Epidemic louse-borne typhus fever due to Rickettsia prowazekii

**Definition:** This is a form of typhus so named because the disease often causes epidemics following wars and natural disasters. The causative organism is Rickettsia prowazekii, transmitted by the human body louse (Pediculus humanus corporis). This diagnosis is due to a species of gram-negative, obligate intracellular parasitic, aerobic bacteria (belonging to the class Alphaproteobacteria) that is the aetiologic agent of epidemic typhus, transmitted in the faeces of lice.