Lyme disease is an infection caused by a bacterium, Borrelia burgdorferi, which is carried primarily by the deer tick. People bitten by an infected tick develop this inflammatory disease, which first affects the skin and then may spread to the joints, nervous system, and other body systems. A rash may appear within 3 to 30 days. The rash usually is red and may surround the location of the tick bite in what is sometimes referred to as a "bull's eye" pattern. Other symptoms may include arthritis-like joint pain, fever, headache, muscle aches, fatigue, and stiff neck.

Since these symptoms are similar to those of other illnesses, diagnosis of Lyme disease is often delayed. This is problematic because, if untreated, more severe symptoms can develop, including painful arthritis, joint swelling, heart problems, and central nervous system problems that could lead to mental disorders. Fortunately, with early detection and treatment, Lyme disease can be cured. There are several oral antibiotics available to treat this disease.

Standard precautions, such as wearing protective clothing, using a tick repellant, and checking for (and removing) ticks at regular intervals, are the best defenses against Lyme disease. In addition, there are tests that can diagnose Lyme disease. One measures the levels of antibodies in the body that have developed against the Borrelia burgdorferi spirochete (bacterium). This test may appear negative if it is done in the first few weeks after infection. Therefore, if symptoms persist, the test should be repeated a few weeks later. A Western blot or DNA-based test also may be performed to confirm an initial screening test. The Western blot test is more accurate because it is used to examine the blood for antibodies specific to Borrelia burgdorferi. A DNA-based test based on the polymerase chain reaction (PCR) may also be done and is even more sensitive; it is used to detect the genetic material of the infecting bacteria.