The human body louse, Pediculus humanus corporis is the primary vector of the bacterial agents of louse-borne relapsing fever, trench fever, and epidemic typhus. Epidemic typhus, one of the most significant historical diseases of humans, is caused by Rickettsia prowazekii, a category B bioterrorism agent that can cause persistent human infection. Besides its notoriety as the agent of the recurrent chronic disease, trench fever, Bartonella quintana can cause endocarditis and is a common infection among the homeless. Borrelia recurrentis causes another recurrent fever in central and Eastern Africa that is characterized by significant morbidity and mortality. The genome sequences of R. prowazekii and B. quintana have been determined, as well as those of two species of Borrelia, so the body louse genome will enhance studies of host-vector-pathogen interactions.