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Lyme Disease

by Matthew E. Levison, MD

Lyme disease is caused by the bacteria Borrelia burgdorferi, which is usually transmitted to people by deer ticks.

  • Most people are infected when they go outdoors in wooded areas where the disease is common.

  • Typically, a large, red spot appears at the site of the bite and slowly enlarges, often surrounded by several red rings.

  • Untreated, the disease can cause fever, muscle aches, swollen joints, and eventually problems related to brain and nerve malfunction.

  • The diagnosis is based on typical symptoms, opportunity for exposure, and blood tests to detect antibodies to the bacteria.

  • Taking antibiotics usually cures the disease, but some symptoms, such as joint pain, may persist.

Lyme disease was recognized and named in 1975 when a cluster of cases occurred in Lyme, Connecticut. It is now the most common insect-borne infection in the United States. It occurs in 49 states. About 80% of the cases occur along the northeastern coast from Massachusetts to Maryland. Most of the remaining reported cases occur in Wisconsin, Minnesota, and the coastal regions of northern California and Oregon. Lyme disease also occurs in Europe, China, Japan, Australia, and the former Soviet Union.

Usually, people get Lyme disease in the summer and early fall. Children and young adults who live in wooded areas are most often infected.

The bacteria that cause Lyme disease are transmitted by the deer tick ( Ixodes ), so named because the adult ticks often feed on the blood of deer. Young deer ticks (larvae and nymphs) feed on the blood of rodents, particularly the white-footed mouse, which is a carrier of Lyme disease bacteria. Ticks are usually in the nymph stage when they infect people. Deer do not carry or transmit Lyme disease bacteria. They are only a source of blood for adult ticks.

Preventing Tick Bites

People can reduce their chances of picking up or being bitten by a tick by doing the following:

  • Staying on paths and trails when walking in wooded areas

  • Walking in the center of trails to avoid brushing up against bushes and weeds

  • Not sitting on the ground or on stone walls

  • Wearing long-sleeved shirts

  • Wearing long pants and tucking them into boots or socks

  • Wearing light-colored clothing, which makes ticks easier to see

  • Applying an insect repellent containing diethyltoluamide (DEET) to the skin

  • Applying an insect repellent containing permethrin to clothing

Usually, Lyme disease is transmitted by young deer ticks (nymphs), which are very small, much smaller than dog ticks. So people who may have been exposed to ticks should check the whole body very carefully, especially hairy areas, every day. Inspection is effective because ticks must be attached for more than a day to transmit Lyme disease.

To remove a tick, people should use fine-pointed tweezers to grasp the tick by the head or mouthparts right where they enter the skin and should gradually pull the tick straight off. The tick's body should not be grasped or squeezed. Petroleum jelly, alcohol, lit matches, or any other irritants should not be used.

The bacteria that cause Lyme disease are transmitted to people when an infected tick bites and stays attached for one or two days. Brief periods of attachment rarely transmit disease. At first, the bacteria multiply at the site of the tick bite. After 3 to 32 days, the bacteria migrate from the site of the bite into the surrounding skin, causing a rash (erythema migrans). The bacteria enter the bloodstream and spread to other organs, such as the skin in other areas of the body and the heart, nervous system, and joints.

Did You Know...

  • Usually, people get Lyme disease only if a tick remains attached to them for at least a day.


Lyme disease has three stages: early localized, early disseminated (widespread), and late. The early and late stages are usually separated by a period without symptoms.

Early-Localized Stage

Typically, a large, raised, red spot (erythema migrans) appears at the site of the bite, usually on the thigh, buttock, or trunk or in the armpit. Usually, the spot slowly expands to a diameter of 6 inches (15 centimeters), often clearing in the center, resulting in several concentric red rings. Although erythema migrans does not itch or hurt, it may be warm to the touch. The spot usually disappears after about 3 to 4 weeks. About 25% of infected people never develop—or at least never notice—the characteristic red spot.

Early-Disseminated Stage

This stage begins when the bacteria spread through the body. Fatigue, chills, fever, headaches, stiff neck, muscle aches, and painful, swollen joints are common. In nearly half of people, more, usually smaller erythema migrans spots appear on other parts of the body. Less commonly, people have a backache, nausea, vomiting, sore throat, swollen lymph nodes, and an enlarged spleen. Although most symptoms come and go, feelings of illness and fatigue may persist for weeks. These symptoms are often mistaken for influenza or common viral infections, especially if erythema migrans is not present.

