Definition of Lyme disease:

Lyme disease is a bacterial infection spread through the bite of the blacklegged tick.

See also: Lyme disease - what to ask your doctor

Causes, incidence, and risk factors:

Lyme disease is caused by bacteria called Borrelia burgdorferi (B. burgdorferi). Blacklegged ticks 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 you are bitten by an infected tick.

Lyme disease was first reported in the United States in the town of Old Lyme, Connecticut, in 1975. In the United States, most Lyme disease infections occur in the following areas:

• Northeastern states, from Virginia to Maine
• North-central states, mostly in Wisconsin and Minnesota
• West Coast, particularly northern California

There are 3 stages of Lyme disease. (See below for symptoms.)

• Stage 1 is called early localized Lyme disease. The infection is not yet widespread throughout the body.
• Stage 2 is called early disseminated Lyme disease. The bacteria have begun to spread throughout the body.
• Stage 3 is called late disseminated Lyme disease. The bacteria have spread throughout the body.

Risk factors for Lyme disease include:

• Doing outside activities that increase tick exposure (for example, gardening, hunting, or hiking) in an area where Lyme disease is known to occur
• Having a pet that may carry ticks home
• Walking in high grasses

Important facts about tick bites and Lyme disease:

• In most cases, a tick must be attached to your body for 24 - 36 hours to spread the bacteria to your blood.
• Blacklegged ticks can be so small that they are almost impossible to see. Many people with Lyme disease never even saw a tick on their body.
• Most people who are bitten by a tick do not get Lyme disease.