Scientists used to separate ehrlichiosis into two entities caused by the bacterium Ehrlichia: Human Monocytic Ehrlichiosis (HME) and Human Granulocytic Ehrlichiosis (HGE).  After futher study, they determined that HGE is actually caused by a bacterium, Anaplasma phagacytophilum.  HME is caused by a bacterium, Ehrlichia chaffeensis.

Symptoms of both ehrlichiosis and anaplasmosis include fever, malaise, headaches, chills, severe muscle aches, vomiting, anemia, lung infection, decreased white blood cells and platelets, elevated liver enzymes, seizures, encephalopathy, meningitis, confusion, ataxia, and cranial nerve palsy. Co-infection with Lyme can cause more severe symptoms. Death can result. Treatment is with doxycycline. 

Ticks that transmit anaplasmosis include Ixodes scapularis (deer tick) and Ixodes pacificus (western black legged).

Ticks that transmit ehrlichiosis (HME) include Amblyomma americanum (lone star) and Dermacentor variabilis (American dog).  Ixodes scapularis (deer) and Ixodes pacificus (western black legged) ticks have been shown to carry the ehrlichiosis bacterium, but to date, transmission is still in question.