Several species of Bartonella bacteria cause disease in people. Infection with any one of these bacteria is referred to broadly as bartonellosis, although some forms of infection also have common names (for example, cat scratch disease). Bartonella bacteria are spread to humans by fleas, body lice, sand flies, or contact with flea-infested animals. There is no evidence that ticks spread Bartonella infection to people. In the United States, the most common form of bartonellosis is caused by Bartonella henselae.