Lyme disease is caused by four main species of bacteria. Borrelia burgdorferi and Borrelia mayonii cause Lyme disease in the United States, while Borrelia afzelii and Borrelia garinii are the leading causes in Europe and Asia. The most common tick-borne illness in these regions, Lyme disease is transmitted by the bite of an infected black-legged tick, commonly known as a deer tick.

You're more likely to get Lyme disease if you live or spend time in grassy and heavily wooded areas where ticks carrying Lyme disease thrive. It's important to take common-sense precautions in tick-infested areas.

The signs and symptoms of Lyme disease vary. They usually appear in stages, but the stages can overlap.

Early signs and symptoms

A small, red bump, similar to the bump of a mosquito bite, often appears at the site of a tick bite or tick removal and resolves over a few days. This normal occurrence doesn't indicate Lyme disease.

However, these signs and symptoms can occur within a month after you've been infected:

• Rash. From three to 30 days after an infected tick bite, an expanding red area might appear that sometimes clears in the center, forming a bull's-eye pattern. The rash (erythema migrans) expands slowly over days and can spread to 12 inches (30 centimeters) across. It's typically not itchy or painful but might feel warm to the touch.

  Erythema migrans is one of the hallmarks of Lyme disease, although not everyone with Lyme disease develops the rash. Some people develop this rash at more than one place on their bodies.

• Other symptoms. Fever, chills, fatigue, body aches, headache, neck stiffness and swollen lymph nodes can accompany the rash.

Later signs and symptoms

If untreated, new signs and symptoms of Lyme infection might appear in the following weeks to months. These include:

• Erythema migrans. The rash may appear on other areas of your body.
• Joint pain. Bouts of severe joint pain and swelling are especially likely to affect your knees, but the pain can shift from one joint to another.
• Neurological problems. Weeks, months or even years after infection, you might develop inflammation of the membranes surrounding your brain (meningitis), temporary paralysis of one side of your face (Bell's palsy), numbness or weakness in your limbs, and impaired muscle movement.

Less common signs and symptoms

Several weeks after infection, some people develop:

• Heart problems, such as an irregular heartbeat
• Eye inflammation
• Liver inflammation (hepatitis)
• Severe fatigue

When to see a doctor

If you've been bitten by a tick and have symptoms

Only a minority of tick bites leads to Lyme disease. The longer the tick remains attached to your skin, the greater your risk of getting the disease. Lyme infection is unlikely if the tick is attached for less than 36 to 48 hours.

If you think you've been bitten and have signs and symptoms of Lyme disease — particularly if you live in an area where Lyme disease is common — contact your doctor. Treatment for Lyme disease is more effective if begun early.

See your doctor even if symptoms disappear

Visit your doctor even if signs and symptoms disappear — the absence of symptoms doesn't mean the disease is gone. Untreated, Lyme disease can spread to other parts of your body for several months to years after infection, causing arthritis and nervous system problems. Ticks can also transmit other illnesses, such as babesiosis and Colorado tick fever.

In the United States, Lyme disease is caused by the bacteria Borrelia burgdorferi and Borrelia mayonii, carried primarily by black-legged or deer ticks. Young brown ticks often are no bigger than a poppy seed, which can make them nearly impossible to spot.

To contract Lyme disease, an infected deer tick must bite you. The bacteria enter your skin through the bite and eventually make their way into your bloodstream.

In most cases, to transmit Lyme disease, a deer tick must be attached for 36 to 48 hours. If you find an attached tick that looks swollen, it may have fed long enough to transmit bacteria. Removing the tick as soon as possible might prevent infection.

Where you live or vacation can affect your chances of getting Lyme disease. So can your profession and the outdoor activities you enjoy. The most common risk factors for Lyme disease include:

• Spending time in wooded or grassy areas. In the United States, deer ticks are found mostly in the heavily wooded areas of the Northeast and Midwest. Children who spend a lot of time outdoors in these regions are especially at risk. Adults with outdoor jobs also are at increased risk.
• Having exposed skin. Ticks attach easily to bare flesh. If you're in an area where ticks are common, protect yourself and your children by wearing long sleeves and long pants. Don't allow your pets to wander in tall weeds and grasses.
• Not removing ticks promptly or properly. Bacteria from a tick bite can enter your bloodstream if the tick stays attached to your skin for 36 to 48 hours or longer. If you remove a tick within two days, your risk of getting Lyme disease is low.

Untreated Lyme disease can cause:

• Chronic joint inflammation (Lyme arthritis), particularly of the knee
• Neurological symptoms, such as facial palsy and neuropathy
• Cognitive defects, such as impaired memory
• Heart rhythm irregularities

The best way to prevent Lyme disease is to avoid areas where deer ticks live, especially wooded, bushy areas with long grass. You can decrease your risk of getting Lyme disease with some simple precautions:

• Cover up. When in wooded or grassy areas, wear shoes, long pants tucked into your socks, a long-sleeved shirt, a hat and gloves. Try to stick to trails and avoid walking through low bushes and long grass. Keep your dog on a leash.

