Lyme disease is an infection caused by Borrelia burgdorferi, a type of bacteria found in animals like mice and deer. Deer ticks (also called black-legged ticks) feed on these animals and then infect people through tick bites.

More to Know

Lyme disease is divided into three stages of illness based on the symptoms: early localized, early disseminated, and late disseminated disease.

Early localized lyme disease begins with flu-like symptoms like swollen lymph nodes, tiredness, headache, and muscle aches. A red rash often appears at the bite site, which sometimes looks like a "target" with white and red rings (but not all people will develop one). Treated early with antibiotics, Lyme disease symptoms will fade within several weeks and have no lasting effects.

Left untreated, Lyme disease can spread and affect the nervous system, joints, and heart (disseminated Lyme disease). Symptoms of early disseminated disease may include irregular heart rhythm, facial paralysis (Bell's palsy), a spreading rash, or headache and neck stiffness due to meningitis.

Late disseminated Lyme disease usually leads to recurrent arthritis in the knee or other large joints and, rarely, nervous system problems. Disseminated and late disseminated stages are also treated with antibiotics, but the length of treatment and type of antibiotics used depend on the symptoms.

Keep in Mind

Lyme disease can be hard to detect. Typically, the tick has to be attached to the body for 48 hours to spread the bacteria to a person, but deer ticks are tiny and many people won't even know they've been bitten. Fortunately, most ticks do not transmit Lyme disease.

You can minimize your family's risk by being aware of ticks when outside in moist, wooded, brushy areas. If you live in a high-risk area, wear light-colored protective clothing, use insect repellant, do a daily tick check, and be sure to remove ticks the moment you spot them. If you think you've been bitten by a deer tick or have symptoms of Lyme disease, see your doctor.

All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts.