Which hard-tick species is most associated with Lyme disease in the United States, and what is the primary reservoir host?

• A. Ixodes scapularis (black-legged tick); white-footed mouse (Peromyscus leucopus).
• B. Rhipicephalus sanguineus (brown dog tick); raccoon.
• C. Dermacentor variabilis (American dog tick); deer.
• D. Amblyomma americanum (lone star tick); dog.

Answer: (A)

Lyme disease in the United States is most closely linked to a specific tick vector and a small mammal reservoir. The main hard-tick vector responsible for transmitting Borrelia burgdorferi to humans is Ixodes scapularis, the black-legged tick. The bacteria are largely maintained in nature by the white-footed mouse, Peromyscus leucopus, which serves as the primary reservoir host. Ticks acquire the infection when feeding on an infected reservoir as larvae or nymphs, and then can pass it to humans during subsequent feeds. Deer, while important for supporting adult tick populations, are not the primary reservoirs for the bacteria. That combination—Ixodes scapularis and the white-footed mouse—best fits the scenario of Lyme disease transmission in the U.S.