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Lyme disease is transmitted to humans by the bite of infected blacklegged ticks. Typical symptoms include fever, headache, fatigue, and a characteristic skin rash. If left untreated, infection can spread to joints, the heart, and the nervous system. Most cases of Lyme disease can be treated successfully with a few weeks of antibiotics.

The Lyme disease bacterium, Borrelia burgdorferi, normally lives in mice, squirrels and other small animals. It is transmitted among these animals—and to humans—through the bites of certain species of ticks. In the northeastern and north-central United States, the blacklegged tick (or deer tick, Ixodes scapularis) transmits Lyme disease.

Most cases of human illness occur in the late spring and summer when ticks are most active and human outdoor activity is greatest. Although adult ticks often feed on deer, these animals do not become infected. Deer are nevertheless important in transporting ticks and maintaining tick populations.

Not all patients with Lyme disease will have all symptoms, and many of the symptoms can occur with other diseases as well. If you believe you may have Lyme disease, it is important that you consult your health care provider for proper diagnosis.

The first sign of infection is usually a circular rash. This rash occurs in approximately 70-80% of infected persons and begins at the site of a tick bite after a delay of 3-30 days. Patients also experience symptoms of fatigue, chills, fever, headache, and muscle and joint aches, and swollen lymph nodes. In some cases, these may be the only symptoms of infection.

Patients treated with antibiotics in the early stages of the infection usually recover rapidly and completely. A few patients, particularly those who are first diagnosed with later stages of the disease, may have persistent or recurrent symptoms. These patients may benefit from a second 4-week course of therapy.

Avoid tick-infested areas! This is especially important in May, June, and July. Walk in the center of trails to avoid contact with overgrown grass, brush, and leaf litter at trail edges.

Use insect repellent! Sprays insect repellent containing a 20-30% concentration of DEET on clothes and on exposed skin; use 10% DEET for children.

Wear protective clothing! Long pants and long sleeves help keep ticks off your skin.

Perform daily tick checks! Always check for ticks after being outdoors, even in your own yard.

Image of Ticks

Image showing appearance and relative sizes of adult male and female, nymph and larval ticks including deer ticks (Ixodes scapularis), Lone star ticks (Amblyomma americanum), and Dog ticks (Dermacentor variabilis). Of those pictured, only the Ixodes scapularis ticks are known to transmit Lyme disease.


Lyme Disease Cases by Month

Reported Month of Illness Onset, U.S. Lyme Disease Cases, 1992-2003
Lyme disease patients are most likely to have illness onset in June, July, or August and are less likely to have illness onset during December through March.

Update by H. Lougee-Heimer 9/09/05