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Proper Nomenclature for the Human Granulocytic Ehrlichiosis Agent.

To the Editor: In their recent article, "Antigenic variations in vector-borne pathogens," Barbour and Restrepo discuss the outer membrane protein components of Anaplasma marginale and related bacteria (1). Citing a reference by Zhi et al. (2), they state that Ehrlichia granulocytophila is the agent of human granulocytic ehrlichiosis (HGE).

The use of new names and combinations not widely recognized for genera and species lends increasing confusion to a group of bacteria already in taxonomic disarray. Several other species names have been suggested for the HGE agent since the initial description of the clinical illness caused by this agent and the in vitro technique used to isolate the agent in blood samples (3,4). Both E. phagocytophila and E. equi are genetically nearly identical to the HGE agent, and the three are probably conspecific. Thus, most scientists in the field today would support use of the name Ehrlichia phagocytophila to describe these bacteria.

Recent phylogenetic analyses show that E. phagocytophila strains align into a clade that includes Anaplasma marginale, the historical precedent in this grouping. Such phylogenetic analyses, which are also supported by comparative antigenic and biological studies, have resulted in a proposal for reclassification of several Ehrlichia spp., including E. phagocytophila, into the genus Anaplasma (5). Until a cogent reclassification based on objective criteria is firmly accepted, the creation and use of new scientific name combinations for a single bacterium yield clinical and laboratory confusion and should be avoided.


(1.) Barbour AG, Restrepo BI. Antigenic variations in vector-borne pathogens. Emerg Infect Dis 2000;6:449-57.

(2.) Zhi N, Ohashi N, Rikihisa Y. Multiple p44 genes encoding major outer membrane proteins are expressed in the human granulocytic ehrlichiosis agent. J Biol Chem 1999;274:17828-36.

(3.) Bakken JS, Dumler JS, Chen S-M, Eckman MR, VanEtta LL, Walker DH. Human granulocytic ehrlichiosis in the upper midwest United States: A new species emerging? JAMA 1994;272:212-8.

(4.) Goodman JL, Nelson C, Vitale B, Madigan JE, Dumler JS, Munderloh UG. Direct cultivation of the causative agent of human granulocytic ehrlichiosis. N Engl J Med 1996;334:209-15.

(5.) Dumler JS, Rihihisa Y, Dasch GA, Barbet AF, Palmer GH, Ray SC. Proposal for taxonomic reorganization of the order Rickettsiales, family Rickettsiaceae, and tribe Ehrlichieae. [abstract 75]. In: Program and Abstracts of the 15th Sesqui-Annual Meeting of the American Society for Rickettsiology; April 30-May 5, 2000; Captiva Island, Florida. American Society for Rickettsiology; 2000.

Johan S. Bakken(*) and J. Stephen Dumler([dagger])

(*) St. Mary's Duluth Clinic, Duluth, Minnesota, USA; and ([dagger]) Johns Hopkins Medical Institutions, Baltimore, Maryland, USA
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Article Details
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Author:Dumler, J. Stephen
Publication:Emerging Infectious Diseases
Article Type:Brief Article
Geographic Code:1USA
Date:May 1, 2001
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