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Q fever is caused by infection with Coxiella burnetii. This organism is uncommon but may be found in cattle, sheep, goats and other domestic mammals, including cats and dogs. The infection results from inhalation of contaminated particles in the air, and from contact with the vaginal mucus, milk, feces, urine or semen of infected animals. The incubation period is 9-40 days. It is considered possibly the most infectious disease in the world, as a human being can be infected by a single bacterium .
Additional recommended knowledge
It was first described by Edward Holbrook Derrick in abattoir workers in Brisbane, Queensland, Australia. The "Q" stands for “query” and was applied historically at a time when the causative agent was unknown.
The pathogen of Q Fever was was discovered in 1937, when Frank Macfarlane Burnet and Mavis Freeman isolated the bacterium from one of Derrick’s patients. It was originally identified as a species of Rickettsia. H.R. Cox and Davis isolated it from ticks in Montana, USA in 1938, and called it Rickettsia diasporica. R. diasporica was considered non-pathogenic until laboratory investigators were infected; it was officially renamed Coxiella burnetii the same year. It is a zoonotic disease whose most common animal reservoirs are cattle, sheep and goats. Coxiella burnetii is no longer regarded as closely related to Rickettsiae.
Incubation period is usually 2 to 3 weeks. The most common manifestation is flu-like symptoms with abrupt onset of fever, malaise, profuse perspiration, severe headache, myalgia (muscle pain), joint pain, loss of appetite, upper respiratory problems, dry cough, pleuritic pain, chills, confusion and gastro-intestinal symptoms such as nausea, vomiting and diarrhea. The fever lasts approximately 7-14 days.
During the course, the disease can progress to an atypical pneumonia, which can result in a life threatening acute respiratory distress syndrome (ARDS), whereby such symptoms usually occur during the first 4-5 days of infection.
Less often the Q fever causes (granulomatous) hepatitis which becomes symptomatic with malaise, fever, liver enlargement (hepatomegaly), pain in the right upper quadrant of the abdomen and jaundice (icterus).
The chronic form of the Q fever is virtually identical with the inflammation of the inner lining of the heart (endocarditis), which can occur after months or decades following the infection. It is usually deadly if untreated. However, with appropriate treatment this lethality is around 10%
Appearance and incidence
The pathogenic agent is to be found everywhere except Antarctica and New Zealand. In Europe it appears as hepatitis rather than pneumonia as in the United States. The bacterium is extremely sustainable and infectious: a single organism is able to cause an infection. The common way of infection is inhalation of contaminated dust, contact with contaminated milk, meat, wool and particularly birthing products. Ticks can transfer the pathogenic agent to other animals. Transfer between humans seems extremely rare and has so far been described in very few cases.
Men are slightly more often affected than women, which most likely is attributed to different employment rates in typical professions.
"At risk" occupations include, but are not limited to:
Diagnosis is usually based on serology (looking for an antibody response) rather than looking for the organism itself. Serology allows to detect chronic infection as high antibody levels are found against the virulent form of the bacterium.Molecular detection of bacterial DNA is increasingly used. Culture is technically difficult and not routinely available in most microbiology laboratories.
Q-fever can cause endocarditis (infection of the heart valves) which may require transoesophageal echocardiography to diagnose. Q-fever hepatitis manifests as an elevation of ALT and AST, but a definitive diagnosis is only possible on liver biopsy which shows the characteristic fibrin ring granulomas.
Treatment of the acute Q fever with antibiotics is very effective and should take place in consultation with the infectiologist. Commonly used are doxycycline, tetracycline, chloramphenicol, ciprofloxacin, ofloxacin, and hydroxychloroquine. 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.
Q fever in pregnancy is especially difficult to treat because doxycycline and ciprofloxacin are contraindicated in pregnancy. The preferred treatment is five weeks of co-trimoxazole.
Q fever is effectively prevented by intradermal vaccination with a vaccine composed of killed Coxiella burnetii organisms. Skin and blood tests should be done before vaccination to identify preexisting immunity; the reason is that vaccinating subjects who already have an immunity can result in a severe local reaction. After a single dose of vaccine, protective immunity lasts for many years. Revaccination is not generally required. Annual screening is typically recommended. 
In 2001, Australia introduced a national Q fever vaccination program for people working in "at risk" occupations.
Because of its route of infection it can be used as biological warfare agent. See also bioterrorism. Q-fever is a category "B" agent. It is highly contagious and very stable in aerosols in a wide range of temperatures. Just 1-2 particles are enough to infect an individual. Q-fever microorganisms may survive on surfaces up to 60 days (like sporulating bacteria) and C. burnetii is known to reproduce and grow well in chicken egg embryos reaching very high concentrations. Protection against the disease is offered by Q-Vax, a whole cell inactivated vaccine developed by a leading Australian vaccine manufacturing company CSL. (http://www.csl.com.au/QFever.asp)
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Q_fever". A list of authors is available in Wikipedia.|