Merck Manual

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Lyme Disease


Larry M. Bush

, MD, FACP, Charles E. Schmidt College of Medicine, Florida Atlantic University

Reviewed/Revised Nov 2022
Topic Resources

Lyme disease is a tick-transmitted infection caused by Borrelia species, primarily by Borrelia burgdorferi and sometimes by Borrelia mayonii in the United States. These spiral-shaped bacteria are called spirochetes (see figure ).

  • Most people are infected when they go outdoors in wooded areas where Lyme disease is common and are bitten by ticks infected with the bacteria Borrelia species.

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

  • Untreated, Lyme disease can cause fever, muscle aches, swollen joints, abnormalities of the electrical conduction system of the heart, and eventually problems related to brain and nerve malfunction.

  • The diagnosis is based on the typical rash and symptoms, opportunity for exposure to ticks, 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 1976 when a cluster of cases occurred in Lyme, Connecticut. It is now the most common tick-borne infection in the United States. It occurs in 49 states. More than 90% of the cases occur along the northeastern coast from Maine to Virginia and in Wisconsin, Minnesota, and Michigan. On the West Coast, most cases occur in northern California and Oregon. Lyme disease also occurs in Europe, China, Japan, and the former Soviet Union.

Did You Know...

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

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

Overview of Lyme Disease

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 in the United States. 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. In Europe, larger mammals such as sheep are hosts for the adult tick.

Did You Know...

  • Lyme disease is the most common tick-borne infection in the United States.

  • Deer do not carry or transmit Lyme disease bacteria and are only a source of blood for adult ticks.

Deer ticks also carry other infections (such as babesiosis Babesiosis Babesiosis is infection of red blood cells caused by the protozoa Babesia. Babesiosis is transmitted by the same type of deer ticks (Ixodidae) that transmits Lyme disease. Babesiosis... read more Babesiosis and anaplasmosis Ehrlichiosis and Anaplasmosis Ehrlichiosis and anaplasmosis are tick-borne bacterial infections that cause fever, chills, muscle aches, headache, and a general feeling of illness (malaise). Symptoms of ehrlichiosis and anaplasmosis... read more Ehrlichiosis and Anaplasmosis ) and may have several infections at the same time. These infections occur mainly in the same places as Lyme disease in the United States—the Northeast and upper Midwest. So when ticks transmit Lyme disease, they may also transmit these other infections, and people may have more than one infection at a time.

The bacteria that cause Lyme disease are transmitted to people when an infected tick bites and stays attached for more than 36 hours. 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 called erythema migrans. The bacteria may enter the lymphatic system and infect lymph nodes. Or the bacteria may 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.

Symptoms of Lyme Disease

Lyme disease has three stages:

  • Early localized

  • Early disseminated (widespread)

  • Late

The early and late stages of Lyme disease are usually separated by a period without symptoms.

Early localized–stage Lyme disease

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. The spot occurs in about 75% of people and typically appears 3 to 32 days after the tick bite. However, because deer tick nymphs are so small, most people do not realize they have been bitten.

Usually, the spot slowly expands to a diameter of up to 20 inches (50 centimeters), often clearing in the center. But the appearance can vary. For example, the center may remain red, or several rings may appear around the red center (looking like a bull's eye or target). 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.

Images of the Rash of Lyme Disease

Early disseminated–stage Lyme disease

This stage begins when the bacteria spread through the body. This stage can begin days to weeks after the spot first appears.

Fatigue, chills, fever, headaches, stiff neck, muscle aches, and painful, swollen joints are common. These symptoms of Lyme disease may last for weeks. In nearly half of people who are not treated, 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 last for weeks. These symptoms are often mistaken for influenza or common viral infections, especially if erythema migrans is not present.

These problems may last for months. Nerve pain and weakness may develop in other areas and last longer.

Up to 8% of infected people develop heart problems. These problems include

The arrhythmias may cause palpitations, light-headedness, or fainting.

Late-stage Lyme disease

If the initial infection is untreated, other problems often 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.

Diagnosis of Lyme Disease

  • Blood tests

  • Sometimes examination of a sample of joint fluid or cerebrospinal fluid (obtained by spinal tap)

The diagnosis of Lyme disease is usually based on all of the following:

  • Typical symptoms, including rash (particularly erythema migrans)

  • Opportunity for exposure (living in or visiting an area where Lyme disease is common)

  • Test results

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 last for many years. Thus, antibodies may be present after Lyme disease has resolved or in people who have had an infection that did not cause symptoms.

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 last a long time. 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 Spinal Tap Diagnostic procedures may be needed to confirm a diagnosis suggested by the medical history and neurologic examination. Imaging tests commonly used to diagnose nervous system (neurologic) disorders... read more 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 and detected using the polymerase chain reaction (PCR) technique Polymerase chain reaction (PCR) Genetic diagnostic technologies are scientific methods that are used to understand and evaluate an organism's genes. (See also Genes and Chromosomes.) Genes are segments of deoxyribonucleic... read more . This technique produces many copies of a gene and enables doctors to identify Borrelia burgdorferi bacteria rapidly.

