Coxiella burnetii
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| Coxiella burnetii | ||||||||||||||
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 C. burnetii, the causative agent of Q fever
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| Coxiella burnetii (Derrick 1939) Philip 1948 |
Coxiella burnetii is a species of intracellular, pathogenic bacteria, and is the causative agent of Q fever. The genus Coxiella is morphologically similar to Rickettsia, but with a variety of genetic and physiological differences. C. burnetii are small Gram negative bacteria with two growth phases, as well as a spore form which lies idle in soil.[1] It can survive standard disinfectants, and is resistant to many other environmental changes like those presented in the phagolysosome.[2]
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[edit] History and naming
Research in the 1920s and 1930s identified what appeared to be a new type of Rickettsia, isolated from ticks, that was able to pass through filters. The first description of what may have been Coxiella burnetii was published in 1925 by Hideyo Noguchi, but since his samples did not survive, it remains unclear if it was the same organism. The definitive descriptions were published in the late 1930s as part of research into the cause of Q fever, by Edward Holbrook Derrick and Macfarlane Burnet in Australia, and Herald Rea Cox and Gordon Davis at the Rocky Mountain Laboratory (RML) in the United States.[3]
The RML team proposed the name Rickettsia diaporica, derived from the Greek word for having the ability to pass through, to avoid naming it after either Cox or Davis if indeed Noguchi's description had priority. Around the same time, Derrick proposed the name Rickettsia burnetii, in recognition of Burnet's contribution in identifying the organism as a Rickettsia. As it became clear that the species differed significantly from other Rickettsia, it was first elevated to a subgenus named after Cox, Coxiella, and then in 1948 to its own genus of that name, proposed by Cornelius B. Philip, another RML researcher.[3]
[edit] Pathogenesis
The ID50 (the dose needed to infect 50% of experimental subjects) is one via inhalation — i.e. inhalation of one organism will yield disease in 50% of the population. This is an extremely low infectious dose, making C. burnetii the most infectious organism known to man.[4] Disease occurs in two stages: an acute stage that presents with headaches, chills, and respiratory symptoms, and an insidious chronic stage.
While most infections clear up spontaneously, treatment with tetracycline or doxycycline appears to reduce the symptomatic duration and reduce the likelihood of chronic infection. A combination of erythromycin and rifampin is highly effective in curing and prevention of disease and so is vaccination with Q-vax vaccine (CSL).
The bacteria use a Type IVB secretion system known as Icm/Dot to inject effector proteins called Ank proteins into the host. These effectors increase the bacteria's ability to survive inside the host cell. In Legionella pneumophila, which uses the same secretion system and also injects Ank proteins, survival is enhanced because these Ank proteins interfere with fusion of the bacteria-containing vacuole with the host's degradation endosomes.[5]
[edit] Use as a biological weapon
The United States ended its biological warfare program in 1969. When it did, C. burnetii was one of seven agents it had standardized as biological weapons.[6]
[edit] References
- ^ Ryan KJ; Ray CG (editors) (2004). Sherris Medical Microbiology (4th ed. ed.). McGraw Hill. ISBN 0-8385-8529-9.
- ^ Sankaran, Neeraja (2000). "Coxiella burnetii". Microbes and people : an A-Z of microorganisms in our lives. Phoenix, Arizona: The Oryx Press. pp. 72. ISBN 1-57356-217-3. "In contrast to other rickettsiae, which are highly sensitive and easily killed by chemical disinfectants and changes in their surroundings, C. burnetii is highly resistant" & "Q fever". Centers for Disease Control and Prevention; National Center for Infectious Diseases; Division of Viral and Rickettsial Diseases; Viral and Rickettsial Zoonoses Branch. 2003-02-13. http://www.cdc.gov/ncidod/dvrd/qfever/index.htm. Retrieved on 2006-05-24. "The organisms are resistant to heat, drying, and many common disinfectants."
- ^ a b Joseph E. McDade (1990). "Historical Aspects of Q Fever". in Thomas J. Marrie. Q Fever, Volume I: The Disease. CRC Press. pp. 5–22. ISBN 0849359848.
- ^ Q fever caused by Coxiella burnetii
- ^ Pan X, Lührmann A, Satoh A, Laskowski-Arce MA, Roy CR. Ankyrin repeat proteins comprise a diverse family of bacterial type IV effectors. Science. 2008 Jun 20;320(5883):1651-4. PMID 18566289. DOI:10.1126/science.1158160
- ^ Croddy, Eric C. and Hart, C. Perez-Armendariz J., Chemical and Biological Warfare, (Google Books), Springer, 2002, pp. 30-31, (ISBN 0387950761), accessed October 24, 2008.
[edit] External links
- Coxiella (from PATRIC the PathoSystems Resource Integration Center, a NIAID Bioinformatics Resource Center)
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