Rocky Mountain Spotted Fever

''Rickettsia rickettsii'' is a Gram-negative, intracellular, coccobacillus bacterium that is around 0.8 to 2.0 μm long. ''R. rickettsii'' is the causative agent of Rocky Mountain spotted fever. ''R. rickettsii'' is one of the most pathogenic ''Rickettsia'' strains. It affects a large majority of the Western Hemisphere and small portions of the Eastern Hemisphere.