Is human granulocytic ehrlichiosis a new Lyme disease? Review and comparison of clinical, laboratory, epidemiological, and some biological features

Human granulocytic ehrlichiosis (HGE) and Lyme disease are caused by infectious agents transmitted by deer ticks (Ixodes scapularis). Because of the shared tick vector and increased seroprevalence of HGE in patients with Lyme disease, there is some confusion about the identity of these infectious agents and the clinicopathologic spectrum of the disease. HGE is an acute febrile illness associated with leukopenia, thrombocytopenia, and increased serum activities of hepatic transaminases. In contrast, Lyme disease is most often subacute, with the frequent presence of erythema migrans rash and infrequent leukopenia, thrombocytopenia, or elevated serum hepatic transaminase activities. Some ehrlichia infections in animals and humans may become persistent, and Ehrlichia-mediated defects in host defense and immune suppression can allow secondary and opportunistic infections. Because of these properties of Ehrlichia species, their role in modifying the clinical course of Lyme disease may be hypothesized and should be tested.