rickettsia

(redirected from rickettsial)
Also found in: Dictionary, Thesaurus, Medical, Wikipedia.
Related to rickettsial: Rickettsia rickettsii

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.
.

The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The leech is reported to be a potential vector for human rickettsial infections (7,8).
These findings match with Shrivastava and Shukla (2013) who reported higher incidence of rickettsial and haemoparasitic infections in hairy breed dogs, which may be due to more tick infestation and difficulties during tick control because of their long hair coat.
Since the Rocky Mountain spotted fever (RMSF) is well known to aggressively affect humans and we found the presence of a tick species that frequently transmits RMSF, it is possible to say that the rural population of Yucatan must be at high risk of acquiring rickettsial infection; however, there must be other biological, ecological, or mainly social factors that decrease this risk and which should be analyzed from an eco-epidemiological point of view [19].
Varghese, who has published frequently on the epidemiology of scrub typhus, said that it is still appropriately grouped among rickettsial infections.
The ubiquitous occurrence of A americanum collected at Fort Eustis along with the aggressive man-biting character of this tick species indicates that the potential risk of rickettsial and ehrlichial human infections could be high in the summer months in this area.
Scrub typhus is an important cause of acute febrile illness caused by Rickettsial species Orientia tsutsugamushi, presents as a systemic vasculitis like infection with wide range of clinical manifestations and often fatal complications.
Rocky Mountain spotted fever, the most fatal tickborne rickettsial disease, has a death rate between 5 and 10 percent.
Diagnosis and management of tickborne rickettsial diseases: Rocky Mountain spotted fever and other spotted fever group rickettsioses, ehrlichioses, and anaplasmosis--United States.
Rickettsial suspensions for use in experiments were prepared from heavily infected L929 cells.
While the ticks were not directly associated with the birds, this survey of birds was conducted to determine if they may have been exposed to rickettsial agents in similar regions in Tennessee.
[6] Blood samples were collected from these patients to test for rickettsial antibodies by commercially obtained WeilFelix test (PROGEN, Tulip Diagnostics (P) Ltd., Verna, Goa, India).
Rickettsial diseases are the most common febrile illness in patients returning from international travel.