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

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 occupations 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 acquiring 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