Anaplasmosis [an-a-plas-mo-sis] and Ehrlichiosis [ehr-lich-i-o-sis] are caused by Anaplasma and Ehrlichia species, which are members of the rickettsiae and are obligate intracellular coccobacilli. The spectrum of disease caused by these species ranges from asymptomatic to fatal. Wild and domestic stock are some of the reservoir-competent hosts.Human Granulocytotropic Anaplasmosis (HGA), formally known as Human Granulocytic Ehrlichiosis (HGE), is caused by Anaplasma phagocytophilum. This organism is also responsible for Tick-borne Fever in both cattle and sheep, and can cause clinical disease in other animals. It parasitizes the white blood cells of its host, weakening the immune system.