Dictionary:
rick·ett·si·a (rĭ-kĕt'sē-ə)  |
[New Latin Rickettsia, genus name, after Howard Taylor Ricketts (1871-1910), American pathologist.]
rickettsial rick·ett'si·al adj.| 5min Related Video: rickettsia |
| Britannica Concise Encyclopedia: rickettsia |
For more information on rickettsia, visit Britannica.com.
| Dental Dictionary: Rickettsia |
A genus of microorganisms that combine aspects of both bacteria and viruses. Examples of rickettsial diseases are Rocky Mountain spotted fever and typhus.
| Columbia Encyclopedia: rickettsia |
Types of Rickettsial Diseases
Rickettsia prowazekii causes louse-borne typhus, carried from person to person by two species of lice. Flea, or murine, typhus, caused by R. mooseri, is transmitted from rodents to people by fleas. Trench fever, caused by R. quintana, was an epidemic disease in World War I; it is transmitted by the rat flea from rat to person or from person to person. Trench fever disease reservoirs (perpetuation of the disease in wild animal populations) exist in some parts of E Europe, Mexico, and N Africa. Various typhuslike rickettsial diseases, such as Rocky Mountain spotted fever and African tick typhus, are transmitted by ticks from animal hosts to people. Mite-borne rickettsial infections include rickettsialpox, caused by Rickettsia akari and transmitted from house mice to people, and scrub typhus, or tsutsugamushi fever, caused by R. tsutsugamushi and found in Japan and SE Asia. Q fever, caused by Coxiella burnetii, a more hardy rickettsia viable outside the living host, is usually transmitted to humans by inhalation of contaminated airborne particles or from contaminated materials, often from infected livestock; it is an occupational hazard among dairy farm and slaughterhouse workers. A new rickettsia, Ehrlichia chaffeenis, which results in human ehrlichiosis, was identified in 1986.
Symptoms and Treatment
The similar symptoms of rickettsial infections often make it difficult to distinguish one disease from another. In people the organisms grow in cells lining blood and lymph vessels; a rash, fever, and flulike symptoms are usually present. Q fever also causes lung damage. All rickettsial diseases respond to treatment with antibiotics such as doxycycline (a tetracycline) and chloramphenicol.
| Veterinary Dictionary: rickettsia |
Pl. rickettsiae; an organism in the order Rickettsiales.
| Wikipedia: Rickettsia |
| Rickettsia | |
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| Rickettsia rickettsii | |
| Scientific classification | |
| Domain: | Bacteria |
| Phylum: | Proteobacteria |
| Class: | Alpha Proteobacteria |
| Order: | Rickettsiales |
| Family: | Rickettsiaceae |
| Genus: | Rickettsia da Rocha-Lima, 1916 |
| Species | |
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Rickettsia felis |
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Rickettsia is a genus of motile, Gram-negative, non-sporeforming, highly pleomorphic bacteria that can present as cocci (0.1 μm in diameter), rods (1–4 μm long) or thread-like (10 μm long). Obligate intracellular parasites, the Rickettsia survival depends on entry, growth, and replication within the cytoplasm of eukaryotic host cells (typically endothelial cells).[1] Because of this, Rickettsia cannot live in artificial nutrient environments and are grown either in tissue or embryo cultures (typically, chicken embryos are used). In the past they were regarded as microorganisms positioned somewhere between viruses and true bacteria. The majority of Rickettsia bacteria are susceptible to antibiotics of the tetracycline group.
Rickettsia species are carried as parasites by many ticks, fleas, and lice, and cause diseases such as typhus, rickettsialpox, Boutonneuse fever, African tick bite fever, Rocky Mountain spotted fever, Australian Tick Typhus, Flinders Island Spotted Fever and
The method of growing Rickettsia in chicken embryos was invented by Ernest William Goodpasture and his colleagues at Vanderbilt University in the early 1930s.
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The classification of Rickettsia into three groups (spotted fever, typhus and scrub typhus) was based on serology. This grouping has since been confirmed by DNA sequencing. All three of these contain human pathogens. The scrub typhus group has been reclassified as a new genus – Orientia – but many medical textbooks still list this group under the ricketsial diseases.
However more recently it has become apparent that rickettsia are more widespread than previously believed and are known to be associated with arthropods, leeches and protists. Divisions have also been identified in the spotted fever group and it has been suggested that this should be divided into two clades.[3] The arthropod species appear to be ancestral to the vertebrate species and the species infecting leeches and protists are unrelated.[4]
The following plant diseases have been associated with Rickettsia-like organisms[5].
Infection occurs in non-human mammals; for example, species of Rickettsia have been found to afflict the South Amercian Guanaco, Lama guanacoe.[6]
Certain segments of Rickettsial genomes resemble that of mitochondria.[7] The deciphered genome of R. prowazekii is 1,111,523 bp long and contains 834 protein-coding genes.[8] Unlike free-living bacteria, it contains no genes for anaerobic glycolysis or genes involved in the biosynthesis and regulation of amino acids and nucleosides. In this regard it is similar to mitochondrial genomes; in both cases, nuclear (host) resources are used. ATP production in Rickettsia is the same as that in mitochondria. In fact, of all the microbes known, the Rickettsia is probably the closest "relative" (in phylogenetic sense) to the mitochondria. Unlike the latter, the genome of R. prowazekii, however, contains a complete set of genes encoding for the tricarboxylic acid cycle and the respiratory chain complex. Still, the genomes of the Rickettsia as well as the mitochondria are frequently said to be "small, highly derived products of several types of reductive evolution".
The recent discovery of another parallel between Rickettsia and viruses may become a basis for fighting HIV infection.[9] Human immune response to the scrub typhus pathogen, Orientia tsutsugamushi rickettsia, appears to provide a beneficial effect against HIV infection progress, negatively influencing the virus replication process. A probable reason for this actively studied phenomenon is a certain degree of homology between the rickettsia and the virus – namely, common epitope(s) due to common genome fragment(s) in both pathogens. Surprisingly, the other infection reported to be likely to provide the same effect (decrease in viral load) is the virus-caused illness dengue fever.
The genus Rickettsia is named after Howard Taylor Ricketts (1871–1910), who studied Rocky Mountain spotted fever in the Bitterroot Valley of Montana, and eventually died of typhus after studying that disease in Mexico City. Despite the similar name, Rickettsia bacteria do not cause rickets, which is a result of vitamin D deficiency.
This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)
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 | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved. Read more |
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| Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 2006 Encyclopædia Britannica, Inc. All rights reserved. Read more |
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| Dental Dictionary. Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved. Read more |
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| Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2003, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/. Read more |
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| Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved. Read more |
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| Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Rickettsia". Read more |
