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Rickettsia is a genus of nonmotile, gram-negative, nonspore-forming, highly pleomorphic bacteria that may occur in the forms of cocci (0.1 μm in diameter), bacilli (1–4 μm long), or threads (up to about 10 μm long).
Within the Rickettsia species, these bacteria are divided into four clades. The clades include the ancestral group, spotted fever group (SFG), typhus group, and transitional group, and the determining factors for classifying into each group depends on phenotypic characteristics, phylogenetic organization, or the type of vector host they inhabit.
They are obligate intracellular parasites, and some are notable pathogens, including Rickettsia, which causes a variety of diseases in humans, and Ehrlichia, which causes diseases in livestock. Another genus of well-known Rickettsiales is the Wolbachia , which infect about two-thirds of all arthropods and nearly all filarial nematodes. [ 2 ]
Rickettsia rickettsii can be transmitted to human hosts through the bite of an infected tick. As with other bacterium transmitted via ticks, the process generally requires a period of attachment of 4 to 6 hours. However, in some cases a Rickettsia rickettsii infection has been contracted by contact with tick tissues or fluids. [19]
The Rickettsiaceae are a family of bacteria.The genus Rickettsia is the most prominent genus within the family. The bacteria that eventually formed the mitochondrion (an organelle in eukaryotic cells) is believed to have originated from this family.
Scrub typhus - caused by Orientia tsutsugamushi (formerly classified as a Rickettsia), this disease is transmitted by chigger bites and is common in parts of Asia and the Pacific. Typhus - there are different types of typhus, including epidemic typhus caused by Rickettsia prowazekii (transmitted by lice) and murine typhus caused by Rickettsia ...
Rickettsia typhi is a small, aerobic, obligate intracellular, rod shaped gram negative bacterium. [1] It belongs to the typhus group of the Rickettsia genus, along with R. prowazekii . [ 2 ] R. typhi has an uncertain history, as it may have long gone shadowed by epidemic typhus ( R. prowazekii ). [ 3 ]
Rickettsia prowazekii is a species of gram-negative, obligate intracellular parasitic, aerobic bacilliform bacteria of class Alphaproteobacteria that is the etiologic agent of epidemic typhus, transmitted in the feces of lice. In North America, the main reservoir for R. prowazekii is the flying squirrel.