Pathogen Description

Pathogen Life Cycle

Innate Immune Response

Humoral Immune Response

Cellular Immune Response

Evasion of Immune System Detection

Future Directions


Rickettsia rickettsii


Photo courtesy of the CDC -

Physical Description

Rickettsia rickettsii is a species of small bacterium that are the causal agents of the infection known as Rocky Mountain Spotted Fever. These obligate intracellular bacteria have cell walls, lack flagella, are gram-negative, perform aerobic respiration, and multiply through binary fission in the nucleus or the cytoplasm of their host cells. Once inside they have multiplied, they often will damage and kill a large number of cells by causing blood to leak through tiny holes in blood vessel walls into adjacent tissues. They occur either singly, in pairs, or in strands. They range in size from 0.2 by 0.3 um to 0.5 by 2.0 um. (Emerging Infection Diseases, 1998) They are difficult to see in tissues using routine histologic stains and often require special staining methods. (CDC, 2005) They have diplococcoid bodies and are maintained in nature by through the transstadial and transovarial passage beween different tick vectors. (Wattam, 2004) They can infect, remain for extended periods of time, and multiply in numerous types of hosts, but most commonly infect mammals and arthropods in a relatively complex host-parasite interaction. (Emerging Infection Diseases, 1998)

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