Rickettsia (redirected from Hungarian spotted fever)

rickettsia (rĭkĕt`sēə), any of a group of very small microorganisms, many disease-causing, that live in vertebrates and are transmitted by bloodsucking parasitic arthropods such as fleas, lice (see louse), and ticks. Rickettsias are named after their discoverer, the American pathologist Harold Taylor Ricketts, who died of typhus 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 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.

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rickettsia

Any of the rod-shaped bacteria that make up the family Rickettsiaceae (named for Howard Ricketts). They are rod-shaped or variably spherical, and most are gram-negative (see gram stain). Natural parasites of certain arthropods, they can cause serious diseases in humans and other animals, to which they are usually transmitted by a bite from an arthropod carrier. Because certain species can survive considerable drying, rickettsias can also be transmitted when arthropod feces are inhaled or enter the skin through abrasion. Typhus, trench fever, and Rocky Mountain spotted fever are rickettsial infections. The most effective treatment includes timely and prolonged administration of broad-spectrum antibiotics.

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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