- A member of a group of microorganisms that (like viruses) require other living cells for growth but (like bacteria) use oxygen, have metabolic enzymes and cell walls, and are susceptible to antibiotics. Rickettsiae cause a series of diseases named for the American pathologist Howard Ricketts who discovered that ticks spread Rocky Mountain spotted fever and then isolated from the blood of infected animals and eggs of infected ticks the microorganism responsible for Rocky Mountain spotted fever, typhus, trench fever and other similar conditions. While in Mexico in 1910 studying a typhus epidemic, Ricketts contracted the disease and died at age 39.(See Rickettsial diseases).
* * *A genus of bacteria (order Rickettsiales) containing small (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 typhus, murine, or endemic typhus, Rocky Mountain spotted fever, tsutsugamushi disease, rickettsialpox, and other diseases; type species is R. prowazekii. [Howard T. Ricketts]- R. africae a species of R. studied principally in Zimbabwe that appears to be carried by the tick Amblyomma hebraeum; a cause of spotted fever.- R. akari a bacterial species causing human rickettsialpox; transmitted by the house mouse mite, Liponyssoides sanguineus; a mild febrile disease of 7–10 days is produced with an urban distribution in the northeastern U.S. and in wild or commensal rodents in the countries of the former USSR and Africa.- R. australis a bacterial species causing a spotted fever, North Queensland tick typhus, clinically and serologically similar to the disease caused by the agent of rickettsialpox; Ixodes holocyclus and I. tasmani are probable vectors. Small marsupials are suspected reservoirs of this agent, which is found over much of coastal Queensland, especially in secondary scrub and savannah.- R. burnetii former name for Coxiella burnetii.- R. canis former name for Ehrlichia canis.- R. conorii a species of bacteria causing boutonneuse fever in southern Europe, Africa, and the Middle East; transmitted by various ticks, such as the dog tick Rhipicephalis sanguineus.- R. mooseri a species similar to R. prowazekii but with less variation in appearance; the resultant endemic typhus is milder and has a somewhat slower onset.- R. prowazekii a bacterial species causing epidemic and recrudescent typhus, transmitted by body lice; type species of the genus R..- R. psittaci former name for Chlamydia psittaci.- R. rickettsii a bacterial species, the agent of Rocky Mountain spotted fever, South African tick-bite fever, São Paulo exanthematic typhus of Brazil, Tobia fever of Colombia, and spotted fevers of Minas Gerais and Mexico; transmitted by infected ixodid ticks, especially Dermacentor andersoni and D. variabilis.- R. sennetsu SYN: Ehrlichia sennetsu.- R. sibirica a bacterial species, the agent of Siberian or North Asian tick typhus, transmitted by various ixodid ticks, which also serve as reservoirs, possibly aided by rodents and hares; the disease resembles Rocky Mountain spotted fever.- R. slovaca a bacterial species causing a newly recognized rickettsiosis associated with local erythema and possibly meningoencephalitis; transmitted by the tick Dermacentor marginatus.- R. tsutsugamushi former name for Orientia tsutsugamushi.
* * *rick·ett·sia ri-'ket-sē-ə n1) cap the type genus of the family Rickettsiaceae comprising rod-shaped, coccoid, or diplococcus-shaped often pleomorphic bacteria that live intracellularly in biting arthropods (as lice or ticks) and when transmitted to humans by the bite of an arthropod host cause a number of serious diseases (as Rocky Mountain spotted fever and typhus)2) pl -si·ae -.ē also -sias or -sia any bacterium of the order Rickettsiales and esp. of the family Rickettsiaceae
* * *Rick·ett·sia (rĭ-ketґse-ə) [Howard Taylor Ricketts, American pathologist, 1871â€“1910] a genus of bacteria of the family Rickettsiaceae, made up of small rod-shaped to coccoid, often pleomorphic microorganisms. The cells have typical cell walls, possess no flagella, are gram-negative, and multiply only inside host cells. They occur in the cytoplasm of cells or free in the lumen of the gut in lice, fleas, ticks, and mites, by which they are transmitted to mammals. Various species contain organisms that cause typhus fevers and spotted fevers. The type species is R. prowazeґkii.
Medical dictionary. 2011.