**Core Concept**
Lyme disease is a tick-borne zoonotic infection caused by the spirochete bacterium *Borrelia burgdorferi*. It is transmitted to humans through the bite of infected black-legged ticks (*Ixodes scapularis*). The disease is characterized by a distinctive skin rash (erythema migrans) and can progress to involve the nervous system, joints, and heart.

**Why the Correct Answer is Right**
The correct answer is related to the fact that Lyme disease is caused by a spirochete bacterium. *Borrelia burgdorferi* is a helical-shaped bacterium that is transmitted to humans through the bite of an infected tick. The disease is characterized by an initial skin rash, which is a hallmark of Lyme disease, and can progress to involve the nervous system, joints, and heart. The bacteria invade the host's cells and evade the immune system, leading to the characteristic symptoms of Lyme disease.

**Why Each Wrong Option is Incorrect**
* **Option A:** Lyme disease is not caused by a virus, so this option is incorrect.
* **Option B:** Lyme disease is not transmitted through mosquito bites, so this option is incorrect.
* **Option C:** Lyme disease is not caused by a protozoan parasite, so this option is incorrect.

**Clinical Pearl / High-Yield Fact**
A key clinical feature of Lyme disease is the distinctive skin rash (erythema migrans), which typically appears within 3-30 days after the tick bite. The rash is usually a single, expanding lesion that can reach up to 12 inches in diameter.

**Correct Answer:** C.