Lyme disease is an infectious disease spread through a tick bite.

Primary Lyme disease is the first stage of the disease. For specific information on the other stages or general information about Lyme disease, see:

• Lyme disease
• Stage 2 Lyme disease
• Stage 3 Lyme disease

Lyme disease is caused by the bacterium Borrelia burgdorferi (B. burgdorferi). Certain ticks may carry these bacteria. The ticks pick up the bacteria when they bite mice or deer that are infected with Lyme disease. You can get the disease if an infected tick bites you.

Risk factors for Lyme disease include:

• Having a pet that may carry ticks home
• Taking part in activities that increase tick exposure
• Walking in high grasses

The parts of the United States where the chance of getting Lyme disease is higher include:

• New England
• The mid-Atlantic states
• The north-central states

Note: Deer ticks can be so small that they are almost impossible to see. Therefore, many people with Lyme disease never knew they had a tick bite. Unlike a mosquito bite, a tick bite cannot be felt. In most cases, the tick must stay on the body for 48 hours to transmit the bacteria to humans.