Merck Manual

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Quick Facts

Lyme Disease


The Manual's Editorial Staff

Last full review/revision Oct 2019| Content last modified Oct 2019
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What is Lyme disease?

Lyme disease is a certain disease you get from being bitten by infected ticks. It's called Lyme disease because it was first discovered in Lyme, Connecticut.

A type of tick called the deer tick spreads Lyme disease. A deer tick gets the bacteria that cause Lyme disease when it feeds on infected mice. (It's called the deer tick, because these ticks also feed on deer).

  • You're more likely to get Lyme disease if you live in or go to wooded areas

  • Usually, you get a large, red spot where the tick bit you

  • The spot slowly grows and gets red rings around it like a target or bull's eye

  • Lyme disease can also give you a fever, muscle aches, and swollen joints

  • If you don’t get treatment, you can get long-term problems with your brain, nerves, and joints

  • Doctors treat Lyme disease with antibiotics

What causes Lyme disease?

The bacteria Borrelia burgdorferi cause Lyme disease. If you're bitten by a deer tick, you don't get Lyme disease right away. The deer tick needs to be attached to you for at least a day and a half.

Deer ticks are much smaller than the dog ticks you often find on your pets.

Deer Tick

Deer Tick

What are the symptoms of Lyme disease?

The symptoms of Lyme disease depend on what stage of the disease you’re in.

Early symptoms include:

  • Usually, a large, raised, red spot where the tick bit you

  • The red spot gets bigger, turns clear in the center, and gets red rings around it (bull's eye rash)

  • The spot doesn't itch or hurt, but it may be warm

  • The spot usually goes away after about 3 to 4 weeks

Some people with Lyme disease never have the spot or rash.

Then the bacteria begins to spread through your body and you may have symptoms like:

  • Feeling tired for weeks

  • Fever, chills, and headaches

  • Stiff neck and muscle aches

  • Pain and swelling in your joints

  • Sometimes, more small red spots on your body

  • Headache and stiff neck (meningitis)

  • Weakness on one side of your face (Bell palsy)

Late symptoms happen if you aren't treated. Months or years after infection, you can have symptoms like:

  • Arthritis, with swelling, pain, and stiffness in your joints, especially your knees

  • Sometimes, numbness or shooting pain in your back, legs, and arms

  • Sometimes mood, speech, memory, and sleep problems

How can doctors tell if I have Lyme disease?

Doctors diagnose Lyme disease based on:

  • Your symptoms

  • If you live in or visited an area where Lyme disease is common

  • A blood test

The blood test often isn't positive for Lyme disease when you first get sick. Doctors often have to repeat the test after a few weeks.

How do doctors treat Lyme disease?

Doctors try to treat Lyme disease as early as possible to prevent more problems. Doctors will use:

  • Antibiotics

  • Over-the-counter medicines, such as ibuprofen or aspirin, if you have joint pain

How can I prevent Lyme disease?

You can prevent Lyme disease by trying to prevent tick bites:

  • Stay on paths and trails when you walk in wooded areas and don’t brush up against bushes and weeds

  • Don’t sit on the ground or on stone walls

  • Wear light-colored long-sleeved shirts and long pants tucked into your boots or socks

  • Use bug sprays on your skin and clothes

  • Check your whole body very carefully, especially hairy parts, after you've been in a wooded area

  • Take off any ticks you find crawling on you right away

If a deer tick bites you:

  • Pull the tick straight off with tweezers by gripping it by its head or mouth, not its body (you don’t want to squeeze the body)

  • Don't use petroleum jelly, alcohol, or matches to try to remove the tick

  • Your doctor may give you an antibiotic right away or may watch the bite area to see if you get symptoms of Lyme disease

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
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