Reorganization of genera in the families Rickettsiaceae and Anaplasmataceae in the order Rickettsiales: unification of some species of Ehrlichia withAnaplasma, Cowdria with Ehrlichia and Ehrlichia with Neorickettsia, descriptions of six new species combinations and designation of Ehrlichia equi and 'HGE agent' as subjective synonyms of Ehrlichia phagocytophila

The genera Anaplasma, Ehrlichia, Cowdria, Neorickettsia and Wolbachia encom pass a group of obligate intracellular bacteria that reside in vacuoles of eukaryotic cells and were previously placed in taxa based upon morphologica l, ecological, epidemiological and clinical characteristics. Recent genetic analyses of 16S rRNA genes, groESL and surface protein genes have indicate d that the existing taxa designations are flawed. All 16S rRNA gene and gro ESL sequences deposited in GenBank prior to 2000 and selected sequences dep osited thereafter were aligned and phylogenetic trees and bootstrap values were calculated using the neighbour-joining method and compared with trees generated with maximum-probability, maximum-likelihood, majority-rule conse nsus and parsimony methods. Supported by bootstrap probabilities of at leas t 54%,16S rRNA gene comparisons consistently clustered to yield four distin ct clades characterized roughly as Anaplasma (including the Ehrlichia phago cytophila group, Ehrlichia platys and Ehrlichia bovis) with a minimum of 96 .1% similarity, Ehrlichia (including Cowdria ruminantium) with a minimum of 97.7% similarity, Wolbachia with a minimum of 95.6% similarity and Neorick ettsia (including Ehrlichia sennetsu and Ehrlichia risticii) with a minimum of 94.9% similarity. Maximum similarity between clades ranged from 87.1 to 94.9%. Insufficient differences existed among E. phagocytophila, Ehrlichia egui and the human granulocytic ehrlichiosis (HGE) agent to support separa te species designations, and this group was at least 98.2% similar to any A naplasma species. These 16S rRNA gene analyses are strongly supported by si milar groESL clades, as well as biological and antigenic characteristics. I t is proposed that all members of the tribes Ehrlichieae and Wolbachieae be transferred to the family Anaplasmataceae and that the tribe structure of the family Rickettsiaceae be eliminated. The genus Anaplasma should be emen ded to include Anaplasma (Ehrlichia) phagocytophila comb. nov. (which also encompasses the former E. egui and the HGE agent), Anaplasma (Ehrlichia) bo vis comb. nov. and Anaplasma (Ehrlichia) platys comb. nov., the genus Ehrli chia should be emended to include Ehrlichia (Cowdria) ruminantium comb. nov . and the genus Neorickettsia should be emended to include Neorickettsia (E hrlichia) risticii comb. nov. and Neorickettsia (Ehrlichia) sennetsu comb. nov.