an·​a·​plas·​ma ˌa-nə-ˈplaz-mə How to pronounce anaplasma (audio)
plural anaplasmas or anaplasmata ˌa-nə-ˈplaz-mə-tə How to pronounce anaplasma (audio)
: any of a genus (Anaplasma of the family Anaplasmataceae) of parasitic, gram-negative, nonmotile bacteria that are transmitted chiefly by ticks and biting flies and infect the blood cells of humans and animals see anaplasmosis

Word History


New Latin Anaplasma, genus of gram-negative bacteria, from ana- ana- (perhaps erroneously for a- a- entry 2) + -plasma -plasm

Note: The genus name Anaplasma was introduced by the Swiss veterinarian Arnold Theiler (1867-1936) in "Anaplasma marginale (Gen. and spec. nov.): The Marginal Points in the Blood of Cattle Suffering from a Specific Disease," Transvaal Department of Agriculture, Report of the Government Veterinary Bacteriologist for the Year 1908-09 (Pretoria, 1910), pp. 7-63. Anaplasma marginale was the first rickettsial pathogen to be investigated, and Theiler was unsure of the nature of the organism: "All these various reasons induce me to consider the marginal points as parasites of protozoic [protozoan] character. They differ from any known blood parasite by the absence of a protoplasmatic [of protoplasm] body and consist only of chromatin substance, thus resembling, to a certain extent, the bacteria. They represent, in my opinion, a new genus of protozoa which I propose to call Anaplasma, and the species under consideration Anaplasma marginale" (p. 29). This comment would lead one to believe that Theiler actually had alpha privative in mind, and should have named the organism Aplasma rather than Anaplasma—it is not evident what significance the spatiotemporal prefix ana- could have here.

First Known Use

1911, in the meaning defined above

Time Traveler
The first known use of anaplasma was in 1911

Dictionary Entries Near anaplasma

Cite this Entry

“Anaplasma.” Dictionary, Merriam-Webster, Accessed 24 Apr. 2024.

Medical Definition


an·​a·​plas·​ma ˌan-ə-ˈplaz-mə How to pronounce anaplasma (audio)
capitalized : a genus of parasitic, gram-negative, nonmotile bacteria of the family Anaplasmataceae that are transmitted chiefly by ticks and biting flies and infect the blood cells of humans and animals see anaplasmosis
plural anaplasmas or anaplasmata -mət-ə How to pronounce anaplasma (audio) : any bacterium of the genus Anaplasma
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