Ehrlichiosis and anaplasmosis are two closely related tickborne diseases, caused by different germs. Although both diseases concentrate east of the Rocky Mountains, they usually occur in different areas. Ehrlichiosis, or human monocytic ehrlichiosis (HME), is found mainly in the mid-Atlantic, southeastern, and south central states. Anaplasmosis (formerly called human granulocytic ehrlichiosis, or HGE) occurs more often in the Northeast and upper Midwest.
Ehrlichiosis and anaplasmosis are emerging infectious diseases in the United States and other countries. (Emerging infectious diseases are diseases first described by researchers within the last two decades.) In 2005, 786 cases of anaplasmosis and 506 cases of HME were reported to the Centers for Disease Control and Prevention. Neither HME nor anaplasmosis were reported from states west of the Continental Divide, though some cases of an unknown ehrlichiosis-like disease were reported in California.
Understanding Ehrlichiosis and Anaplasmosis