False-colour scanning electron micrograph (SEM) of a colony of bacteria Rickettsia prowazeki, agent of typhus disease. These bacteria are non-motile, rod-like and Gram-negative. They cause epidemic typhus, a human disease transmitted by the human body louse. R. prowazeki 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 un- treated. Treatment is with antibiotic drugs and elimination of the lice. This was a classic Euro- pean disease. Magnification: x8,000 at 6x7cm size.