rickettsia

(rĭkĕt`sēə), any of an order (Rickettsiales) of very small microorganisms, many disease-causing, that live in vertebrates and are transmitted by bloodsucking parasitic arthropods such as fleasflea,
common name for any of the small, wingless insects of the order Siphonaptera. The adults of both sexes eat only blood and are all external parasites of mammals and birds. Fleas have hard bodies flattened from side to side and piercing and sucking mouthparts.
..... Click the link for more information. , lice (see louselouse,
common name for members of either of two distinct orders of wingless, parasitic, disease-carrying insects. Lice of both groups are small and flattened with short legs adapted for clinging to the host.
..... Click the link for more information. ), and ticks. Rickettsias are named after their discoverer, the American pathologist Harold Taylor Ricketts, who died of typhustyphus,
any of a group of infectious diseases caused by microorganisms classified between bacteria and viruses, known as rickettsias. Typhus diseases are characterized by high fever and an early onset of rash and headache.
..... Click the link for more information. in Mexico after confirming the infectious agent of that rickettsial disease. Rickettsias are gram-negative, coccoid-shaped or rod-shaped bacteria; unlike other bacteria, but like viruses, they require a living host (a living cell) to survive. Rickettsias from infected vertebrates, usually mammals, live and multiply in the gastrointestinal tract of an arthropod carrier but do not cause disease there; they are transmitted to another vertebrate, possibly one of another species, by the arthropod's mouthparts or feces.

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 Ro+cky Mountain spotted feverRocky Mountain spotted fever,
infectious disease caused by a rickettsia. The bacterium is harbored by wild rodents and other animals and is carried by infected ticks of several species that attach themselves to humans.
..... Click the link for more information. 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. A new rickettsia, Ehrlichia chaffeenis, which results in human ehrlichiosisehrlichiosis
, any of several diseases caused by rickettsia of the genera Ehrlichia and Anaplasma. Ehrlichiosis is transmitted by ticks. Both human forms tend to develop about nine days after a tick bite.
..... Click the link for more information. , was identified in 1986. Q feverQ fever,
disease caused by Coxiella burnetii, a small, Gram-negative bacterium. The bacterium infects livestock (cattle, goats, and sheep) and other domesticated animals, and is found in the urine, feces, amniotic fluid and other birth products, and milk of infected
..... Click the link for more information. was formerly classified as a rickettsial disease, but its causative agent, Coxiella burnetii, although similar to the rickettsia, is more closely related to the bacteria that causes Legionnaire's diseaseLegionnaire's disease
, infectious, sometimes fatal, disease characterized by high fever, dry cough, lung congestion, and subsequent pneumonia. Major organs, such as the heart, may be damaged as the disease progresses.
..... Click the link for more information. and is now included in the order Legionellales.

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. All rickettsial diseases respond to treatment with antibiotics such as doxycycline (a tetracyclinetetracycline
, any of a group of antibiotics produced by bacteria of the genus Streptomyces. Effective against a wide range of Gram positive and Gram negative bacteria, tetracycline interferes with protein synthesis in these microorganisms (see Gram's stain).
..... Click the link for more information. ) and chloramphenicolchloramphenicol
, antibiotic effective against a wide range of gram-negative and gram-positive bacteria (see Gram's stain). It was originally isolated from a species of Streptomyces bacteria.
..... Click the link for more information. .

Rickettsia

a genus of small pathogenic bacteria that multiply only in host cells. It is named after the American pathologist H. T. Ricketts (1871–1910), who in 1909 discovered the causative agent of Rocky Mountain spotted fever. Rickettsia is a short rod (0.3 × 0.3 to 2 μm) with rounded ends occurring singly or in pairs. The rods are nonsporogenous, nonmotile, and gram-negative; they multiply by transverse division. The rickettsiae are no larger than some viruses but are classified as bacteria since they divide and have cell walls, cytoplasmic membranes, ribosomes, and nuclei. In addition, they synthesize protein, the nucleic acids DNA and RNA, ATP, and the enzymes of intermediate metabolism, chiefly those of the tricarboxylic acid cycle.

Being intracellular parasites, the rickettsiae make use of growth factors from cells of the host organism. The cytoplasmic membrane of the rickettsiae is highly permeable, a result of their adaptation to a parasitic mode of life. The rickettsiae do not grow on the ordinary nutrient media and require chick embryos or animal cell cultures. They are sensitive to unfavorable physical or chemical factors and to some antibiotics.

