Ehrlichiosis / anaplasmosis

Bone marrow nonneoplastic

Infectious / inflammatory

Author: Dragos C. Luca, M.D.

Topic Completed: 1 March 2015

Minor changes: 2 August 2019

Copyright: 2002-2019, PathologyOutlines.com, Inc.

PubMed Search: Ehrlichiosis bone marrow

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Table of Contents

Cite this page: Luca DC. Ehrlichiosis / anaplasmosis. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/bonemarrowHGL.html. Accessed March 9th, 2021.

Definition / general

Ehrlichia: obligate intracellular gram negative bacteria belonging to recently reorganized family Anaplasmataceae
Species producing disease in humans (3):
- E. chaffeensis: human monocytic ehrlichiosis (HME)
- Anaplasma phagocytophilia: human granulocytotropic anaplasmosis (HGA, formally termed human granulocytic ehrlichiosis)
- E. ewingii: rare granulocytic disease (increased frequency in transplant patients)
Vector borne disease transmitted through bite of Ixodes ticks
Bacteria is obligate intracellular pathogen that binds to P selectin glycoprotein ligand 1 (PSGL1 / CD162)
Susceptibility also associated with expression of CD15s (J Clin Invest 1999;103:407)
First described in USA in 1994
Geographic distribution of E. chaffeensis (HME) and A. phagocytophilia (HGA) reflects regions of US where their hard tick vectors reside:
- HME: south central, southeastern and mid Atlantic states
- HGA: northeastern states, northwest Wisconsin, eastern Minnesota and Pacific northwest states

Clinical presentation and diagnosis

HME and HGA have similar clinical symptoms but HME is more often serious with hospitalization in 50% of patients; septic shock-like syndrome possible, especially if immunosuppressed
Both present with fever, leukopenia, thrombocytopenia (70 - 90%) and elevated liver enzymes
Mortality rate is 2 - 3% for HME and 0.5 - 1% for HGA
Particularly severe infections occur in elderly / immunocompromised
Characteristic intracytoplasmic morulae (morula is Latin for mulberry): cytoplasmic membrane bound vacuoles with irregular edges containing hundreds to thousands of clustered gram negative bacteria
Infected cells typically contain only 1 or 2 morulae although as many as 15 may be seen in immunosuppressed individuals
Morulae are present in less than 0.2% of circulating WBCs in HME infection; examination of buffy coats facilitates detection
Greatly variable percentage of peripheral blood films with detectable morulae in the literature (3 - 80%) with a higher number seen with HGA infection (50 - 80%) and in immunosuppressed individuals

Case reports

78 year old man with Anaplasma phagocytophilum infection and CML (J Clin Pathol 2004;57:499)
3 pancreas transplant recipients with HGA / human granulocytic ehrlichiosis (Transpl Infect Dis 2001;3:34)

Treatment

Most patients are seronegative during first few weeks of acute infection (60 - 97%), so therapeutic decisions must be based on clinical suspicion, peripheral blood findings and PCR (sensitivity is 60 - 85%, high degree of false positive results)
Became a nationally reportable disease to US Centers for Disease Control in 1999
Organisms are susceptible to tetracyclines and their derivatives, particularly doxycycline

Microscopic (histologic) description

Peripheral blood: buffy coat examination may reveal intracytoplasmic inclusions (morulae - spherical structures with irregular edges) within neutrophils or monocytes
Bone marrow: epithelioid granulomas; usually normo or hypercellular with intact trilineage maturation; rare hypoplasia; possible increased megakaryocytes
Histopathologic bone marrow findings: inconsistent and likely to change during the course of the disease
HGA organisms preferentially infect more mature rather than immature granulocytic cells in bone marrow

Microscopic (histologic) images

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