**Core Concept**
Epidemic relapsing fever is a vector-borne disease caused by **Borrelia** species. The transmission of this disease involves an arthropod vector.

**Why the Correct Answer is Right**
The correct answer is the vector responsible for transmitting **Borrelia** species to humans. Epidemic relapsing fever is primarily transmitted through the bite of an infected **louse**. When an infected louse feeds on a human's blood, it regurgitates the **Borrelia** bacteria into the wound.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not associated with epidemic relapsing fever.
**Option B:** Incorrect as it is not the primary vector.
**Option D:** Incorrect because, although ticks transmit other diseases, they are not the primary vector for epidemic relapsing fever.

**Clinical Pearl / High-Yield Fact**
Epidemic relapsing fever is characterized by recurring episodes of fever, which is a key clinical feature. The disease is often associated with poor hygiene and **louse** infestations.

**Correct Answer:** D. Louse