Microbiology & infectious diseases

Atypical bacteria


Borrelia burgdorferi

Last author update: 1 February 2016
Last staff update: 8 February 2024

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PubMed Search: Borrelia burgdorferi

See Also: Erythema migrans

Abha Soni, D.O., M.P.H.
Andrzej Slominski, M.D., Ph.D.
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Cite this page: Soni A, Slominski A. Borrelia burgdorferi. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/microbiologybburgdorferi.html. Accessed May 19th, 2024.
Definition / general
  • Lyme disease is a multisystem disorder caused by spirochete Borrelia burgdorferi
  • In the United States, Lyme disease most commonly occurs in the northeast and upper midwest
  • Worldwide, more commonly found in northern Asia and eastern and central Europe
  • The bite of an infected Ixodes dammini tick causes proliferation of spirochetes in the dermis
  • The host dermal inflammatory response causes a rash known as erythema chronicum migrans
  • Over days, the spirochetes spread to the nervous system, cardiac tissue and joints via the blood stream
  • The spirochetes may induce host cells to produce quinolinic acid, which stimulates NMDA receptors and manifests as malaise in lyme encephalopathy (Neurology 1992;42:43)
  • Note: Lyme disease spirochetes are never seen in peripheral blood
  • Usually transmitted by Ixodes dammini tick
Clinical features
  • Causes erythema chronicum migrans (red papule with central clearing that expands slowly), acrodermatitis chronica atrophicans (disease of extremities, usually women, with erythematous, edematous, pruritic phase, followed by sclerosis and atrophy), cutaneous lymphoid hyperplasia of skin
  • Also affects heart, joints, nervous system
Staging / staging classifications
  • Stage 1: skin lesion (erythema chronicum migrans)
  • Stage 2: cardiovascular and nervous system involvement
  • Stage 3: arthritis stage characterized by migratory polyarthritis; however, cutaneous lesions and peripheral nervous system involvement are also encountered in this stage
  • Clinical symptoms such as erythema migrans, fever, facial palsy or arthritis
  • Biopsy interpretation
  • EIA or ELISA for total Lyme titer or IgG and IgM titers
  • If EIA / ELISA test results come back positive or equivocal, Western blot IgG and IgM titers are performed
  • Lyme titers should be done if the above tests are positive
  • PCR in synovial fluid (for spirochetes)
  • CSF analysis
  • ECG for Lyme carditis
  • Darkfield microscopy for spirochetes
Case reports
  • Early infection: Antibiotics such as doxycycline, amoxicillin, azithromycin
  • Late infection: IV ceftriaxone is considered treatment of choice
Clinical images

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Skin rash

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Erythema migrans

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Various rash presentations

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Erythema migrans lesions

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Late stage: osteoarthritis

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Adult deer tick

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Normal and engorged

Microscopic (histologic) description
  • Superficial and deep perivascular polymorphic infiltrate of neutrophils, lymphocytes, plasma cells, eosinophils and mast cells
  • Vascular proliferation and dermal necrosis may be present
  • Identification of spirochetes by silver stain or immunocytochemistry is diagnostic
  • Borrelia spirochetes are long spiral bacilli (5 - 20 microns in length) with relatively regular undulations
  • Typically Borrelia burgdorferi does NOT reach sufficient levels in blood to be seen on peripheral blood smear
  • PCR can also be used for diagnosis
Microscopic (histologic) images

Contributed by Bobbi Pritt, M.D.

Giemsa stained thin blood films from patient in northwest North America with recurrent fevers: Borrelia, relapsing fever group (not Lyme disease causing Borrelia species), probably Borrelia hermsii

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Perivascular lymphocytic infiltrate

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Darkfield microscopy

Positive stains
  • Warthin-Starry (for spirochetes)
  • Immunocytochemistry with monoclonal antibodies against Borrelia species
Differential diagnosis
  • Bacteria that are not spirochetes but have curved or wavy rods include Vibrio, Campylobacter, Helicobacter
  • Other spirochetes include Treponema and Leptospira, but they are not typically seen in blood
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