Category:Rickettsioses

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