Lyme Disease

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  • A multisystem infection caused by Borrelia spirochetes, transmitted primarily by ixodid ticks
    • Ixodes scapularis (deer ticks) in the Northeast and Great Lakes areas
    • Ixodes pacificus in the West (black-legged ticks and Western black-legged ticks)
    • Ixodes ricinus in Europe
    • Ixodes persulcatus in Asia and Russia
  • Early localized Lyme disease includes a characteristic expanding skin rash (erythema migrans [EM]) (80%) and constitutional flulike symptoms (1).
  • Early neurologic manifestations 15%: cranial nerve palsy, meningitis, acute radiculopathy, or mononeuropathy
  • Disseminated Lyme disease presents with involvement of ≥1 organ systems; most commonly neurologic, cardiac, and pauciarticular arthritis
  • Lyme carditis: AV block, myopericarditis 1%
  • Post–Lyme disease syndrome includes arthritis (50%) and chronic neurologic syndromes.
  • System(s) affected: hemic/lymphatic/immunologic; musculoskeletal; skin/exocrine; cardiac; neurologic
  • Synonym(s): Lyme arthritis; Lyme borreliosis


  • 95% of U.S. cases (2015) reported from 14 states—primarily Connecticut, Delaware, Maine, Massachusetts, Minnesota, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, Virginia, Wisconsin (1)
  • During 2016 >26,000 confirmed U.S. cases (1)
  • In endemic states, the incidence is 0.5 per 1,000 but can be substantially higher in certain areas.
  • Cases have been reported from all 50 states.

  • The most reported vector-borne illness in the United States
  • Estimated 106 cases per 100,000 persons
  • Predominant age: most common in children ages 5 to 14 years and in adults aged 55 to 70 years of age
  • Predominant sex: male > female in the United States

Etiology and Pathophysiology

  • Infection with spirochete Borrelia burgdorferi in the United States, or Borrelia afzelii or Borrelia garinii in Europe, transmitted by the bite of ixodid ticks
  • Approximately 90% of cases are transmitted during the nymph stage of the tick life cycle.
  • Average incubation period 7 to 10 days
  • Most transmissions occur in late May to September when nymphal tick activity is highest.
  • If a tick is infected, the chance of transmission increases with time attached: 12% at 48 hours, 79% at 72 hours, and 94% at 96 hours of attachment.
  • Primary animal reservoir is the white-footed mouse.
  • Spirochetes multiply and spread within dermis. Host response results in characteristic (EM) rash. Hematogenous dissemination results in disease within CNS, cardiovascular, or other organ systems.
  • Star ticks (Amblyomma americanum), the American dog tick (Dermacentor variabilis), the Rocky Mountain wood tick (Dermacentor andersoni), and the brown dog tick (Rhipicephalus sanguineus) are not known to transmit Lyme disease.

Human leukocyte antigen: Patients with haplotype DR4 or DR2 may be more susceptible to prolonged arthritis.

Risk Factors

  • Exposure in tick-infested area, particularly from April to November
  • Those who reside or are employed in endemic areas where ixodid ticks are found are at increased risk.
  • Ixodid ticks are common on deer; hunters at increased risk

General Prevention

  • “Tick checks”: Examine skin after outdoor activities.
  • Remove ticks within 36 hours to limit transmission.
  • Wear clothing covering the ankles in endemic areas.
  • Use insect repellents containing N,N-diethyl-meta-toluamide (DEET).
  • Apply permethrin to clothes, shoes, and tents.
  • Antibiotic prophylaxis is recommended for the prevention of Lyme disease in endemic areas following an Ixodes tick bite.
  • Prophylactic treatment with 1 dose of 200 mg of doxycycline within 72 hours of a tick bite in highly endemic areas is 87% effective. Contraindicated in pregnancy and in children; no prophylactic agent is approved for these groups (1)[A].

Commonly Associated Conditions

  • Coinfection (e.g., babesiosis) increasingly reported
  • Southern tick–associated rash illness may be mistaken for Lyme disease. It is seen in the Southeastern and South Central United States and is associated with the bite of the lone star tick, A. americanum.
  • Comorbid human granulocytic anaplasmosis and/or babesiosis in patients living in endemic regions

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