The Distribution and Relationships of Rickettsiae
The Seventh Edition of Bergey's Manual of Determinative Bacteriology separated the rickettsiae from the blue-green algae and bacteria and placed them in a new class with the viruses. The Rickettsiales and Chlamydiales possess most of the characteristics attributable to other scotobacteria. They can be differentiated from them by being intracellular parasites of eukaryotic cells and from the Mycoplasmatales by possessing cell walls. In their revision of the Anaplasmataceae for the Eighth Edition of Bergey's Manual, Ristic and Kreier expanded the family to include Anaplasma, Paranaplasma, Aegyptianella, Haemobartonella, and Eperythrozoon. Haemobartonella and Eperythrozoon were included in the family Bartonellaceae in the Seventh Edition of Bergey's Manual. Before the invention and application of the electron microscope, it was not clear that the so-called larger viruses and even the rickettsiae were actually cellular organisms possessing complex membranes, cytoplasmic structures, and nuclear material. The various groups of tickborne rickettsiae occur in geographically distinct regions separated for the most part by natural boundaries.