title: Ehrlichia chaffeensis: a prevalent, life-threatening, emerging pathogen.
abstract: Ehrlichia chaffeensis are small, obligately intracellular, endosomal bacteria with tropism for macrophages. Persistent infection in reservoir white-tailed deer is transmitted by lone star ticks. Flu-like illness can progress to severe multisystem disease with toxic shock-like syndrome, meningitis, or ARDS. The case-fatality rate is 2.7%. Leukopenia and thrombocytopenia are diagnostically useful. Granulomas are associated with control of the infection. Ehrlichial proteins and glycoproteins have been sequenced and expressed for diagnostic serology and vaccine development. Mouse models (mild disease and persistent infection with E. muris and fatal monocytotropic ehrlichiosis with a Japanese tick isolate) revealed that CD4 and CD8 T type 1 lymphocyte responses, IFN-gamma, TNF-alpha, and antibodies play roles in protective immunity, while a weak CD4 T-helper response, overproduction of TNF-alpha, and very high IL-10 are associated with toxic shock-like mortality. Protection against fatal ehrlichiosis was achieved by prior infection with low virulence E. muris. Acute clinical diagnosis is difficult except by PCR. Response to doxycycline is dramatic.
authors.affiliation: Department of Pathology, University of Texas Medical Branch, World Health OrganizationCollaborating Center for Tropical Diseases, UTMB Center for Biodefense and EmergingInfectious Diseases, Galveston, Texas 77555-0609, USA.dwalker@utmb.edu
authors.forename: David H
authors.initials: DH
authors.lastname: Walker
authors.forename: Nahed
authors.initials: N
authors.lastname: Ismail
authors.forename: Juan P
authors.initials: JP
authors.lastname: Olano
authors.forename: Jere W
authors.initials: JW
authors.lastname: McBride
authors.forename: Xue-Jie
authors.initials: XJ
authors.lastname: Yu
authors.forename: Hui-Min
authors.initials: HM
authors.lastname: Feng
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D004195:Disease Models, Animal; D004197:Disease Reservoirs / Q000821:virology; D004318:Doxycycline / Q000627:therapeutic use; D018469:Ehrlichia chaffeensis / Q000472:pathogenicity*; D016873:Ehrlichiosis / Q000175:diagnosis / Q000188:drug therapy / Q000453:epidemiology / Q000209:etiology*; D006801:Humans; D051379:Mice; D009656:North America / Q000453:epidemiology
chemical_list: D000900:Anti-Bacterial Agents; D004318:Doxycycline