## **Core Concept**
Louse-borne relapsing fever (LBRF) is a type of relapsing fever caused by the bacterium *Borrelia recurrentis*. This condition is transmitted to humans through the bite of an infected body louse (*Pediculus humanus corporis*). LBRF is characterized by recurring episodes of fever and is a significant public health concern in areas with poor hygiene and sanitation.

## **Why the Correct Answer is Right**
The correct answer, *, is right because *Borrelia recurrentis* is the specific bacterium responsible for causing louse-borne relapsing fever. This spirochete is transmitted by the body louse and leads to a disease that presents with recurring febrile episodes. The bacteria evade the host's immune system by changing their surface antigens, which results in the relapsing nature of the fever.

## **Why Each Wrong Option is Incorrect**
- **Option A:** * is incorrect because it is associated with tick-borne relapsing fever, not louse-borne.
- **Option B:** * is incorrect as it causes a different condition.
- **Option D:** * is incorrect because it is not associated with relapsing fever.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that louse-borne relapsing fever has a high mortality rate if left untreated, but it is effectively treated with antibiotics such as penicillin or doxycycline. Public health measures, including improved hygiene and louse control, are crucial in preventing outbreaks.

## **Correct Answer:** B. *Borrelia recurrentis*.