Persons of all ages and both sexes are equally susceptible, although the highest rates are in children up to 15 years of age and in adults 30 years and older (Figure 3). Race-specific rates appear to approximate the general population racial breakdown in the geographic areas with tick vectors.

Figure 3

Transmission

Lyme disease is caused by a spirochete bacterium Borrelia burdorferi (Bb) transmitted by the Ixodes scapularis tick (commonly known as the deer tick) in the eastern U.S. and the Ixodes pacificus tick along the Pacific coast of the U.S. Spirochetes are transmitted through the saliva of feeding ticks and possibly by regurgitation of tick midgut contents into the bite site. In northeast and north central states deer ticks can be found especially on white-footed mice and chipmunks, and in the Pacific coastal regions on dusky wood rats and kangaroo rats.