Bartonella species are bacteria which can cause a variety of human illnesses ranging from benign lymph node enlargement to life-threatening systemic diseases. Of the ten Bartonella species believed to produce infections in humans, the most commonly encountered are Bartonella henselae, Bartonella quintana and Bartonella bacilliformis.
Bartonella infections mostly occur worldwide, except B. bacilliformis which only exists in certain parts of South America.