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Thursday 2 February 2006

Human ehrlichiosis is a tick-borne zoonosis caused by the newly described human hematotropic rickettsiae, Ehrlichia chaffeensis.

The pathology and pathogenesis of human ehrlichiosis have not been adequately studied. Even with immunoperoxidase, the only previously known method to detect these organisms in tissue, ehrlichae are difficult or impossible to identify. This led many investigators to speculate that the pathogenesis of ehrlichiosis was not caused directly by the organism but could be caused by host-mediated injury.


- progressive central nervous system symptoms
- severe thrombocytopenia
- hemorrhages in multiple organs
- mononuclear inclusions of infection with a monocytic ehrlichia
- widespread lymphohistiocytic perivascular infiltrates
- focal hepatic necroses
- interstitial pneumonitis
- interstitial nephritis
- mononuclear phagocyte invasion and proliferation in splenic, liver, and bone marrow
- hemophagocytosis

Differential diagnosis

- thrombotic thrombocytopenic purpura (TTP)


- Marty AM, Dumler JS, Imes G, Brusman HP, Smrkovski LL, Frisman DM. Ehrlichiosis mimicking thrombotic thrombocytopenic purpura. Case report and pathological correlation. Hum Pathol. 1995 Aug;26(8):920-5. PMID: 7635455