Coxiella burnetii
Encyclopedia
Coxiella burnetii is an obligate intracellular
bacterial pathogen, 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 that are highly resistant to environmental stresses such as high temperature, osmotic pressure, and ultraviolet light. These characteristics are attributed to a small cell variant (SCV) form of the organism that is part of a biphasic developmental cycle including a more metabolically and replicatively active large cell variant (LCV) form. It can survive standard disinfectants, and is resistant to many other environmental changes like those presented in the phagolysosome.
s, 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.
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.
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.
This is the main target of milk pasteurization.
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.
program in 1969. When it did, C. burnetii was one of seven agents it had standardized as biological weapons.
Obligate intracellular parasite
Intracellular parasites are parasitic microorganisms - microparasites that are capable of growing and reproducing inside the cells of a host.-Facultative:...
bacterial pathogen, and is the causative agent of Q fever
Q fever
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 genus Coxiella is morphologically similar to Rickettsia
Rickettsia
Rickettsia is a genus of non-motile, Gram-negative, non-sporeforming, highly pleomorphic bacteria that can present as cocci , rods or thread-like . Being obligate intracellular parasites, the Rickettsia survival depends on entry, growth, and replication within the cytoplasm of eukaryotic host cells...
, but with a variety of genetic and physiological differences. C. burnetii are small Gram-negative
Gram-negative
Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
bacteria that are highly resistant to environmental stresses such as high temperature, osmotic pressure, and ultraviolet light. These characteristics are attributed to a small cell variant (SCV) form of the organism that is part of a biphasic developmental cycle including a more metabolically and replicatively active large cell variant (LCV) form. It can survive standard disinfectants, and is resistant to many other environmental changes like those presented in the phagolysosome.
History and naming
Research in the 1920s and 1930s identified what appeared to be a new type of Rickettsia, isolated from tickTick
Ticks are small arachnids in the order Ixodida, along with mites, constitute the subclass Acarina. Ticks are ectoparasites , living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians...
s, that was able to pass through filters
Air filter
A particulate air filter is a device composed of fibrous materials which removes solid particulates such as dust, pollen, mold, and bacteria from the air. A chemical air filter consists of an absorbent or catalyst for the removal of airborne molecular contaminants such as volatile organic compounds...
. The first description of what may have been Coxiella burnetii was published in 1925 by Hideyo Noguchi
Hideyo Noguchi
, also known as , was a prominent Japanese bacteriologist who discovered the agent of syphilis as the cause of progressive paralytic disease in 1911.-Early life:...
, 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
Q fever
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...
, by Edward Holbrook Derrick
Edward Holbrook Derrick
Edward Holbrook Derrick was an Australian pathologist, best known for his role in identifying Q fever.Derrick was born in Victoria, and earned an M.D. from Melbourne University in 1922. He subsequently worked for a short period of time at the Walter and Eliza Hall Institute in Melbourne, and spent...
and Macfarlane Burnet in Australia, and Herald Rea Cox and Gordon Davis at the Rocky Mountain Laboratory (RML) in the United States.
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.
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
Axenic
In biology, axenic describes a culture of an organism that is 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...
culture and suggested the technique may be useful for study of other pathogens.
This is the main target of milk pasteurization.
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. 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
Doxycycline
Doxycycline INN is a member of the tetracycline antibiotics group, and is commonly used to treat a variety of infections. Doxycycline is a semisynthetic tetracycline invented and clinically developed in the early 1960s by Pfizer Inc. and marketed under the brand name Vibramycin. Vibramycin...
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.
Use as a biological weapon
The United States ended its biological warfareBiological warfare
Biological warfare is the use of biological toxins or infectious agents such as bacteria, viruses, and fungi with intent to kill or incapacitate humans, animals or plants as an act of war...
program in 1969. When it did, C. burnetii was one of seven agents it had standardized as biological weapons.
External links
- Coxiella burnetii genomes and related information at PATRIC, a Bioinformatics Resource Center funded by NIAID