Which tick-borne disease is characterized by a rash that spreads from ankles to wrists?

Rocky Mountain spotted fever is the tick-borne disease characterized by a rash that typically starts on the wrists and ankles and can spread to the trunk and other areas of the body. This disease is caused by the bacterium Rickettsia rickettsii, which is transmitted through tick bites, particularly from the American dog tick or the Rocky Mountain wood tick.

The rash associated with Rocky Mountain spotted fever often appears as small, flat, pink spots that can become petechial (small, pinpoint red spots) and may eventually turn into larger patches. This distinctive pattern helps in differentiating it from other tick-borne diseases. Early recognition is crucial, as prompt treatment with antibiotics can be life-saving.

Other tick-borne diseases, such as Lyme disease, usually present with different initial symptoms such as a distinct “bull's-eye” rash. Babesiosis and tick-borne encephalitis also have their unique presentations and are not associated with a rash that fits the description given in the question. Thus, Rocky Mountain spotted fever is the clear answer due to its characteristic rash spreading from ankles to wrists.