Endemic typhus is transmitted to humans by fleas infected with which organism?

• A. Rickettsia akari
• B. Rickettsia conorii
• C. Rickettsia prowazekii
• D. Rickettsia typhi

Answer: (D)

Endemic typhus, or murine typhus, is caused by Rickettsia typhi and is transmitted to humans by fleas infected with this organism. The classic vector is the rat flea, Xenopsylla cheopis, which becomes infected after feeding on an infected rat. Transmission to people occurs when the flea bites or when flea feces containing the bacteria are scratched into the skin, allowing entry. This flea–rat cycle is the hallmark of endemic typhus and distinguishes it from other rickettsial diseases, such as epidemic typhus (transmitted by the human body louse, Rickettsia prowazekii) and tick- or mite-borne forms (e.g., Rickettsia conorii with ticks, Rickettsia akari with mites).