USMLE

Borrelia burgdorferi (Lyme Disease)

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Bacteria - Gram Negative
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  18. Klebsiella pneumoniae
  19. Campylobacter jejuni
  20. Vibrio spp.
  21. Helicobacter pylori
  22. Borrelia burgdorferi (Lyme Disease)
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Borrelia burgdorferi 

  • Characteristics
    • Spirochete (spiral-shaped with axial filaments) 
      • Doesn’t gram-stain well due to thin cell walls 
  • Transmission 
    • Common in northeastern US
      • Often in patients who do outdoor activities (hiking, camping) in northeast US
    • Transmitted by the Ixodes tick
      • Also a vector for Anaplasma spp. and Babesia; coinfection is common
      • Natural reservoir is the mouse
  • Lyme disease
    • Stage 1 – localized
      • flu-like symptoms
      • Erythema migrans ("bulls-eye" or “target” lesion)
        • Expanding ring-shaped erythematous rash that begins 1-2 weeks around site of bite
    • Stage 2 – early disseminated
      • Occurs weeks to months after inoculation without treatment
      • “FACE” mnemonic: facial nerve, arthralgias, cardiac block, erythema migrans
      • Facial nerve (Bell) palsy
        • Extremely rare presentation of Lyme disease
      • Migratory arthralgias
        • Transient migratory joint pain
      • Heart block (AV block)
        • Due to Lyme carditis and localized inflammation in conductive tissue of heart
    • Stage 3 – late disseminated
      • Occurs months or years after inoculation without treatment
      • Encephalopathy
      • Chronic arthritis (knees)
  • Diagnosis 
    • Visualized by dark-field microscopy, or direct fluorescent antibody (DFA) microscopy 
    • Can use ELISA to detect serologic immunoglobulins
  • Treatment
    • Doxycycline (1st line)
    • Amoxicillin (and ceftriaxone if severe illness – CNS signs or heart block)
    • Macrolides 
      • Second line in those who are allergic to first line