Coxiella burnetii

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Coxiella burnetii
Coxiella burnetii, the bacteria that causes Q Fever.jpg
A dry fracture of a Vero cell exposing the contents of a vacuole where Coxiella burnetii is growing
Scientific classification
C. burnetii
Binomial name
Coxiella burnetii
(Derrick 1939)
Philip 1948

Coxiella burnetii is an obligate intracellular bacterial pathogen, and is the causative agent of Q fever. [1] The genus Coxiella is morphologically similar to Rickettsia , but with a variety of genetic and physiological differences. C. burnetii is a small Gram-negative, coccobacillary bacterium that is highly resistant to environmental stresses such as high temperature, osmotic pressure, and ultraviolet light. These characteristics are attributed to a small cell variant form of the organism that is part of a biphasic developmental cycle, including a more metabolically and replicatively active large cell variant form. [2] It can survive standard disinfectants, and is resistant to many other environmental changes like those presented in the phagolysosome. [3]

Q fever disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals; the most common manifestation is flu-like symptoms; the name Q stands for “query”, so named when the pathogen was unknown

Q fever is a disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals. 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 a spore-like small-cell variant, and from contact with the milk, urine, feces, vaginal mucus, or semen of infected animals. Rarely, the disease is tick-borne. The incubation period is 9–40 days. Humans are vulnerable to Q fever, and infection can result from even a few organisms. The bacterium is an obligate intracellular pathogenic parasite.

<i>Rickettsia</i> type of bacteria that causes typhus, among other diseases

Rickettsia is a genus of nonmotile, Gram-negative, non-spore-forming, highly pleomorphic bacteria that may occur in the forms of cocci 0.1 μm in diameter, rods 1–4 μm long, or threads of up to about 10 μm long. The term "rickettsia" has nothing to do with rickets, which is a deficiency disease resulting from lack of vitamin D; the bacterial genus Rickettsia was named after Howard Taylor Ricketts, in honour of his pioneering work on tick-borne spotted fever.


A coccobacillus is a type of bacterium with a shape intermediate between cocci and bacilli. Coccobacilli, then, are very short rods which may be mistaken for cocci.


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 as to whether 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. [4]

Tick order of arachnids

Ticks are small arachnids, typically 3 to 5 mm long, part of the order Parasitiformes. Along with mites, they constitute the subclass Acari. Ticks are ectoparasites, living by feeding on the blood of mammals, birds, and sometimes reptiles and amphibians. Ticks had evolved by the Cretaceous period, the most common form of fossilisation being immersed in amber. Ticks are widely distributed around the world, especially in warm, humid climates.

A particulate air filter is a device composed of fibrous or porous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. Filters containing an adsorbent or catalyst such as charcoal (carbon) may also remove odors and gaseous pollutants such as volatile organic compounds or ozone. Air filters are used in applications where air quality is important, notably in building ventilation systems and in engines.

Hideyo Noguchi Japanese bacteriologist

Hideyo Noguchi, also known as Seisaku Noguchi, was a prominent Japanese bacteriologist who in 1911 discovered the agent of syphilis as the cause of progressive paralytic disease.

The RML team proposed the name Rickettsia diaporica, derived from the Greek word for having the ability to pass through filter pores, 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. [4]

Coxiella was difficult to study because it could not be reproduced outside a host. However, in 2009, scientists reported a technique allowing the bacteria to grow in an axenic culture and suggested the technique may be useful for study of other pathogens. [5]

In biology, axenic describes the state of a culture in which only a single species, variety, or strain of organism is present and entirely free of all other contaminating organisms. The earliest axenic cultures were of bacteria or unicellular eukaryotes, but axenic cultures of many multicellular organisms are also possible. Axenic culture is an important tool for the study of symbiotic and parasitic organisms in a controlled environment.


Immunohistochemical detection of C. burnetii in resected cardiac valve of a 60-year-old man with Q fever endocarditis, Cayenne, French Guiana, monoclonal antibody against C. burnetii and hematoxylin were used for staining: Original magnification x50 Immunohistochemical detection of Coxiella burnetii in resected cardiac valve of a 60-year-old man with Q fever endocarditis.jpg
Immunohistochemical detection of C. burnetii in resected cardiac valve of a 60-year-old man with Q fever endocarditis, Cayenne, French Guiana, monoclonal antibody against C. burnetii and hematoxylin were used for staining: Original magnification ×50

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 (only 1-10 organisms required), making C. burnetii one of the most infectious known organisms. [6] [7] 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 the disease, and vaccination with Q-VAX vaccine (CSL) is effective for prevention of it.[ citation needed ]

Tetracycline chemical compound

Tetracycline, sold under the brand name Sumycin among others, is an antibiotic used to treat a number of infections. This includes acne, cholera, brucellosis, plague, malaria, and syphilis. It is taken by mouth.

Doxycycline chemical compound

Doxycycline is an antibiotic that is used in the treatment of infections caused by bacteria and certain other parasites. It is useful for bacterial pneumonia, acne, chlamydia infections, early Lyme disease, cholera and syphilis. It is also useful for the treatment of malaria when used with quinine and for the prevention of malaria. Doxycycline can be used either by mouth or intravenously.

Erythromycin chemical compound

Erythromycin is an antibiotic used for the treatment of a number of bacterial infections. This includes respiratory tract infections, skin infections, chlamydia infections, pelvic inflammatory disease, and syphilis. It may also be used during pregnancy to prevent Group B streptococcal infection in the newborn, as well as to improve delayed stomach emptying. It can be given intravenously and by mouth. An eye ointment is routinely recommended after delivery to prevent eye infections in the newborn.

The bacteria use a type IVB secretion system known as Icm/Dot (intracellular multiplication / defect in organelle trafficking genes) 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. [8]

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. [9]


At least five completely sequenced genomes of Coxiella burnetii exist, [10] which contain about 2.1 Mbp of DNA each and encode around 2,100 open reading frames; 746 (or about 35%) of these genes have no known function.

In bacteria small regulatory RNAs are activated during stress and virulence conditions. Coxiella burnetii small RNAs (CbSRs 1, 11, 12, and 14) are encoded within intergenic region (IGR). CbSRs 2, 3, 4 and 9 are located antisense to identified ORFs. The CbSRs are up-regulated during intracellular growth in host cells. [11]

Additional images

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<i>Rickettsia rickettsii</i> species of bacterium

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In cell biology, a phagosome is a vesicle formed around a particle engulfed by a phagocyte via phagocytosis. Professional phagocytes include macrophages, neutrophils, and dendritic cells (DCs). A phagosome is formed by the fusion of the cell membrane around a microorganism, a senescent cell or an apoptotic cell. Phagosomes have membrane-bound proteins to recruit and fuse with lysosomes to form mature phagolysosomes. The lysosomes contain hydrolytic enzymes and reactive oxygen species (ROS) which kill and digest the pathogens. Phagosomes can also form in non-professional phagocytes, but they can only engulf a smaller range of particles, and do not contain ROS. The useful materials from the digested particles are moved into the cytosol, and waste is removed by exocytosis. Phagosome formation is crucial for tissue homeostasis and both innate and adaptive host defense against pathogens.

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