Typhus, TY fuhs, is any one of a group of important diseases caused by rickettsias. These are tiny organisms that look like small bacteria but often behave like viruses (see Rickettsia). In human beings, they damage the lining and walls of blood vessels, causing bleeding and skin rashes. Some types of these germs infect animals as well as people. Scientists often call the infected animals "reservoirs" of the disease. Typhus diseases may be transmitted from person to person or from animals to people by lice, fleas, ticks, or mites. The diseases are named for the way they affect the human population (epidemic typhus), for the type of reservoir host (murine, or rat, typhus), or for the vector, or carrier (tick typhus). In the United States, tick typhus is called Rocky Mountain spotted fever (see Rocky Mountain spotted fever).