Rickettsia

Definition

A genus of obligate intracellular, gram-negative bacteria (Alphaproteobacteria: Rickettsiales) that replicate only within eukaryotic host cells and are transmitted primarily by blood-feeding arthropods. These pleomorphic, nonmotile bacteria cause a spectrum of diseases in humans and other vertebrates, including spotted fevers and typhus. The genus is named for Howard Taylor Ricketts, who identified the tick-borne agent of Rocky Mountain spotted fever.

Etymology

Named after American pathologist Howard Taylor Ricketts (1871–1910), who died from typhus while investigating its transmission; Latinized feminine form with the taxonomic suffix -ia.

Example

Rickettsia rickettsii, the agent of Rocky Mountain spotted fever, is transmitted to humans through the bite of infected Dermacentor ticks; Rickettsia prowazekii, carried by human body lice (Pediculus humanus corporis), causes epidemic typhus.

Related Terms

• vector-borne disease
• spotted fever
• typhus
• Rocky Mountain spotted fever
• Epidemic typhus
• endosymbiont
• obligate intracellular parasite
• tick-borne pathogen
• louse-borne disease
• Orientia
• Wolbachia

Usage Notes

In strict usage, 'Rickettsia' refers to the genus; 'rickettsiae' (plural) refers to individual organisms or species collectively. The term is sometimes used more loosely in medical literature to encompass related genera such as Orientia (formerly Rickettsia tsutsugamushi). Distinguish from 'rickettsial diseases,' the clinical syndromes caused by these and related bacteria. Many Rickettsia species also act as reproductive manipulators or nutritional mutualists in arthropod hosts, complicating their classification as purely pathogenic.