Rickettsioses

Species	Disease	Vector	Geographic Area	Eschar	Rash	Lymphadenopathy	Other Symptoms	Mortality
Rickettsiae: Spotted Fever Group (Tick-Borne)
Rickettsia rickettsii	Rocky Mountain spotted fever	Multiple Dermacentor, Amblyomma, and Rhipicephalus	Americas	rare	yes; centripetal	no	fever	>15%
Rickettsia conorii	Boutonneuse fever, Mediterranean spotted fever	Rhipicephalus sanguineus	Southern Europe, Africa, and southern Asia	frequent	maculopapular	no	fever	2-7%
Rickettsia africae	African tick-bite fever	Amblyomma hebraeum and Amblyomma variegatum	Africa and the West Indies	frequent and often multiple	papular or vesicular; may be absent	yes	fever	≤1%
Rickettsia parkeri	maculatum disease	Amblyomma maculatum	Americas	yes	often	yes	fever	≤1%
Rickettsia japonica	oriental spotted fever	Dermacentor, Haemaphysalis, or Ixodes	Asia	yes	yes
Rickettsia sibirica mongolitimonae		Rhipicephalus sanguineus	Europe, Africa and Asia	yes	yes
Rickettsia sibirica sibirica		Dermacentor	Asia or southern Russia	yes	yes
Rickettsia australis		Ixodes	Australia	yes	yes, vesicular
Rickettsia slovaca	tick-borne lymphadenopathy	Dermacentor marginatus	Europe	yes, often on scalp		regional lymphadenopathy
Rickettsia honei		Bothriocroton, Haemaphysalis, Ixodes, or Rhipicephalus	Flinders Islands, eastern Australia, Thailand, or Nepal	yes	yes
Rickettsia aeschlimanii		Hyalomma or Rhipicephalus	Africa and Europe	yes	yes
Rickettsia helvetica		ticks
Rickettsia heilongjianghensis		Dermacentor or Haemaphysalis	Asia	yes	yes
Rickettsia raoultii		Dermacentor	Europe	yes, often on scalp		regional lymphadenopathy
Rickettsia massiliae		Rhipicephalus sanguineus	Europe, Africa, and the Americas	yes	yes
Rickettsia amblyommii		ticks
Rickettsia monacensis		ticks
Rickettsia philipii strain 364D		Dermcentor occidentalis	California	yes, often on scalp		regional lymphadenopathy
Rickettsiae: Spotted Fever Group (Flea-, Louse, and Mite-Borne)
Rickettsia felis		Flea	flea exposure	yes	yes
Rickettsia akari	rickettsialpox	Liponyssoides sanguineus house mouse mites	worldwide	yes	yes, vesicular	yes	fever	≤1%
Rickettsiae: Typhus Group
Rickettsia typhi	endemic (murine) typhus	Xenopsylla cheopis (rat flea) and Ctenocephalides felis (cat flea)	tropics or subtropics, with flea exposure	may or may not	yes, centrifugal
Rickettsia prowazekii	epidemic (louse-borne) typhus	Pediculus humanus humanus (human body louse) and the fleas and live of flying squirrels	United States, especially homeless shelters	no	yes, centrifugal	no	fever	≤1% to >15%
Rickettsiae: Scrub Typhus Group
Orientia tsutsugamushi	scrub typhus	Leptotrombidium mites (chiggers, trombiculid mites)	Asian Pacific, Chile, and Dubai	yes	yes
Anaplasma
Amblyomma phagocytophilum	human granulocytotropic anaplasmosis	ticks
Ehrlichia
Ehrlichia chaffeensis	human monocytotropic ehrlichiosis	Amblyomma americanum ticks (the Lone Star tick)
Ehrlichia ewingii	human monocytotropic ehrlichiosis	Amblyomma americanum and Dermacentor variabilis ticks
Ehrlichia canis		ticks
Other Related Organisms
Neoehrlichia mikurensis		ticks
Neorickettsia sennetsu		raw fish
Wolbachia species		helminths

Diagnosis

• The mainstay of diagnosis is serology
  • Indirect immunofluorescence antibody assays of IgG antibodies
    • IgM do not appear any earlier in the course of disease and are less specific
  • Usually as acute and convalescent titres drawn 2 to 4 weeks apart showing a 4-fold increase in titres
    • Rickettsia africae may take up to 4 weeks after onset of illness to seroconvert
  • Cross-reactivity is common within each group
    • Serologic tests for Rickettsia conorii or Rickettsia rickettsii may be used to diagnosis other spotted fever group diseases such as Rickettsia africae, Rickettsia akari, Rickettsia australis, and Rickettsia sibirica
    • Serologic tests for Rickettsia typhi may be used to diagnose other typhus group diseases such as Rickettsia prowazekii
    • Cross-reactivity also common between the two groups, but the titres will usually be highest in the group containing the causative organism
• PCR is becoming more widely available
  • Blood and tissue (e.g. eschar biopsy)
  • Done as PCR for the group followed by species-specific sequencing

Management

• First-line for essentially all infections is doxycycline 100 mg po BID, continue for 3 days following resolution of symptoms
• Alternatives include azithromycin and chloramphenicol

Further Reading

• Syndromic classification of rickettsioses: an approach for clinical practice. Int J Infect Dis. 2014;28:126-39. doi: 10.1016/j.ijid.2014.05.025