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Q fever

Q fever is a zoonose caused by the bacteria Coxiella burnetii (small, tough, gram-negative, exists in three forms - phase I, phase II and spore). The infectious organism is commonly found in cattle, sheep, goats and other domestic mammals. It does not produce many clinical symptoms in the animals but is excreted in waste and milk as well as during birth.

Human infection is usually be inhalation or ingestion of aerosol particles or by tick bite. Humans are highly susceptible to the disease, but over half of infections are asymptomatic and it is rarely transmitted by person to person contact. When the organism does cause clinical symptoms, after a incubation period of 10 to 40 days it is marked by high fever, severe headache, myalgia, confusion, nausea, vomiting, diarrhea, generalized chest pains, and weight loss. The fever usually lasts 7 to 14 days. Up to 50% of acute patients will develop pneumonia. The liver is often also damaged and some patients will later develop hepatitis. However, most patients will return to good health within 60 days, even without treatment. Only 1%-2% of people with acute Q fever die.

As well as the acute form the disease also has a much less common chronic form, with the infection persisting for more than 6 months. Patients who have suffered acute Q fever may develop the chronic form within 1 to 20 years after initial infection. The most serious effect of chronic infection is endocarditis. Most patients who develop chronic Q fever have pre-existing valvular problems or a history of vascular graft. As many as 65% of persons with chronic Q fever will die of the disease.

Acute Q fever is treated with antibiotics, usually the tetracycline antibiotic doxycycline, or quinolone antibiotics. The chronic form is more difficult to treat and can require up to four years of treatment with doxycycline and quinolones or doxycycline with hydroxychloroquine. A vaccine has been developed.

The disease was first described in 1935 in Australia as of unknown etiology, it was named Q (query) fever.