What is it?
This illness was named “Q (for query) fever” in 1937 when the first cases of the disease were reported but very little was known about it. Since then, the cause and routes of the disease have been discovered but the name has been retained.
Q fever is caused by an intracellular bacterium called Coxiella burnetii. The name is derived from the Australian and American researchers who discovered the microorganism. Macfarlane Burnet and Edward Derrick isolated it from patients in Queensland and Herald Cox recovered bacteria from ticks collected in Montana.
Characteristically, this bacterium has two states or phases. Bacteria obtained directly from patients are in phase I, but those obtained from laboratory cultures present itself in phase II.
Q fever can be an acute or chronic disease and long-term sequelae, such as chronic fatigue, are gaining acceptance as a third category of the disease.
Acute Q fever has an incubation period of 15 to 25 days and commonly presents as an influenza-like illness with fever, severe headache often worst behind the eyes, rigors, drenching sweats, muscle pain and acute weight loss. There is usually some evidence of liver disease. In addition, acute infection can include pneumonia with a cough and chest pain. The acute illness lasts 2 to 6 weeks. Evidence suggests that the microrganism may persist in the body for some time after the acute illness.
Chronic disease may occur months or years after acute illness and most commonly presents as endocarditis. It usually develops in people with underlying immunosuppression or pre-existing heart disease. About 10% of acutely ill people may develop fatigue lasting more than 6 months.
Disease is endemic to much of the world including Australia. Diagnosis of Q fever is not easy as signs and symptoms are non-specific. A history of exposure to cattle, sheep or goats may be a useful pointer to the diagnosis but contact may be also indirect and unrecognised.
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