Prevention of Lyme Disease

People should take precautions to avoid being bitten by a tick. If people may have been exposed to ticks, they should check their whole body very carefully after each possible exposure and remove any ticks they find. Checking is effective because ticks must usually be attached for more than a day and a half to transmit Lyme disease.

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 or wearing clothing commercially pretreated with permethrin

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 usually for more than a day and a half 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 it enters 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.

Deer ticks

If a person is bitten by a tick, doctors sometimes give the person a single dose of doxycycline by mouth to prevent Lyme disease from developing. Alternatively, doctors may have the person observe the area of the bite and give antibiotics only if the person develops the typical rash or other symptoms that suggest early Lyme disease.

Treatment of Lyme Disease

  • Antibiotics

Although all stages of Lyme disease respond to antibiotics, early treatment is more likely to prevent complications.

Antibiotics such as doxycycline, amoxicillin, or cefuroxime, taken by mouth for 10 to 14 days, are effective during the early stages of the disease. If early disease is localized, people may need treatment for only 10 days. If people cannot take any of these antibiotics, azithromycin or erythromycin is used. Usually, doxycycline is not given to children under 8 years old or to pregnant or breastfeeding women.

Antibiotics can also help relieve many of the complications caused by Lyme disease.

For Bell palsy, doxycycline is given by mouth (orally) for 2 to 3 weeks.

For meningitis, ceftriaxone, cefotaxime, or penicillin is given by vein (intravenously) for 2 to 3 weeks.

For arthritis, amoxicillin, cefuroxime, or doxycycline is given orally or ceftriaxone is given intravenously for 4 weeks.

For an abnormal heart rhythm (arrhythmia) called third-degree heart block (complete heart block), ceftriaxone or penicillin is given intravenously. Sometimes a temporary pacemaker Artificial Pacemakers There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,... read more Artificial Pacemakers is needed for complete heart block. For mild heart involvement, doxycycline, amoxicillin, or cefuroxime is given orally for 2 to 3 weeks.

Antibiotics also are effective during the late stage of the disease. They eradicate the bacteria and, in most people, relieve arthritis. However, arthritis sometimes lasts even after all the bacteria are gone because inflammation continues. Even after successful antibiotic treatment, some people still have other symptoms such as fatigue, headache, joint and muscle aches, and mental problems. These symptoms are collectively referred to as post-treatment Lyme disease syndrome (PTLDS). The cause of these continuing symptoms is unknown, but treatment with more antibiotics does not help.

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.

More Information

The following English-language resources may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Acticlate, Adoxa, Adoxa Pak, Avidoxy, Doryx, Doxal, Doxy 100, LYMEPAK, Mondoxyne NL, Monodox, Morgidox 1x, Morgidox 2x , Okebo, Oracea, Oraxyl, Periostat, TARGADOX, Vibramycin, Vibra-Tabs
Amoxil, Dispermox, Moxatag, Moxilin , Sumox, Trimox
Alti-Cefuroxime , Ceftin, Kefurox, Zinacef, Zinacef Powder
Azasite, Zithromax, Zithromax Powder, Zithromax Single-Dose , Zithromax Tri-Pak, Zithromax Z-Pak, Zmax, Zmax Pediatric
A/T/S, Akne-mycin, E.E.S., Emcin Clear , EMGEL, E-Mycin, ERYC, Erycette, Eryderm , Erygel, Erymax, EryPed, Ery-Tab, Erythra Derm , Erythrocin, Erythrocin Lactobionate, Erythrocin Stearate, Ilosone, Ilotycin, My-E, PCE, PCE Dispertab , Romycin, Staticin, T-Stat
Ceftrisol Plus, Rocephin
Anacin Adult Low Strength, Aspergum, Aspir-Low, Aspirtab , Aspir-Trin , Bayer Advanced Aspirin, Bayer Aspirin, Bayer Aspirin Extra Strength, Bayer Aspirin Plus, Bayer Aspirin Regimen, Bayer Children's Aspirin, Bayer Extra Strength, Bayer Extra Strength Plus, Bayer Genuine Aspirin, Bayer Low Dose Aspirin Regimen, Bayer Womens Aspirin , BeneHealth Aspirin, Bufferin, Bufferin Extra Strength, Bufferin Low Dose, DURLAZA, Easprin , Ecotrin, Ecotrin Low Strength, Genacote, Halfprin, MiniPrin, St. Joseph Adult Low Strength, St. Joseph Aspirin, VAZALORE, Zero Order Release Aspirin, ZORprin
Advil, Advil Children's, Advil Children's Fever, Advil Infants', Advil Junior Strength, Advil Migraine, Caldolor, Children's Ibuprofen, ElixSure IB, Genpril , Ibren , IBU, Midol, Midol Cramps and Body Aches, Motrin, Motrin Children's, Motrin IB, Motrin Infants', Motrin Junior Strength, Motrin Migraine Pain, PediaCare Children's Pain Reliever/Fever Reducer IB, PediaCare Infants' Pain Reliever/Fever Reducer IB, Samson-8
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