Information AboutRickettsia |
| CATEGORIES ABOUT RICKETTSIA | |
| rickettsiales | |
| bacteriology | |
| SHOPPER'S DELIGHT | |
Bacteria of the genus ''Rickettsia'' are carried as Parasite s by many Tick s, Flea s, and Lice , and cause Disease s such as Typhus , Rickettsialpox , Brill-Zinsser Disease , Boutonneuse Fever , Rocky Mountain Spotted Fever , and Endemic Typhus in human beings. Like Virus es, they grow only in living cells. The name rickettsia is often used for any member of the Rickettsiales . ''Rickettsia'' are Non-motile , Gram-negative , Non-sporeforming , highly pleomorphic organisms 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'' depend 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 Antibiotic s of the Tetracycline group. PATHOGENESIS The ''Rickettsia'' human pathogens are generally grouped as follows: Spotted Fever group
:: Rocky Mountain Spotted Fever
:: Rickettsialpox
:: Boutonneuse Fever
::Siberian tick typhus
::Australian tick typhus
::Oriental spotted fever Typhus group
::Epidemic, recrudescent and sporadic Typhus
::Murine typhus Scrub typhus group''
::(now a separate genus, '' Orientia '') :: Scrub Typhus GENOMICS Certain segments of Rickettsial Genome s resemble that of Mitochondria .2 }} The deciphered genome of ''R. prowazekii'' is 1,111,523 Bp long and contains 834 protein-coding genes.3 }} Unlike free-living bacteria, it contains no genes for anaerobic glycolysis or genes involved in the biosynthesis and regulation of Amino Acid s and Nucleoside s. 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.4 }} Human immune response to the Scrub Typhus pathogen, '' Orientia Tsutsugamushi '' rickettsia, appears to provide a beneficial effect on 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 a virus-caused fever - Dengue . HISTORICAL The genus ''Rickettsia'' is named after Howard Taylor Ricketts ( 1871 – 1910 ), who worked on and eventually died of typhus. Despite the similar name, ''Rickettsia'' bacteria do not cause Rickets . The disease of rickets takes its name from the Greek word for Spine , ''rhakhis'', and is a Vitamin Deficiency Disease , not an infectious disease. REFERENCES |