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Category: Clinical Microbiology
Ehrlichia, Anaplasma, and Related Intracellular Bacteria * , Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555816728/9781555814632_Chap62-1.gif /docserver/preview/fulltext/10.1128/9781555816728/9781555814632_Chap62-2.gifAbstract:
Members of the genus Ehrlichia and Anaplasma are now recognized to be important human pathogens. They are obligate intracellular bacteria currently placed in the Proteobacteria phylum (Alphaproteobacteria), order Rickettsiales, and family Anaplasmataceae. Anaplasma phagocytophilum, within the genus Anaplasma, now includes Ehrlichia phagocytophila, Ehrlichia equi, and the human granulocytic ehrlichiosis (HGE) agent. Ehrlichia and Anaplasma spp. are gram-negative obligate intracellular bacteria that reside and propagate within membrane-lined vacuoles found in the cytoplasm of bone marrow-derived cells, such as granulocytes, monocytes, erythrocytes, and platelets. The causative agent of human monocytic ehrlichiosis (HME) is E. chaffeensis, a monocytotropic ehrlichia that was first identified as a human pathogen in a patient with a severe febrile illness after tick bites in 1986. The culture conditions for Ehrlichia and Anaplasma species are still being optimized. The most widely used method is polymerase chain reaction (PCR) amplification of DNA from E. chaffeensis in clinical samples using the HE1/HE3 primer set. In a prospective study, the overall sensitivity and specificity of PCR were 56% and 100%, respectively, using the 16S rRNA subunit, nadA, and 120-kDa protein genes. In this study several samples had high titers of antiehrlichial antibodies by immunofluorescence assay (IFA), suggesting that the pathogen may have already been cleared. Routine antimicrobial susceptibility testing of Ehrlichia or Anaplasma species isolates is unnecessary. The typical morphology of an Ehrlichia or Anaplasma spp. morula is observed, an assessment as to the hematopoietic lineage and the percentage of cells that contain morulae should be made and reported.
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Neighbor-joining phylogenetic tree inferred from 16S rRNA gene sequences of selected Ehrlichia,“Candidatus Neoehrlichia,” Anaplasma, Neorickettsia, and Wolbachia spp. Escherichia coli and Rickettsia rickettsii are used as outgroups. The bar represents the estimated number of substitutions per site.
Neighbor-joining phylogenetic tree inferred from 16S rRNA gene sequences of selected Ehrlichia,“Candidatus Neoehrlichia,” Anaplasma, Neorickettsia, and Wolbachia spp. Escherichia coli and Rickettsia rickettsii are used as outgroups. The bar represents the estimated number of substitutions per site.
(A) E. chaffeensis cultured in the canine histiocyte cell line DH82. Note the presence of basophilic, stippled, intracytoplasmic inclusions approximately 2 to 3 µm in diameter (arrows). The smaller intracytoplasmic granules may also be ehrlichial morulae. Romanowsky (Leukostat) stain; original magnification, ×1,000. (B) A. phagocytophilum cultured in the human promyelocytic cell line HL-60 from the blood of an infected patient. Note the presence of multiple basophilic, stippled, intracytoplasmic inclusions (arrowheads) in an HL-60 cell. Wright stain; original magnification, ×1,000. (C and D) E. chaffeensis (C) and A. phagocytophilum (D) in peripheral blood leukocytes. Note that an E. chaffeensis morula (arrowhead) is present in a monocyte (C) and that an A. phagocytophilum morula (arrow) is present in a neutrophil (D). Wright stain; original magnification, ×1,000.
(A) E. chaffeensis cultured in the canine histiocyte cell line DH82. Note the presence of basophilic, stippled, intracytoplasmic inclusions approximately 2 to 3 µm in diameter (arrows). The smaller intracytoplasmic granules may also be ehrlichial morulae. Romanowsky (Leukostat) stain; original magnification, ×1,000. (B) A. phagocytophilum cultured in the human promyelocytic cell line HL-60 from the blood of an infected patient. Note the presence of multiple basophilic, stippled, intracytoplasmic inclusions (arrowheads) in an HL-60 cell. Wright stain; original magnification, ×1,000. (C and D) E. chaffeensis (C) and A. phagocytophilum (D) in peripheral blood leukocytes. Note that an E. chaffeensis morula (arrowhead) is present in a monocyte (C) and that an A. phagocytophilum morula (arrow) is present in a neutrophil (D). Wright stain; original magnification, ×1,000.
Selected features of Ehrlichia, Anaplasma, Neorickettsia, and Aegyptianella species of human and veterinary interest
a EGE, equine granulocytic ehrlichiosis; CGE, canine granulocytic ehrlichiosis; CME, canine monocytic ehrlichiosis.
Selected features of Ehrlichia, Anaplasma, Neorickettsia, and Aegyptianella species of human and veterinary interest
a EGE, equine granulocytic ehrlichiosis; CGE, canine granulocytic ehrlichiosis; CME, canine monocytic ehrlichiosis.