Rickettsia

Background

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

Species	Disease	Vector	Distribution
Typhus Group
R. prowazekii	epidemic typhus	body louse
R. typhi	murine/endemic typhus	rat/cat fleas
Spotted Fever Group
R. rickettsii	Rocky Mountain spotted fever (RMSF)	Dermacentor variabilis ticks	eastern, central, and Pacific coast of US
		Dermacentor andersoni ticks	western US
		Rhipicephalus sanguineus ticks	Mexico and southern US
		Amblyomma cajennense ticks	Central and South America
R. parkeri	American tick-borne fever	Amblyommma maculatum ticks	southern US
		Amblyomma triste ticks	Uruguay, Brazil, and Argentina
R. conorrii	Mediterranean spotted fever	Rhipicephalus sanguineus ticks
R. japonica	Oriental spotter fever
R. heilongiangensis	Far Eastern spotted fever		eastern Russia, Thailand, and China
R. africae	African tick bite fever	Amblyomma ticks
R. slovaca	tick-borne lymphadenopathy (TIBOLA)	Dermacentor marginatus ticks
Transitional Group
R. akari	rickettsialpox	Liponyssoides sanguineus house mouse mites
R. australis	North Queensland tick typhus
R. felis	flea-borne spotted fever
Ancestral Group
Rickettsia bellii
Rickettsia canadensis
Other Rickettsiae
Orientia tsutsugamushi	scrub typhus	chiggers
Ehrlichia species	human monocytotropic ehrlichiosis	Amblyomma americanum and other ticks
Anaplasma species	human granulocytic anaplasmosis	Ixodes scapularis and Ixodes pacificus ticks
Neorickettsia		helminths
Wolbachia		helminths and arthropods

Management

Spotted Fever Group

• 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 TMP-SMX, which appears to worsen severity of disease!