<unk>  (abbreviated as<unk>  is a gram-negative, intracellular, coccobacillus bacterium that is around 0.8 to 2.0 μm long.<unk>  is the causative agent of Rocky Mountain spotted fever.<unk>  is one of the most pathogenic<unk>  strains. It affects a large majority of the Western Hemisphere and small portions of the Eastern Hemisphere.
Rickettsia rickettsii
Yersinia pestis
Babesia microti
Plasmodium unalis
Borrelia burgdorferi
Plasmodium chabaudi
Francisella tularensis
Plasmodium malariae