Rickettsia bacteria (red rods) inside a cell, computer illustration. The most common species is R. prowazekii. These bacteria are non-motile, rod-like and Gram-negative. They cause epidemic typhus, a human disease transmitted by the human body louse. R. prowazekii multiply within the louse and exit in louse faeces. Due to louse bites, or scratching by the human victim, these bacteria enter the human bloodstream. Fever, rash and delirium may result, and death may occur if untreated. Treatment is with antibiotic drugs and elimination of the lice. This was a classic European disease.