Which louse species vectors epidemic typhus?

• A. Pediculus humanus humanus (body louse)
• B. Pediculus capitis (head louse)
• C. Pthirus pubis (pubic louse)
• D. Pediculus schistaceus (nonexistent)

Answer: (A)

Epidemic typhus is transmitted by the body louse because this parasite lives in clothing and bites humans, spreading the causative bacterium Rickettsia prowazekii via its feces. When an infested person is scratching the bite, the feces can be rubbed into the skin, allowing infection to occur. This mode of transmission, coupled with the louse’s tendency to thrive in crowded, unsanitary conditions, makes the body louse the classic vector of epidemic typhus. The head louse stays mainly on the scalp and is not a known vector for typhus, while the pubic louse has a different epidemiology and does not transmit this disease. A nonexistent louse cannot vector pathogens.