DefinitionEhrlichiosis is an infectious disease transmitted by the bite of a tick.Alternative NamesHuman monocytic ehrlichiosis; HME; Human granulocytic ehrlichiosis; HGE; Human granulocytic anaplasmosis; HGACauses, incidence, and risk factorsEhrlichiosis is caused by bacteria that belong to the family called Rickettsiae. Rickettsial bacteria cause a number of serious diseases worldwide, including Rocky Mountain spotted fever and typhus. All of these diseases are spread to humans by a tick, flea, or mite bite.Scientists first described ehrlichiosis in 1990, and have identified two types in the United States:Human monocytic ehrlichiosis (HME) is caused by the rickettsial bacteria called Ehrlichia chaffeensis.Human granulocytic ehrlichiosis (HGE) is also called human granulocytic anaplasmosi