The disease often begins as a rash. Bacteria called Borrelia burgdorferi cause Lyme disease. The disease is spread to human beings by the bite of a small tick infected with the bacteria. These ticks are found in vegetation and on animals in woodlands, grasslands, and marshlands. Wild birds, mice, raccoons, and deer, as well as cats, dogs, horses, and cows, can carry the infected ticks.
People usually become infected during the summer, when they are more likely to be exposed to ticks.
Hikers, campers, hunters, and people living in wooded or rural areas are at a high risk for Lyme disease. This infection has been found on all continents except Antarctica. In the U.S. the infection is more common in the northern states. Lyme disease is hard to diagnose because its symptoms can vary greatly from person to person. The first symptoms may not even be noticed.