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. more...
The infection results from inhalation of contaminated particles of the inhaled 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.
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.
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.
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