Images of Memorable Cases: Case 44 Peripheral blood film from a patient with fever, severe myalgia, thrombocytopenia, and leukopenia. 44. Human granulocytic ehrlichiosis A tick-borne infectious disease caused by Ehrlichia phagocytophilia, a small, coccoid bacterium with a Gram-negative cell wall. The leukocyte in the image contains a morula (arrow), a mulberry-like cytoplasmic cluster of ehrlichiae.