## **Core Concept**
Tick-borne relapsing fever (TBRF) is caused by several species of the genus *Borrelia*, which are transmitted to humans through the bite of infected soft ticks (genus *Ornithodoros*). The disease is characterized by recurring episodes of fever and is found in various parts of the world, particularly in mountainous regions.

## **Why the Correct Answer is Right**
*Borrelia recurrentis* is the correct answer because it is the causative agent of louse-borne relapsing fever (LBRF), not tick-borne relapsing fever. LBRF is transmitted by the human body louse (*Pediculus humanus*) and causes epidemics in areas with poor hygiene. The other options, *B. hermsii*, *B. turicatae*, and *B. duttonii*, are indeed associated with tick-borne relapsing fever.

## **Why Each Wrong Option is Incorrect**
* **Option A:** *B. hermsii* is a well-known cause of tick-borne relapsing fever in North America.
* **Option C:** *B. turicatae* causes tick-borne relapsing fever in the southwestern United States and Latin America.
* **Option D:** *B. duttonii* is responsible for tick-borne relapsing fever in Africa.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that while *Borrelia* species cause relapsing fever, the epidemiology and vectors differ significantly between tick-borne and louse-borne forms. *Borrelia recurrentis* is classically associated with epidemics of louse-borne relapsing fever, particularly in Africa.

## **Correct Answer:** .