**Core Concept**
Tick-borne Relapsing Fever (TBRF) is a tick-borne illness caused by several species of Borrelia bacteria, which are transmitted to humans through the bite of infected ticks. The disease is characterized by recurring episodes of fever, headache, and muscle pain, followed by periods of remission.

**Why the Correct Answer is Right**
TBRF is caused by various Borrelia species, including Borrelia hermsii, which is a common causative agent in North America. These bacteria have a unique ability to change their outer membrane proteins, leading to the development of relapsing fever. The bacteria are transmitted to humans through the bite of infected ticks, such as the soft tick (Ornithodoros spp.). The disease is typically self-limiting, but can be severe in some cases, particularly in individuals with underlying medical conditions.

**Why Each Wrong Option is Incorrect**
**Option A:** Borrelia recurrentis is the causative agent of Louse-borne Relapsing Fever (LBRF), not Tick-borne Relapsing Fever (TBRF). LBRF is transmitted through the bite of infected body lice.

**Option B:** Borrelia burgdorferi is the causative agent of Lyme disease, a different tick-borne illness characterized by a distinctive skin rash and a range of systemic symptoms.

**Option C:** Rickettsia prowazekii is the causative agent of Epidemic Typhus, a different tick-borne illness transmitted through the bite of infected fleas and lice.

**Clinical Pearl / High-Yield Fact**
To distinguish between TBRF and LBRF, look for the presence of body lice (Pediculus humanus) in patients with LBRF, and soft ticks (Ornithodoros spp.) in patients with TBRF.

**Correct Answer:**
✓ Correct Answer: D. Borellia hermsii