They can be observed by Giemsa or Wright's stains. They range in appearance from amphophilic to highly basophilic condensed or loose aggregates of bacteria. Ehrlichia pathogens were previously known only as agents of veterinary disease. Cross-reactive with E. equi or E. phagocytophila . The two infections are clinically indistinguishable.
Patients often present with fever, headache, and malaise within one month after exposure to a tick.
Because of the nonspecific clinical presentation, empirical therapy should be started as soon as possible after the onset of symptoms. Therapy should not be delayed until a serologic diagnosis is confirmed, since this may take several weeks. The HGE agent has been cultured from 3 patients using HL60 cells. Diagnosis of acute infection can only be made by demonstrating a significant rise in antibody level between acute and convalescent specimens where both tests are done in the same laboratory at the same time. Appearance of an IgM antibody response normally occurs 7-14 days after the onset of disease.