**Core Concept:** Borrelia recurrentis is a spirochete bacterium that causes human louse-borne relapsing fever. It is transmitted by the human body louse, Pediculus humanus corporis, also known as the human body louse.

**Why the Correct Answer is Right:** Borrelia recurrentis is transmitted by the human body louse, Pediculus humanus corporis, because this louse serves as an obligate vector for the bacteria. In endemic regions, the louse acquires the bacteria during feeding on an infected person and transmits the bacteria to a newly acquired host during the subsequent feeding. The bacteria can persist in the louse's gut and remain infectious for several weeks.

**Why Each Wrong Option is Incorrect:**

A. Option A: Borrelia recurrentis is not transmitted by the human head louse (Pediculus humanus capitis) or the human pubic louse (Pthirus pubis). These lice are not vectors for the bacteria.

B. Option B: While the bacteria can cause relapsing fever, the mode of transmission is incorrect. The correct mode is via the human body louse, not the bed bug (Cimex lectularius) that feeds on blood from exposed skin.

C. Option C: The mode of transmission is incorrect as the bacteria is transmitted by the human body louse, not the human hair louse (Pediculus humanus capitis).

D. Option D: The bacteria is not transmitted by the human scabies mite (Sarcoptes scabiei), which causes scabies, not relapsing fever.

**Clinical Pearl:** Understanding the correct mode of transmission is crucial in controlling the spread of Borrelia recurrentis infections in endemic areas. Identifying and treating lice infestations can prevent the transmission of this bacterium.