Coxiela burnetti
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Coxiela burnetti
Coxiella burnetti is an obligate intracellular Gram-negative coccobacillus bacterium that is known to be the main pathogen that causes Q fever in mammals and humans. Harold Cox and MacFarlane Burnet initially identified Q fever as “query fever” in 1935 when a number of infections were found to be from an Australian slaughterhouse. Once this disease was elucidated to be a human pathogen, the name was properly changed to Q fever. Its global pathogenic effect demonstrates the need for preventive measures to control the rate of infection worldwide and its potential use for bioterrorism. The significance of a completed sequenced genome is the benefit of being able to further understand the mechanisms of pathogenesis and use this knowledge to fight against this infectious disease. Sheep, cattle, and goats are major sources of Coxiella burnetti that can potentially help spread the disease to other organisms. The most common mode of transmission to humans is primarily through external waste excretions from infected animals. The aerosol route to infection is frequent by inhalation of contaminated air that contains many of these organisms or through an insect vector. Coxiella burnetti live in a wildlife livestock environment and can withstand heat, dryness, and antibacterial compounds, allowing this bacterium to persist outside the host for an extensively long period of time. It is an acidophile, meaning it tends to surround itself in an environment with low pH. Uniquely enough, it can be endocytosed by a macrophage and complete replication inside the phagolysozyme during its life cycle.
| Kingdom | Bacteria |
|---|---|
| Phylum | Proteobacteria |
| Class | Gamma Proteobacteria |
| Order | Legionellales |
| Family | Coxiellaceae |
| Genus | Coxiella |
| Species | C. burnetii |
| Binomial | Coxiella burnetii |
Contents |
[edit] Surface Characteristics
Being that Coxiella burnetti is a Gram-negative bacterium, this distinction marks important properties about the cell structure. Gram-negative bacteria have two membranes, an inner and outer membrane. The outer membrane lacks an energy source, but compensates by having porins fused into the membrane. The organism does not have a thick cell wall composed of peptidoglycan like Gram-positive bacteria. In between the two membranes lies the periplasmic space. Lipopolysaccharides are anchored to the membrane. During its life cycle, phagocytosis brings the bacteria into the host cell, where it remains in phagocytic vacuoles and replicates in the phagolysozyme.
[edit] Pathogenic Activity
Coxiella burnetti does not display a pathogenic effect for all organisms it encounters. For example, B. La Scola and D. Raoult discovered that Coxiella burnetti and free-living amoeba Acanthamoeba castellanii are able to co-exist in a benign relationship upon infection. The bacterium was able to produce spore-like structures in vacuoles within the amoeba, demonstrating its ability to differentiate without any interference from the other species. The bacterium does not cause any diseases in the amoeba. Likewise, the amoeba did not utilize the bacterium as food, so it contributes to the survival of Coxiella burnetti by supplying an intracellular niche for it to differentiate into a structure similar to a spore and resist harmful environmental conditions.
Besides surviving in a host cell, Coxiella burnetti can adapt to a shared intracellular niche with another parasite without inhibition of development for either. According to research accomplished by Andreoli and colleagues, Vero cells that were previously inhabited by Coxiella burnetti were co-infected with another type of parasite such as Trypanosoma cruzi. Parasitophorous vacuoles (PV) of T. cruzi trypomastigotes and bacterial vacuoles fused together upon co-infection. T. cruzi was able to proceed with differentiation into amastigotes and division in Coxiella burnetti vacuoles. The co-existence of both parasites depends on the ability of Coxiella burnetti to provide sufficient amount of nutrients for T. cruzi.
[edit] Virulence
Q fever is a global disease caused by the pathogen Coxiella burnetti. Without any symptoms and a low dosage that leads to infection, the disease can go unnoticed until serious health consequences begin to present themselves. Because of its natural high resistance to harsh environmental conditions, including dessication, heat, and antibacterial compounds, the transmission of Q fever to other organisms is very effective through contaminated air, the main mode of transmission. In reference to virulence factors, genes encoding adhesive structures in the genome such as pili are absent, but there are 13 ankyrin domains that may assist in the bacterium’s attachment to its host. (3) The method in which humans get infected is by infected animals such as sheep, cattle, goat, dogs, and cats. These infected animals can produce excretions through urine, feces, and milk that contain infectious dosages of this pathogenic bacterium, which can be dangerously mistakenly inhaled, consumed, or be in contact with. The bacterium can be isolated in the placentas of infected animals and can cause abortions due to inflammation. Not just livestock and domestic animals can get infected. Even fish and rodents can acquire Q fever as well.
Humans who are exposed to or handle infected animals, such as farmers or veterinarians, have a higher risk of infection and then the disease develops. Typically, there are no obvious symptoms after infection. Only about 50% of people who are infected show signs of the disease. Symptoms similar to the flu may appear, but it is not specific and not always diagnosed as Q fever. The disease takes the form of pneumonia or hepatitis commonly. As the infection becomes more serious, chronic Q fever develops. Endocarditis, inflammation of the aortic heart valves, has been associated with the chronic complications of the disease. The survival rate is higher for those who do not suffer from chronic Q fever.
