rick·​ett·​sia | \ ri-ˈket-sē-ə \
plural rickettsias or rickettsiae\ ri-​ˈket-​sē-​ˌē , -​ˌī \ also rickettsia

Definition of rickettsia

: any of a various gram-negative, parasitic bacteria (order Rickettsiales and especially genus Rickettsia) that are transmitted by biting arthropods (such as lice or ticks) and cause a number of serious diseases (such as Rocky Mountain spotted fever and typhus)

Note: Rickettsia are often pleomorphic, and may be coccoid, rod-shaped, or irregularly-shaped.

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Other Words from rickettsia

rickettsial \ ri-​ˈket-​sē-​əl \ adjective

Examples of rickettsia in a Sentence

Recent Examples on the Web

Ticks can transmit a variety of diseases such as Borrelia burgdoferi, also known as Lyme disease, and Rickettsia rickettsia that can cause Rocky Mountain Spotty Fever. Gabriela Moraru, M.d., miamiherald, "Summer is coming. Are you ready for the bugs?," 4 June 2018

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'rickettsia.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

First Known Use of rickettsia

1916, in the meaning defined above

History and Etymology for rickettsia

New Latin, genus name, from Howard T. Ricketts †1910 American pathologist

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The first known use of rickettsia was in 1916

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More Definitions for rickettsia


rick·​ett·​sia | \ ri-ˈket-sē-ə \

Medical Definition of rickettsia

1 capitalized : a genus of rod-shaped, coccoid, or diplococcus-shaped often pleomorphic bacteria (family Rickettsiaceae) that are transmitted by biting arthropods (as lice or ticks) and cause a number of serious diseases (as Rocky Mountain spotted fever and typhus)
2 plural rickettsiae\ -​ˌē \ also rickettsias or rickettsia : any bacterium of the genus Rickettsia, the family Rickettsiaceae, or the order Rickettsiales

More from Merriam-Webster on rickettsia

Britannica.com: Encyclopedia article about rickettsia

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