Ultrastructural and antigenic characterization of a granulocytic ehrlichiosis agent directly isolated and stably cultivated from a patient in New York state

A human granulocytic ehrlichiosis (HGE) agent with 16S rDNA sequence identical to the pub-lished sequence of HGE agents was isolated from a patient from New York State by inoculation of the blood leukocyte fraction directly into a human promyelocytic leukemia cell line HL-60. The HGE agent was also isolated from the leukocyte fraction of the blood and bone marrow of a mouse inoculated with the leukocyte fraction of the patient's blood. The isolate has been passaged in tissue culture 30 times over 8 months. Electron microscopy revealed pleomorphic coccobacilli with a thin and highly rippled outer membrane in the clear inclusion matrix. Comparison of IFA reactivity of antisera obtained from a variety of sources with the cell-cultured HGE agent revealed that 3 HGE agent strains (New York isolate, Wisconsin [BDS] isolate, and a tick-derived isolate) are highly cross-reactive and there are diverse antigenic cross-reactivities between HGE agent and Ehrlichia chaffeensis. Two tickborne diseases caused by Ehrlichia species have been recognized in humans in the United States: human mono-cytic ehrlichiosis, caused by Ehrlichia chaffeensis, and human granulocytic ehrlichiosis (HOE), caused by an agent closely related to Ehrlichia equi or Ehrlichia phagocytophila [1]. HOE was first described in 1994 among patients in Minnesota and Wisconsin [1, 2]. In addition to these cases, acquisition of HO