**Core Concept**
Lyme disease is a tick-borne zoonotic infection caused by the bacterium *Borrelia burgdorferi*. It is transmitted to humans through the bite of an infected black-legged tick (*Ixodes scapularis*).

**Why the Correct Answer is Right**
*Borrelia burgdorferi* infects the skin, joints, and nervous system, causing a range of symptoms from a characteristic skin rash (erythema migrans) to neurological and cardiac complications. The bacteria are transmitted to humans through the saliva of infected ticks, which inject the spirochetes into the host's bloodstream during feeding. The spirochetes then multiply and spread through the body, causing the various manifestations of Lyme disease.

**Why Each Wrong Option is Incorrect**
* **Option A:** Borrelia recurrentis is the causative agent of louse-borne relapsing fever, a different tick-borne disease.
* **Option B:** Rickettsia rickettsii is the bacterium responsible for Rocky Mountain spotted fever, another tick-borne illness.
* **Option C:** Bartonella henselae is the causative agent of cat-scratch disease, a condition transmitted through scratches from infected cats.

**Clinical Pearl / High-Yield Fact**
The characteristic "bull's-eye" rash of Lyme disease (erythema migrans) often appears within 3-30 days after the tick bite and can be accompanied by fever, headache, and fatigue.

**Correct Answer: D. Borrelia burgdorferi**