Human monocytic and granulocytic ehrlichioses. Discovery and diagnosis of emerging tick-borne infections and the critical role of the pathologist.

Human monocytic ehrlichiosis and human granulocytic ehrlichiosis are emerging tick-borne infections in the United States. The clinical presentations of these two distinct, potentially life-threatening infections are fever, headache, myalgia, and other diagnostically nonspecific symptoms. Physician awareness is lacking and appropriate diagnostic tests are still not widely available. Because few documented cases have been autopsied, the pathology of human monocytic ehrlichiosis and human granulocytic ehrlichiosis is incompletely described. In human monocytic ehrlichiosis, bone marrow and hepatic granulomas and multiorgan perivascular lymphohistiocytic infiltrates have been observed. In human granulocytic ehrlichiosis, opportunistic fungal and viral infections have been important findings. To expedite an analysis of the pathology and pathogenesis of the human ehrlichioses, it is proposed that a Registry of Pathology of Human Ehrlichioses be established.