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On a warm summer afternoon, a 32-year-old woman presents with a 5-day history of low-grade fever and a rash. On physical examination, the physician notes a large, erythematous, annular patch with central clearing on her back (Figure 227-1). The patient states that the rash has gotten progressively larger during the last 3 days and she has had a recent onset of intermittent joint pain. She does not recall being bitten by an insect. She denies taking medications within the past month and has no known allergies. When asked about recent travel, she admits to a camping trip in eastern Massachusetts, which she returned from 4 days ago. The patient was diagnosed with Lyme borreliosis and started on doxycycline 100 mg twice daily for 14 days. She responded quickly to the antibiotics and never developed the persistent stage of Lyme disease.

FIGURE 227-1

A 32-year-old woman with the typical eruption of erythema migrans on her upper back. Note the expanding annular lesion with a target-like morphology. (Reproduced with permission from Thomas Corson, MD.)


Lyme disease is an infection caused by the spirochete Borrelia burgdorferi, transmitted via tick bite. Most cases of Lyme disease occur in the northeast United States between April and November. Patients experience flu-like symptoms and may develop the pathognomonic rash, erythema migrans. Lyme disease is prevented by avoiding exposure to the tick vector using insect repellant and protective clothing.


  • In 1977, clusters of patients in Old Lyme, Connecticut, began reporting symptoms originally thought to be juvenile rheumatoid arthritis.1

  • In 1981, American entomologist Dr. Willy Burgdorfer isolated the infectious pathogen responsible for Lyme disease from the midgut of Ixodes scapularis (a.k.a., black-legged deer ticks) (Figure 227-2), which serve as the primary transmission vector in the United States.1

  • The infectious agent was identified as a bacterial spirochete and named B. burgdorferi in honor of its discoverer.

  • Based on Centers for Disease Control and Prevention (CDC) data reported in 2007, Lyme disease (or Lyme borreliosis) is the most common tick-borne illness in the United States, with an overall incidence of 7.9 per 100,000 persons.2

  • In 2013, 95% of Lyme disease cases were reported from 14 states: Connecticut, Delaware, Maine, Maryland, Massachusetts, Minnesota, New Jersey, New Hampshire, New York, Pennsylvania, Rhode Island, Vermont, Virginia, and Wisconsin.3

  • Patients living between Maryland and Maine accounted for 93% of all reported cases in the United States in 2005, with an overall incidence of 31.6 cases for every 100,000 persons.2

  • More than 90% of cases report onset between April and November.2

FIGURE 227-2

The deer tick transmits the Borrelia spirochete. This is an unengorged female black-legged deer tick. The tick is tiny and can be undetected in its ...

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