American pathologist Howard Taylor Ricketts (1871-1910) discovered and was killed by the unique pathogen of Rocky Mountain typhus in 1909, hence the name Rickettsia. Rickettsia belongs to the Gram-negative bacteria, is a class of specialized parasitic in the eukaryotic cells G - prokaryotic organisms, is between bacteria and viruses close to a class of prokaryotic organisms, generally spherical or rod-shaped, is a specialized intracellular parasitic organisms, mainly parasitic in the arthropods, often cause Q fever, Rocky Mountain typhus fever or typhoid fever.

Rickettsiae can be shown by the Giemsa, Macchiavello technique, and the Leagene Rickettsial Stain (modified Macchiavello method) modified by Culling, which stains rickettsiae and certain viral inclusion bodies red.