Rickettsia are non-motile, rod shaped, non-filterable, non-spore-forming, gram-negative bacteria. Its name was given by Howard Taylor Ricketts (USA). It possesses a typical gram negative cell wall which can’t be stained by gram staining. R. rickettsii is difficult to observe in tissues under microscope without special staining technique, but it can be used to visualize the direct fluorescent antibody (DFA) techniques such as Giemsa, Gimenez and Macchiavello staining for identification and classification of slow-growing or fastidious bacterial infections in tissue samples. Their genome size ranged from 1 to 1.5 million base pairs. Rickettsias depend on entry, growth, and replication surrounded by the cytoplasm of living eukaryotic host cells. Rickettsia cannot grow in artificial medium; they must be grown either in tissue or embryo. Rickettsiae cannot be grown in standard artificial agar medium plates or in broth. Instead, they required viable host cells for their growth and multiplication. They must be cultivated in environments such as embryonated eggs, cell cultures or within susceptible animals. It can be primarily disseminated to humans and plants by means of the feeding and biting of fleas, lice, ticks or mites. The dependency on living host cells is due to their obligate intracellular parasitic nature, making them reliant on the host for essential nutrients and its replication. Bartonella quintana (formerly known as Rochalimaea quintana) is one such exception because, despite being an intracellular pathogen, it can also survive and grow outside (auxenically) host cells under certain conditions, but was traditionally considered all rickettsiae can synthesize ATP.