Rickettsia prowazekii is a species of gram-negative, obligate intracellular parasitic, aerobic bacilliform bacteria of class Alphaproteobacteria that is the etiologic agent of epidemic typhus, transmitted in the feces of lice.

A form of R. prowazekii that exists in the feces of arthropods remains stably infective for months.

Both Prowazek and Rocha Lima had been infected with typhus while studying its causative agent in a prisoner-of-war camp hospital in Cottbus, Germany.

[1] Vaccines against R. prowazekii were developed in the 1940s, and were highly effective in reducing typhus deaths among U.S. soldiers during World War II.

However, R. prowazekii can establish a latent infection, which can reactivate after years or decades (referred to as Brill-Zinsser disease).