Rickettsia

Rickettsia species

• A genus of obligate mostly-tick-borne intracellular Gram-negative bacteria

Typhus Group

• R. prowazekii: causes [epidemic typhus](Epidemic typhus (R. prowazekii).md), transmitted by the body louse
• R. typhi: causes [murine/endemic typhus](Murine typhus (R. typhi).md), transmitted by rat/cat fleas

Spotted Fever Group

• R. rickettsii: causes [Rocky Mountain spotted fever (RMSF)](Rocky Mountain spotted fever (RMSF) (R. rickettsii).md)
• R. parkeri: carried by A. maculatum in the southern US and A. triste in Uruguay, Brazil, and Argentina
• R. conorii: causes [boutonneuse fever](Boutonneuse fever (R. conorii).md)
• R. japonica: causes oriental spotter fever
• R. heilongiangensis: causes Far Eastern spotted fever in eastern Russia, Thailand, and China
• R. africae: causes [African tick bite fever](African tick-bite fever (ATBF) (R. africae).md)
• R. slovaca: causes tick-borne lymphadenopathy (TIBOLA)
  • Transmitted by Dermacentor marginatus ticks

Transitional Group

• R. akari: causes [rickettsialpox](Rickettsialpox (R. akari).md), transmitted by the house mouse mite, Liponyssoides sanguineus
• R. australis: causes North Queensland tick typhus
• R. felis: causes flea-borne spotted fever
  • Cats are host to the flea vector Ctenocephalides felis, which has worldwide distribution
  • Fevers with headache, myalgia, maculopapular rash, neurologic involvement, vomiting, abdo pain, resp involvement

Management

• Doxycycline 100 mg po bid for 7 to 10 days
  • Alternatively: tetracycline 2 g/day or chloramphenicol 2 g/d
  • Alternatively: ciprofloxacin 750 mg po bid for 5 to 7 days
    • But no good evidence for this
• Can use doxycycline safely for these duration in children <8 years, and is strongly indicated for rickettsioses
• May use azithromycin or clarithromycin in pregnant women
• Avoid Septra, which appears to worsen severity of disease!

Ancestral Group

• Rickettsia bellii
• Rickettsia canadensis

Other Rickettsiae

• Orientia tsutsugamushi: causes [scrub typhus](Scrub typhus (O. tsutsugamushi).md), transmitted by chiggers
• Ehrlichia: transmitted by ticks
• Anaplasma: transmitted by ticks
• Neorickettsia: transmitted by helminths
• Wolbachia: transmitted by helminths and arthropods