• Use insect repellents. Apply insect repellent with a 20% or higher concentration of DEET to your skin. Parents should apply repellant to their children, avoiding their hands, eyes and mouth.

  Keep in mind that chemical repellents can be toxic, so follow directions carefully. Apply products with permethrin to clothing or buy pretreated clothing.

• Do your best to tick-proof your yard. Clear brush and leaves where ticks live. Mow your lawn regularly. Stack wood neatly in dry, sunny areas to discourage rodents that carry ticks.

• Check your clothing, yourself, your children and your pets for ticks. Be especially vigilant after spending time in wooded or grassy areas. Deer ticks are often no bigger than the head of a pin, so you might not discover them unless you search carefully.

  It's helpful to shower as soon as you come indoors. Ticks often remain on your skin for hours before attaching themselves. Showering and using a washcloth might remove unattached ticks.

• Don't assume you're immune. You can get Lyme disease more than once.
• Remove a tick as soon as possible with tweezers. Gently grasp the tick near its head or mouth. Don't squeeze or crush the tick, but pull carefully and steadily. Once you've removed the entire tick, dispose of it by putting it in alcohol or flushing it down the toilet, and apply antiseptic to the bite area.

Many signs and symptoms of Lyme disease are often found in other conditions, so diagnosis can be difficult. What's more, ticks that transmit Lyme disease can also spread other diseases.

If you don't have the characteristic Lyme disease rash, your doctor might ask about your medical history, including whether you've been outdoors in the summer where Lyme disease is common, and do a physical exam.

Lab tests to identify antibodies to the bacteria can help confirm or rule out the diagnosis. These tests are most reliable a few weeks after an infection, after your body has had time to develop antibodies. They include:

• Enzyme-linked immunosorbent assay (ELISA) test. The test used most often to detect Lyme disease, ELISA detects antibodies to B. burgdorferi. But because it can sometimes provide false-positive results, it's not used as the sole basis for diagnosis.

  This test might not be positive during the early stage of Lyme disease, but the rash is distinctive enough to make the diagnosis without further testing in people who live in areas infested with ticks that transmit Lyme disease.

• Western blot test. If the ELISA test is positive, this test is usually done to confirm the diagnosis. In this two-step approach, the Western blot detects antibodies to several proteins of B. burgdorferi.

Antibiotics are used to treat Lyme disease. In general, recovery will be quicker and more complete the sooner treatment begins.

Antibiotics

• Oral antibiotics. These are the standard treatment for early-stage Lyme disease. These usually include doxycycline for adults and children older than 8, or amoxicillin or cefuroxime for adults, younger children, and pregnant or breast-feeding women.

  A 14- to 21-day course of antibiotics is usually recommended, but some studies suggest that courses lasting 10 to 14 days are equally effective.

• Intravenous antibiotics. If the disease involves the central nervous system, your doctor might recommend treatment with an intravenous antibiotic for 14 to 28 days. This is effective in eliminating infection, although it may take you some time to recover from your symptoms.

  Intravenous antibiotics can cause various side effects, including a lower white blood cell count, mild to severe diarrhea, or colonization or infection with other antibiotic-resistant organisms unrelated to Lyme.

After treatment, a small number of people still have some symptoms, such as muscle aches and fatigue. The cause of these continuing symptoms, known as post-treatment Lyme disease syndrome, is unknown, and treating with more antibiotics doesn't help.

Some experts believe that certain people who get Lyme disease are predisposed to develop an autoimmune response that contributes to their symptoms. More research is needed.

Antibiotics are the only proven treatment for Lyme disease. Some people who have unexplained signs and symptoms or chronic disease might believe they have Lyme disease even if it's not been diagnosed. There are a variety of alternative treatments that people with Lyme disease or people who think they have Lyme disease turn to for relief.

Unfortunately, these treatments either haven't been proved effective by scientific evidence or haven't been tested. In many cases, they can be harmful, even deadly. If you're considering any alternative treatments for Lyme disease, talk to your doctor first.

You're likely to start by seeing your family doctor or a general practitioner who might refer you to a rheumatologist, infectious disease specialist or other specialist.

Here's some information to help you get ready for you appointment.

What you can do

If you know you've been bitten by a tick or have spent time in an area known to harbor ticks, be sure to tell your doctor. Make a list of:

• Your symptoms, and when they began
• All medications, vitamins and other supplements you take, including doses
• Questions to ask your doctor.

Take a family member or friend along, if possible, to help you remember the information you receive.

For Lyme disease, some basic questions to ask your doctor include:

• What is likely causing my symptoms?
• Other than the most likely cause, what are other possible causes for my symptoms?
• What tests do I need?
• What is the best course of action?
• What alternatives are there to the primary approach you're suggesting?
• I have other health conditions. How can I best manage them together?
• Are there restrictions I need to follow?
• Should I see a specialist?
• Are there brochures or other printed material I can have? What websites do you recommend?

Don't hesitate to ask other questions.

What to expect from your doctor

Your doctor is likely to ask you a number of questions, including:

• Have your symptoms been continuous or occasional?
• How severe are your symptoms?
• What, if anything, seems to improve your symptoms?
• What, if anything, appears to worsen your symptoms?