The genera Anaplasma, Ehrlichia, Cowdria, Neorickettsia and Wolbachia encompass a group of obligate intracellular bacteria that reside in vacuoles of eukaryotic cells and were previously placed in taxa based upon morphological, ecological, epidemiological and clinical characteristics. Recent genetic analyses of 16S rRNA genes, groESL and surface protein genes have indicated that the existing taxa designations are flawed. All 16S rRNA gene and groESL sequences deposited in GenBank prior to 2000 and selected sequences deposited 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 consensus and parsimony methods. Supported by bootstrap probabilities of at least 54 %, 16S rRNA gene comparisons consistently clustered to yield four distinct clades characterized roughly as Anaplasma (including the Ehrlichia phagocytophila 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 Neorickettsia (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 equi and the human granulocytic ehrlichiosis (HGE) agent to support separate species designations, and this group was at least 98 2 % similar to any Anaplasma species. These 16S rRNA gene analyses are strongly supported by similar groESL clades, as well as biological and antigenic characteristics. It 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 emended to include Anaplasma (Ehrlichia) phagocytophila comb. nov. (which also encompasses the former E. equi and the HGE agent), Anaplasma (Ehrlichia) bovis comb. nov. and Anaplasma (Ehrlichia) platys comb. nov., the genus Ehrlichia should be emended to include Ehrlichia (Cowdria) ruminantium comb. nov. and the genus Neorickettsia should be emended to include Neorickettsia (Ehrlichia) risticii comb. nov. and Neorickettsia (Ehrlichia) sennetsu comb. nov. Keywords : J. S. Dumler and others INTRODUCTIONRecent improvements in molecular technologies have significantly advanced our abilities to conduct genetic analyses and, for the first time, clearly indicated the proper phylogenetic positions of most of the fastidious bacterial species in the families Rickettsiaceae, Bartonellaceae and Anaplasmataceae in the order Rickettsiales (Woese et al., 1990 ;Weisburg et al., 1989 ; Brenner et al., 1993 ; Birtles et al., 1995). By 16S rRNA sequencing, Weisburg et al. (1989) demonstrated that Coxiella burnetii and Wolbachia persica belonged to the γ-Proteobacteria, while the remaining members of the order Ri...

A previously undescribed obligate intracellular bacterium was isolated from an aborted bovine fetus. The organism was resistant to penicillin, replicated within cytoplasmic vacuoles, exhibited structural characteristics compatible with the rickettsias, and shared antigenic determinants with Cowdria ruminantium.

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The DNA probe pCS20, which was cloned from the DNA of the Crystal Springs heartwater strain from Zimbabwe, cross-reacted with DNAs of heartwater strains from all endemic areas, including four heartwater strains from Zimbabwe, two strains from South Africa, one strain from Nigeria, and the Gardel strain from the Caribbean island of Guadeloupe. By nucleic acid hybridization, the pCS20 DNA probe detected Cowdria ruminantium DNA in all DNA preparations made from plasma samples from infected sheep before and during the febrile reaction. Synthetic oligonucleotides were prepared for amplification of specific C. ruminantium DNA sequences by the polymerase chain reaction (PCR). Amplification of two DNA products (181 and 279 bp) from pCS20 DNA and C. ruminantium genomic DNA of heartwater strains was demonstrated. In contrast, amplification of these products or any other products was not possible from genomic DNAs of Anaplasma marginale, Babesia bigemina, Trypanosoma brucei brucei, Eschenichia coli, and bovine endothelial cells. The cross-reactivities of the 32P-labeled PCR products with genomic DNAs from several heartwater strains were similar to those with the pCS20 DNA probe. A nucleic acid-based test that uses hybridization assays and PCR provides a sensitive method for the detection of heartwater in both animals and ticks and has applications in epidemiological studies for the disease, which may allow for improved disease control.

The results from several experiments demonstrated that an effective vaccine for contagious caprine pleuropneumonia could be made with inactivated F38 mycoplasma. Evaluation of the amounts of lyophilised F38 mycoplasma plus saponin showed that the optimum formulation was 0.15 mg of mycoplasma in saponin. Saponin inactivates the mycoplasma and provides the adjuvant effect necessary to stimulate a protective immune response. The lyophilised F38 mycoplasma could be stored for 14 months at either 4 degrees C or 22 degrees C without losing its immunising potential. A single immunisation with the optimum formulation produced a protective immune response in goats that lasted for longer than one year.