Applied Evidence

Beyond the bull's eye: Recognizing Lyme disease

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A rash occurs in 80% of Lyme disease cases, but only about a third of the rashes develop into a classic bull's-eye lesion. Here’s what to look for and how best to treat.


From The Journal of Family Practice | 2016;65(6):373-379.



› Consider the duration of a tick’s attachment and whether it was engorged when assessing an individual’s risk of acquiring Lyme disease. C
› Start treatment for Lyme disease without lab testing if a patient has the painless skin rash—erythema migrans—and a history of tick exposure. C
› Choose doxycycline as first-line treatment for early Lyme disease unless a patient has contraindications. Amoxicillin or cefuroxime axetil are suitable alternatives. B

Strength of recommendation (SOR)

A Good-quality patient-oriented evidence
B Inconsistent or limited-quality patient-oriented evidence
C Consensus, usual practice, opinion, disease-oriented evidence, case series

CASE › Alice L, a 39-year-old woman with an unremarkable medical history asks to see her primary care provider right away, concerned she might have contracted Lyme disease. She had been hiking the overgrown trails on her family-owned ranch in Florida, and the next day she noticed a black tick stuck to her forearm. Using tweezers, she pulled the whole tick off intact, put it in a plastic cup, and immediately sought medical attention. How should her family physician (FP) advise her?

Lyme disease is the most common tick-borne illness in the United States, with more than 25,000 cases confirmed in this country in 2014.1 It is concentrated mostly in the northeast and upper Midwest, and less frequently occurs in the Pacific coastal regions of Oregon and northern California. Cases have also increasingly been reported in the southwest region of the Appalachian Mountains and the mountainous regions of southern Virginia.2

In 2014, the only states reporting no incidence of Lyme disease were Colorado, Hawaii, Louisiana, New Mexico, and Oklahoma.1 Lyme disease is also endemic in several regions in Northern Europe, Eastern Asia, and Northern Africa.1,3-7 According to the Centers for Disease Control and Prevention (CDC), boys ages 5 to 9 years are most affected.1

Disease transmission: Duration of tick attachment is important

The spirochete that causes Lyme disease, Borrelia burgdorferi, is transmitted to humans by the Ixodes tick. The Ixodes scapularis (deer tick) is common in the eastern and northern midwestern states and I pacificus is common in the western United States.

The life cycle. These small, dark-colored ticks have a 2-year life cycle that is comprised of 4 developmental stages: egg, larva, nymph, and adult. Eggs are laid in spring and hatch into larvae during late summer. The larvae feed on small animals (eg, mice, chipmunks, birds) and can acquire B burgdorferi infection at this stage. The larvae then molt into nymphs (<2 mm, and difficult to see), which feed again the following spring to early summer and may transmit the infection to a new host. Nymphs become adult ticks in mid-October to early-November, when the females feed again, mainly on large animals.


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