Sometimes more serious symptoms develop. The nervous system is affected in about 15% of people. The most common problems are headache, stiff neck, meningitis, and Bell’s palsy, which causes weakness on one or occasionally both sides of the face. These problems may last for months. Nerve pain and weakness may develop in other areas and persist longer. About 8% of infected people have irregular heartbeats (arrhythmias) and inflammation of heart tissue (myocarditis) and the sac around the heart (pericarditis) with chest pain. Irregular heartbeats may cause palpitations, light-headedness, or fainting.

Late Stage

If the initial infection is untreated, other problems develop months to years later. Arthritis develops in more than half of people, usually within several months. Swelling and pain typically recur in a few large joints, especially the knee, for several years. The knees are commonly more swollen than painful, often hot to the touch, and, rarely, red. Cysts may develop and rupture behind the knees, suddenly increasing the pain. In about 10% of people with arthritis, knee problems last longer than 6 months.

A few people develop abnormalities related to brain and nerve malfunction. Mood, speech, memory, and sleep may be affected. Some people have numbness or shooting pains in the back, legs, and arms.


The diagnosis is usually based on typical symptoms (particularly erythema migrans), opportunity for exposure (living in or visiting an area where Lyme disease is common), and test results.

Usually, doctors use tests that measure antibodies to the bacteria in blood. However, antibodies may be absent if the test is done during the first several weeks of infection or if antibiotics are given before antibodies develop. Antibodies develop in more than 95% of people who have had the infection for at least a month, particularly if they have not taken antibiotics. Once antibodies develop, they persist permanently. Thus, antibodies may be present after Lyme disease has resolved.

Interpreting the results of blood tests is difficult. The uncertainty causes several problems. For example, in areas where Lyme disease is common, many people who have painful joints, trouble concentrating, or persistent fatigue worry that they have late-stage Lyme disease, even though they never had a rash or any other symptoms of early-stage Lyme disease. Usually, Lyme disease is not the cause. But they may have antibodies for the bacteria because they were infected years before and the antibodies persist indefinitely. Thus, if a doctor treats people based solely on results of antibody tests, many people who do not have Lyme disease are treated with long, useless courses of antibiotics.

Cultures are not helpful because Borrelia burgdorferi is difficult to grow in the laboratory.

Sometimes doctors insert a needle into a joint to take a sample of joint fluid or do a spinal tap (lumbar puncture) to take a sample of the fluid that surrounds the brain and spinal cord (cerebrospinal fluid). Fragments of the bacteria’s genetic material may be present.


If people are bitten by a tick but have no rash or other symptoms, antibiotics are usually used only if they can be given within 72 hours after an engorged tick is found attached. These people may be given one dose of doxycycline by mouth to prevent Lyme disease from developing.

Although all stages of Lyme disease respond to antibiotics, early treatment is more likely to prevent complications. Antibiotics such as doxycycline, amoxicillin, cefuroxime, or azithromycin, taken by mouth for 2 weeks, are effective during the early stages of the disease. They can also help treat a type of arrhythmia called first-degree heart block and probably Bell’s palsy. Doxycycline is not given to children under 9 years old or to pregnant women.

For arthritis, antibiotics such as amoxicillin or doxycycline are given by mouth for 30 to 60 days, or ceftriaxone or penicillin is given intravenously for 2 to 4 weeks.

For most neurologic abnormalities (except possibly Bell’s palsy) and more severe (third-degree) heart block, ceftriaxone or penicillin is given intravenously for 2 to 4 weeks.

Antibiotics eradicate the bacteria and, in most people, relieve arthritis. However, arthritis sometimes persists even after all the bacteria are gone because inflammation continues. Nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin or ibuprofen, may relieve the pain of swollen joints. Fluid that collects in affected joints may be drained. Using crutches may help.

Antibiotics do not appear to relieve the chronic fatigue.

A vaccine that was only moderately effective against Lyme disease was removed from the market because it was not widely used.

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