The Lyme disease bacterium, Borrelia burgdorferi,
normally lives in mice, squirrels and other small animals. It is
transmitted among these animals – and to humans – through the bites of
certain species of ticks. In the northeastern and north-central United
States, the black-legged tick (or deer tick, Ixodes scapularis) transmits Lyme disease. In the Pacific coastal United States, the disease is spread by the western black-legged tick (Ixodes pacificus). Other major tick species found in the United States have not been shown to transmit Borrelia burgdorferi.
This image shows the stages and relative sizes of these tick
species. Only the blacklegged ticks are known to transmit Lyme disease.
For large image click here