The blacklegged ticks, Ixodes pacificus, (depicted here), and Ixodes scapularis, are known vectors for the zoonotic spirochetal bacteria Borrelia burgdorferi, which is the pathogen responsible for causing Lyme disease. The ticks, inoculated with the bacterium when they bite infected mice, squirrels and other small animals, subsequently pass the pathogens to their human victims when they obtain a blood meal. B. burgdorferi bacteria can infect several parts of the body, producing different symptoms at different times. Not all patients with Lyme disease will have all symptoms, and many of the symptoms can occur with other diseases as well. If you believe you may have Lyme disease, it is important that you consult your health care provider for proper diagnosis.