rickettsia
noun
rick·ett·sia ri-ˈket-sē-ə 
plural rickettsias or rickettsiae ri-ˈket-sē-ˌē
-ˌī
also 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.
rickettsial
ri-ˈket-sē-əl
adjective 
Example Sentences
Recent Examples on the Web Tidewater fever, or rickettsia parkeri, is a form of Rocky Mountain spotted fever. 
Michael Reschke, Indianapolis Star, 23 Dec. 2019 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, 4 June 2018
Michael Reschke, Indianapolis Star, 23 Dec. 2019 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, 4 June 2018 Word History
Etymology
New Latin, genus name, from Howard T. Ricketts †1910 American pathologist
First Known Use
1916, in the meaning defined above
Medical Definition
rickettsia
noun
rick·ett·sia ri-ˈket-sē-ə
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
also rickettsias or rickettsia : any bacterium of the genus Rickettsia, the family Rickettsiaceae, or the order Rickettsiales