The rickettsiae include the causative agents of epidemic typhus (Rickettsia prowazekii), murine typhus (R. mooseri), Q fever (Coxiella burnetii), and other endemic or widespread rickettsioses.

A. A. IMSHENETSKII

Rickettsia

[rĭ-ket´se-ah] a genus of bacteria of the tribe Rickettsiae, made up of small, gram-negative, rod-shaped to coccoid, often pleomorphic microorganisms, which multiply only in host cells. Organisms occur in the cytoplasm of tissue cells or free in the gut lumen of lice, fleas, ticks, and mites and are transmitted by their bites. R. cono´rii is the etiologic agent of boutonneuse fever and is transmitted by the bite of ixodid ticks. R. prowaze´kii is the agent of scrub typhus and Brill-Zinsser disease; it is transmitted between humans by the human body louse and from flying squirrels to humans by fleas and lice. R. ty´phi is the cause of murine typhus, which is transmitted to humans chiefly by rat fleas. Rickettsial diseases are not common in communities with good sanitary standards, since prevention depends on controlling the rodent and insect populations. Major epidemics have occurred, especially in times of war when standards of sanitation drop.

rickettsia

[rĭ-ket´se-ah] (pl. rickett´siae) An individual organism of the family Rickettsiaceae.

Rickettsia

(ri-ket'sē-ă), A genus of bacteria (order Rickettsiales) containing small (that is, nonfilterable), often pleomorphic, coccoid to rod-shaped, gram-negative organisms that usually occur intracytoplasmically in lice, fleas, ticks, and mites but do not grow in cell-free media; pathogenic species infect humans and other animals, causing epidemic, murine, or endemic typhus, Rocky Mountain spotted fever, tsutsugamushi disease, rickettsialpox, and other diseases; type species is Rickettsia prowazekii. [Howard T. Ricketts]

rickettsia

(rĭ-kĕt′sē-ə)n. pl. rickett·siae (-sē-ē′) Any of various bacteria of the genus Rickettsia, carried as parasites by many ticks, fleas, and lice, that cause diseases such as typhus and Rocky Mountain spotted fever in humans.

rick·ett′si·al adj.

Rick·ett·si·a

(ri-ket'sē-ă) A genus of bacteria containing small (nonfilterable), often pleomorphic, coccoid to rod-shaped, gram-negative organisms that usually occur intracytoplasmically in lice, fleas, ticks, and mites; pathogenic species are parasitic in humans and other animals, causing epidemic typhus, murine or endemic typhus, Rocky Mountain spotted fever, tsutsugamushi disease, rickettsialpox, and other diseases; type species is Rickettsia prowazekii.

Rickettsia

A micro-organism intermediate in size between the largest viruses and the smallest bacteria. Rickettsiae are spread by ticks and small insects, and cause TYPHUS, Q FEVER, and ROCKY MOUNTAIN SPOTTED fever. The eponymous discoverer of the genus died of typhus while investigating the cause. (Howard Taylor Ricketts, 1871–1910, American pathologist).

Rickettsia

a GENUS of bacteria within the phylum PURPLE BACTERIA. Rickettsias are INTRACELLULAR PATHOGENS of animals, including humans. They are smaller than some of the largest VIRUSES, and like viruses can only reproduce within a host CELL. They are rod-shaped, about 1–2 μ m in length and are generally transmitted to man by INSECTS and TICKS. For example, Rocky Mountain spotted fever is caused by Rickettsia rickettsii which is transmitted by ticks.

Rickettsia

A rod-shaped infectious microorganism that can reproduce only inside a living cell. Scrub typhus is a rickettsial disease.Mentioned in: Scrub Typhus

Rick·ett·si·a

(ri-ket'sē-ă) Genus of bacteria that usually occur intracytoplasmically in lice, fleas, ticks, and mites; pathogenic species infect humans and other animals, causing epidemic, murine, or endemic typhus, Rocky Mountain spotted fever other diseases.

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Types of Rickettsial Diseases

Symptoms and Treatment

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Words related to rickettsia

noun any of a group of very small rod-shaped bacteria that live in biting arthropods (as ticks and mites) and cause disease in vertebrate hosts

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