii is also maintained in nature through an animal-tick cycle, but arthropods are not involved in human infection.