The kinds of ticks that carry Lyme disease are primarily black-legged ticks of the genus Ixodes. Specifically:
- The black-legged tick (Ixodes scapularis) , also known as the deer tick, is the main vector in the northeastern, mid-Atlantic, and north-central United States
- The western black-legged tick (Ixodes pacificus) transmits Lyme disease along the Pacific Coast
These ticks acquire the Lyme disease bacteria (Borrelia burgdorferi and rarely B. mayonii) from infected small mammals such as white-footed mice and then transmit it to humans through their bites
. Nymphal ticks, which are very small (about the size of a poppy seed), cause most Lyme disease infections because they are hard to detect and active in late spring and summer
. Adult ticks can also transmit Lyme disease but are larger and more likely to be noticed and removed before infection occurs
. In summary, Lyme disease is spread by bites from infected black-legged ticks-Ixodes scapularis in the eastern and midwestern U.S. and Ixodes pacificus on the West Coast
