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Category: Clinical Microbiology
Ehrlichia, Anaplasma, and Related Intracellular Bacteria, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555817381/9781555817381.ch65-1.gif /docserver/preview/fulltext/10.1128/9781555817381/9781555817381.ch65-2.gifAbstract:
Members of the genera Ehrlichia and Anaplasma are now recognized to be important human pathogens. Ehrlichia and Anaplasma species infect bone marrow-derived cells, such as granulocytes, monocytes, erythrocytes, and platelets, of humans and other mammals. Ehrlichia and Anaplasma spp. are Gram-negative obligate intracellular bacteria that reside and propagate within membrane-lined vacuoles in the cytoplasm of the bone marrow-derived cells. They are zoonotic agents transmitted to animals and humans by ticks. Recognized natural reservoirs for Ehrlichia chaffeensis include deer, domestic dogs, and perhaps other animals that host Amblyomma ticks. The causative agent of human monocytic ehrlichiosis (HME) is E. chaffeensis, a monocytotropic ehrlichia first identified as a human pathogen in a patient with a severe febrile illness after tick bites in 1986. The causative agent of human granulocytic anaplasmosis (HGA) is Anaplasma phagocytophilum. Other human ehrlichioses include Venezuelan human ehrlichiosis, E. ewingii ehrlichiosis, Ehrlichia muris-like agent ehrlichiosis, “Candidatus Neoehrlichia mikurensis” ehrlichiosis, and neorickettsiosis. Currently, there are 3 methods for diagnosis of acute HME or HGA: (i) PCR amplification of nucleic acids from Ehrlichia or Anaplasma species in blood, (ii) detection of morulae in the cytoplasm of infected leukocytes by Romanowsky stains (e.g., Giemsa or Wright) or by specific immunostains using E. chaffeensis or A. phagocytophilum antibodies, and (iii) culture of Ehrlichia or Anaplasma from blood or cerebrospinal fluid. Although disease can be severe or fatal, in retrospective studies and routine clinical practice, patients with either HME or HGA defervesce within 48 h of therapy with doxycycline, the drug of choice.
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Neighbor-joining phylogenetic tree inferred from rrs (16S ribosomal RNA 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. Modified from Juan P. Olano and Maria E. Aguero-Rosenfeld in chapter 67 of the 9th edition of this Manual (156). doi:10.1128/9781555817381.ch65.f1
Neighbor-joining phylogenetic tree inferred from rrs (16S ribosomal RNA 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. Modified from Juan P. Olano and Maria E. Aguero-Rosenfeld in chapter 67 of the 9th edition of this Manual (156). doi:10.1128/9781555817381.ch65.f1
(A and C) Wright stains (original magnification, ×1,000) of E. chaffeensis (A) and A. phagocytophilum (C) in peripheral blood leukocytes. Note that an E. chaffeensis morula (arrowhead) is present in a monocyte (A) and that an A. phagocytophilum morula (arrow) is present in a neutrophil (C). (B) Romanowsky (Leukostat) stain (original magnification, ×1,000) of 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. (D) Wright stain (original magnification, × 1,000) of A. phagocytophilum from the blood of an infected patient cultured in the human promyelocytic cell line HL-60. Note the presence of multiple basophilic, stippled, intracytoplasmic inclusions (arrowheads) in an HL-60 cell. doi:10.1128/9781555817381.ch65.f2
(A and C) Wright stains (original magnification, ×1,000) of E. chaffeensis (A) and A. phagocytophilum (C) in peripheral blood leukocytes. Note that an E. chaffeensis morula (arrowhead) is present in a monocyte (A) and that an A. phagocytophilum morula (arrow) is present in a neutrophil (C). (B) Romanowsky (Leukostat) stain (original magnification, ×1,000) of 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. (D) Wright stain (original magnification, × 1,000) of A. phagocytophilum from the blood of an infected patient cultured in the human promyelocytic cell line HL-60. Note the presence of multiple basophilic, stippled, intracytoplasmic inclusions (arrowheads) in an HL-60 cell. doi:10.1128/9781555817381.ch65.f2
Selected features of Ehrlichia, Anaplasma, Neorickettsia, “Candidatus Neoehrlichia mikurensis,” and Aegyptianella species of human and veterinary interest a
Selected features of Ehrlichia, Anaplasma, Neorickettsia, “Candidatus Neoehrlichia mikurensis,” and Aegyptianella species of human and veterinary interest a