Q fever
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Q fever is a zoonosis caused by the strictly intracellular, gram negative bacterium Coxiella burnetii which proceeds asymptomatic and self-limiting in 60% of the cases. The infectious organism is commonly found in cattle, sheep, goats and other domestic mammals. The infection results from inhalation of contaminated particles in the air. The incubation time 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.
History
It was first described by Edward Holbroock Derrick in abattoir workers in Brisbane, Queensland, Australia as a disease of unknown origin and therefore “query fever”. In 1937 the bacterium was isolated by Frank MacFarlane Burnet and Freeman from one of Derrick’s patients for the first time and identified as Rickettsia-species. H.R. Cox and Davis isolated the pathogen from ticks in Montana, USA in 1938, described the transmission and it was officially named Coxiella burnetii the same year. Meanwhile Coxiella burnetii is no longer regarded as closely related to Rickettsiae.
Manifestations
The most common manifestation is flu-like symptoms with abrupt onset of fever, malaise, severe headache, myalgia (muscle pain), loss of appetite, dry cough, pleuritic pain, chills, confusion and gastro-intestinal symptoms such as nausea, vomiting and diarrhoea. The fever lasts approximately 7-14 days.
During the course, the disease can progress to an atypical pneumonia, which often results 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 rather appears as hepatitis and rather as pneumonia in the United States. The bacterium is extremely sustainable and infectious: a single one 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, what most likely is attributed to exposition in typical professions such as livestock breeding, dairy and meat production. A vaccination exists and its use is recommended to exposed people in some countries.
Diagnosis
The diagnosis is dependent on serologic investigations, that reveal the response of the immunic system. The cultivation of the bacterium usually fails and is quite dangerous. Signs of inflammation in the blood are neither sufficient nor significant. For example: there is no increase white blood cell count (leucocytosis) in 70-90% of the cases. If questionable the heart, liver or the cerebrospinal fluid (Liquor cerebrospinalis) have to be investigated.
Treatment
Treatment of the acute Q fever with antiinfectiva = 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.
Other
Because of its route of infection it can be used as biological warfare agent. See also bioterrorism.
Literature
Q Fever, "Clinical Microbiology Reviews", Oct. 1999, 518 - 583
External links
- [National Center for Infectious diseases]
- [WHO-site: Immunization, Vaccines and Biologicals]
- [Johns Hopkins University Antibiotic Guide]
- [EMedicine - Free medical knowledge base]
- [The Cochrane Collaboration]
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